The transverse cracks of LSAW steel pipe after measurement and rework are as follows:
1. Confirmation of defects
All welds are inspected by 100% UT. The location, length, depth and direction of cracks are marked. If the whole weld is defective, it is suggested to dig out the whole re-submerged arc welding and repair the SMAW partially.


2. Planing preheating
The preheating temperature is 110 - 170 C. The detection position of the preheating temperature on both sides of the weld seam is not less than 150 mm, and the heating range is about 500 mm.


3, planing.
The weld integrity is not less than 50 mm in the middle of the outlet, and the end of the air planer transits smoothly. The transition surface and the vertical line are at least more than 45 degrees. The angle of the planned carbon rod should be 60 degrees or less, especially in the cracks at the smallest possible angle.


4, polishing
Polished to black-free, polished surface should be smooth after transition, there should be no sharp pits.


5, PT
Penetration test (PT) was performed after cooling to appropriate temperature.


6, polishing
According to the test results, PT is grinded until there is no red line.


7, MT
After grinding, magnetic powder testing (MT) is done to confirm that there is no residual crack, or polishing should be continued until MT can not detect cracks.


8, preheating
It is suggested that the preheating temperature should be 110-170 C. The position of the two sides of the weld should be no less than 150 mm and the heating distance of the weld should be 500 mm.


9, welding
Welding operation is carried out in accordance with the instructions. The width of the weld is not more than 15mm. It can be welded on the lane. SMAW or automatic submerged arc welding can be used.


10. After welding, insulation, slow cooling


11. Postweld heat treatment
PWHT is mainly the diffusion of hydrogen, and the residual stress of stiffness weldment after welding is low. PWHT is committed to "eliminate hydrogen treatment" and "stress relief heat treatment". The recommended heat treatment system is to heat the ceramic blanket at 200 C immediately after welding, and power off for 2 hours after slow cooling.


12. After welding inspection
After 48 hours of welding, the qualifications are confirmed according to NDT inspection requirements.