LSAW Pipe: A Strong Straight-Seam Steel Sheet Deformed

LSAW Pipe: A Strong Straight-Seam Steel Sheet "Deformed"

In the large-diameter welded pipe workshop of Huayang steel pipe in Hebei Province, three LSAW (longitudinal submerged arc welded pipe) production lines have always maintained efficient operation. As a "just-needed pipe" for major projects such as oil and gas high-pressure gathering and transportation and deep-sea exploitation, LSAW pipe is endowed with irreplaceable axial strength advantage by its "deformation forming" process with a single steel plate as raw material. Huayang has been deeply involved in LSAW pipe production for 20 years, with an annual production capacity of 300,000 tons. The X70 LSAW pipe supplied by Huayang has been successfully applied to the 10MPa high-pressure scene in Bohai Oilfield. Today, we will combine the actual production and project experience of Huayang to unveil the veil of this "straight-stitched strong man".

The full name of LSAW pipe is "longitudinal submerged arc welding pipe", and its most distinctive label is "deformation forming of single steel plate"-different from continuous steel strip winding of SSAW pipe, it is made of single wide and thick steel plate as the only raw material through forming, welding, straightening and other processes, and its key feature is that the weld is completely parallel to the axis of steel pipe. This characteristic determines its strength gene from the source.

In Huayang's raw material warehouse, the "rations" of LSAW pipes are clear at a glance: they are all high-strength steel plates such as Q345B and X70 produced by Angang and Shougang, with a thickness of 9mm to 50mm and a maximum width of 1.4 meters. "Choosing a single steel sheet instead of a steel strip is to ensure the uniform performance of raw materials." After integral rolling, the mechanical properties of the steel plate are more stable, which avoids the possible performance fluctuation caused by steel strip splicing. Relying on these high-quality raw materials, the largest diameter of LSAW pipe in Huayang can reach DN1400, which fully meets the needs of super-large projects.

"Single steel sheet deformation forming" is the core technology of LSAW pipe, and Huayang's "U-O forming" technology makes this process millimeter-level accurate. Taking DN800 LSAW pipe produced for Sinopec's high-pressure gathering and transportation project in 2023 as an example, the whole molding process can be called "meticulous work".

The first step is pre-bending and "setting". X70 steel plate with a thickness of 16mm first enters the pre-bending machine, and the equipment accurately presses the edges of both sides of the steel plate into arcs consistent with the curvature of the tube blank, and the error is controlled within ±0.5mm-this step can avoid stress concentration at the edges during subsequent molding. The second step is U-O "shaping": the pre-bent steel plate is sent to a 4,000-ton hydraulic press, first pressed into a U shape, and then pressed into an O-shaped tube blank by a special die. The pressure accuracy of the hydraulic press should be kept within 0.1MPa, otherwise the roundness deviation of the tube blank will exceed the standard, which will affect the subsequent welding.

The formed tube blank immediately enters the welding process. Huayang adopts double-wire submerged arc welding technology, and the arc covered with flux isolates the air to avoid weld oxidation, and the composition of welding wire and base metal is accurately matched. After welding, the tensile strength of weld can reach 570MPa, which is 5% higher than that of base metal. Finally, after straightening, hydrostatic test and ultrasonic flaw detection, a qualified LSAW pipe is considered as "born", and the whole process is monitored by Huayang AI detection system to ensure that there is no deviation in each process.

LSAW tube can become the "darling" of high-pressure scene, and the core lies in the axial strength advantage brought by straight seam structure. The test data of CNAS certification laboratory in Huayang show that under the same specifications (DN300, wall thickness 10mm, Q345B), the axial tensile strength of LSAW pipe reaches 570MPa and the yield strength is 345MPa, while the axial tensile strength of SSAW pipe is only 500MPa.

Although LSAW tube has excellent performance, the traditional process efficiency is low. Through technological upgrading, Huayang not only retains its strength advantage, but also solves the efficiency problem. In order to solve the problem of slow welding speed, Huayang introduced the "digital double-wire submerged arc welding system", which increased the welding speed from 0.3 m/min to 0.5 m/min, and the qualified rate of weld jumped from 98.5% to 99.8%.

In terms of toughness optimization, Huayang added the process of "stress relief annealing after welding". LSAW pipe produced for a chemical project in Northeast China in 2024, after annealing treatment, the impact toughness at -20℃ is improved to 45J, which is completely suitable for cold regions. At the same time, the AI vision inspection system installed on the production line can monitor the weld residual height and width in real time, and control the defect rate below 0.2%, far below the industry average of 1.2%. These upgrades have made Huayang's LSAW pipes more competitive. In 2023, when 12,000 tons of DN800 LSAW pipes were produced for Sinopec, the construction period was shortened from 40 days to 30 days, meeting the lifting requirements of the project in advance.

The "strong gene" of LSAW pipe originates from the high-quality substrate of a single steel plate, and is formed by precise deformation forming process, which is stronger than irreplaceable axial strength. The 15-year deep-rooted technology of Hebei Huayang Steel Pipe makes this "straight-seam strong man" more suitable for the needs of major projects in China. From Bohai deep sea to Shanxi coal mine, the LSAW pipe of Huayang has proved by its stable performance that it will always be a trustworthy "guardian" on the high-pressure and safe track.