Std-130 671x3o
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OISD - 130 FOR RESTRICTED CIRCULATION No.
INSPECTION OF PIPES, VALVES AND FITTINGS
OISD - STANDARD-130 First Edition, November 1988 Reaffirmed, August, 1999
OIL INDUSTRY SAFETY DIRECTORATE Government of India Ministry of Petroleum & Natural Gas OISD STANDARD - 130 First Edition, November 1988
1
Reaffirmed, August, 1999 FOR RESTRICTED CIRCULATION No.
INSPECTION OF PIPES, VALVES AND FITTINGS
Prepared by
COMMITTEE ON INSPECTION OF STATIC EQUIPMENT
OIL INDUSTRY SAFETY DIRECTORATE 2ND FLOOR, “KAILASH” 26, KASTURBA GANDHI MARG, NEW DELHI – 110 001
2
NOTES
OISD publications are prepared for use in the Oil and gas industry under Ministry of Petroleum and Natural Gas. These are the property of Ministry of Petroleum and Natural Gas and shall not be reproduced or copied and loaned or exhibited to others without written consent from OISD. Though every effort has been made to assure the accuracy and reliability of data contained in these documents, OISD hereby expressly disclaims any liability or responsibility for loss or damage resulting from their use. These documents are intended only to supplement and not replace the prevailing statutory requirements.
3
FOREWORD The Oil Industry in India is 100 years old. Because of various collaboration agreements, a variety of international codes, standards and practices have been in vogue. Standardisation in design philosophies and operating and maintenance practices at a national level was hardly in existence. This, coupled with feed back from some serious accidents that occurred in the recent past in India and abroad, emphasized the need for the industry to review the existing state of art in deg, operating and maintaining oil and gas installations. With this in view, the Ministry of Petroleum & Natural Gas, in 1986, constituted a Safety Council assisted by Oil Industry Safety Directorate (OISD), staffed from within the industry, in formulating and implementing a series of self regulatory measures aimed at removing obsolescence, standardising and upgrading the existing standards to ensure safer operations. Accordingly, OISD constituted a number of Functional Committees of experts nominated from the industry to draw up standards and guidelines on various subjects. The present document on “Inspection of Pipes, Valves & Fittings” was prepared by the Functional Committee on “Inspection of Static Equipment”. This document is based on the accumulated knowledge and experience of industry and the various national and international codes and practices. It is hoped that the provisions of this document, when adopted may go a long way to improve the safety and reduce accidents in the Oil and Gas Industry. s of this standard are cautioned that no standard can be a substitute for a responsible, qualified Inspection Engineer. Suggestions are invited from the s, after it is put into practice, to improve the document further. This standard in no way supersedes the statutory regulations of CCE, Factory Inspectorate or any other Govt. body which must be followed as applicable. Suggestions for amendments to this document should be addressed to : The Co-ordinator, Committee on “Inspection of Static Equipment, Oil Industry Safety Directorate, 2nd Floor, “Kailash” 26, Kasturba Gandhi Marg, New Delhi – 110 001
4
COMMITTEE ON INSPECTION OF STATIC EQUIPMENT List of --------------------------------------------------------------------------------------------------------------------------Name Designation & Position in Organisation Committee --------------------------------------------------------------------------------------------------------------------------1.
Sh. R.K. Sabharwal
CMNM-IOC (R & P)
Leader
2.
Sh.A.S. Soni
DGM (P)-ONGC
3.
Sh.R.H. Vohra
DGM-(E) IOC (Mktg.)
4.
Sh.D.P. Dhall
CH INSP & AE MGR-BPC (REF) Member
5.
Sh.P. Dasgupta
Sr.Manager( Inspection) IOC (R & P)
Member
6.
Sh.I.M. Advani
MGR (PROJ) HPC (REF)
Member
7.
Sh.R.M.N. Marar
Jt.Director OISD
Member Member
Member Co-ordinator.
--------------------------------------------------------------------------------------------------------------------------In addition to the above, several other experts from the industry contributed in the preparation, review and finalisation of this Recommended Practices.
5
INSPECTION OF PIPES, VALVES AND FITTINGS CONTENTS SECTION 1.0
Introduction
2.0
Scope
PAGE NO.
3.0 Definition and Types of Pipes 3.1 Pipes 3.2 Types of Pipes 3.2.1 Electric Resistance Welded Pipes 3.2.2 Electric Fusion Welded Pipes 3.2.3 Double Submerged Arc Welding Pipes 3.2.4 Spiral Welded Pipes 4.0 Role of Inspection 5.0 Inspection Tools 6.0 Inspection of Piping during Fabrication 7.0 Check List for Inspection of Piping prior to Commissioning 8.0 Likely Areas of Metal Wastage 8.1 External Corrosion 8.2 Internal Corrosion 9.0 Frequency of Inspection 9.1 Onsite Piping 9.2 Offsite Piping 9.2.1 Hydrocarbon Service 9.2.2 Utilities 9.2.3 Underground Piping 10.0 Inspection Procedures 10.1 Onstream Inspection 10.1.1 Visual Inspection 10.1.2 Ultrasonic Inspection 10.1.3 Radiographic Inspection 10.1.4 Corrosion Probes 10.1.5 Corrosion Coupons 10.2 Inspection during Shutdown 10.2.1 Inspection for Corrosion, Erosion and Fouling 10.2.2 Inspection for Cracks 10.2.3 Inspection of Gasket Faces of Flanges 10.2.4 Inspection of Hot Spots
6
10.2.5 Hammer Testing 10.3 Inspection of High Temperature Piping 10.4 Inspection of Piping in Corrosive Streams 10.5 Inspection of Underground Piping 10.5.1 Cathodically Protected Piping 10.5.2 Wrapped and coated pipelines without Cathodic Protection 10.5.3 Internal Corrosion of Underground Piping 10.6 Inspection of Valves, Flanges, Gaskets & Bolts 10.6.1 Valves 10.6.2 Flanges, Gaskets and Bolts 11.0 Retiring Limit 12.0 Method of Pipeline Repair and Inspection 12.1 Inspection During Repairs/Replacements 12.2. Pressure Testing 12.2.1 Test Pressure and Procedures 12.2.2 Test Fluid 12.2.3 Water Quality 13.0 Documentation 14.0 References ANNEXURES I Safety Practices to be followed during Pressure Testing II Inspection Report (Proforma )
7
INSPECTION OF PIPES, VALVES AND FITTINGS 1.0
INTRODUCTION
3.2.3
Safety in petroleum installations comes through continues efforts at all stages and as such it can be ensured by observing that plant and equipment are designed, constructed, tested and maintained as per Engineering Standards and subsequent modifications and repairs are conforming to the same standard.
2.0
SCOPE
This standard covers minimum inspection requirements for plant piping and off-site piping constructed as per Standard ANSI B-31.3 or equivalent. Areas to be inspected, facilities needed for inspection, frequency of inspection, likely causes of deterioration of pipelines in service and inspection of pipe fittings and repairs have been specified. Also included briefly are the inspection and testing requirements for the new pipelines during fabrication and prior to commissioning.
Double Submerged Arc Welding Pipes
Pipe having a longitudinal butt t produced by at least two es, one of which is one the inside of the pipe. Coalescence is produced by heating with an electric arc or arcs between the bare metal electrode or electrodes and the work. The welding is shielded by a blanket of granular fusible material on the work. Pressure is not used and filter metal for the inside and outside welds is obtained from the electrode or electrodes. 3.2.4
Spiral Welded Pipes
Pipe having a helical seam with butt t which is welded using either an electrical resistance, electric fusion or double submerged arc welding process. 3.2.5
Seamless Pipes
Pipe produced by piercing a billet followed by rolling or drawing or both.
3.0
DEFINITION AND TYPES OF PIPES
4.0
3.1
PIPE
The following are the activities of the inspection division.
A pipe is a pressure-tight used to convey a fluid or to transmit a fluid pressure. 3.2
TYPES OF PIPES
3.2.1
Electric Resistance Welded Pipes
Pipes produced in individual lengths or in continuous lengths from coiled skelp and subsequently cut into individual lengths having a longitudinal or spiral butt t wherein coalescence is produced by the heat obtained from resistance of the pipe to the flow of electric current in a circuit of which the pipe is a part, and by the application of pressure. 3.2.2
Electric Fusion Welded Pipes
Pipe having a longitudinal butt t wherein coalescence is produced in the preformed tube by manual or automatic electric-arc welding. The weld may be single or double and may be with or without the use of tilter metal.
8
ROLE OF INSPECTION
i)
To inspect, measure and record the deterioration of materials and to evaluate present physical condition of the piping for its soundness in service.
ii)
To co-relate the deterioration rate with design life for further run.
iii) To determine causes of deterioration and to advise remedial measures. iv) To recommend / forecast short-term and long-term repairs and replacements to ensure further run length on the basis of economics and safety. v) To advise materials requirement for recommended repairs / replacement needs. vi) To inspect during and upon completion of repairs. vii) To maintain up-to-date inspection records and history of piping.
viii) To keep the concerned operating and maintenance personnel fully informed as to the condition of the various piping.
specifications, drawings, etc. This inspection requires regular checks on the work at various stages as it progresses.
ix) To advise regarding schedules of piping inspection and also statutory requirement schedules.
The inspection shall include:
5.0
INSPECTION TOOLS
The following tools may be used as aids for carrying out piping inspection. i)
Ultrasonic thickness meter.
iii) Magnetic particle testing equipment.
v) Fibroscope.
viii) Dye Penetrant testing kit.
viii) Ensuring proper preheating, maintaining proper inter temperature and postweld heat treatment as specified.
ix) Holiday detector. x) Portable hardness tester.
ix) Radiographic and/or ultrasonic inspection of weld ts as specified.
xi) Inspector’s hammer.
x) Ensuring repairs of the defective welds, if any, before giving clearances for hydrostatic testing.
xii) Paint and coating thickness gauge. xiii) Pit depth gauge.
xi) Ensuring proper repairs to damaged lining (cement/rubber), if any.
xiv) Inside and outside calipers. xv) Magnet.
xii) Hydrostatic testing.
xvi) Measuring tape.
Safety torches.
xiii) Ensuring all approved deviations from the drawing are noted and as built drawing prepared. xiv) Ensuring proper surface preparation and painting.
xix) Crayons.
xv) Ensuring installation of proper insulation wherever applicable.
xx) Small mirror. xxi) Material identification kit.
6.0
iii) Approval of welding procedures in accordance with code and tender requirement.
vii) Dye-penetrant examination of the prepared edges for low allow steel and stainless steel.
vii) Ag-Agcl / Cu-so4 half-cell.
xviii)
Identification and inspection of material.
vi) Inspection of weld t fit-ups.
vi) Radiographic equipment.
Magnifying glass.
ii)
v) Ensuring that welding is carried out as per agreed procedures, by approved welders with specified electrodes.
Infrared pyrometer / petroscanner.
xvii)
Study of tender document and all the technical specifications.
iv) Carrying out of performance qualification test.
ii) Ultrasonic flaw detector.
iv)
i)
INSPECTION OF PIPING DURING FABRICATION
The inspection of piping during fabrication shall be carried our as per the requirement of applicable codes.
9
xvi) Ensuring underground protection for buried piping, has been provided as specified.
