1. Straight seam submerged arc welded steel pipe (LSAW)

Characteristics and advantages

Strength and toughness: LSAW Steel Pipes have high strength and good toughness, which enables them to withstand complex stress environments at sea. In deep-sea areas, steel pipes need to withstand enormous water pressure, and the high strength of LSAW steel pipes can effectively prevent deformation or rupture of pipelines due to external pressure. The weld quality is high, and through the straight seam submerged arc welding process, the strength and toughness of the weld are similar to those of the base metal, which can ensure the reliability of the overall structure of the steel pipe.

High dimensional accuracy: The straight seam structure enables LSAW steel pipes to perform excellently in terms of dimensional accuracy. The precise size of steel pipes is crucial for the installation and connection of pipelines in offshore engineering. For example, in the connection process between offshore platforms and subsea pipelines, high-precision LSAW steel pipes can better interface with other equipment, reduce installation errors, and improve construction efficiency.

Application scenarios

Subsea oil pipeline: used in offshore oil extraction to transport oil from subsea oil wells to offshore platforms or onshore terminals. Due to the high internal pressure of pipelines during oil transportation, LSAW steel pipes can meet the requirements of high-pressure transportation, and their good corrosion resistance (with appropriate anti-corrosion measures) can ensure the safety of oil during long-term transportation.

Support structures and process pipelines for offshore platforms: In the construction of offshore platforms, some support structures and process pipelines will also use LSAW steel pipes. Its strength can support the weight of platform equipment and resist dynamic loads caused by sea waves, currents, etc.

2. Spiral submerged arc welded steel pipe (SSAW)

Characteristics and advantages

Flexibility and adaptability: The spiral weld structure of SSAW Steel Pipe gives it a certain degree of flexibility. During the process of laying offshore pipelines, especially when it is necessary to bypass some underwater obstacles or adapt to complex terrain, SSAW steel pipes can better bend and adjust the pipeline direction. This flexibility gives it an advantage in some special offshore pipeline laying projects.

Cost effectiveness: In some cases, the production cost of SSAW steel pipes is relatively low. Due to its manufacturing process characteristics, SSAW steel pipes may have a higher cost-effectiveness when the pipe diameter is large and the requirement for dimensional accuracy is not extremely high. For some large-scale offshore pipeline projects, if the performance requirements of steel pipes can be met, choosing SSAW steel pipes can reduce costs to a certain extent.

Application scenarios

Shallow and nearshore pipeline engineering: SSAW steel pipes can leverage their advantages in shallow or nearshore pipeline projects, such as the inlet and outlet pipelines of seawater desalination plants, and nearshore oil and gas gathering and transportation pipelines. The pipeline laying environment in these areas is relatively simple, with relatively low requirements for the dimensional accuracy and strength of steel pipes. SSAW steel pipes can meet the usage requirements and have certain cost advantages.

Offshore wind power infrastructure and cable protection conduit: Used in offshore wind power projects for certain pipelines and cable protection conduits in wind power infrastructure. The SSAW steel pipe with spiral structure can be bent appropriately according to the shape of the wind power foundation and the cable laying path, playing a role in protecting the cable and assisting in supporting the foundation structure.

3. Seamless steel pipe

Characteristics and advantages

High internal quality: Seamless steel pipes have no welds and a continuous and uniform internal structure, which prevents stress concentration caused by weld defects when subjected to internal pressure. When transporting high-pressure, high-purity media (such as deep-sea natural gas transportation), seamless steel pipes can ensure the sealing and safety of the media. The uniformity of its material also gives it a certain advantage in corrosion resistance, as there is no weak link such as the weld seam that is easily corroded.

Size range and accuracy: Seamless steel pipes have high dimensional accuracy and can produce small-diameter steel pipes, which is very suitable for some offshore special purpose pipelines (such as fine instrument pipelines, small hydraulic system pipelines, etc.). It can accurately meet various complex size requirements, ensuring precise connection and normal operation of offshore equipment.

Application scenarios

The key part of deep-sea high-pressure natural gas transmission pipelines: In deep-sea natural gas extraction and transportation, seamless steel pipes can effectively prevent natural gas leakage for some key parts, such as the starting section of high-pressure transmission pipelines near the wellhead. Its excellent pressure resistance and sealing performance can ensure the safe transportation of natural gas in high-pressure environments.

