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Pressure resistance and fatigue resistance: the difference of weld shape

The pressure resistance of steel pipe depends largely on the distribution of weld. The straight seam weld of LSAW is parallel to the axis of steel pipe, and the stress distribution is uniform during pressure transmission, and the blasting pressure can reach 4 times of the design pressure. The spiral weld of SSAW is distributed at about 45, with good stress dispersion and better fatigue resistance than LSAW. After 1 million fatigue tests, the weld integrity rate of SSAW steel pipe in Huayang is still 98%, which is suitable for reciprocating pressure scenarios of long-distance pipelines. The straight seam weld of ERW is short (consistent with the circumference of the steel pipe) and the probability of welding defects is low. In the Tianjin Port oil product project in 2024, 15,000 tons of ERW steel pipe operated continuously for half a year under the working pressure of 1.6MPa without leakage, and the weld stress value was only 5MPa different from that of the pipe body.

It should be noted that the upper voltage limit of ERW is lower than that of HFW and LSAW. The test data of Huayang show that the design pressure of ordinary ERW steel pipe is usually ≤2.0MPa, while that of HFW steel pipe can reach 4.0MPa and LSAW can exceed 10MPa, so LSAW is still the first choice in ultra-high pressure scenarios (such as deep-sea oil and gas transportation).