7.0
CHECK LIST FOR INSPECTION OF PIPING PRIOR TO COMMISSIONING
The checklist format following information Pipe sketch No/drg. No. Location Service Material Dimensions Max. allowable working pressure Max. allowable working temperature Stress relief
shall
include
Dia
Thk.
the
Radiography Hydrostatic test pressure Insulation Internal lining Underground protection Erection contractor Contractor's inspector Company's inspector Date of inspection
CHECK LIST CHECK
REMARKS
1. Inspect weld ts visually. 2. Check and inspect small connections e.g. drains and vents. 3. Check and inspect all threaded connections for proper engagement of threads, backwelding and gusseting. 4. Check for any alteration/deviation from the drawing during construction. 5. Check wall thicknesses (to serve as initial readings for corrosion data). 6. Check installation of gaskets. 7. Check installation of pressure relieving devices. 8. Check installation of check valves. 9. Check bolting of flange ts. 10. Check for proper alignment of s (on pipe-racks or sleepers) 11. Check steam tracings and steam traps. 12. Check painting. 13. Check insulation. 14. Check for proper hook-up with cathodic protection system wherever applicable.
10
8.0
LIKELY AREAS OF METAL WASTAGE
8.1 EXTERNAL CORROSION The following areas of piping are prone external corrosion. i)
Piping above ground atmospheric corrosion.
is subject to
Usually a greater loss of metal wastage is observed near a restriction in the line or a change in line direction because of the effects of turbulence or velocity. Therefore, is required to inspect pipe bends, elbows, and tees and also at restrictions such as orifice flanges and throttling valves, and areas just down steam of the restriction. Areas most prone to corrosion, erosion, and other forms of deterioration are :
ii) Pipelines touching the ground are subject to corrosion due to dampness of the soil.
i)
Points at which condensation of acid gases and / or water vapour are likely to occur.
iii) Crevice corrosion may take place at the pipe s or sleepers where pipes are resting on them.
ii)
Points at which acid carryover from process operations are likely to occur.
iii)
Points at which naphthenic or other organic acids may be present in the process stream.
iv)
Points at which high sulphur steams of moderate to high temperature exists.
v)
Points at which high temperature and low temperature hydrogen attack may occur.
vi)
Dead-ends and locations where liquidvapour interphasing or condensation occur.
vii)
Valve bodies and trims, fittings, ring grooves and rings, flange faces and unexposed threads.
iv) Deterioration takes place at the pipe locations where relative movement between pipe and pipe s takes place. v) Buried pipelines are subject to soil corrosion. vi) Underground pipelines are subject corrosion due to presence of stray currents. vii) Impingement attack may take place on pipelines in the vicinity of leaky pipes and steam traps. viii) Insulated lines where weather shielding is damaged are subject to external corrosion. ix) Austenetic stainless steel lines where chlorides can leach from external thermal insulation due to water are subject to stress corrosion cracking.
viii) Welded areas (subject to preferential attack). ix)
Catalyst, flue gas, and slurry piping.
x)
Steam systems subject to channeling or where condensation occurs.
xi)
Ferrous and non-ferrous piping subject to stress corrosion cracking.
xi) Piping entering into or emerging from the underground may experience severe corrosion due to coating damage.
xii)
xii) Piping corrodes at locations of water accumulation and acid vapour condensation such as in the vicinity of fire hydrants sulphur recovery plants, cooling towers, jetty, etc.
Alkali lines subject to caustic embrittlement with resultant cracking at stressed areas such as weld ts, bends, etc.
xiii)
Areas near flanges or welded attachments, which act as cooling fins, thereby causing localised corrosion because of condensation.
8.2
xiv) Locations where fluid impinges or fluid velocity changes.
x) Externally concrete-lined pipelines are subject to localised corrosion due to cracks in the concrete.
INTERNAL CORROSION
xv)
Chrome-Nickel and chromemolybdenum lines in high temperature service near points of increased stress such as bends and anchor points.
xvi) Are where steam or electric tracing come in with pipes handling materials such as caustic soda.
should be done on-stream as far as is possible once between two scheduled turnarounds. Inspection, which cannot be made during operation, shall be done during the plant shut down. However, depending on the corrosion rate and type of deterioration, the frequency of inspection of process piping can be varied suitably. 9.2
xvii) Austenetic stainless steel lines where polythionic acid formation takes place with resultant cracking. xviii) Areas immediately downstream of chemical injection points where localised corrosion might occur in the reaction zone.
OFF-SITE PIPING
The following frequencies for inspection of off-site piping shall be followed (see notes): 9.2.1
Hydrocarbon Service
Service
Frequency of Inspection years -----------------------------------External Comprehensive
xix) Dissimilar metals in , which may lead to galvanic corrosion. xx)
Rubber-lined and glass-lined pipes which may get damaged near the flanges or due to cracks in the lining.
xxi) Stagnate conditions in areas of pipelines carrying crude oils with high sulphur/chloride content. xxii) Terminal pipelines ballast water.
carrying
sea/
xxiii) Locations having low pit and high chloride ions.
9.0 FREQUENCY OF INSPECTION
i) Crude: Sweet Sour
5 3
10 6
ii) LP/Natural gas: Sweet Sour
3 2
6 4
iii) Natural gas condensate
2
4
iv) Gasoline/ Naphtha
2
4
v) ATF/HSD/LDO/ SKO/Gas Oil
3
5
The interval between inspections depend upon the -
vi) FO/RCO/VBO/ Bitumen
3
i)
Degree of corrosiveness/erosiveness of the fluid.
vii) Flera/Fuel gas
3
ii)
Remaining corrosion allowance.
iii)
Type of protective coating.
iv)
Atmosphere piping.
v)
Potentially of fire or explosion in case of a leak or failure.
vi)
Statutory requirements.
prevailing
around
the
vii) Importance of operations. 9.1
ONSITE PIPING Inspection of process piping in units
viii) Lube Oil Note:
5
5
5 or during the shutdown of the line 10
WHERE CRUDE SOURCE CANNOT BE ESTABLISHED THE FREQUENCY SPECIFIED FOR SOUR CRUDE SHALL APPLY. 9.2.2 Service
Utilities Frequency of Inspection (years) ----------------------------------External Comprehensive
i) Sweet water: Lined pipe Unlined pipe ii) Salt water: Cement lined pipe Unlined pipe
3 2
5.
3 1
6 2
iii) Fire water: Above ground: Lined pipe Unlined pipe
3 1
5 2
Underground: Lined pipe Unlined pipe
3 2
5 4
3
6
iv) Air/Steam
revealed that failures of most of the Offsite pipelines are due to external corrosion and that internal corrosion failures are minimum.
6 4
Inspection data as well as thickness data of newly constructed pipelines shall be collected at the earliest and with in two years of their commissioning to function as base for establishment of corrosion rates.
9.2.3
v)Steam condensate 2 4 vi) Ammonia 2 4 vii) Caustic 2 4 viii) DEA/MEA 3 5 ix) Sulphur dioxide 2 4 x) Sulphuric acid (conc. 98%) 2 4 xi) Furfural /Phenol 2 3 xii) Lined pipes (excluding water lines) 3 6 xiii) Benzene 2 4 xiv) Toulene 2 4 xv) Sodium Hexametaphosphate 2 4 ----------------------------------------------------------*Notes: 1.
The above frequencies are bases on data collected from various refineries.
2.
External inspection includes both visual inspection and ultrasonic thickness readings taken externally.
3.
Comprehensive inspection covers some or all of the following tests:
i) ii) iii) iv) v) vi) vii)
Visual inspection Hammer test Ultrasonic thickness measurement Dye penetration test Magnetic particle test Radiographic test Hydrotest
4.
Piping is coastal installations and in corrosive environment shall be visually inspected once a year. Years of inspection experience have
Underground piping fire water lines)
(excluding
i) CATHODICALLY PROTECTED LINES Those underground lines having wrapping and coating as well as cathodic protection shall be inspected whenever current leaks are observed and/or any damage to the coating is suspected. The damage to the coating can be located by person survey. Parameters of cathodic protection like pipe-to-soil voltage or pipe-towater voltage shall be monitored once a month. ii)
LINES WITHOUT PROTECTION
CATHODIC
All underground lines having only wrapping and coating shall be inspected once in three years using Person Survey for locating coating damage, if any. Additionally, all these lines shall be visually inspected at random once in ten years by digging at a few locations. Pipelines crossing the roads and dykes shall be inspected once in ten years by digging and exposing the line completely. 10.0 INSPECTION PROCEDURES 10.1 ONSTREAM INSPECTION Piping in Offsite areas can and shall be inspected onstream and a regular inspection programme drawn up. Piping in onsite areas should also be inspected on the run, subject to feasibility as permitted by process parameters (fluid, pressure and temperature). Any abnormalities notices during inspection shall be investigated and corrective steps initiated at the earliest. In setting priorities of inspection of different pipelines, it is recommended that the following categorisation be adopted: i) Where failure is likely to be hazardous. ii) Where failure is likely to cause plant shutdown.
iii) Where there is reason to suspect, based on experience, that there is excessive metal loss.
e) Movement or deterioration of concrete footings.
iv) Remaining piping.
f) Condition of foundation bolts.
Onstream inspection to monitor deterioration should be visual or instrumentaided(ultrasonic, radiographic).
g) Free operation of pipe rollers. h)
Secure attachment of brackets and beams to the s.
10.1.1 Visual Inspection i) LEAKS Visual inspection shall be made to locate leaks. Particular attention should be given to pipe connections, the packing glands of valves and expansion ts. ii) MISALIGNMENT
i) Secure attachment and proper adjustment of pipe hangers, if used. Spring hangers loading shall be checked both cold and hot and the readings obtained shall be checked against the original cold and hot readings. The movement of spring s shell be monitored. j) Broken or otherwise defective pipe anchors.
The piping shall be inspected for mis-alignment. The following are some observations which may indicate misalignment:
k) Free operation of pulleys or pivot points of counter balanced piping system. iv) VIBRATION
a) Pipe dislodged from its so that that weight of the pipe is distributed unevenly on the hangers or the saddles. b) Deformation of the wall of the vessel in the vicinity of the pipe attachment. c) Pipe s forced out of plumb by expansion or contraction of the piping. d) Shifting of base plate or shearing of the foundation bolts of mechanical equipment to which the piping is attached. e) Cracks in the connecting flanges or pump casings and turbines to which the piping is attached. iii) S Pipe s shall inspected for the following:
be
a) If vibrations or swaying is observed, inspection, shall be made for cracks in welds, particularly at points of restraint such as where piping is attached to equipment and in the vicinity of anchors. Additional s should be considered for poorly braced small size piping and valves and for main vibrating line to which they are attached. b)
In case of severe vibration, detailed investigations shall be carried out to determine the source of problems.
v) EXTERNAL CORROSION Inspection of piping for external corrosion shall be carried out with special attention to areas as outlined in 8.1
visually vi) BULGING, BOWING AND SAGGING
a)
Condition of protective coating or fire proofing if any. If fire proofing is found defective, sufficient fire proofing should be removed to determine extent of corrosion.
