Welded steel pipe weld reinforcement control

Welded steel pipe weld reinforcement control

 

 

Mainly expounds the control of conveying submerged arc welded steel pipe, weld the high importance. The stress concentration factor of the weld is large, and the stress corrosion crack is easy to form the stress corrosion cracking in the weld. Outside the weld, I was not conducive to corrosion; in the remaining high, will increase the transmission medium of energy loss, etc..

Submerged arc welded steel pipe for welding quality evaluation, first look at the inner and outer weld height and shape control, OK, weld line is neat. The weld is not tall and smooth, while the weld toe stress comprehensive coefficient, anti SCC negative. In addition, the outside of the weld, will give the pipe of the Chen Jifu operation is increased, the cost increases; the internal welding of Yu Gaoda, the pipeline transport medium of the friction resistance, pipe energy consumption is large. Therefore, in the production of submerged arc welded pipe, must control the inside and outside of the weld. 5L API standard in the higher than the minimum standards, and the oil and gas pipeline and the marine pipe will be higher than the 2.5mm.

Transportation most high seam submerged arc welded steel pipe, in a number of standard provisions are made.

1 negative impact on the weld height

1.1 at the weld toe easily into stress corrosion cracking (SCC)

The stress concentration of the butt joint is mainly caused by the welding residual height. More than Gaoyu weld is serious, it will reduce the strength of welded joints. After welding cut more than high, as long as it is not lower than that of the parent material, reduce the stress concentration, sometimes it can improve the strength of welded joints.

The smaller the radius of the weld seam, the greater the degree of stress concentration, and vice versa, the smaller the stress concentration. Therefore, the requirements of the submerged arc welding seam: one is more than high, the two is the weld to smooth over, so that the R value of the radius of the rotation is increased.

Submerged arc welded steel pipe weld for butt joint welds, if we do not control the good weld reinforcement height and angle radius, the weld toe stress is that welded pipe in serving the process especially in corrosive medium, easy in the weld toe produce stress corrosion cracking.

In the process of forming and welding, the residual stress is inevitable, so the residual stress is eliminated after forming and welding. Residual stress can be eliminated, but the residual stress is very difficult to be completely eliminated. In order to prevent the stress corrosion cracking at the weld toe, it is required to control the formation and welding residual stress, especially the residual stress at the weld toe.

1.2 outside the weld is tall and is not conducive to anti-corrosion

In the anti-corrosion operation, such as the use of epoxy resin glass cloth for anti-corrosion, outside the welding seam, will make the weld toe is not easy to press. At the same time, the higher the welding seam, the more should be thicker, because the standard provisions of the thickness of the coating is outside the top of the weld, which is based on the calculation, which increases the cost of corrosion.

1.3 outside the weld seam I have been greatly affected by the tube shape after the expansion of water pressure

Chinglish is one the "straight edge" phenomenon submerged arc welded steel pipe in hydraulic expanding diameter is expansion through the inner cavity and the pipe size consistent with the left and right part 2 die steel pipe wrapped. Therefore, weld residual high too big, in expanding weld under the shear stress on the big weld 2 side easily. But experience has proved that, when the outside of the weld of the high control in 2mm or so, the water pressure will not appear "small straight edge" phenomenon, the tube will not be affected. This is because of the high and small, the shear stress of the welded joints is also small. As long as the shear stress in the range of elastic deformation, unloading after the rebound, the pipe will be restored to the original state

1.4 inside the weld seam I tall to increase the transmission medium of energy loss

Conveying submerged arc welded pipe surface if not done anticorrosion coating processing, Yu Gaoda weld seam of the, the conveying medium friction resistance is, thus will enable conveying pipeline increases the energy consumption.