Technical requirements for Pipes & Fittings
While preparing the inquiry/purchase requisition of any piping component there are many points which are to be checked and confirmed with the vendor. It is the responsibility of the requisition engineer to include all the technical points & clauses applicable to the piping components in the inquiry & the subsequent technical queries.
The requisition engineer has to refer to the all the project specific standards along with the applicable international codes and standards for the preparation of the inquiry requisition of the piping components. Listed below are few general technical requirements for pipes & fittings which may vary depending upon the project requirements.
1. General requirements
1.1 Material supplied shall be strictly in accordance with the latest codes and standards, mentioned in the Material Requisition Scope of supply. This specification for pipes, fittings and flanges as detailed in subsequent clauses shall supplement the codes and other project specifications.
1.2 All items shall be supplied in accordance with the wall thickness or schedule as stated in Inquiry / Purchase requisition. Wall thickness heavier or thinner than specified tolerance shall not be accepted.
1.3 For all piping components, material type and grade together with NPS and schedule / wall thickness / class shall be as specified in the description within the Material requisition – Scope of Supply.
1.4 Butt weld end preparation for pipes, fittings and flanges shall be as per ASME B16.25.
1.5 All welded items shall be 100% radio graphically examined to give a joint factor of 1.0. Pipes and fitting shall be supplied seamless unless otherwise specified. Seamless is an acceptable alternative for welded pipe and fittings and vice-versa are not acceptable.
1.6 The chemical analysis of CS & LTCS pipes and fittings, forgings, plates shall be in accordance with the applicable product standard with the following limitations:
Carbon 0.23 Maximum wt% (pipes)
Carbon 0.23 Maximum wt% (forgings)
Carbon Equivalent CE shall not exceed 0.43%
Where CE = C + Mn/6 + (Cr+Mo+V)/5 + (Cu+Ni)/15
The above formula for CE is applicable when the carbon content is greater than 0.12%
1.7 All CS & LTCS materials shall be fully killed and fine grained and shall be produced by a low sulphur and low phosphorous refining process. The components shall be shall be supplied in normalized or normalized and tempered condition.
1.8 Repair welding for parent plate / weld end flange is not permitted.
1.9 All Austenitic stainless steel, duplex stainless steel items shall be supplied in solution annealed and quenched condition as per corresponding ASTM standard.
1.10 The carbon content of SS 316 shall not be more than 0.03%. All SS Materials specified as F316 / WP 316/ Type 316 may be dual certified for both SS 316 & 316L, if specifically mentioned in the project specification.
1.11 Austenitic stainless steel shall be capable of passing an inter-granular corrosion test in accordance with ASTM A262, Practice E.
1.12 All duplex stainless steel shall have ferrite content (volume fraction) between 35% – 65% on base metal and on heat affected zone to 35% to 70 % as per ASTM E562 four point count method.
2. Requirements for Pipes
2.1 Dimensions of Carbon steel / Stainless steel / Alloy steel pipe shall comply with ASME B36.10M or ASME B36.19M as applicable.
2.2 Carbon steel pipes shall be supplied in double random lengths (11 to 13m) for pipe sizes 2″ to 36”, and in single random lengths (5 to 7m) for pipe sizes 1.5″ and smaller.
2.3 SS, DSS and CS galvanized pipes shall be supplied in single random lengths (5 to 7m) for all pipe sizes.
2.4 Jointers are not acceptable. It is not permitted to join lengths of pipe by circumferential welds to make single or double random lengths.
2.5 Plain end pipes shall have ends square cut with burrs removed.
2.6 All threaded & coupled pipes shall be supplied with ends threaded in accordance with ASME B1.20.1 (NPT).
2.7 Each length of the threaded pipe shall be supplied with full coupling screwed hand tight at one end.
2.8 Galvanizing of pipes shall be in accordance with ASTM A153. Threaded portion of pipes shall be free of galvanizing.
2.9 Pipes shall be heat treated in accordance with product specification requirements after completion of all forming and welding operations.
2.10 CS & LTCS Pipes shall be fully killed, fine grained and shall be supplied in normalized or normalized and tempered condition. All stainless steel pipes shall be supplied in solution annealed condition.
2.11 Welded pipe shall be supplied with single straight seam for sizes upto 36” and double straight seam for sizes greater than 36” subjected to approval from the contractor.