Line shall be checked for bulging, bowing and sagging in between the s. vii) MECHANICAL DAMAGE EXTERNAL FORCES
FROM
b) Evidence of corrosion c) Distortion
Pipes shall be inspected for dents, scratched etc. from external sources.
d) General physical damage
viii)
FAILURE
OF
PAINT
AND
PROTECTIVE COATING Conditions of paint and protective coating shall be checked.
vi) One ultrasonic scan minimum on straight pipe for every three meters length at lower elevations where possibilities of collection and stagnation of carryover water, or acid condensation or SO2 flow exist.
ix) CRACKS Pipelines shall be inspected for cracks. particular attention should be given to areas near the weld ts. x) INSULATION Damage of insulation shall checked for hot as well as cold lines.
be
vii) Branch connection, dead ends, etc, shall be checked by ultrasonic thickness survey for corrosion and erosion. The details of thickness survey shall be maintained on an isometric sketch (sample as in Annexure II). The above are minimum requirements. Areas of inspection should be increased of thickness readings are low.
xi) CONCRETE LINING Note: Externally coverts lined piping shall be visually inspected for cracking and dislodging of concrete. 10.1.2 Ultrasonic Inspection Ultrasonic thickness survey of the pipelines shall be carried out to ascertain the remaining wall thickness. The following procedure shall be followed for the aboveground pipelines. i) Minimum three readings shall be taken on all the bends of the piping network at the outer curvature. One reading shall be at the centre of the bend and two readings on the same line on either side of this reading. ii) Minimum one ultrasonic scan each on the straight pipes on upstream and downstream of the bend adjacent to welds of the bend to pipe. One ultrasonic scan consists of our readings (3,6,9 and 12 o'clock positions). For pipelines in which there is a possibility of ballast water coming, one ultrasonic scan will consist of six readings (3,5,6,7,9 and 12 o'clock positions) to scan the bottom portions where corrosion may take place. iii)One ultrasonic scan on the entire circumference (four readings) upstream and downstream of the weld t for process pipelines. iv) Minimum one ultrasonic scan (four readings) each on reducer/expander and just downstream on the pipe. v)
One ultrasonic scan on the downstream of valves orifices, etc.
pipe
MOST OF THE ULTRASONIC INSTRUMENTS ARE NOT EXPLOSION PROOF. HENCE HOT WORK PERMIT AS OUTLINED IN OISD-STD-105 SHALL BE COMPLIED WITH. 10.1.3 Radiographic Inspection Critical spots, which cannot be inspected by ultrasonic instruments accurately, shall be radiographed during operation to determine wall thickness as well as internal condition like fouling, scaling, etc. Insulation need not be removed for radiographic inspection. Critical spots where weld-ts, nipples/small dia deadlines are welded, which cannot be inspected ultrasonically shall be radiographed to determine their internal condition. 10.1.4 Corrosion Probes One of the methods of measuring internal corrosion rate of unit piping or Offsite piping is by installing corrosion probes for measuring corrosion rates. Important pipelines like overhead lines can be inspected using corrosion probes. If installed the readings shall be taken weekly and deterioration rate established. 10.1.5 Corrosion Coupons Corrosion coupons should be installed in the important and critical pipelines to measure internal corrosion rate. The coupons are taken out after a specified period and thoroughly cleaned. The weight loss of coupons over a specified period gives the internal corrosion rate of the pipes. 10.2 INSPECTION DURING SHUTDOWN
Shutdown inspection of pipelines relates to inspection of the lines when not carrying any product, and valves and other fittings in the network can be taken out. All piping which cannot be checked on the run shall be inspected during shutdown. These are mostly high temperature piping. During shutdown inspection, hammer-testing and hydrotesting as applicable should be carried out in addition to visual, ultrasonic and radiographic inspections. Pipelines in some of the services like water, phenol and steam are prone to pitting corrosion. Neither ultrasonic nor radiographic testing will reveal the actual internal condition of the pipes in such service. In such cases samples shall be cut for thorough internal examination, at scheduled comprehensive inspections. The samples shall be spilt open in two halves and internal surfaces inspected for pitting, grooving, etc. The internally striplined bends and pipes shall be visually examined for bulging, weld cracking, weld, defects, etc. Thickness of the strip should be measured to find out thinning of the strips. Austenetic SS piping, where there is a chance of stress corrosion cracking due to formation of polythionic acid, shall be kept in inert atmosphere. ivation of the austanetic SS piping shall be done as per NACE-RP-01-70, if all these are to be opened to the atmosphere. 10.2.1 Inspection for Corrosion, Erosion and Fouling Piping shall be opened at various locations by removing valves at flanged locations to permit visual inspection. When erratic corrosion or erosion conditions are noted in areas accessible for visual examination, radiographic examination or ultrasonic testing shall be performed to determine thickness. This is applicable to piping which cannot be inspected during operation. The nature and extent of internal deposits shall be noted. Samples should be collected for chemical analysis.
done. Magnifying glass should be used for crack detection. 10.2.3
Inspection of Gasket Faces of Flanges
The gasket faces of flange ts which have been opened shall be inspected visually for corrosion and for defects such as scratches, cuts and grooving which might cause leakage. Ring gaskets and ts shall be checked for defects like dents, cuts, pitting and grooving. 10.2.4 Inspection of Hot Spots Where hot spots on internally insulated pipe were noted during operation, the internal insulation shall be inspected visually for failure. The pipe wall at the hot spot shall be inspected visually for oxidation and scaling. The scales shall be removed to expose bare metal and the area checked for cracks. The thickness of the metal shall be measured to ensure that sufficient thickness is felt for the service. The outside diameter of piping in high temperature service shall be measured to check for creep deformation. 10.2.5 Hammer Testing Hammer testing shall also be carried out to supplement visual and ultrasonic inspection. While hammer testing, the following precautions shall be taken: i) Hammer testing of valves, pipes and fittings of cast iron construction, chromesteel, austenatic SS lines and stress relieved lines shall not be carried out. ii) Care shall be taken not to hammer so hard as to damage otherwise sound piping. iii) Hammer testing shall not be performed on glass-lined, cement-lined or otherwise internally coated lines. iv) Hammer testing shall not be done on operating lines and lines under pressure.
10.2.2 Inspection For Cracks 10.3 Welds, heat-affected areas ading welds, points of restraint cracking, hydrogen attack and caustic embrittlement shall be inspected for cracks. For spot checks, dyepenetrant or magnetic particle inspection should be used. Alloy and stainless steel piping need close inspection. In-situ metallorgraphy at critical spots may be also
INSPECTION OF TEMPERATURE PIPING
HIGH
Inspection shall be made for hot spots on internally insulated piping. Any bulging or scaling shall be noted for further inspection when the equipment is shut down. Some sot spots can be detected by a red glow, particularly if inspection is made in the
dark. Portable infrared pyrometer or temperature indicating crayon shall be used to determine the skin temperatures. Sometimes thermographic survey of internally insulated hot piping helps in locating the hot spots. Furnace transfer lines and column bottom lines, which are operating at very high temperatures, shall be inspected at every shutdown. Insulation shall be removed at specified locations including all bends and ultrasonic thickness shall be carried out and the corrosion rate established. Spring hangers and spring s of high temperature piping shall also be checked during shutdown. 10.4
INSPECTION OF PIPING CORROSIVE STREAMS
IN
i) HYDROGEN SULPHIDE (H2S) SERVICE All the weld ts in this line shall be stress relieved after fabrication. Weld ts at random shall be checked for suspected cracking. If the line is not thermally insulated, external thickness measurements shall be taken for suspected internal corrosion. When the line is not in operation, magnetic testing method will help in locating cracks in the welds. ii) DI-ETHYL AMINE/MONO-ETHYL AMINE SERVICE
Carbon steel resists phenolic corrosion upto 205oC provided water is not present. Corrosion in phenol is very erratic. However, when it occurs, it may be very severe. All bends and areas of high velocity and where turbulent conditions occur shall be ultrasonically inspected. However, areas which cannot be inspected ultrasonically shall be radiographed to ascertain their internal condition. v)
CAUSTIC SERVICE
(SODIUM
HYDROXIDE)
Caustic is non-corrosive at atmospheric temperatures top carbon steel. Caustic will cause stress corrosion cracking above 94OC and hence all carbon steel lines shall be stress-relieved before commissioning or after repairs. Lines shall be checked for embrittlement and metal loss. vi) CHLORINE SERVICE Chlorine, though not so corrosive in gaseous phase, becomes highly corrosive when even a small amount of moisture comes in with it. Rubber-lined carbon steel pipes are generally used in chlorine services. Rubber-lined, pipes shall be checked for bulging of lining at bends, flanges or at weld ts. vii) ACID SERVICE
Pipelines carrying DEA/MEA are prone to internal corrosion and stress corrosion cracking. All newly constructed piping shall be stress relieved irrespective of the strength and temperature of the chemicals. All weld ts shall be inspected for cracks using wet fluorescent magnetic particle test. External thickness measurements shall be taken at all bends and other flow-restrictions for determining the internal corrosion rate. All socket-welded and seal-welded threaded connections are prone to stress corrosion cracking if not stress-relieved. Hammer testing of the line shall not carried out as it may induce localised stresses. iii) HYDROGEN SERVICE Carbon steals are prone to hydrogen embrittlement at elevated temperatures above 232oC. Pipelines shall be checked for bulging (hydrogen blistering) and distortion whenever they are shut down for inspection.
Sulphuric acid is corrosive in dilute phase. Hydrochloric acid in corrosive at all concentrations while phosphoric acid is corrosive where it mixes with water in carbon steel pipes. The following locations shall be checked for acid corrosion in carbon steel lines: a) Horizontal sections of the line where dilute-acid stagnation may occur. b) Section of the line at bends where elbows tend to corrode due to turbulent acid attack. c) Section of the line adjacent to orifices, reducers, expanders, etc. d) Caustic neutralisation injection points and T-ts due to turbulence. e) Heat affected zones of weld ts due to residual stress concentrations and thermo-galvanic effects.
iv) PHENOL SERVICE f) Locations where temperatures are more
than 50oC. 10.5
INSPECTION OF UNDERGROUND PIPING
Underground piping is mainly checked off-stream. However, development of exigencies may require inspection of the same on the run after exposing the line. 10.5.1 Cathodically Protected Piping Cathodic protection shall be controlled so as not to damage the protective coating. A pipe-to-soil voltage of -0.85, with respect to Cu-CuSO4 half call has been found to give adequate protection to cathodically protected pipelines. Any excess voltage may damage the wrapping and coating on the pipe. All buried or submerged coated piping system shall be electrically isolated at interconnections from the other lines which are not cathodically protected. The pipe-tospot potential readings shall also be checked using Cu-CuSO4 cell. 10.5.2
Wrapped and Coated Pipelines Without Cathodic Protection
The condition of the wrapping and coating shall be checked by Pearson survey once in three years for underground piping not cathodically protected. Excavations shall be done at vulnerable points like regions of low velocity and straight portions downstream of bends. The excavation, once in ten years is optimum requirement. After excavation, the wrapping and coating shall be examined both visually and by holiday detector. Internal metal loss and fouling may be detected by radiographic examination. Ultrasonic thickness measurements shall be carried out on the surface of the pipe after removing a bend of wrapping and coating. The pipeline shall be hydrotested once every five years. The stray current interference of underground pipe should be checked by CuCuSO4 half-cell. All lines shall be inspected at and just before the point where they enter the earth or concrete slab as serious corrosion frequently occurs at such locations. The incidence of stray current interference is high in the underground portion of cathodically protected and noncathodically protected piping separated by insulated flanges or couplings. This current causes severe damage in the unprotected line if the wrapping and coating is damaged. This location should be inspected once a year by exposing the insulating flanges or couplings.
