LSAW Pipes And Their Applications

LSAW pipe (longitudinal submerged arc welded pipe) has always played the role of "ballast stone" in the steel arteries of major projects such as West-East Gas Pipeline, Bohai Deepwater Oilfield and Central Asia Energy Pipeline. With excellent axial strength and stability, this kind of pipe, which is made of a single steel plate and made by precision forming and submerged arc welding, has become a "just-needed choice" for high-pressure and large-caliber scenes. As a national high-tech enterprise that has been deeply involved in steel pipe industry for 20 years, Hebei Huayang Steel Pipe has built three intelligent LSAW production lines with an annual output of 600,000 tons. The X70 and X80 LSAW pipes supplied by it have been exported to more than 20 countries and regions around the world. Today, we will unveil the LSAW tube together and explore its wide application in the fields of energy and infrastructure.

The full name of LSAW pipe is "longitudinal submerged arc welded pipe", that is, longitudinal submerged arc welded pipe. Its core feature is that the weld is parallel to the steel pipe axis, which is different from the oblique weld of spiral submerged arc welded pipe (SSAW). Its production takes a single wide and thick steel plate as the only raw material, and it is made by pre-bending, forming, welding, straightening, testing and other processes. This process of "deformation forming of single steel plate" ensures the uniformity of pipe performance from the source.

In the LSAW production workshop of Huayang Steel Pipe, the steel plates in the raw material warehouse have complete specifications, such as "Q355B, X70, X80" and other brands, with a thickness of 7mm to 50mm and a maximum width of 4.5 meters. "We only use hot-rolled steel plates from large steel enterprises such as Angang and Shougang. These steel plates are rolled as a whole, and the fluctuation range of mechanical properties is controlled within 5%, which is far superior to spliced steel strips." Director of the raw material inspection department of Huayang steel pipe introduced that each batch of steel plates must pass the tensile test, impact test and chemical composition test, and the unqualified raw materials are directly returned, which is the basis for the excellent performance of LSAW pipe. Relying on high-quality raw materials and precision technology, the largest diameter of LSAW pipe in Huayang can reach DN1400, which fully meets the needs of super-large projects.

The "strong gene" of LSAW tube is hidden in its precise forming and welding process. Huayang steel pipe adopts the international advanced JCOE forming process to gradually "carve" flat steel plate into high-pressure pipe, and the whole process is like a "steel shaping".

Taking DN800 X70 LSAW pipe produced by Huayang for Sinopec's high-pressure gathering and transportation project in 2023 as an example, the process flow is divided into three steps: the first step is pre-bending, and the X70 steel plate with a thickness of 16mm enters a four-roll 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 pipe blank, and the error is controlled within ±0.5mm to avoid stress concentration at the edges during subsequent molding; Step 2: U-O forming, that is, the pre-bent steel plate is sent to a 4000-ton hydraulic press, first pressed into a U shape, and then pressed into an O-shaped tube blank by a special die, and the pressure accuracy of the hydraulic press is stabilized at 0.1MPa to ensure that the roundness deviation of the tube blank does not exceed 1 mm; The third step is welding, which adopts double-wire submerged arc welding technology. The arc covered with flux isolates the air and avoids the oxidation of the weld. The welding wire and the base metal are accurately matched, the welding speed reaches 0.5 m/min, and the tensile strength of the weld is 5% higher than that of the base metal.

After the welding is completed, the pipe will go through a strict "quality inspection checkpoint": the water pressure test will be kept at 1.5 times the working pressure for 30 minutes to ensure no leakage; Ultrasonic and X-ray double flaw detection to realize 100% full coverage detection of weld; Finally, straightness is adjusted by straightener to ensure that each pipe meets the installation requirements. The production director of Huayang Steel Pipe revealed: "The automation rate of our LSAW production line is 90%, and the AI vision inspection system monitors the weld quality in real time, and the defect rate is controlled below 0.2%, far below the industry average of 1.2%."

The core reason why LSAW tube can stand in extreme scenes such as high pressure and low temperature lies in the mechanical properties advantages brought by its straight seam structure. According to the test data of CNAS Certification Laboratory of Huayang Steel Pipe, under the same specification (DN300, wall thickness 10mm), the axial tensile strength of LSAW pipe is 570MPa, and the yield strength is 345MPa, while the axial tensile strength of SSAW pipe is only 500MPa, which is particularly critical in high-pressure scenarios.

In a deep-sea exploitation project in Bohai Oilfield in 2023, DN600 LSAW pipe supplied by Huayang has to bear the deep-sea high pressure of 10MPa (equivalent to the pressure of 1000 meters water depth) and cope with the low temperature environment of -20℃. The test data show that the weld impact toughness of this batch of pipes reaches 42J, far exceeding the 30J required by the project. It has been kept under pressure for 1 hour at 1.5 times the working pressure without any leakage, and passed the third-party test at one time. "Straight seams are consistent with the direction of stress and can evenly transmit axial pressure, which is an inherent advantage that spiral slotted pipes cannot replace." In terms of corrosion resistance, Huayang LSAW tube also performed well. In view of the high sulfide soil environment in Central Asia, the LSAW pipe customized by Huayang for local energy projects adopts the process of "sandblasting rust removal +3PE corrosion protection", and the thickness of the corrosion protection layer is 2.5mm, which has been verified by salt spray test and can run stably in high corrosive environment for more than 20 years. The 50-kilometer LSAW pipe sent to Uzbekistan in 2024 has successfully passed the rigorous local anti-corrosion performance test and will soon be put into use in oil field oil pipelines.

