Pipelaying Tender-VOL II - WorleyParsons.com

EPMC SERVICES FOR REWARI – KANPUR PIPELINESPECIFICATION FOR WELDING ON ONSHORE PIPELINEIn addition to the above, special cases where it is considered impractical to meet the specificationrequirements due to some site constraints or the other, the situation has to be considered on caseto case and the staggering distance still be decided by the OWNER.Maximum misalignment or offset shall not exceed 1.6mm prior to welding the root bead.9.3 Pre-Heating and Interpass Temperature and Post-Weld HeatTreatment (PWHT)The need for appropriate levels of welding preheat shall be determined during the weldingprocedure qualification.The minimum preheat temperature shall be applied in accordance with the approved WPS. Theuse of oxyacetylene gas for preheating shall not be permitted. When fuel gas is used forpreheating, full encirclement rings are preferred. If hand held torches are approved by theOWNER, a minimum of two fuel gas torches shall be used on pipe diameters greater than NPS 12,when preheating manually. For all thicknesses greater than 20mm, welding of pipe to fittings orfittings to fittings, for pre-heating induction heating/ electrical mats shall be used. Preheat for fittingto pipe shall be 100 °C min. or as per the approved WPS.All tie-in welds, repairs, fillet welds and fitting-to-pipe welds shall be preheated to 50 ° C abovethat required for similar pipe-to-pipe butt welds. The interpass temperature shall not exceed 275 °C.The entire joint length shall be preheated simultaneously. The pre-heating temperature shall coveran area of at least 25mm width on either side of the weld and shall be maintained over the fulllength of the weld until the weld is completed.Any requirements for post-weld heat treatment shall be established during welding procedurequalification tests. In such cases the specific requirements for heat treatment shall be included inthe welding procedure specification by the CONTRACTOR and shall be subject to the approval ofthe OWNER. For repair welds, preheat shall be a minimum of 100°C.If PWHT is necessary, the CONTRACTOR shall submit a detailed procedure to the OWNER forapproval. This shall include all details required by ASME VIII, Div 1, para UCS 56.Radiographic inspections in accordance with clause 21 of this specification shall be carried out on100% of the length of welds after PWHT has been completed.A chart recording of each post-weld heat treatment shall be produced.9.4 Tack WeldsTack welds when approved by the OWNER shall be a minimum of 50mm long and shall be weldedwith the same Welding Procedure Specification used for the root pass and by a qualified welder.n:\513-mh-2145-rkpl\11 engineering\11.8 pipelines\06 spec\specification for welding on onshorepipeline\mh2145-c000-pl-spc-0020.docMH2145-C000-PL-SPC-0020 RevA Page 19 of 42