Spiral steel pipes are manufactured by helically bending strip steel or coil plates into shape and welding the inner and outer seams using double-sided submerged arc welding. They are widely applied in water, electricity, chemical, and other industrial productions due to the following reasons: By simply adjusting the forming angle, various diameters of steel pipes can be produced from the same width of strip steel, facilitating easy adjustment.
Since the formation is continuous and curved, the fixed length of spiral pipes is not constrained, allowing for customized lengths. The spiral welds are evenly distributed along the entire circumference of the pipe, resulting in high dimensional accuracy and strength. The ease of altering dimensions makes them suitable for small-batch, multi-type production of spiral pipes.
The welds of spiral steel pipes are longer than those of straight-seam pipes of the same standard, and under the same wall thickness, spiral pipes can withstand the greatest pressure. The weld defects in spiral steel pipes are known as "oblique defects." During use, the equivalent defect length in the direction of the principal stress, i.e., the axial direction of the pipe, is shorter than that of straight-seam pipes. Furthermore, as pipeline steel is made from rolled steel plates, the impact toughness exhibits significant anisotropy, with the CVN value along the rolling direction being up to three times higher than that perpendicular to it.
The standards for spiral steel pipes are differentiated based on their areas of application and acceptance criteria. The SY/T5037-2012 standard applies to general fluid transportation pipelines, while the GB/T9711-2011 standard is for steel pipes used in oil and gas pipeline transportation systems. The GB/T3091-2008 standard is intended for low-pressure fluid transportation pipelines such as gas, water gas, air, heating, and steam.
Regarding acceptance criteria, the flaw detection standards for spiral steel pipes under these three standards vary. The GB/T9711 standard is stricter than SY/T5037 and GB/T3091 in terms of flaw detection. Similarly, the geometric dimensions and outer diameters of spiral steel pipes under the GB/T9711 standard are stricter than those under the SY/T5037 and GB/T3091 standards, with GB/T3091 being stricter than SY/T5037 in all acceptance criteria.
Interestingly, the wall thickness deviations are uniform across all three standards. For spiral steel pipes with a wall thickness ranging from 5mm to 15mm, the deviation is ±0.1T (where T is the nominal wall thickness of the spiral steel pipe). For pipes with a wall thickness exceeding 15mm, the deviation is ±1.5mm.
