Repair measures of LSAW steel pipe transverse cracks

In recent years, with the development of national economy, thick wall LSAW steel pipe has gainedwider and wider application in the field of offshore platform, high temperature and high pressurevessel and wind pipe pile.

Steel pipe of this kind generally uses D36 steel, S355 steel and steel plate structure wuth Zperformance. The thicker the plate, the larger the carbon content, and the higher carbon equivalent,the poorer the weldability, the bigger the hardening tendency, lowering the welding performanceof welding joint, easy to produce cold crack, especially appearing the transverse cracks. Onceappearing the welding crack, in addition to the necessary control measures, but also pay attentionto the repair of workpiece in time.

Take S355 steel for example, list the repair measures of welding transverse crack repair measures:

1, confirm the defect100% UT inspection of all weld, mark the location, length, depth and direction of the crack.If the whole welding line has flaws, suggest tearing it up and submerging arc welding seam again,rod arc welding is recommended for local repair welding.

2, preheating before the planePreheat temperature is 110-170, preheat temperature detecting position of weld on both sides ofnot less than 150 mm, heating within range for distance defects around 500 mm.

3, air gougingScope of air gouging crack defects both ends to the outside, good weld outgoing air gougingbetween not less than 50 mm, planer slot at both ends for smooth transition, smooth transitionsurface and vertical line at least more than 45 . Air gouging carbon rod angle should be under 60,especially when approaching the crack, the Angle should be as small as possible.

4, grindingGrinding to no black, surface should be smooth after polishing, not sharp deep pit.

5, PTPenetrant testing (PT) after cooled to a suitable temperature.

6, grindingOn the basis of PT testing results, grinding, polishing until no red line.

7, MTDo magnetic testing (MT) after grinding, make sure no residual crack, otherwise should continueto be polished, until no crack.

8, preheating before welding

Recommended preheating temperature is 110-170 , preheat temperature detecting position ofweld on both sides of not less than 150 mm, weld heating range for distance less than 500 mm.

9, weldingCarried out in accordance with the operation instruction of repair welding, the weld width is nomore than 15 mm, can wend their opposites. Rod arc welding welding or automatic submerged arcwelding process.

10, heat preservation, slow cooling after welding

11, heat treatment after weldingHeat treatment after welding is mainly diffusion hydrogen, reduce the residual stress after welding,for larger stiffness weldment have special "hydrogen elimination processing", "eliminating stressof heat treatment. System of heat treatment is recommended: immediately heated to 200 withceramic electric blanket after completion of welding, the heat preservation shut electric slowcooling after 2 h.

12, test after welding test48 h after welding is complete, NDT test in accordance with requirements to confirm repairqualified.