10.5.3 Internal Corrosion Underground Piping
of
In order to assess the internal condition of underground pipelines, ultrasonic thickness survey by exposing the line shall be done as per frequency specified previously. Bends, reducers, expanders, branch connections and dead-ends shall be exposed and thickness survey at these locations carried out as per the guidelines given for the above-ground pipelines. One location every 100 meters for a straight portion shall be exposed for thickness survey. Internal corrosion monitoring of these lines should be done by installing corrosion probes at vulnerable locations. Readings should be taken once a week to calculate the corrosion rate. 10.6
INSPECTION OF VALVES, FLANGES, GASKETS & BOLTS
10.6.1 Valves Steel gate valves steel globe valves, flanged cast iron gate valves, threaded and socket welded valves, soft-seated ball valves`Fire Safe Type', plug valves, check valves and butterfly valves for water service are used in Petroleum installations.
i) INSPECTION AND TESTING OF NEW VALVES All valves shall be inspected and tested to ensure conformation to required specifications and for leak tightness. All new valves shall be inspected and tested as per requirements of API-598. The closure torque during testing for hand wheel and gear operated valves shall not be greater than that obtainable by hand tightening. (a) Valves in Hydrogen Service All low alloy valve castings (P numbers 3,4 and 5) in hydrogen service with a hydrogen partial pressure of 100 psig shall be 100% magnetic particle and radiographically examined. Examination and acceptance criteria shall be as per ASME Section VIII Appendix 7. (b) Valves in Wet H2S Service
Valves made of steel containing phosphorus or sulphur in excess of 0.5% shall not be used in H2S service. Hardness of the body, bonnet and gate and weld metal and HAZ of any pressure retaining part shall not exceed the limits given below:Material
Brinell hardness,
P-1 P-3, P-4, P-10, P12 P-5, P-6, P-7 inconel, Precipitation hardened
225 225 225 310
(c) Fire Safe Type Ball Valves Each valve shall be tested as per API 598. - Low pressure sect test shall be conducted with the ball and seat dry and free of oil, grease or any lubricant. - The high pressure seat test is not required except for threaded and valves. - No leakage shall be permitted. - Fire-safe test shall be carried out as per API 6070.
ii) INSPECTION OF VALVES IN SERVICE Valves shall be dismantled at the time of specified comprehensive inspection or during the shutdown of the line to permit examination of all internal parts. Body thickness measurements shall be made at locations inaccessible before, dismantling, particularly at locations showing evidence of erosion. Bodies of valves operating in severe cyclic temperature service shall be checked internally for cracks. Gate valves, which have been used for throttling, shall be measured for thickness at the bottom between the seats, as serious deterioration may have occurred because of turbulence. This is particularly weak point because of the wedging action of the disc when the valve is closed. The seating surface shall be inspected visually for defects which might cause leakage. The wedging guides shall be inspected for corrosion and erosion. The stem and threads on the stem and in the bonnet of valves shall be
examined for corrosion which might cause failure., The connection between stem and disc shall be inspected to assure that the disc will not detach from the stem during operating. Swing check valves shall be inspected by removing the cover or cap. The clapper or disc shall be checked for freedom of rotation and the nut holding it to the arm shall be checked for security and presence of a locking pin, lock washer, or tack weld. The arm should be free to swing and the anchor pin shall be inspected for wear. Also the seating surface on both the disc and valve body shall be checked for deterioration by feeling them with the fingers. After the valve has been reassembled, it shall be hydrostatically and/or pneumatically tested for tightness. If tested pneumatically, a soap solution shall be applied to the edges of the seating surface and observed for any evidence of leakage. 10.6.2 Flanges, Gaskets and Bolts The gasket faces of flanged ts, which have been opened, shall be inspected visually for corrosion and for defects such as scratches, cuts and gouges which might cause leakage. The gasket faces shall be checked for true flatness or warping by placing a straight edge across the diameter of the face of the flange and rotating it about an axis through the center line of the flange. Grooves and rings of ring ts shall be checked for defects. Flanges bolts should be inspected for stretching. Where excessive bolt loading is indicated or where flanges are deformed, nuts may be rotated along the entire length of the stud. If studs are stretched, thread pitch will be changed and nuts will not turn freely. Inspection involve checking to determine whether bolts of the proper specification have been used and may involves chemical analyse or physical tests to determine the yield point and the ultimate strength of the material. If flanges are bolted too tightly, they may bends until the outer edges of the flanges are in . When this occurs, there may be insufficient pressure on the gasket to assure a tight t. Visual inspection of the gasket will reveal this condition. Permanently deformed flanges must be replaced. 11.0 RETIRING LIMIT Calculation of retiring limits for unit piping and offsite piping shall be done as per
ANSI B 31-3 end ASME Section VII Div. 1. The retiring limit relates thickness, diameter and allowable stress to the maximum safe working pressure. In addition, ANSI B 31.3 contains a formula with material factors for determining the required thickness but permits the use of the simple formula of Barlow without reservation. The Barlow formula is: t
=-
12.7 P x D -------------SE
Where t= required thickness of the pipewall in mm. P= Pressure within the pipe in kg/sq.cm D= Outside diameter of the pipe in cms. S= Allowable unit stress in kg/sq.cm. at the maximum operating temperature. E= Longitudinal t efficiency. Note: Metallic piping with t = D/4 requires special consideration. The Barlow formula gives results particularly equivalent to those obtained by the more elaborate formula, except at high pressures where thick-walled tubing is required or at high temperatures where creep properties of the pipe metal become important in determining the ultimate service strength. At low pressures and low temperatures, the thickness required by the formula may be so small that the pipe would have insufficient structural strength. For this reason, an absolute minimum thickness shall be determined for each size of pipe below which thickness of the pipewall would not be permitted to deteriorate regardless of the results obtained by the above formula. As a guideline, minimum thickness for C.S. piping are given below: Nominal pipe size (mm) thickness (mm)
Minimum
50 mm and smaller 63-76 101.6 152.4 203.2 254-609.6
1.5 1.8 2.2 2.8 3.0 3.3
12.0
12.1 INSPECTION DURING REPLACEMENTS
REPAIRS /
The portion of the piping, which may reach the retiring limit before the subsequent scheduled inspection, shall be replaced. While replacing the pipe, the following points shall be considered. i) The metallurgy and dimensions of the new pipe shall match with those of the existing pipe. ii) Repairs shall be carried out by a qualified welder using qualified welding procedures. iii) For ERW pipes, the weld seam shall be kept staggered and the ERW seam shall appear in the upper quadrants. iv) Piping systems, which are covered under other statutory requirements, shall be checked for conformation with the appropriate codes, regulations and specifications. v) Inspection of ts shall be done as previously specified. vi) Repaired welds shall be subject to same pre and post-weld heat treatments as required in the case of new pipes. vii)
Painting, insulation, wrapping and coating shall be done as per the code.
12.2 PRESSURE TESTING All installed piping shall be pressure tested prior to commissioning. Piping systems open to atmosphere, such as drains vents and outlet piping for relief valves discharging to atmosphere and underground sewers shall not require any pressure testing. These lines shall be examined to determine that all ts are properly made up. 12.2.1 Test Pressure and Procedures
METHODS OF PIPELINE REPAIR AND INSPECTION
The test pressure and procedure for testing of piping shall be as per ANSI B 31.3 or equivalent. However, the following additional points shall be considered while carrying out testing. i) All floats shall be removed before filling the system with water. ii) All air present in the system shall be
vented while itting the test fluid. iii) Piping designed for vapour and gas shall be provided with additional temporary s, if necessary. iv) Line containing check valves shall have source of test pressure on the upstream side. v) Valves shall not be subjected to a test pressure in excess of manufacturer's allowable test rating. When permitted, the installed valves shall be kept open. vi) Control and relief valves shall be excluded from the test irrespective of their pressure rating. vii) Instrument take-off piping upto the first block valve shall be tested along with piping to which it is connected. Testing of remaining line leading upto the instrument can also be done at the same time provided instruments are blocked off from the source of pressure and vented to atmosphere. viii) Open ends of piping where blanks cannot be used e.g. pumps, compressors, etc. shall be blinded off by using standard blind flanges of same rating as the piping system being tested. ix) Indicating pressure gauges mounted locally may be tested with the line, provided the test pressure is not in excess of their scale ratings. x) Orifice plates in horizontal lines shall not be installed till completion of test. xi) The test shall be carried out at ambient temperature and it should not be less than 50oC. xii) All vent valves during filling up as during draining must be fully open.
i) Portable water free from oil and suspended matter shall be used for ferritic parts and feritic parts associated with non-ferrous parts. ii) Water shall be d-ionized having a conductivity not greater than one micro mho per cm at 250oC for austenetic parts end ferritic parts associated with austenetic parts. 13.0 DOCUMENTATION Isometrics of each circuit as per actual site conditions shall be prepared. The records shall be maintained to give information like: i) Identification of particular piping systems in of location, total length, material specification, general process flow and service condition and location of corrosion probes, if any. ii)
Location of thickness measurement points, replacement carried out, corrosion rate, etc.
An isometric sketch for guidance has been given in Annexure-2. All small connections shall be clearly shown on isometrics and piping drawings. The history and thickness records shall be maintained in history cards and data record cards. On the basis of records of previous and present inspection, a work schedule shall be prepared for future inspection onstream as well as during the next shutdown. 14.0 REFERENCES The following standards, codes and publications have either been referred to or used in the preparation of this document and this standard shall be read in conjunction with the same
12.2.2 Test Fluid Hydraulic testing of ferritic material shall be carried out using suitably inhabited water, which permits an extended period between the start of testing and drying of components. Hydraulic testing of austemotic material shall be carried out using de-ionized water. 12.2.3 Water Quality
i) ANSI B 31.3 Chemical Plant and Petroleum Refinery Piping. ii) API Guide for Inspection of Refinery Equipment Ch. XI.
iii) Piping Handbook-Crocker and King. iv) ASA B 36.10 welded seamless wrought steel pipe. v) ASA B 36.19 stainless steel pipe. vi) NACE RP 01-69. vii) NACE RP-01-70. viii) NACE RP-01-75.
ANNEXURE -1
SAFETY PRACTICES TO BE FOLLOWED DURING PRESSURE TESTING 1. Hammer testing of piping undergoing a pressure test shall not be carried out as this may cause failure resulting in possible injury or death to those performing the test. 2.
Stress due to testing shall not exceed 90% of the yield stress of the material of construction of the piping as it may cause failure resulting in possible injury or death to those performing the test.
3. Pressure test shall not be carried out at metal temperatures near the ductile-tobrittle transition temperature of the material.
4. If the piping is tested pneumatically, the pressure, shall be 110% of the design
pressure. Pneumatic testing involves the hazard due to possible release of energy stored in compressed gas. Therefore, particular care shall be taken to minimize the chance of brittle failure. Any pneumatic test shall include a preliminary check at not more than 25 psi (2kg/cm2) gauge pressure. The pressure shall be increased gradually in steps providing sufficient time to allow the piping to equalise strains during test. 5. In addition to the above, conditions listed out in Appendices F and G of ANSI B 31.3 should be kept note of.-
INSPECTION OF PIPES, VALVES AND FITTINGS
OISD - STANDARD-130 First Edition, November 1988 Reaffirmed, August, 1999
OIL INDUSTRY SAFETY DIRECTORATE Government of India Ministry of Petroleum & Natural Gas OISD STANDARD - 130 First Edition, November 1988
1
Reaffirmed, August, 1999 FOR RESTRICTED CIRCULATION No.
