Welding procedure

Joining NonmetaUic Pipe Thermoplastic piping may be joined by a qiiahfied hot-gas welding procedure, a qnalined solvent-cement procedure, or by a qualified heat-fusion procedure. The general welding and heat-fiision procedures are described in ASTM D-2657 and solvent-cement procedures in ASTM D-2855. Two other techniques, for flared joints and elastomeric-sealed joints, are described in ASTM D-3140 and D-3139, respectively. 

Any tests and associated acceptance criteria which are part of the welding-procedure qualification for filler materials and heat-affected zone need not he repeated. 

Rules for the welded fabrication of pressure vessels cover welding processes, manufacturer s record keeping on welding procedures, welder qualification, cleaning, fit-up alignment tolerances, and repair of weld defects. Procedures for postweld heat treatment are detailed. Checking the procedures and welders and radiographic and ultrasonic examination of welded joints are covered. 

Eiimination. Careful use of appropriate welding procedures and techniques, as these relate to metal temperature, is necessary, especially when welding thin-walled tubes. 

Residual stresses caused by large temperature differences between the weld bead and adjacent metal can be reduced by preheating the metals to be welded, especially if the sections are thick, or by stress-relief-annealing following the welding procedure. Proper welding techniques, especially the use of appropriate weld filler metals to minimize weld-metal shrinkage, can minimize residual stresses. 

Testing, analyses and acceptance of materials in forge or in shop welding procedure, acceptance of electrodes,... 

The basic guidelines for preventing cracking would seem to be to operate at minimum stress levels, at as low an HjS concentration as possible and to make sure that welding procedures are adequately specified and followed. Furthermore, extensive periods of operation at temperatures that might cause sigma phase formation should be avoided. 

Impact tests that meet the requirements of Table GR-2.1.1(a), which are performed as part of the weld procedure qualification, will satisfy all requirements of para. GR-2.1.2(b), and need not be repeated for production welds. 

A welding procedure for the manufacture of pipe or components shall include impact testing of welds and HAZ for any design minimum temperature below -29°C (-20°F), except as provided in Table GR-2.1.2(b)(2), A-3(b). 

A-4 One required for each welding procedure, for each type of filler metal (i.e., AWS E-XXXX classification), and for each flux to be used. Test pieces shall be subjected to essentially the same heat treatment (including time at temperature or temperatures and cooling rate) as the erected piping will have received. 

Materials With Limited Service. The desirability of specifying some degree of production impact testing, in addition to the weld procedure qualification tests, when using materials with limited low-temperature service experience below the minimum temperature stated in Table IX-2. 

Consumable inserts may be used, provided they are of the same nominal composition as the filler metal and will not cause detrimental alloying of the subsequent weld deposit. The welding procedure using consumable inserts shall be qualified as required by para. GR-3.2.4. The consumable insert shall be used for welding the root pass of butt welded pipe components requiring complete weld joint penetration (CWJP) utilizing the GTAW or PAW processes. 

Joints may be made by welding in any material for which it is possible to qualify welding procedures, welders, and welding operators in conformance with the rules in para. IP-9.2. 

The HRC method may be used for welding procedure qualification if the design stress does not exceed two-thirds of SMYS and the welding procedure specification includes postweld heat treatment. 

Other hardness testing methods for welding procedure qualification may be allowed when permitted by engineering design. 

The minimum tensile strength for weld (qualification) and stress values shown shall be multiplied by 0.90 for pipe having an outside diameter less than 51 mm (2 in.) and a D/t value less than 15. This requirement may be waived if it can be shown that the welding procedure to be used will consistently produce welds that meet the listed minimum tensile strength of 165 MPa (24 ksi). 

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