Huayang LSAW tube

From domestic energy hubs to overseas infrastructure sites, the application scenarios of LSAW pipes always focus on the core requirements of "high pressure, large diameter and high reliability", which is also confirmed by the actual order data of Huayang Steel Pipe. In 2024, oil and gas, municipal administration and chemical industry accounted for 55%, 25% and 15% respectively.

High-pressure oil and gas gathering and transportation: the "safety hub" of wellhead and trunk line

In the process of oil and gas exploitation and gathering, the scene of wellhead high-pressure section and long-distance trunk hub requires extremely high pipe strength, and LSAW pipe becomes the first choice. In the high-pressure gathering and transportation project of an oil field of Sinopec in 2023, 12,000 tons of DN800 LSAW pipes supplied by Huayang undertook the task of transporting crude oil from the wellhead to the pressurization station, with a working pressure of 8MPa, and there was no weld leakage after 18 months of operation. The person in charge of the project said: "This pipeline is the core of the whole gathering and transportation system. The strength of LSAW pipe in Huayang not only meets the standard, but also its precise size control reduces the difficulty of on-site installation, and the welding qualification rate is improved to 99.5%."

Large-diameter municipal engineering: the "steel skeleton" of pipe gallery and trunk line

LSAW pipe can not only meet the demand of large diameter, but also ensure the safety of key nodes in municipal utility tunnel and thermal trunk lines above DN600. In the Handan Municipal utility tunnel Project in 2024, Huayang LSAW pipe was selected for the high-pressure gas transmission section (DN600, pressure 4MPa), and used together with SSAW pipe for the medium-pressure section, which not only ensured the safety of the core area, but also controlled the overall cost. The person in charge of the pipe gallery of the project said: "Once there is a problem in the high-pressure section, it will affect the gas supply of the whole city. The LSAW pipe of Huayang has passed the strict water pressure and flaw detection test, which makes us feel at ease." However, in Shijiazhuang thermal trunk line project, Huayang DN1000 LSAW pipe runs continuously for 12 months in high temperature medium transportation at 120℃, and the weld thermal stability is excellent.

Cold and thick-walled scenes: the "solution" of customized requirements

The LSAW pipe can resist the risk of low temperature embrittlement after process optimization in the cold area below -20℃. In 2024, the LSAW pipe customized by Huayang was made of Q355B low-temperature steel. After stress relief annealing after welding, the impact toughness at -30℃ reached 45J, which was completely suitable for the local extreme climate. In the scene of thick-wall demand, the LSAW pipes of Huayang are also outstanding. In a nuclear power auxiliary cooling water pipeline project in 2023, the DN800 LSAW pipes with a wall thickness of 25 mm were supplied, and the qualified rate of weld detection reached 99.8%, which met the strict standards of nuclear power engineering.

The performance advantage of LSAW pipe needs the support of mature production and service system, and the core competitiveness of Huayang steel pipe is reflected in this. At the production end, the LSAW production line introduced the "digital double-wire submerged arc welding system", and 16 parameters such as welding current and voltage were adjusted in real time through AI algorithm, and the weld qualification rate was increased from 98.5% to 99.8%. On the server side, Huayang provides "customization+whole process" service, and participates in the project from raw material selection, process design to on-site installation guidance.

In an energy project in Central Asia in 2024, Huayang customized the anti-ultraviolet coating and high-strength steel-grade formula for LSAW pipes in view of the special local environment with high altitude and high corrosion, and sent three technicians to the site to guide the installation, which solved the technical problems of the local construction team. "We sell not only pipes but also solutions." The manager of the international business department of Huayang Steel Pipe said that it is this service concept with the project demand as the core that makes its LSAW pipe win the recognition of customers at home and abroad.

From single steel plate to high pressure pipe, the production process of LSAW pipe is the epitome of modern industrial precision manufacturing. From the deep sea of Bohai Sea to the grassland of Central Asia, its application scenarios show the hard-core strength of "Made in China". The 22-year deep cultivation of Hebei Huayang steel pipe proves that the value of LSAW pipe lies not only in its excellent mechanical properties, but also in its ability to accurately meet the needs of key scenes such as high pressure and large diameter, and to build a "steel defense line" for energy transmission and urban construction.

With the acceleration of global energy infrastructure, the application prospect of LSAW tube will be broader. China enterprises, represented by Huayang Steel Pipe, will continue to focus on technological innovation, and let more LSAW pipes made in China go global and become a reliable choice for major international projects.