INSPECTION OF PIPES, VALVES AND FITTINGS
Prepared by
COMMITTEE ON INSPECTION OF STATIC EQUIPMENT
OIL INDUSTRY SAFETY DIRECTORATE 2ND FLOOR, “KAILASH” 26, KASTURBA GANDHI MARG, NEW DELHI – 110 001
2
NOTES
OISD publications are prepared for use in the Oil and gas industry under Ministry of Petroleum and Natural Gas. These are the property of Ministry of Petroleum and Natural Gas and shall not be reproduced or copied and loaned or exhibited to others without written consent from OISD. Though every effort has been made to assure the accuracy and reliability of data contained in these documents, OISD hereby expressly disclaims any liability or responsibility for loss or damage resulting from their use. These documents are intended only to supplement and not replace the prevailing statutory requirements.
3
FOREWORD The Oil Industry in India is 100 years old. Because of various collaboration agreements, a variety of international codes, standards and practices have been in vogue. Standardisation in design philosophies and operating and maintenance practices at a national level was hardly in existence. This, coupled with feed back from some serious accidents that occurred in the recent past in India and abroad, emphasized the need for the industry to review the existing state of art in deg, operating and maintaining oil and gas installations. With this in view, the Ministry of Petroleum & Natural Gas, in 1986, constituted a Safety Council assisted by Oil Industry Safety Directorate (OISD), staffed from within the industry, in formulating and implementing a series of self regulatory measures aimed at removing obsolescence, standardising and upgrading the existing standards to ensure safer operations. Accordingly, OISD constituted a number of Functional Committees of experts nominated from the industry to draw up standards and guidelines on various subjects. The present document on “Inspection of Pipes, Valves & Fittings” was prepared by the Functional Committee on “Inspection of Static Equipment”. This document is based on the accumulated knowledge and experience of industry and the various national and international codes and practices. It is hoped that the provisions of this document, when adopted may go a long way to improve the safety and reduce accidents in the Oil and Gas Industry. s of this standard are cautioned that no standard can be a substitute for a responsible, qualified Inspection Engineer. Suggestions are invited from the s, after it is put into practice, to improve the document further. This standard in no way supersedes the statutory regulations of CCE, Factory Inspectorate or any other Govt. body which must be followed as applicable. Suggestions for amendments to this document should be addressed to : The Co-ordinator, Committee on “Inspection of Static Equipment, Oil Industry Safety Directorate, 2nd Floor, “Kailash” 26, Kasturba Gandhi Marg, New Delhi – 110 001
4
COMMITTEE ON INSPECTION OF STATIC EQUIPMENT List of --------------------------------------------------------------------------------------------------------------------------Name Designation & Position in Organisation Committee --------------------------------------------------------------------------------------------------------------------------1.
Sh. R.K. Sabharwal
CMNM-IOC (R & P)
Leader
2.
Sh.A.S. Soni
DGM (P)-ONGC
3.
Sh.R.H. Vohra
DGM-(E) IOC (Mktg.)
4.
Sh.D.P. Dhall
CH INSP & AE MGR-BPC (REF) Member
5.
Sh.P. Dasgupta
Sr.Manager( Inspection) IOC (R & P)
Member
6.
Sh.I.M. Advani
MGR (PROJ) HPC (REF)
Member
7.
Sh.R.M.N. Marar
Jt.Director OISD
Member Member
Member Co-ordinator.
--------------------------------------------------------------------------------------------------------------------------In addition to the above, several other experts from the industry contributed in the preparation, review and finalisation of this Recommended Practices.
5
INSPECTION OF PIPES, VALVES AND FITTINGS CONTENTS SECTION 1.0
Introduction
2.0
Scope
PAGE NO.
3.0 Definition and Types of Pipes 3.1 Pipes 3.2 Types of Pipes 3.2.1 Electric Resistance Welded Pipes 3.2.2 Electric Fusion Welded Pipes 3.2.3 Double Submerged Arc Welding Pipes 3.2.4 Spiral Welded Pipes 4.0 Role of Inspection 5.0 Inspection Tools 6.0 Inspection of Piping during Fabrication 7.0 Check List for Inspection of Piping prior to Commissioning 8.0 Likely Areas of Metal Wastage 8.1 External Corrosion 8.2 Internal Corrosion 9.0 Frequency of Inspection 9.1 Onsite Piping 9.2 Offsite Piping 9.2.1 Hydrocarbon Service 9.2.2 Utilities 9.2.3 Underground Piping 10.0 Inspection Procedures 10.1 Onstream Inspection 10.1.1 Visual Inspection 10.1.2 Ultrasonic Inspection 10.1.3 Radiographic Inspection 10.1.4 Corrosion Probes 10.1.5 Corrosion Coupons 10.2 Inspection during Shutdown 10.2.1 Inspection for Corrosion, Erosion and Fouling 10.2.2 Inspection for Cracks 10.2.3 Inspection of Gasket Faces of Flanges 10.2.4 Inspection of Hot Spots
6
10.2.5 Hammer Testing 10.3 Inspection of High Temperature Piping 10.4 Inspection of Piping in Corrosive Streams 10.5 Inspection of Underground Piping 10.5.1 Cathodically Protected Piping 10.5.2 Wrapped and coated pipelines without Cathodic Protection 10.5.3 Internal Corrosion of Underground Piping 10.6 Inspection of Valves, Flanges, Gaskets & Bolts 10.6.1 Valves 10.6.2 Flanges, Gaskets and Bolts 11.0 Retiring Limit 12.0 Method of Pipeline Repair and Inspection 12.1 Inspection During Repairs/Replacements 12.2. Pressure Testing 12.2.1 Test Pressure and Procedures 12.2.2 Test Fluid 12.2.3 Water Quality 13.0 Documentation 14.0 References ANNEXURES I Safety Practices to be followed during Pressure Testing II Inspection Report (Proforma )
7
INSPECTION OF PIPES, VALVES AND FITTINGS 1.0
INTRODUCTION
3.2.3
Safety in petroleum installations comes through continues efforts at all stages and as such it can be ensured by observing that plant and equipment are designed, constructed, tested and maintained as per Engineering Standards and subsequent modifications and repairs are conforming to the same standard.
2.0
SCOPE
This standard covers minimum inspection requirements for plant piping and off-site piping constructed as per Standard ANSI B-31.3 or equivalent. Areas to be inspected, facilities needed for inspection, frequency of inspection, likely causes of deterioration of pipelines in service and inspection of pipe fittings and repairs have been specified. Also included briefly are the inspection and testing requirements for the new pipelines during fabrication and prior to commissioning.
Double Submerged Arc Welding Pipes
Pipe having a longitudinal butt t produced by at least two es, one of which is one the inside of the pipe. Coalescence is produced by heating with an electric arc or arcs between the bare metal electrode or electrodes and the work. The welding is shielded by a blanket of granular fusible material on the work. Pressure is not used and filter metal for the inside and outside welds is obtained from the electrode or electrodes. 3.2.4
Spiral Welded Pipes
Pipe having a helical seam with butt t which is welded using either an electrical resistance, electric fusion or double submerged arc welding process. 3.2.5
Seamless Pipes
Pipe produced by piercing a billet followed by rolling or drawing or both.
3.0
DEFINITION AND TYPES OF PIPES
4.0
3.1
PIPE
The following are the activities of the inspection division.
A pipe is a pressure-tight used to convey a fluid or to transmit a fluid pressure. 3.2
TYPES OF PIPES
3.2.1
Electric Resistance Welded Pipes
Pipes produced in individual lengths or in continuous lengths from coiled skelp and subsequently cut into individual lengths having a longitudinal or spiral butt t wherein coalescence is produced by the heat obtained from resistance of the pipe to the flow of electric current in a circuit of which the pipe is a part, and by the application of pressure. 3.2.2
Electric Fusion Welded Pipes
Pipe having a longitudinal butt t wherein coalescence is produced in the preformed tube by manual or automatic electric-arc welding. The weld may be single or double and may be with or without the use of tilter metal.
8
ROLE OF INSPECTION
i)
To inspect, measure and record the deterioration of materials and to evaluate present physical condition of the piping for its soundness in service.
ii)
To co-relate the deterioration rate with design life for further run.
iii) To determine causes of deterioration and to advise remedial measures. iv) To recommend / forecast short-term and long-term repairs and replacements to ensure further run length on the basis of economics and safety. v) To advise materials requirement for recommended repairs / replacement needs. vi) To inspect during and upon completion of repairs. vii) To maintain up-to-date inspection records and history of piping.
viii) To keep the concerned operating and maintenance personnel fully informed as to the condition of the various piping.
specifications, drawings, etc. This inspection requires regular checks on the work at various stages as it progresses.
ix) To advise regarding schedules of piping inspection and also statutory requirement schedules.
The inspection shall include:
5.0
INSPECTION TOOLS
The following tools may be used as aids for carrying out piping inspection. i)
Ultrasonic thickness meter.
iii) Magnetic particle testing equipment.
v) Fibroscope.
viii) Dye Penetrant testing kit.
viii) Ensuring proper preheating, maintaining proper inter temperature and postweld heat treatment as specified.
ix) Holiday detector. x) Portable hardness tester.
ix) Radiographic and/or ultrasonic inspection of weld ts as specified.
xi) Inspector’s hammer.
x) Ensuring repairs of the defective welds, if any, before giving clearances for hydrostatic testing.
xii) Paint and coating thickness gauge. xiii) Pit depth gauge.
xi) Ensuring proper repairs to damaged lining (cement/rubber), if any.
xiv) Inside and outside calipers. xv) Magnet.
xii) Hydrostatic testing.
xvi) Measuring tape.
Safety torches.
xiii) Ensuring all approved deviations from the drawing are noted and as built drawing prepared. xiv) Ensuring proper surface preparation and painting.
xix) Crayons.
xv) Ensuring installation of proper insulation wherever applicable.
xx) Small mirror. xxi) Material identification kit.
6.0
iii) Approval of welding procedures in accordance with code and tender requirement.
vii) Dye-penetrant examination of the prepared edges for low allow steel and stainless steel.
vii) Ag-Agcl / Cu-so4 half-cell.
xviii)
Identification and inspection of material.
vi) Inspection of weld t fit-ups.
vi) Radiographic equipment.
Magnifying glass.
ii)
v) Ensuring that welding is carried out as per agreed procedures, by approved welders with specified electrodes.
Infrared pyrometer / petroscanner.
xvii)
Study of tender document and all the technical specifications.
iv) Carrying out of performance qualification test.
ii) Ultrasonic flaw detector.
iv)
i)
INSPECTION OF PIPING DURING FABRICATION
The inspection of piping during fabrication shall be carried our as per the requirement of applicable codes.
9
xvi) Ensuring underground protection for buried piping, has been provided as specified.
