1.Submerged Arc Welding Process Difference.
Compared with spiral submerged arc welding process, longitudinal submerged arc welding process can inevitably have a lot of T-weld, so the existence of welding defects has great increased. The welding residual T-welds stress is large, and the weld metal are often in three-dimensional stress state which can increase the likelihood of cracks. Besides, according to the provisions of submerged arc welding process, each weld shall have the arc at the place and extinction. However, in each longitudinal submerged arc welding ring, it is unable to meet the conditions which causes more weld defects during longitudinal submerged arc welding process.
2.Production Range Difference
Under the same operating pressure to produce the same outside diameter longitudinal weld pipe and spiral weld pipe, spiral weld pipe can produce thinner wall thickness pipe than longitudinal weld pipe. Because when the pressure in the pipe to withstand, it typically produces two main stress on the pipe wall. These two main stress are radial stress and axial stress. On spiral weld pipe, these two main stress are divided by the helix angle of the weld, therefore synthetic spiral weld stresses are the main stress.
3.The Hydro Static Burst Strength
The yield stress and burst pressure on spiral weld pipe is lower than the longitudinal weld pipe, even though there are certain relevant comparison test has says the yield pressure and burst pressure measured and theoretical values are basic the same on spiral and longitudinal weld pipe. In the blasting test, it also proved that the hoop blasting mouth deformation rate for spiral weld pipe is significantly greater than the longitudinal weld pipe. It confirmed that spiral weld pipe has a greater plastic deformation than longitudinal weld pipe.
Compared with the same specification spiral weld pipe and longitudinal weld pipe, spiral weld pipe has a higher impact of toughness. With the increasing needs for large diameter pipe with high strength and with the development of new steel grades, It requires greater ductile fracture tip.
5.Fatigue Strength Difference
With the same test data in the same area, under the same pipe distribution and resistance, longitudinal submerged arc weld pipe has a higher level of fatigue strength. Because of the transfer pipeline output volume changes, in the actual operation, the pipe is subjected to random alternating loads of action. It is very significant to judge the life of pipeline by learning the cycle fatigue strength of steel.