2.12 Spiral seam welds are not acceptable.
2.13 All DSS welded pipes with a wall thickness greater than 30 mm shall also be 100% ultrasonically examined.
3. Requirements for Fittings
3.1 Dimensions of butt welded fittings shall be in accordance with ASME B16.9. Forged threaded and socket welded fittings shall be in accordance with ASME B16.11. Other fittings dimensions shall comply with MSS SP-75, MSS SP-95, MSS SP-97 or BS 3799 as applicable. Vendor shall provide calculations as per ASME B31.3 for the fittings not covered under the above mentioned standards.
3.2 All screwed fittings shall be threaded NPT in accordance with ASME B1.20.1.
3.3 Branch reinforcing fittings (i.e. sockolets, weldolets etc.) shall be designed in accordance with the requirements of ASME B31.3. The vendor shall submit drawings during bid stage and calculations for review and approval after award of contract.
3.4 Butt weld elbows shall be long radius type (radius =1.5 nominal pipe size). Short radius elbows are not permitted.
3.5 For reducing fittings specified with two schedules in the Inquiry / Purchase description, the first schedule refers to the larger end or run pipe, the second schedule refers to the smaller end or branch pipe.
3.6 Fittings shall be forged to the final shape and size. Fittings shall not be machined from bar stock or solid forged billets without specific approval.
3.7 Union dimensions shall be in accordance with BS 3799.
3.8 Galvanizing of fittings shall be in accordance with ASTM A153. Threaded portion of fittings shall be supplied with threads free of galvanizing.
3.9 Swage nipple shall be pipe swaged by forging only. Machining of bar stock, forgings or heavy wall pipe not permitted. Dimensions shall be in accordance with MSS-SP-95.
3.10 All reduction sizes for tees and reducers to be in accordance with ASME B16.9.
3.11 CS & LTCS fittings shall be fully killed and fine grained and shall be supplied in normalized or normalized and tempered condition.
3.12 100% of CS & LTCS welded fittings, with wall thickness greater than Sch 80 shall be examined by Magnetic Particle Examination for weld bevel ends. Acceptance standards shall be in accordance with ASME VIII Division 1, Appendix 6. This shall be done after final heat treatment.
3.13 100% of CS, LTCS & SS forged fittings, with wall thickness greater than Sch 80 shall be examined by Magnetic Particle / Dye penetrant examination. Acceptance standards shall be in accordance with ASME VIII Division 1, Appendix 6 / 8. This shall be done after final heat treatment.
3.14 100% of SS & DSS wrought fittings having wall thickness more than 20mm shall have the bevel and weld end over a width of 25mm, examined by Dye penetrant Method.
Acceptance standards shall be in accordance with ASME VIII Division 1, Appendix 8.
3.15 100% of DSS welded fittings with a wall thickness greater than 30mm shall be 100% ultrasonically examined in accordance with ASME VIII Division 1.
3.16 100% of DSS forged fittings weld bevels shall be examined by Dye Penetrant inspection.
4. Sour service requirements
4.1 All materials specified for sour service shall, as a minimum, meet the requirements of NACE MR0175 / ISO 15156 – latest edition.
4.2 All welded pipes / fittings in sour service shall be HIC tested, if required by the project specification. It shall be conducted for one pipe / fitting per heat in accordance with NACE TM-0284 Solution – A with acceptance criteria as specified in NACE MR-0175.
5. Positive material identification
5.1 Positive Material Identification (PMI) shall be conducted for all SS / CRA alloy piping items as per the project specification included in the Inquiry / Purchase requisition.
6. Impact test requirements
6.1 All CS, LTCS, welded austenitic and duplex stainless steel piping components shall be impact tested in accordance with ASME B31.3.
6.2 For carbon steel pipes and fittings, the impact test temperature shall be the ‘minimum metal temperature’ as defined in the project. The impact test requirement and acceptance criteria shall be as per Cl. 323.2.2 and Cl. 323.3.5 of ASME B31.3 respectively.
6.3 For LTCS items, the impact test temperature shall be (-460C). Test results shall be atleast 27 joules as an average of three tests (for standard specimen 10 x 10 mm), oneresult may be lower, but not lower than 21 joules.
6.4 For welded SS and DSS items, the impact test temperature shall be the ‘minimum metal temperature’ as defined in the project but not more than (-1010C) and (-500C) respectively. For SS items, the acceptance criteria shall be as per Cl. 323.3.5 of ASME B 31.3. For DSS items, test results shall be at least 40 joules in transverse direction (for standard specimen 10 x 10 mm) as an average of three tests, one result may be lower but not less than 30 joules.