The large straight seam steel pipe generally refers to the straight seam steel pipe with an outer diameter of more than 500mm. At present, the double weld diameter can reach 2020mm and the single weld diameter can reach 1220mm.

According to GB/T3091-2008 "Welded Steel Pipes for Low-pressure Fluid Transportation" standard, the internal and external surfaces of steel pipes should be smooth, and folding, cracks, layering, lap welding, arc breaking, burning through and other local defects whose depth does not exceed the deviation under the wall thickness are allowed.

The steel pipe shall be subjected to mechanical property test, tensile test, bending test, flattening test, guided bending test and hydraulic test, and shall meet the requirements specified in the standard. The steel pipe should be able to withstand certain internal pressure, the test pressure is 5.05mpa, the retention time is not less than 5S, during the experiment, the steel pipe does not appear leakage phenomenon. Ultrasonic testing or eddy current testing instead of hydraulic testing is allowed for resistance welded steel tubes. Ultrasonic or radiographic inspection is allowed instead of hydraulic testing for submerged arc welded steel tubes