7.0
CHECK LIST FOR INSPECTION OF PIPING PRIOR TO COMMISSIONING
The checklist format following information Pipe sketch No/drg. No. Location Service Material Dimensions Max. allowable working pressure Max. allowable working temperature Stress relief
shall
include
Dia
Thk.
the
Radiography Hydrostatic test pressure Insulation Internal lining Underground protection Erection contractor Contractor's inspector Company's inspector Date of inspection
CHECK LIST CHECK
REMARKS
1. Inspect weld ts visually. 2. Check and inspect small connections e.g. drains and vents. 3. Check and inspect all threaded connections for proper engagement of threads, backwelding and gusseting. 4. Check for any alteration/deviation from the drawing during construction. 5. Check wall thicknesses (to serve as initial readings for corrosion data). 6. Check installation of gaskets. 7. Check installation of pressure relieving devices. 8. Check installation of check valves. 9. Check bolting of flange ts. 10. Check for proper alignment of s (on pipe-racks or sleepers) 11. Check steam tracings and steam traps. 12. Check painting. 13. Check insulation. 14. Check for proper hook-up with cathodic protection system wherever applicable.
10
8.0
LIKELY AREAS OF METAL WASTAGE
8.1 EXTERNAL CORROSION The following areas of piping are prone external corrosion. i)
Piping above ground atmospheric corrosion.
is subject to
Usually a greater loss of metal wastage is observed near a restriction in the line or a change in line direction because of the effects of turbulence or velocity. Therefore, is required to inspect pipe bends, elbows, and tees and also at restrictions such as orifice flanges and throttling valves, and areas just down steam of the restriction. Areas most prone to corrosion, erosion, and other forms of deterioration are :
ii) Pipelines touching the ground are subject to corrosion due to dampness of the soil.
i)
Points at which condensation of acid gases and / or water vapour are likely to occur.
iii) Crevice corrosion may take place at the pipe s or sleepers where pipes are resting on them.
ii)
Points at which acid carryover from process operations are likely to occur.
iii)
Points at which naphthenic or other organic acids may be present in the process stream.
iv)
Points at which high sulphur steams of moderate to high temperature exists.
v)
Points at which high temperature and low temperature hydrogen attack may occur.
vi)
Dead-ends and locations where liquidvapour interphasing or condensation occur.
vii)
Valve bodies and trims, fittings, ring grooves and rings, flange faces and unexposed threads.
iv) Deterioration takes place at the pipe locations where relative movement between pipe and pipe s takes place. v) Buried pipelines are subject to soil corrosion. vi) Underground pipelines are subject corrosion due to presence of stray currents. vii) Impingement attack may take place on pipelines in the vicinity of leaky pipes and steam traps. viii) Insulated lines where weather shielding is damaged are subject to external corrosion. ix) Austenetic stainless steel lines where chlorides can leach from external thermal insulation due to water are subject to stress corrosion cracking.
viii) Welded areas (subject to preferential attack). ix)
Catalyst, flue gas, and slurry piping.
x)
Steam systems subject to channeling or where condensation occurs.
xi)
Ferrous and non-ferrous piping subject to stress corrosion cracking.
xi) Piping entering into or emerging from the underground may experience severe corrosion due to coating damage.
xii)
xii) Piping corrodes at locations of water accumulation and acid vapour condensation such as in the vicinity of fire hydrants sulphur recovery plants, cooling towers, jetty, etc.
Alkali lines subject to caustic embrittlement with resultant cracking at stressed areas such as weld ts, bends, etc.
xiii)
Areas near flanges or welded attachments, which act as cooling fins, thereby causing localised corrosion because of condensation.
8.2
xiv) Locations where fluid impinges or fluid velocity changes.
x) Externally concrete-lined pipelines are subject to localised corrosion due to cracks in the concrete.
INTERNAL CORROSION
xv)
Chrome-Nickel and chromemolybdenum lines in high temperature service near points of increased stress such as bends and anchor points.
xvi) Are where steam or electric tracing come in with pipes handling materials such as caustic soda.
should be done on-stream as far as is possible once between two scheduled turnarounds. Inspection, which cannot be made during operation, shall be done during the plant shut down. However, depending on the corrosion rate and type of deterioration, the frequency of inspection of process piping can be varied suitably. 9.2
xvii) Austenetic stainless steel lines where polythionic acid formation takes place with resultant cracking. xviii) Areas immediately downstream of chemical injection points where localised corrosion might occur in the reaction zone.
OFF-SITE PIPING
The following frequencies for inspection of off-site piping shall be followed (see notes): 9.2.1
Hydrocarbon Service
Service
Frequency of Inspection years -----------------------------------External Comprehensive
xix) Dissimilar metals in , which may lead to galvanic corrosion. xx)
Rubber-lined and glass-lined pipes which may get damaged near the flanges or due to cracks in the lining.
xxi) Stagnate conditions in areas of pipelines carrying crude oils with high sulphur/chloride content. xxii) Terminal pipelines ballast water.
carrying
sea/
xxiii) Locations having low pit and high chloride ions.
9.0 FREQUENCY OF INSPECTION
i) Crude: Sweet Sour
5 3
10 6
ii) LP/Natural gas: Sweet Sour
3 2
6 4
iii) Natural gas condensate
2
4
iv) Gasoline/ Naphtha
2
4
v) ATF/HSD/LDO/ SKO/Gas Oil
3
5
The interval between inspections depend upon the -
vi) FO/RCO/VBO/ Bitumen
3
i)
Degree of corrosiveness/erosiveness of the fluid.
vii) Flera/Fuel gas
3
ii)
Remaining corrosion allowance.
iii)
Type of protective coating.
iv)
Atmosphere piping.
v)
Potentially of fire or explosion in case of a leak or failure.
vi)
Statutory requirements.
prevailing
around
the
vii) Importance of operations. 9.1
ONSITE PIPING Inspection of process piping in units
viii) Lube Oil Note:
5
5
5 or during the shutdown of the line 10
WHERE CRUDE SOURCE CANNOT BE ESTABLISHED THE FREQUENCY SPECIFIED FOR SOUR CRUDE SHALL APPLY. 9.2.2 Service
Utilities Frequency of Inspection (years) ----------------------------------External Comprehensive
i) Sweet water: Lined pipe Unlined pipe ii) Salt water: Cement lined pipe Unlined pipe
3 2
5.
3 1
6 2
iii) Fire water: Above ground: Lined pipe Unlined pipe
3 1
5 2
Underground: Lined pipe Unlined pipe
3 2
5 4
3
6
iv) Air/Steam
revealed that failures of most of the Offsite pipelines are due to external corrosion and that internal corrosion failures are minimum.
6 4
Inspection data as well as thickness data of newly constructed pipelines shall be collected at the earliest and with in two years of their commissioning to function as base for establishment of corrosion rates.
9.2.3
v)Steam condensate 2 4 vi) Ammonia 2 4 vii) Caustic 2 4 viii) DEA/MEA 3 5 ix) Sulphur dioxide 2 4 x) Sulphuric acid (conc. 98%) 2 4 xi) Furfural /Phenol 2 3 xii) Lined pipes (excluding water lines) 3 6 xiii) Benzene 2 4 xiv) Toulene 2 4 xv) Sodium Hexametaphosphate 2 4 ----------------------------------------------------------*Notes: 1.
The above frequencies are bases on data collected from various refineries.
2.
External inspection includes both visual inspection and ultrasonic thickness readings taken externally.
3.
Comprehensive inspection covers some or all of the following tests:
i) ii) iii) iv) v) vi) vii)
Visual inspection Hammer test Ultrasonic thickness measurement Dye penetration test Magnetic particle test Radiographic test Hydrotest
4.
Piping is coastal installations and in corrosive environment shall be visually inspected once a year. Years of inspection experience have
Underground piping fire water lines)
(excluding
i) CATHODICALLY PROTECTED LINES Those underground lines having wrapping and coating as well as cathodic protection shall be inspected whenever current leaks are observed and/or any damage to the coating is suspected. The damage to the coating can be located by person survey. Parameters of cathodic protection like pipe-to-soil voltage or pipe-towater voltage shall be monitored once a month. ii)
LINES WITHOUT PROTECTION
CATHODIC
All underground lines having only wrapping and coating shall be inspected once in three years using Person Survey for locating coating damage, if any. Additionally, all these lines shall be visually inspected at random once in ten years by digging at a few locations. Pipelines crossing the roads and dykes shall be inspected once in ten years by digging and exposing the line completely. 10.0 INSPECTION PROCEDURES 10.1 ONSTREAM INSPECTION Piping in Offsite areas can and shall be inspected onstream and a regular inspection programme drawn up. Piping in onsite areas should also be inspected on the run, subject to feasibility as permitted by process parameters (fluid, pressure and temperature). Any abnormalities notices during inspection shall be investigated and corrective steps initiated at the earliest. In setting priorities of inspection of different pipelines, it is recommended that the following categorisation be adopted: i) Where failure is likely to be hazardous. ii) Where failure is likely to cause plant shutdown.
iii) Where there is reason to suspect, based on experience, that there is excessive metal loss.
e) Movement or deterioration of concrete footings.
iv) Remaining piping.
f) Condition of foundation bolts.
Onstream inspection to monitor deterioration should be visual or instrumentaided(ultrasonic, radiographic).
g) Free operation of pipe rollers. h)
Secure attachment of brackets and beams to the s.
10.1.1 Visual Inspection i) LEAKS Visual inspection shall be made to locate leaks. Particular attention should be given to pipe connections, the packing glands of valves and expansion ts. ii) MISALIGNMENT
i) Secure attachment and proper adjustment of pipe hangers, if used. Spring hangers loading shall be checked both cold and hot and the readings obtained shall be checked against the original cold and hot readings. The movement of spring s shell be monitored. j) Broken or otherwise defective pipe anchors.
The piping shall be inspected for mis-alignment. The following are some observations which may indicate misalignment:
k) Free operation of pulleys or pivot points of counter balanced piping system. iv) VIBRATION
a) Pipe dislodged from its so that that weight of the pipe is distributed unevenly on the hangers or the saddles. b) Deformation of the wall of the vessel in the vicinity of the pipe attachment. c) Pipe s forced out of plumb by expansion or contraction of the piping. d) Shifting of base plate or shearing of the foundation bolts of mechanical equipment to which the piping is attached. e) Cracks in the connecting flanges or pump casings and turbines to which the piping is attached. iii) S Pipe s shall inspected for the following:
be
a) If vibrations or swaying is observed, inspection, shall be made for cracks in welds, particularly at points of restraint such as where piping is attached to equipment and in the vicinity of anchors. Additional s should be considered for poorly braced small size piping and valves and for main vibrating line to which they are attached. b)
In case of severe vibration, detailed investigations shall be carried out to determine the source of problems.
v) EXTERNAL CORROSION Inspection of piping for external corrosion shall be carried out with special attention to areas as outlined in 8.1
visually vi) BULGING, BOWING AND SAGGING
a)
Condition of protective coating or fire proofing if any. If fire proofing is found defective, sufficient fire proofing should be removed to determine extent of corrosion.
