1. In terms of mechanical properties

compressive strength

LSAW Steel Pipe: The straight seam structure makes the stress distribution of LSAW steel pipe relatively uniform when subjected to external water pressure. In deep-sea environments, it can more effectively resist high pressure. Its compressive strength can be precisely controlled during design and manufacturing based on specific seabed depth and pressure requirements. For example, for a 3000 meter deep sea oil pipeline, the wall thickness and material of LSAW steel pipes can be optimized to achieve higher compressive strength standards, making them more suitable for use in high-pressure areas.

SSAW Steel Pipe: The presence of spiral welds makes the stress distribution of SSAW steel pipe slightly more complex when subjected to axial pressure. Under the same wall thickness and pipe diameter, the compressive strength is slightly lower than that of LSAW steel pipe. In shallower waters (such as depths less than 1000 meters), this difference in compressive strength has little impact on pipelines, but in deep-sea environments, its compressive performance is relatively limited.

Resistance to bending and flexibility

LSAW steel pipe: The straight seam structure of LSAW steel pipe mainly relies on the overall material properties of the steel pipe to resist bending deformation. When turning or bypassing underwater obstacles, a larger bending radius is required, usually not less than 50 times the pipe diameter. If the bending radius is too small, it may cause excessive local stress in the steel pipe, affecting the safety of the pipeline.

SSAW steel pipe: The spiral weld of SSAW steel pipe gives it better flexibility. When encountering complex underwater terrain or obstacles during the laying process, it can be laid with a relatively small bending radius, which is a significant advantage in its application in underwater pipelines. For example, in areas with many shallow reefs, SSAW steel pipes can better adapt to terrain changes for installation.

Fatigue resistance performance

LSAW steel pipe: The straight seam welding quality is high, and the fusion between the weld and the base metal is good. Under long-term exposure to cyclic loads such as waves, currents, and internal oil flow, it has good fatigue resistance. Through reasonable material selection and welding process optimization, the fatigue strength at the weld seam can reach a high level, comparable to the base material, which is conducive to ensuring the reliability of the pipeline during long-term use.

SSAW steel pipe: Under long-term dynamic loads, local fatigue cracks may occur in spiral welds due to the characteristics of weld shape and stress distribution. Its fatigue resistance is slightly inferior to LSAW steel pipes. During the design service life, it is necessary to pay closer attention to the fatigue damage at the spiral weld seam, and to consider the detection and repair of weld fatigue in the maintenance plan of the pipeline.

2. In terms of corrosion resistance

Coating construction and effect

LSAW steel pipe: The outer surface is relatively flat, and the straight seam structure is convenient for the construction of anti-corrosion coating. For example, when using 3PE coating (three-layer polyolefin coating), the epoxy powder bottom layer can be sprayed more evenly on the surface of the steel pipe, and it is also easier to ensure the quality and thickness uniformity of the coating at straight seams. This helps to improve the corrosion resistance of steel pipes to seawater and reduce the risk of localized corrosion caused by coating defects.

SSAW steel pipe: Due to the presence of spiral welds, the construction of anti-corrosion coatings is relatively difficult. When spraying coatings, special attention should be paid to the coverage of spiral welds to avoid uneven coating thickness or missed coating. For example, when using epoxy powder coating, special spray gun angles and spraying processes may be required to ensure the coating quality at the spiral weld seam, otherwise the weld seam is prone to become a weak point of corrosion.

Cathodic protection adaptability

LSAW steel pipe: In the application of cathodic protection systems such as sacrificial anode protection or impressed current cathodic protection, the straight seam structure makes the current distribution relatively uniform. It is easier to achieve uniform control of potential on the surface of pipelines, reducing local overprotection or underprotection phenomena. For example, when using sacrificial anode protection, the arrangement of anodes can be more regularly distributed along the pipeline, effectively providing cathodic protection for the entire steel pipe.

SSAW steel pipe: Spiral welds can cause certain interference with the distribution of cathodic protection current. When designing and implementing cathodic protection, it is necessary to consider the impact of spiral welds, which may require increasing the number of reference electrodes to more accurately monitor the potential, and adjusting the distribution and current output of the anode to ensure that all parts of the pipeline are well protected, which increases the complexity and cost of the cathodic protection system.

3. Manufacturing process and dimensional accuracy

The influence of manufacturing process on pipeline quality

LSAW steel pipe: The straight seam submerged arc welding process is relatively complex, requiring high quality and dimensional accuracy of the steel plate. There are many quality control steps in the manufacturing process, including steel plate cutting, edge processing, welding parameter control, etc., to ensure the quality of straight seam welding. The quality of steel pipes produced by this process is relatively stable, with high dimensional accuracy and small deviations in diameter and wall thickness, which can better meet the high-precision connection requirements of submarine pipelines.

SSAW steel pipe: The spiral submerged arc welding process is to weld the steel strip by spiral curling, and the process is relatively flexible. During the manufacturing process, there are certain requirements for the width, thickness, and curling accuracy of the steel strip. Due to the characteristics of the process, the dimensional accuracy of steel pipes is slightly lower than that of LSAW steel pipes. The diameter and wall thickness may vary in the circumferential direction, but it is acceptable in some shallow water pipeline applications where dimensional accuracy requirements are not particularly high.

The influence of dimensional accuracy on pipeline laying and connection

LSAW steel pipe: The high-precision dimensions make LSAW steel pipe more convenient and tight for underwater pipeline connections (such as flange connections or welded connections). A small deviation in pipe diameter can ensure good sealing between pipelines and reduce the risk of oil leakage. In deep-sea pipeline laying, high precision is required for pipeline connection, and the size advantage of LSAW steel pipe is more obvious.

SSAW steel pipe: Due to relatively low dimensional accuracy, more adjustment measures may be required to ensure connection quality when connecting subsea pipelines. For example, in welding connections, it may be necessary to compensate for differences in pipe diameter and wall thickness, which increases construction difficulty and time costs. In shallow water areas, the increase in connection difficulty has relatively little impact, but may be limited in high-precision connection scenarios in deep sea.

4. In terms of cost and economy

Production cost difference

LSAW steel pipe: Due to its complex manufacturing process, high requirements for equipment accuracy and raw material quality, the production cost of LSAW steel pipe is relatively high. In the production process, straight seam welding requires high-precision equipment and strict quality control, resulting in its price being usually higher than SSAW steel pipes.

SSAW steel pipe: The spiral submerged arc welding process is relatively simple, with lower equipment investment and production costs. In situations where the diameter of the pipe is large and the requirements for dimensional accuracy and mechanical properties are not extremely high, SSAW steel pipes have a significant price advantage, making them more competitive in some cost sensitive shallow water pipeline projects.

Using economic considerations

LSAW steel pipe: In deep-sea high-pressure and high-precision underwater oil pipeline applications, although the procurement cost is high, the high performance of LSAW steel pipe (such as high compressive strength, good fatigue resistance, and dimensional accuracy) can ensure the long-term stable operation of the pipeline, reduce maintenance and replacement costs. From the perspective of full lifecycle cost, it has good economic viability in this environment.

SSAW steel pipe: In shallow and nearshore environments, SSAW steel pipe's lower procurement cost and better flexibility make it economically attractive. For example, in projects such as nearshore shallow water oil pipelines or inlet and outlet pipelines for seawater desalination plants, SSAW steel pipes can reduce initial investment costs while meeting usage requirements. However, when considering the long-term maintenance of pipelines and potential performance risks (such as slightly poor fatigue resistance), it is necessary to comprehensively evaluate their economic viability.