Advantages of ERW steel in subsea development

Date:2024-06-19Tags:ERW steel pipe, seamless steel pipe, SSAW steel pipe

With the continuous expansion of submarine oil and gas resource exploration and exploitation, the demand for submarine pipelines has increased year by year. Due to the complexity and harshness of the submarine environment, the quality requirements for pipelines are extremely strict, especially the strength, toughness, weldability and corrosion resistance of pipelines. The resistance welding (ERW steel pipe) pipe making technology has the advantages of high dimensional accuracy, uniform wall thickness, and strong anti-collapse ability due to its forming method and welding process, so it occupies an important position in the manufacture of submarine pipelines. This article will focus on the application advantages of ERW steel pipe technology in submarine pipelines.


ERW steel pipe technology and its advantages

During the manufacturing process of ERW steel pipeline, the edge of the steel strip is melted by resistance heat, and then a weld is formed under the action of the extrusion roller. This process determines that ERW steel pipeline has significant advantages in the following aspects:

High dimensional accuracy: The diameter and wall thickness of ERW steel pipe can be precisely controlled, which is especially important for submarine pipelines that require high precision and consistency.

Uniform wall thickness: Uniform wall thickness not only improves the strength and stability of the pipeline, but also makes the pipeline more durable under high pressure.

Strong anti-collapse ability: Since the steel is evenly stressed during the manufacturing process of ERW steel pipeline, its anti-collapse ability is significantly higher than that of traditional welded pipelines. The impact toughness of ERW steel pipe is higher than that of seamless steel pipe.

High weld quality: Weld quality is a key indicator that determines the service safety of steel pipes. The weld of ERW steel pipeline can achieve higher welding strength and consistency through high-frequency straight seam resistance welding process. The length of ERW steel pipe weld is shorter than that of SSAW steel pipe.

ERW steel pipes

Challenges of ERW steel pipe submarine pipelines

With the development of deeper seabed resources, the demand for thick-gauge (wall thickness ≥ 20mm) ERW submarine pipelines is increasing, but there are many challenges in the welding process. First, the size of the opening angle directly affects the quality of the weld. A larger opening angle helps to obtain a stable weld, but it also significantly increases the welding power requirement. Secondly, the setting of the extrusion amount is crucial to the purity and strength of the weld. The appropriate extrusion amount is conducive to squeezing out inclusions in the weld and improving the quality of the weld. However, inclusions are inevitably generated during the welding process, which will reduce the impact performance of the weld and thus affect the overall quality of the pipeline.


Improve welding process to improve weld quality

In order to overcome the challenges in the welding process of thick-gauge ERW steel pipe submarine pipelines and improve the quality and impact performance of welds, relevant research and practice have proposed a series of improvement measures. The use of argon protection device can effectively inhibit the oxidation of metal in the welding area and improve the welding quality. Argon gas is evenly distributed above the welding area through the gas pipe to form a protective atmosphere. By optimizing the design of plate composition, such as using ultra-low carbon, low manganese, low sulfur, and low phosphorus steel, and adding micro-alloying elements such as niobium and molybdenum, the performance of the weld can be significantly improved. Specifically, controlling the content of carbon and manganese within a reasonable range can maintain the toughness and strength of the material; reducing the content of sulfur and phosphorus as much as possible to reduce the negative impact on the performance of steel; adding niobium and titanium in appropriate amounts to utilize their solid solution strengthening and fine grain strengthening effects, but their content needs to be strictly controlled to ensure weldability; molybdenum should be controlled within a reasonable range to improve the hardenability and strength of the material while avoiding cost increases and reduced welding performance.


Optimization of production process flow

When manufacturing thick-gauge ERW steel pipe submarine pipeline welded pipe, optimization of production process flow is crucial. The following are the key steps and their optimization points:

Raw material inspection: The composition and performance of hot-rolled coils are tested to ensure that the quality of raw materials meets the requirements.

Open coil butt welding: The tail of the previous coil is butt welded with the head of the next coil by submerged arc welding, and sent to the loop storage system to ensure the continuity of feeding.

Milling edge: Before the steel strip enters the forming process, it is milled to the set width by the milling machine to meet the requirements of high-quality forming and welding process.

Steel pipe forming: The steel strip is continuously bent into a round steel pipe by a series of rollers.

Steel pipe welding: High-frequency straight seam resistance welding is used for welding, and an argon protection device is introduced in the welding area to improve the quality of the weld.

Weld heat treatment: The microstructure of the weld and its heat-affected zone is improved by medium-frequency heat treatment to ensure that the weld has high strength and high toughness.

Weld air cooling and water cooling: The weld after heat treatment is air-cooled and water-cooled to control the temperature and geometric dimensions of the weld.

Steel pipe sizing: The diameter and ovality of the steel pipe are controlled by the sizing rack to ensure that it meets the design requirements.

Steel pipe flaw detection: The weld and the range of 50mm above and below are tested to ensure that the weld is defect-free.


Through the above optimization measures, the weld quality and impact performance of thick-gauge ERW steel pipe submarine pipeline welded pipes have been significantly improved. The experimental results show that the impact energy of the ERW steel pipe submarine pipeline weld after the improved process can reach more than 300J, which is significantly higher than the 50J of the traditional process, thereby greatly improving the service safety and reliability of the submarine pipeline.


Conclusion

ERW steel pipe pipe technology has significant advantages in the manufacture of submarine pipelines. By optimizing the plate composition design, introducing argon protection devices, controlling welding parameters and improving the weld heat treatment process, the weld quality and impact performance of thick-gauge ERW steel pipe submarine pipelines can be significantly improved. With the continuous improvement of these technologies, ERW pipelines will play a more important role in the future development of submarine oil and gas resources.

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