Line shall be checked for bulging, bowing and sagging in between the s. vii) MECHANICAL DAMAGE EXTERNAL FORCES
FROM
b) Evidence of corrosion c) Distortion
Pipes shall be inspected for dents, scratched etc. from external sources.
d) General physical damage
viii)
FAILURE
OF
PAINT
AND
PROTECTIVE COATING Conditions of paint and protective coating shall be checked.
vi) One ultrasonic scan minimum on straight pipe for every three meters length at lower elevations where possibilities of collection and stagnation of carryover water, or acid condensation or SO2 flow exist.
ix) CRACKS Pipelines shall be inspected for cracks. particular attention should be given to areas near the weld ts. x) INSULATION Damage of insulation shall checked for hot as well as cold lines.
be
vii) Branch connection, dead ends, etc, shall be checked by ultrasonic thickness survey for corrosion and erosion. The details of thickness survey shall be maintained on an isometric sketch (sample as in Annexure II). The above are minimum requirements. Areas of inspection should be increased of thickness readings are low.
xi) CONCRETE LINING Note: Externally coverts lined piping shall be visually inspected for cracking and dislodging of concrete. 10.1.2 Ultrasonic Inspection Ultrasonic thickness survey of the pipelines shall be carried out to ascertain the remaining wall thickness. The following procedure shall be followed for the aboveground pipelines. i) Minimum three readings shall be taken on all the bends of the piping network at the outer curvature. One reading shall be at the centre of the bend and two readings on the same line on either side of this reading. ii) Minimum one ultrasonic scan each on the straight pipes on upstream and downstream of the bend adjacent to welds of the bend to pipe. One ultrasonic scan consists of our readings (3,6,9 and 12 o'clock positions). For pipelines in which there is a possibility of ballast water coming, one ultrasonic scan will consist of six readings (3,5,6,7,9 and 12 o'clock positions) to scan the bottom portions where corrosion may take place. iii)One ultrasonic scan on the entire circumference (four readings) upstream and downstream of the weld t for process pipelines. iv) Minimum one ultrasonic scan (four readings) each on reducer/expander and just downstream on the pipe. v)
One ultrasonic scan on the downstream of valves orifices, etc.
pipe
MOST OF THE ULTRASONIC INSTRUMENTS ARE NOT EXPLOSION PROOF. HENCE HOT WORK PERMIT AS OUTLINED IN OISD-STD-105 SHALL BE COMPLIED WITH. 10.1.3 Radiographic Inspection Critical spots, which cannot be inspected by ultrasonic instruments accurately, shall be radiographed during operation to determine wall thickness as well as internal condition like fouling, scaling, etc. Insulation need not be removed for radiographic inspection. Critical spots where weld-ts, nipples/small dia deadlines are welded, which cannot be inspected ultrasonically shall be radiographed to determine their internal condition. 10.1.4 Corrosion Probes One of the methods of measuring internal corrosion rate of unit piping or Offsite piping is by installing corrosion probes for measuring corrosion rates. Important pipelines like overhead lines can be inspected using corrosion probes. If installed the readings shall be taken weekly and deterioration rate established. 10.1.5 Corrosion Coupons Corrosion coupons should be installed in the important and critical pipelines to measure internal corrosion rate. The coupons are taken out after a specified period and thoroughly cleaned. The weight loss of coupons over a specified period gives the internal corrosion rate of the pipes. 10.2 INSPECTION DURING SHUTDOWN
Shutdown inspection of pipelines relates to inspection of the lines when not carrying any product, and valves and other fittings in the network can be taken out. All piping which cannot be checked on the run shall be inspected during shutdown. These are mostly high temperature piping. During shutdown inspection, hammer-testing and hydrotesting as applicable should be carried out in addition to visual, ultrasonic and radiographic inspections. Pipelines in some of the services like water, phenol and steam are prone to pitting corrosion. Neither ultrasonic nor radiographic testing will reveal the actual internal condition of the pipes in such service. In such cases samples shall be cut for thorough internal examination, at scheduled comprehensive inspections. The samples shall be spilt open in two halves and internal surfaces inspected for pitting, grooving, etc. The internally striplined bends and pipes shall be visually examined for bulging, weld cracking, weld, defects, etc. Thickness of the strip should be measured to find out thinning of the strips. Austenetic SS piping, where there is a chance of stress corrosion cracking due to formation of polythionic acid, shall be kept in inert atmosphere. ivation of the austanetic SS piping shall be done as per NACE-RP-01-70, if all these are to be opened to the atmosphere. 10.2.1 Inspection for Corrosion, Erosion and Fouling Piping shall be opened at various locations by removing valves at flanged locations to permit visual inspection. When erratic corrosion or erosion conditions are noted in areas accessible for visual examination, radiographic examination or ultrasonic testing shall be performed to determine thickness. This is applicable to piping which cannot be inspected during operation. The nature and extent of internal deposits shall be noted. Samples should be collected for chemical analysis.
done. Magnifying glass should be used for crack detection. 10.2.3
Inspection of Gasket Faces of Flanges
The gasket faces of flange ts which have been opened shall be inspected visually for corrosion and for defects such as scratches, cuts and grooving which might cause leakage. Ring gaskets and ts shall be checked for defects like dents, cuts, pitting and grooving. 10.2.4 Inspection of Hot Spots Where hot spots on internally insulated pipe were noted during operation, the internal insulation shall be inspected visually for failure. The pipe wall at the hot spot shall be inspected visually for oxidation and scaling. The scales shall be removed to expose bare metal and the area checked for cracks. The thickness of the metal shall be measured to ensure that sufficient thickness is felt for the service. The outside diameter of piping in high temperature service shall be measured to check for creep deformation. 10.2.5 Hammer Testing Hammer testing shall also be carried out to supplement visual and ultrasonic inspection. While hammer testing, the following precautions shall be taken: i) Hammer testing of valves, pipes and fittings of cast iron construction, chromesteel, austenatic SS lines and stress relieved lines shall not be carried out. ii) Care shall be taken not to hammer so hard as to damage otherwise sound piping. iii) Hammer testing shall not be performed on glass-lined, cement-lined or otherwise internally coated lines. iv) Hammer testing shall not be done on operating lines and lines under pressure.
10.2.2 Inspection For Cracks 10.3 Welds, heat-affected areas ading welds, points of restraint cracking, hydrogen attack and caustic embrittlement shall be inspected for cracks. For spot checks, dyepenetrant or magnetic particle inspection should be used. Alloy and stainless steel piping need close inspection. In-situ metallorgraphy at critical spots may be also
INSPECTION OF TEMPERATURE PIPING
HIGH
Inspection shall be made for hot spots on internally insulated piping. Any bulging or scaling shall be noted for further inspection when the equipment is shut down. Some sot spots can be detected by a red glow, particularly if inspection is made in the
dark. Portable infrared pyrometer or temperature indicating crayon shall be used to determine the skin temperatures. Sometimes thermographic survey of internally insulated hot piping helps in locating the hot spots. Furnace transfer lines and column bottom lines, which are operating at very high temperatures, shall be inspected at every shutdown. Insulation shall be removed at specified locations including all bends and ultrasonic thickness shall be carried out and the corrosion rate established. Spring hangers and spring s of high temperature piping shall also be checked during shutdown. 10.4
INSPECTION OF PIPING CORROSIVE STREAMS
IN
i) HYDROGEN SULPHIDE (H2S) SERVICE All the weld ts in this line shall be stress relieved after fabrication. Weld ts at random shall be checked for suspected cracking. If the line is not thermally insulated, external thickness measurements shall be taken for suspected internal corrosion. When the line is not in operation, magnetic testing method will help in locating cracks in the welds. ii) DI-ETHYL AMINE/MONO-ETHYL AMINE SERVICE
Carbon steel resists phenolic corrosion upto 205oC provided water is not present. Corrosion in phenol is very erratic. However, when it occurs, it may be very severe. All bends and areas of high velocity and where turbulent conditions occur shall be ultrasonically inspected. However, areas which cannot be inspected ultrasonically shall be radiographed to ascertain their internal condition. v)
CAUSTIC SERVICE
(SODIUM
HYDROXIDE)
Caustic is non-corrosive at atmospheric temperatures top carbon steel. Caustic will cause stress corrosion cracking above 94OC and hence all carbon steel lines shall be stress-relieved before commissioning or after repairs. Lines shall be checked for embrittlement and metal loss. vi) CHLORINE SERVICE Chlorine, though not so corrosive in gaseous phase, becomes highly corrosive when even a small amount of moisture comes in with it. Rubber-lined carbon steel pipes are generally used in chlorine services. Rubber-lined, pipes shall be checked for bulging of lining at bends, flanges or at weld ts. vii) ACID SERVICE
Pipelines carrying DEA/MEA are prone to internal corrosion and stress corrosion cracking. All newly constructed piping shall be stress relieved irrespective of the strength and temperature of the chemicals. All weld ts shall be inspected for cracks using wet fluorescent magnetic particle test. External thickness measurements shall be taken at all bends and other flow-restrictions for determining the internal corrosion rate. All socket-welded and seal-welded threaded connections are prone to stress corrosion cracking if not stress-relieved. Hammer testing of the line shall not carried out as it may induce localised stresses. iii) HYDROGEN SERVICE Carbon steals are prone to hydrogen embrittlement at elevated temperatures above 232oC. Pipelines shall be checked for bulging (hydrogen blistering) and distortion whenever they are shut down for inspection.
Sulphuric acid is corrosive in dilute phase. Hydrochloric acid in corrosive at all concentrations while phosphoric acid is corrosive where it mixes with water in carbon steel pipes. The following locations shall be checked for acid corrosion in carbon steel lines: a) Horizontal sections of the line where dilute-acid stagnation may occur. b) Section of the line at bends where elbows tend to corrode due to turbulent acid attack. c) Section of the line adjacent to orifices, reducers, expanders, etc. d) Caustic neutralisation injection points and T-ts due to turbulence. e) Heat affected zones of weld ts due to residual stress concentrations and thermo-galvanic effects.
iv) PHENOL SERVICE f) Locations where temperatures are more
than 50oC. 10.5
INSPECTION OF UNDERGROUND PIPING
Underground piping is mainly checked off-stream. However, development of exigencies may require inspection of the same on the run after exposing the line. 10.5.1 Cathodically Protected Piping Cathodic protection shall be controlled so as not to damage the protective coating. A pipe-to-soil voltage of -0.85, with respect to Cu-CuSO4 half call has been found to give adequate protection to cathodically protected pipelines. Any excess voltage may damage the wrapping and coating on the pipe. All buried or submerged coated piping system shall be electrically isolated at interconnections from the other lines which are not cathodically protected. The pipe-tospot potential readings shall also be checked using Cu-CuSO4 cell. 10.5.2
Wrapped and Coated Pipelines Without Cathodic Protection
The condition of the wrapping and coating shall be checked by Pearson survey once in three years for underground piping not cathodically protected. Excavations shall be done at vulnerable points like regions of low velocity and straight portions downstream of bends. The excavation, once in ten years is optimum requirement. After excavation, the wrapping and coating shall be examined both visually and by holiday detector. Internal metal loss and fouling may be detected by radiographic examination. Ultrasonic thickness measurements shall be carried out on the surface of the pipe after removing a bend of wrapping and coating. The pipeline shall be hydrotested once every five years. The stray current interference of underground pipe should be checked by CuCuSO4 half-cell. All lines shall be inspected at and just before the point where they enter the earth or concrete slab as serious corrosion frequently occurs at such locations. The incidence of stray current interference is high in the underground portion of cathodically protected and noncathodically protected piping separated by insulated flanges or couplings. This current causes severe damage in the unprotected line if the wrapping and coating is damaged. This location should be inspected once a year by exposing the insulating flanges or couplings.
