PIPING DESIGN AND FABRICATION IN INDIA :

4.1.  GENERAL – Piping Fabrication and Erection Specification

Fabrication works shall comply with the drawings and this specification including relevant Engineering and Construction Specifications.

4.1.1.    All weld numbers and welder’s identification number shall be painted close to the weld, to enable trace ability of each weld and each welder, socket welds shall be numbered per fitting, e.g. S.W tee has one weld number.

4.1.2.     Construction Contractor shall maintain the color coding on piping materials to allow easy and quick reference in accordance with the project engineering specification.

4.1.3.       All materials included in the finished piping systems shall be undamaged.

4.1.4.       Construction Contractor must provide adequate protection for piping, flange faces, threaded connections, etc. to prevent damage during handling and storage. Construction Contractor shall ensure that flange faces are protected from corrosion or rust.

4.1.5.      Piping shall be stored in a relatively clean, dry or well drained area on elevated dunnage and protected against contact with salts or salty water.

4.1.6.   All attachments to piping, i.e. saddles, pads, etc. are to be made of same material to the pipe.

4.2.            DIMENSIONAL – Piping Fabrication and Erection Specification

TOLERANCE

4.2.1.      Wrought Bends 

A.     Wrought bends shall show no significant marks or corrugations and shall be smooth and regular in outline.  Flattening shall not exceed 8% of the pipe outside diameter for pressure duties, or 3% of the pipe outside diameter for vacuum duties. There shall be no significant thinning when the pipe bend radius is 5 x nominal diameter or greater.

B.   In general thickness stainless steel pipe of equivalent to schedule 10S and thinner shall not be bent.

4.2.2.      Pipe Dimensions

Tolerances shall be ±1.5mm from flange face to flange face, or centerline of pipe to flange face.

4.2.3.      Flange Face

Flange faces shall not be concave.  Convexity from flange bore to joint face periphery shall not exceed 0.15mm per centimeter width of joint face.

4.2.4.      Squareness of Flanges

Flanges shall be square to the axis of the pipe to within an angle of 0° ‑ 18′ (0.3°) I.E.  0.05mm per centimeter measured across the face of the flange, with the pipe adequately supported.

4.2.5.      Bolt Holes of Flanges

Flange bolt holes shall straddle the established centerlines (Horizontal or vertical). However, flanged connections on equipment may vary and should be individually checked.  When these connections differ, the bolt hole orientation shall be indicated on the isometric piping detail sheet. Holes in double flanged pipes shall be correctly aligned. 

4.3.            WELD DETAILS – Piping Fabrication and Erection Specification

4.3.1.       Butt Welds

The term “Butt‑Weld” refers to circumferential butt joints only. Special requirements may be imposed where longitudinal welds are to be made and these welds shall not be carried out before Consultant has approved the methods to be used.  Longitudinal and spiral welds existing in pipes as produced at the mill are outside the scope of this specification.

4.3.2.      Weld Preparation

Weld preparation shall be in accordance with the following:

A.   Preparation standard shall be applied to ASME B31.3 and the modifications to the standard contained within clause 5.3.6 of this specification.

B.  Ends shall be beveled or square cut for welding as follows:

1)  Beveled for wall thickness greater than 2.3mm

2)  Square cut for wall thickness 2.3 mm and less

4.3.3.      Root Gaps

Spacers shall be used while tack welding pipe and fittings in position to insure proper gap and full penetration in welding. The tack welds complying with the requirements of ASME B31.3, 328.5.1(C) may be allowed to become a part of the finished weld, whereas those not complying are not acceptable and must be chipped out before completing the weld.

4.3.4.      Bore Matching and Alignment

Bore matching and alignment shall be in accordance with ASME B31.3.  Where pipe, fittings and flanges are to be joined by circumferential butt‑welds, the corresponding parts shall be modeled and matched so that any misalignment at the inside of the piping shall not exceed 1/16 inch at any point of the circumference of the joint.

Fit‑up work may include pressing, hammering, local heating or grinding as required to reduce any misalignment due to diameter tolerances, out‑of‑roundness or unequal wall thickness of the parts of less than 1/16 inch. parts having unequal wall thickness and bores shall be prepared in accordance with one of the  details  shown  in  ASME  B31.3.

4.3.5.      Cutting

A.  Pipes may be cut mechanically by sawing or grinding machine.

B. Cutting method involving heating e.g. Flame or arc cutting for carbon steel are allowed providing the cut edge is machined or ground back sufficiently far to give specified parent material properties at the cut edge with a minimum of 1.5 mm.

C. Plasma‑jet cutting may be use to cut austenitic stainless steel pipes and other materials.

D.   Flame cutting of austenitic stainless steel pipe is not allowed.

E.   Other methods of cutting may be used providing written approval is obtained from Consultant.

4.3.6.      Welding Position of Longitudinal Seams

Longitudinal seams in seam welded pipe shall be located so as to clear openings and external attachments possible.  Longitudinal seams in adjoining courses shall be  preperably at 180°but a minimum between seams are in accordance with construction specification. 

4.4.            BRANCH WELDS – Piping Fabrication and Erection Specification

Branch connections shall be located as indicated on the piping detail sheet or isometric piping drawings. All branch connections shall be designed in accordance with Para. 304.3 of ASME B31.3.   Forged or extruded branch connections are preferred.

4.4.1.      No Fitting

Branches shall be of  ‘Stub‑in’ design in accordance with Construction Specification 0000-S1830-003 and ASME B31.3.

4.4.2.   Forged branch attachments (Brancholets) shall be of the type specified on Consultant’s drawings and fitted accurately to the contours of the run pipe.

4.4.3.      Reinforcing Pads

A.    For pressure reinforcement

Reinforcing pads required by the referenced code or by piping detail sheets shall be provided with at least one vent hole if fully welded. The hole shall be drilled and tapped with a 1/8 inch pipe thread for testing and venting. The tapped hole shall be plugged using wood, plastic or mastic material not capable of retaining pressure. 

B.    For structural attachment

Reinforcing pads for structural attachment shall be provided with an untapped hole of 1/4 inch (6 mm) diameter for venting.

C.  Where reinforcing pads are fitted either for branches or structural attachments they shall be  accurately shaped so that no gap larger than 1/8 inch (3.0mm), measured before welding, shall exist between the periphery of the pad and the pipe to which it fits.

4.4.4.      Mitered Bends

Mitered bends shall be in accordance with piping material specification ——. The number of cuts shall be as stated on the drawing.  Mitered bends are used only when specified on the drawings and shall be in accordance with ASME B31.3 Chapter V. A joint efficiency not exceeding 70% shall be used in the strength calculations for mitered bends. The welds in mitered bends shall penetrate the full thickness of the pipe and the bead on the inside of the throat shall be smooth and have an even curvature. In order to prevent a notch effect.

4.4.5.      Beveled Ends

Refer to Construction Specification XXX

4.4.6.      Fillet Welds

Refer to Construction Specification XXX

4.5.            BENDING – Piping Fabrication and Erection Specification

4.5.1. Bends shall conform dimensionally to the drawings and relevant clauses of this specification. Hot bend is not permitted.

4.5.2.      Cold Bending

A.  Cold bends to a centerline radius greater than five (5) times the nominal pipe diameter may be manufactured without a subsequent heat treatment unless a heat treatment is specified on the project specification, piping detail sheets, or isometric drawings.

B.    Cold bends to a radius less than five (5) times the nominal pipe diameter is not allowed.

C.   Bending after completion of fabrication to meet dimensional requirements shall not be carried out without the approval of the engineer.