- Field welding of pipelines TIE-IN joints shall be done by Shielded Metal Arc Welding (SMAW ) process as per approved WPS.
- A TIE-IN pit or bell hole of suitable length, depth and width shall be cut to enable to work freely inside the trench. Proper care shall be taken so as not to allow pit to collapse or pit wall caving in. Necessary supports shall be used wherever required. An angle of repose of 10º at such area is preferred.
- In connecting pipes, special items, fittings on joints of differing material thickness as supplied transition piece with 1: 4 taper shall be used and the welds shall be subjected to Radiographic and Ultrasonic (wherever applicable) examination.
- Cut pipe ends shall be examined wherever applicable for laminations by Ultrasonic Testing & Dye Penetrant Testing over distance of 25 mm minimum.
- Defective pipe length shall be cut back until laminated section is removed and re-beveled for pipe which have been cut, Pipe No., Heat No., Coating yard No., Balance length has to be transferred on to remaining pipe length. The cut piece which is used shall be
- Designated by XA & the balance pipe length should designate by say pipe B specify XA, XB. Any subsequent cutting of the pipe shall be designated as XBA, XBB.
- Alignment of the TIE-IN joint shall be done using external hydraulic clamp capable of removing offset and misalignment shall be minimized.
- Seam orientation of welded pipe shall be selected to ensure that the longitudinal welds shall be staggered in the top 90º of the pipeline or 150 mm. whichever is the less and shall be positioned in the upper half of the pipe, not applicable with HSAW pipes. In case the seams come closer than as defined above, a pup piece of minimum 1.0 m shall be used. For pipes of same wall thickness the offset shall not exceed 3.0 mm.
ALL TIE-IN JOINTS SHALL BE WELDED IN ONE HEAT CYCLE.
- TIE-IN shall be done in such a way as to leave minimum stress in the pipe. If any pup end is required for TIE-IN, the minimum length shall not be less than 1.0 meter and two or more such pups shall not be welded together. TIE-IN with two or more pups of length more than 1.0 meter may be used providing a space of entire length of pipe. In no case more than three welds shall be permitted in a 10 meter length of pipeline.
- TIE-IN joint welding including necessary cutting, beveling, grinding and line up etc. shall be carried out as per this procedure and approved WPS.
- The new field bevels shall be examined visually before offering for ultrasonic (wherever applicable) testing. All reports of TIE-IN along with NDT reports approval. Cleaning, Priming, Coating and other activities shall be performed as per approved procedures.
- The root gap shall be accurately checked and shall conform to the qualified welding procedure. All spaces between bars or at least 60% of first pass shall be welded before the clamp is released and pipe remaining adequately supported on each side of the joint.
- Segments thus welded shall be equally spaced around the circumference of the pipe. Slag etc. shall be cleaned off and the ends of the pass shall be prepared by grinding, so as to ensure continuity of the weld bead.
- Qualified welders shall carry out welding. While welding is in progress, care shall be taken to avoid any kind of movement of the components / pipe, shocks vibration and stresses to prevent occurrence of weld cracks.
- Electrode starting and finishing points shall be staggered from pass to pass.
- Arc strikes outside the bevel on the pipe surface shall not be permitted. Accidental arc strikes shall be repaired as per approved procedure.
- All finished welds shall be visually inspected for parallel and axial alignment of the work, welds, surface porosity and other surface defects.
- Parts being welded and the welds shall be protected by windshields made of metallic frame covered by Canvas, whenever necessary, to protect from rain and strong winds.
- The completed welds shall be covered with asbestos cloth covered by GI sheets, whenever necessary, to protect from bad weather conditions.
- For TIE-IN of adjacent sections of pipeline already pressure tested also called golden joints and for final joints, a single length pup or off cuts, which have been hydro statically pre-tested shall be used.