10.5.3 Internal Corrosion Underground Piping
of
In order to assess the internal condition of underground pipelines, ultrasonic thickness survey by exposing the line shall be done as per frequency specified previously. Bends, reducers, expanders, branch connections and dead-ends shall be exposed and thickness survey at these locations carried out as per the guidelines given for the above-ground pipelines. One location every 100 meters for a straight portion shall be exposed for thickness survey. Internal corrosion monitoring of these lines should be done by installing corrosion probes at vulnerable locations. Readings should be taken once a week to calculate the corrosion rate. 10.6
INSPECTION OF VALVES, FLANGES, GASKETS & BOLTS
10.6.1 Valves Steel gate valves steel globe valves, flanged cast iron gate valves, threaded and socket welded valves, soft-seated ball valves`Fire Safe Type', plug valves, check valves and butterfly valves for water service are used in Petroleum installations.
i) INSPECTION AND TESTING OF NEW VALVES All valves shall be inspected and tested to ensure conformation to required specifications and for leak tightness. All new valves shall be inspected and tested as per requirements of API-598. The closure torque during testing for hand wheel and gear operated valves shall not be greater than that obtainable by hand tightening. (a) Valves in Hydrogen Service All low alloy valve castings (P numbers 3,4 and 5) in hydrogen service with a hydrogen partial pressure of 100 psig shall be 100% magnetic particle and radiographically examined. Examination and acceptance criteria shall be as per ASME Section VIII Appendix 7. (b) Valves in Wet H2S Service
Valves made of steel containing phosphorus or sulphur in excess of 0.5% shall not be used in H2S service. Hardness of the body, bonnet and gate and weld metal and HAZ of any pressure retaining part shall not exceed the limits given below:Material
Brinell hardness,
P-1 P-3, P-4, P-10, P12 P-5, P-6, P-7 inconel, Precipitation hardened
225 225 225 310
(c) Fire Safe Type Ball Valves Each valve shall be tested as per API 598. - Low pressure sect test shall be conducted with the ball and seat dry and free of oil, grease or any lubricant. - The high pressure seat test is not required except for threaded and valves. - No leakage shall be permitted. - Fire-safe test shall be carried out as per API 6070.
ii) INSPECTION OF VALVES IN SERVICE Valves shall be dismantled at the time of specified comprehensive inspection or during the shutdown of the line to permit examination of all internal parts. Body thickness measurements shall be made at locations inaccessible before, dismantling, particularly at locations showing evidence of erosion. Bodies of valves operating in severe cyclic temperature service shall be checked internally for cracks. Gate valves, which have been used for throttling, shall be measured for thickness at the bottom between the seats, as serious deterioration may have occurred because of turbulence. This is particularly weak point because of the wedging action of the disc when the valve is closed. The seating surface shall be inspected visually for defects which might cause leakage. The wedging guides shall be inspected for corrosion and erosion. The stem and threads on the stem and in the bonnet of valves shall be
examined for corrosion which might cause failure., The connection between stem and disc shall be inspected to assure that the disc will not detach from the stem during operating. Swing check valves shall be inspected by removing the cover or cap. The clapper or disc shall be checked for freedom of rotation and the nut holding it to the arm shall be checked for security and presence of a locking pin, lock washer, or tack weld. The arm should be free to swing and the anchor pin shall be inspected for wear. Also the seating surface on both the disc and valve body shall be checked for deterioration by feeling them with the fingers. After the valve has been reassembled, it shall be hydrostatically and/or pneumatically tested for tightness. If tested pneumatically, a soap solution shall be applied to the edges of the seating surface and observed for any evidence of leakage. 10.6.2 Flanges, Gaskets and Bolts The gasket faces of flanged ts, which have been opened, shall be inspected visually for corrosion and for defects such as scratches, cuts and gouges which might cause leakage. The gasket faces shall be checked for true flatness or warping by placing a straight edge across the diameter of the face of the flange and rotating it about an axis through the center line of the flange. Grooves and rings of ring ts shall be checked for defects. Flanges bolts should be inspected for stretching. Where excessive bolt loading is indicated or where flanges are deformed, nuts may be rotated along the entire length of the stud. If studs are stretched, thread pitch will be changed and nuts will not turn freely. Inspection involve checking to determine whether bolts of the proper specification have been used and may involves chemical analyse or physical tests to determine the yield point and the ultimate strength of the material. If flanges are bolted too tightly, they may bends until the outer edges of the flanges are in . When this occurs, there may be insufficient pressure on the gasket to assure a tight t. Visual inspection of the gasket will reveal this condition. Permanently deformed flanges must be replaced. 11.0 RETIRING LIMIT Calculation of retiring limits for unit piping and offsite piping shall be done as per
ANSI B 31-3 end ASME Section VII Div. 1. The retiring limit relates thickness, diameter and allowable stress to the maximum safe working pressure. In addition, ANSI B 31.3 contains a formula with material factors for determining the required thickness but permits the use of the simple formula of Barlow without reservation. The Barlow formula is: t
=-
12.7 P x D -------------SE
Where t= required thickness of the pipewall in mm. P= Pressure within the pipe in kg/sq.cm D= Outside diameter of the pipe in cms. S= Allowable unit stress in kg/sq.cm. at the maximum operating temperature. E= Longitudinal t efficiency. Note: Metallic piping with t = D/4 requires special consideration. The Barlow formula gives results particularly equivalent to those obtained by the more elaborate formula, except at high pressures where thick-walled tubing is required or at high temperatures where creep properties of the pipe metal become important in determining the ultimate service strength. At low pressures and low temperatures, the thickness required by the formula may be so small that the pipe would have insufficient structural strength. For this reason, an absolute minimum thickness shall be determined for each size of pipe below which thickness of the pipewall would not be permitted to deteriorate regardless of the results obtained by the above formula. As a guideline, minimum thickness for C.S. piping are given below: Nominal pipe size (mm) thickness (mm)
Minimum
50 mm and smaller 63-76 101.6 152.4 203.2 254-609.6
1.5 1.8 2.2 2.8 3.0 3.3
12.0
12.1 INSPECTION DURING REPLACEMENTS
REPAIRS /
The portion of the piping, which may reach the retiring limit before the subsequent scheduled inspection, shall be replaced. While replacing the pipe, the following points shall be considered. i) The metallurgy and dimensions of the new pipe shall match with those of the existing pipe. ii) Repairs shall be carried out by a qualified welder using qualified welding procedures. iii) For ERW pipes, the weld seam shall be kept staggered and the ERW seam shall appear in the upper quadrants. iv) Piping systems, which are covered under other statutory requirements, shall be checked for conformation with the appropriate codes, regulations and specifications. v) Inspection of ts shall be done as previously specified. vi) Repaired welds shall be subject to same pre and post-weld heat treatments as required in the case of new pipes. vii)
Painting, insulation, wrapping and coating shall be done as per the code.
12.2 PRESSURE TESTING All installed piping shall be pressure tested prior to commissioning. Piping systems open to atmosphere, such as drains vents and outlet piping for relief valves discharging to atmosphere and underground sewers shall not require any pressure testing. These lines shall be examined to determine that all ts are properly made up. 12.2.1 Test Pressure and Procedures
METHODS OF PIPELINE REPAIR AND INSPECTION
The test pressure and procedure for testing of piping shall be as per ANSI B 31.3 or equivalent. However, the following additional points shall be considered while carrying out testing. i) All floats shall be removed before filling the system with water. ii) All air present in the system shall be
vented while itting the test fluid. iii) Piping designed for vapour and gas shall be provided with additional temporary s, if necessary. iv) Line containing check valves shall have source of test pressure on the upstream side. v) Valves shall not be subjected to a test pressure in excess of manufacturer's allowable test rating. When permitted, the installed valves shall be kept open. vi) Control and relief valves shall be excluded from the test irrespective of their pressure rating. vii) Instrument take-off piping upto the first block valve shall be tested along with piping to which it is connected. Testing of remaining line leading upto the instrument can also be done at the same time provided instruments are blocked off from the source of pressure and vented to atmosphere. viii) Open ends of piping where blanks cannot be used e.g. pumps, compressors, etc. shall be blinded off by using standard blind flanges of same rating as the piping system being tested. ix) Indicating pressure gauges mounted locally may be tested with the line, provided the test pressure is not in excess of their scale ratings. x) Orifice plates in horizontal lines shall not be installed till completion of test. xi) The test shall be carried out at ambient temperature and it should not be less than 50oC. xii) All vent valves during filling up as during draining must be fully open.
i) Portable water free from oil and suspended matter shall be used for ferritic parts and feritic parts associated with non-ferrous parts. ii) Water shall be d-ionized having a conductivity not greater than one micro mho per cm at 250oC for austenetic parts end ferritic parts associated with austenetic parts. 13.0 DOCUMENTATION Isometrics of each circuit as per actual site conditions shall be prepared. The records shall be maintained to give information like: i) Identification of particular piping systems in of location, total length, material specification, general process flow and service condition and location of corrosion probes, if any. ii)
Location of thickness measurement points, replacement carried out, corrosion rate, etc.
An isometric sketch for guidance has been given in Annexure-2. All small connections shall be clearly shown on isometrics and piping drawings. The history and thickness records shall be maintained in history cards and data record cards. On the basis of records of previous and present inspection, a work schedule shall be prepared for future inspection onstream as well as during the next shutdown. 14.0 REFERENCES The following standards, codes and publications have either been referred to or used in the preparation of this document and this standard shall be read in conjunction with the same
12.2.2 Test Fluid Hydraulic testing of ferritic material shall be carried out using suitably inhabited water, which permits an extended period between the start of testing and drying of components. Hydraulic testing of austemotic material shall be carried out using de-ionized water. 12.2.3 Water Quality
i) ANSI B 31.3 Chemical Plant and Petroleum Refinery Piping. ii) API Guide for Inspection of Refinery Equipment Ch. XI.
iii) Piping Handbook-Crocker and King. iv) ASA B 36.10 welded seamless wrought steel pipe. v) ASA B 36.19 stainless steel pipe. vi) NACE RP 01-69. vii) NACE RP-01-70. viii) NACE RP-01-75.
ANNEXURE -1
SAFETY PRACTICES TO BE FOLLOWED DURING PRESSURE TESTING 1. Hammer testing of piping undergoing a pressure test shall not be carried out as this may cause failure resulting in possible injury or death to those performing the test. 2.
Stress due to testing shall not exceed 90% of the yield stress of the material of construction of the piping as it may cause failure resulting in possible injury or death to those performing the test.
3. Pressure test shall not be carried out at metal temperatures near the ductile-tobrittle transition temperature of the material.
4. If the piping is tested pneumatically, the pressure, shall be 110% of the design
pressure. Pneumatic testing involves the hazard due to possible release of energy stored in compressed gas. Therefore, particular care shall be taken to minimize the chance of brittle failure. Any pneumatic test shall include a preliminary check at not more than 25 psi (2kg/cm2) gauge pressure. The pressure shall be increased gradually in steps providing sufficient time to allow the piping to equalise strains during test. 5. In addition to the above, conditions listed out in Appendices F and G of ANSI B 31.3 should be kept note of.-
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