Precision equipment pipelines on offshore platforms: Seamless steel pipes are required in the connecting pipelines of some precision instruments and equipment on offshore platforms, such as chemical analysis instruments, high-precision hydraulic control systems, etc., to ensure the quality and accuracy of the pipelines and ensure the normal operation of these equipment.

Comparison between them

1. In terms of mechanical properties

Strength and pressure resistance

LSAW steel pipe: It has high strength, and the straight seam welding process makes the weld quality high, close to the strength of the base material, and can withstand high internal pressure. It performs well in the application of oil and gas pipelines in deep-sea high-pressure environments, and its compressive strength can meet the pressure requirements at depths of thousands of meters on the seabed.

SSAW steel pipe: Its strength can also meet many conventional offshore application scenarios, but under the same wall thickness and pipe diameter conditions, its compressive strength is slightly inferior to LSAW steel pipe. This is because the stress distribution of spiral welds is relatively complex when subjected to axial pressure, which may result in local stress concentration. However, in shallow waters or environments with low pressure requirements, its strength is sufficient to meet the demand.

Seamless steel pipe: Due to the absence of weld seams, there is no stress concentration problem at the weld seam, and the overall strength distribution is uniform. When subjected to high pressure, it has excellent pressure resistance performance, especially suitable for high-pressure and high-precision medium transportation, such as the initial transportation section of deep-sea natural gas, and its pressure resistance strength can reach a very high standard.

Resilience and fatigue resistance performance

LSAW steel pipe: Through reasonable material selection and welding processes, good toughness can be obtained. In the face of complex dynamic loads at sea, such as wave impact, tidal changes, and platform vibrations, it can effectively resist fatigue failure. The straight seam structure is beneficial for force transmission to a certain extent, reducing local deformation and thus improving fatigue resistance.

SSAW steel pipe: Its spiral weld structure gives the steel pipe a certain degree of flexibility, exhibiting good toughness when subjected to bending and torsional forces. When encountering changes in underwater terrain or bending adjustments during pipeline laying, it can adapt well without easily breaking. However, the fatigue performance of spiral welds may be slightly worse than that of straight welds, and fatigue cracks are more likely to occur at the weld under long-term dynamic loads.

Seamless steel pipe: The uniformity of the material ensures its good toughness and excellent performance in fatigue resistance. Seamless steel pipes can work stably for a long time in environments with frequent pressure fluctuations and vibrations, such as connecting pipelines to precision equipment on offshore platforms, reducing the risk of damage caused by fatigue.

2. Manufacturing process and dimensional accuracy

Manufacturing process complexity

LSAW steel pipe: The straight seam submerged arc welding process is relatively complex, requiring high equipment accuracy and welding technology. It requires cutting the steel plate into a suitable shape first, and then performing high-precision straight seam welding. There are many quality control links in the production process to ensure the quality of the weld and the overall performance of the steel pipe.

SSAW steel pipe: The spiral submerged arc welding process is relatively flexible, which is made by welding steel strips by coiling them in a spiral shape. The manufacturing process is relatively simple, and the equipment investment cost may be slightly lower. However, precise control of the curling speed and welding parameters of the steel strip is required during its production process to ensure the quality of the spiral weld seam.

Seamless steel pipe: The manufacturing process of seamless steel pipe mainly includes complex processes such as perforation and rolling. For example, in the process of hot perforation, solid steel billets need to be heated and perforated through a perforating machine, and then undergo multiple rolling processes to form seamless steel pipes. This process is complex and the production cost is relatively high.

dimensional accuracy

LSAW steel pipe: The straight seam structure makes the dimensional accuracy easy to control, and can produce steel pipes that meet strict standards with small deviations in diameter and wall thickness. In situations where high precision is required for offshore pipeline connections, such as flange connections for deep-sea pipelines or docking with underwater equipment, LSAW steel pipes have more advantages.

SSAW steel pipe: The dimensional accuracy is relatively poor, and due to the presence of spiral welds, the diameter and wall thickness may vary in the circumferential direction. In some situations where dimensional accuracy is not particularly high, such as large-diameter drainage pipelines in shallow waters, this difference in accuracy is acceptable.

