Surface to be welded shall be cleaned to bright metal for a distance of not less than 25mm from the edges of weld groove and all surface shall be free from oil, grease, water, loose scale, paint or any foreign material.All temporary attachments shall be cut from a good condition plate and shall match the adjoining members in term of weld ability. All temporary attachment shall be removed by grinder or thermal cutting to minimum of 03mm from the surface of the material and subsequently ground flush with the surface.Temporary attachments shall not be removed by breaking, knocking or other means which will cause damage to surface of the structural.Temporary attachments shall not be welded within 100mm of T, K, and Y stubs to barrel welds, conical transition weld and of closing welds. Welding SequenceWhere shrinkage and distortion is likely to affect the adequacy of the member or structure, welding sequences shall be developed to control distortion, wrapping, creeping and the build-up of excessive internal stresses in the structure and the shall be submitted to Company for approval before the weld activity commence.The approved welding sequence shall be briefed to the welders and displayed prominently at the working area.Welding Engineer or Supervisor shall supervise the welding of the assembly to ensure the planed sequences are followed.Welding sequence shall include: WPS to be applied Sequence of joints to be welded Number and location of welders at each stage of assembly Tack weld, temporary attachments and spacers used in the assembly of components Preheating of joint to be welded PWHT (if required)Whenever practical, two welders are required to weld a joint from both sides simultaneously. For welding of pipes or tubular with diameter greater than 20 inch, two or more welders are required to weld simultaneously.Avoid welding component at both ends simultaneously because this will cause high stress in the component due to weld metal shrinkage when cooling. The high stress can cause distortion of component or crack in the weld joint.Special attention is required when welding a large panel of tubular, beam, or plates to minimum distortion. Welding of the panel shall start from the centre and out to the perimeter. Preparation Prior WeldingAll approved WPS shall be posted at site for welding supervisor and welder's reference. Welders shall adhere to the parameters as specified in the related WPS. The welding supervisor shall ensure that the welders follow the parameters in the WPS.
đang được dịch, vui lòng đợi..