Seamless steel pipe: With high dimensional accuracy, it can produce various small-diameter and high-precision steel pipes. Its inner and outer diameter accuracy can meet the strict requirements of offshore precision equipment pipelines, ensuring precise connections and sealing performance between pipelines.

3. In terms of cost and economy

production costs

LSAW steel pipe: Due to its complex manufacturing process and high equipment precision requirements, the production cost is relatively high. Its raw material and processing costs (including welding, non-destructive testing, etc.) are relatively high, which may result in a higher price than SSAW steel pipes.

SSAW steel pipe: The manufacturing process is relatively simple, the utilization rate of raw materials is high, and it has certain advantages in production costs. Especially in the large-scale production of large-diameter steel pipes, its cost advantage may be more apparent. This makes it more competitive in some cost sensitive offshore pipeline projects.

Seamless steel pipe: The manufacturing process of seamless steel pipe is complex, requiring multiple processes and high requirements for raw material quality and equipment, resulting in the highest production cost. Its price is usually higher than that of LSAW and SSAW steel pipes, especially in the production of large-diameter steel pipes, where the cost difference is more significant.

Economy of use

LSAW steel pipe: In high-pressure and high-precision application scenarios such as deep sea, although the procurement cost is high, due to its reliable performance and long service life, it can ensure long-term stable pipeline transportation function. From the perspective of full life cycle cost, it has good economy.

SSAW steel pipe: In environments with relatively low pressure and slightly lower precision requirements such as shallow waters and nearshore areas, its lower procurement cost and better adaptability make it economically advantageous. For example, in the inlet and outlet pipeline project of a nearshore seawater desalination plant, SSAW steel pipes can reduce costs while meeting usage requirements.

Seamless steel pipe: Although seamless steel pipe is expensive, its high quality can ensure the safety and reliability of the system in some critical offshore application scenarios that require extremely high pipeline quality and performance (such as key sections of deep-sea high-pressure natural gas transportation and precision equipment pipelines on offshore platforms), avoiding high maintenance and shutdown losses caused by pipeline failures. From this perspective, it is economically reasonable.

4. In terms of corrosion resistance performance

The influence of welds on corrosion

LSAW steel pipe: The quality of straight seam welding is high. If the weld is treated properly, such as using appropriate welding materials and welding processes, and with effective anti-corrosion measures, the corrosion resistance performance at the weld can be similar to that of the base material. In the marine anti-corrosion environment, straight seam structures are relatively easy to apply anti-corrosion coatings and install cathodic protection systems.

SSAW steel pipe: Spiral welds may face some challenges in anti-corrosion. Due to the complex shape of the weld seam, more attention needs to be paid to ensuring the integrity and uniformity of the coating at the spiral weld seam during anti-corrosion coating construction. The weld seam may also be more susceptible to corrosion due to stress concentration and other factors, and anti-corrosion measures need to be strengthened in strong corrosive environments such as seawater.

Seamless steel pipe: There is no weak link in the weld seam that is prone to corrosion, and it has a natural advantage in corrosion resistance. The uniformity of its material enables the anti-corrosion coating to adhere more evenly, and reduces the risk of medium leakage caused by weld corrosion during internal medium transportation.

Applicability of anti-corrosion measures

LSAW steel pipe: suitable for various conventional anti-corrosion methods of offshore steel pipes, such as external coating (epoxy powder coating, 3PE coating, etc.) and cathodic protection (sacrificial anode method or external current method). The straight seam structure facilitates the automated construction and quality control of anti-corrosion coatings, as well as the uniform distribution of cathodic protection current.

SSAW steel pipe: During the implementation of anti-corrosion measures, special treatment is required for spiral welds. For example, during the external coating construction, special spray guns or construction processes may be required to ensure the coating quality at the spiral weld seam. In terms of cathodic protection, due to the influence of spiral welds on current distribution, it is necessary to design and adjust the protection system more finely.

Seamless steel pipe: The seamless structure makes it simpler and more effective when using anti-corrosion measures. The anti-corrosion coating can be better utilized to protect the surface of steel pipes, and the anti-corrosion advantage of seamless steel pipes is more obvious when the internal medium requires high purity and cannot be contaminated by corrosion products.