Selecting Submarine Pipelines
Submarine pipelines are an essential component of the global energy infrastructure, enabling the transportation of oil and gas from offshore production sites to onshore processing facilities. These pipelines are typically constructed from high-strength steel or composite materials and are designed to withstand the harsh conditions of the ocean environment. Despite their importance, submarine pipelines face a range of challenges that can impact their reliability and safety. Corrosion is a major concern, as saltwater can cause significant damage to pipeline materials over time. Additionally, underwater currents and geological features can create stresses on the pipeline that must be carefully managed. To address these challenges, engineers have developed advanced monitoring systems that allow operators to detect potential problems before they become serious. Regular maintenance is also critical to ensure that pipelines remain in good condition over their lifespan. Overall, submarine pipes play a vital role in meeting global energy demand while minimizing environmental impact. As technology continues to advance, these pipelines will likely become even more reliable and efficient in the years ahead.
Mechanical composite pipes and metallurgical composite pipes have their advantages and disadvantages, which are as follows:
(1) The production process of the mechanical composite pipe is relatively simple; the cost is low, but the bonding force is small. It is easy to separate when the pipe is subjected to excessive bending or high temperature, failing the composite pipe; the metallurgical composite pipe has high bonding strength, but the cost is high and production complex.
(2) The bending process of mechanical composite pipes is difficult, and defects such as bulges and bubbles are easy to occur; the production of metallurgical composite pipes is relatively easy, and the bonding strength is better.
(3) After the mechanical composite pipe is transported to the construction site, the cutting can only be carried out in the surfacing area, and the groove cannot be processed outside the surfacing area; the metallurgical composite pipe can be cut at will.
(4) The mechanical composite pipe is suitable for mass production, and the production efficiency of the metallurgical composite pipe made by surfacing welding is low, which is only suitable for small batch production; the production efficiency of the metallurgical composite pipe made of the steel plate by the hot rolling process is high, but the process requirements are high.
The NORSOK M-001 material selection standard stipulates that when the conveying medium is corrosive, the minimum internal corrosion allowance of carbon steel pipes is 3mm, and the maximum corrosion allowance is 10mm. When the corrosion rate is high, the corrosion inhibitor may not be able to effectively reduce the corrosion rate. The anti-corrosion scheme using carbon steel plus corrosion inhibitor easily fails. When the risk of internal corrosion is high, carbon steel is not used, and corrosion-resistant alloy materials are required. Therefore, when the internal corrosion allowance does not exceed 10mm, carbon steel pipes are recommended for subsea pipelines. The grades of carbon steel pipes for subsea pipelines are usually API 5L PSL 2 X65 and X70, mainly depending on the mechanical performance requirements for subsea pipelines.
In general, seamless steel pipes are used for pipes of 2 to 10 inches, high-frequency electric resistance welded steel pipes are generally used for pipes with 12 to 24 inches, and submerged arc welded steel pipes are used for pipes larger than 24 inches. The selection of specific pipe materials also needs to consider the pipe production capacity of the steel pipe manufacturer.
When the internal corrosion allowance exceeds 10mm, it is recommended to use corrosion-resistant alloy composite pipes for submarine pipelines. There is no difference between the base pipe and ordinary carbon steel pipe. The base pipe of mechanical composite pipes is usually seamless steel pipes and high-frequency electric resistance welded steel pipes, and the base pipe of metallurgical composite pipes is usually seamless steel pipes and submerged arc welded steel pipes. The base pipe steel grade is usually API 5L PSL 2 X65 and X70, mainly depending on the requirements for the mechanical properties of the base pipe. The material of the liner depends on the corrosiveness of the medium, generally austenitic stainless steel 316L or nickel-based alloy 625, and the material of the surfacing layer and ring welding seam is generally nickel-based alloy 625. The material of the flat pipe of the submarine pipeline is generally a mechanical composite pipe, and the material of the standpipe and expansion bend is a mechanical composite pipe or a metallurgical composite pipe.
Suggestions on the selection of long-distance and highly corrosive oil and gas field subsea pipelines
For long-distance, highly corrosive oil and gas field subsea pipelines, if corrosion-resistant alloy composite pipes are used throughout the whole process, not only the cost of pipes will be high, but also the efficiency of offshore welding will be greatly affected, which will greatly increase project investment. Different pipelines can be considered in sections of material. In areas with high medium temperatures and a high risk of top corrosion, it is recommended to use corrosion-resistant alloy composite pipes. As the temperature of the conveying medium continues to decrease along the conveying direction, after reaching the critical temperature, the risk of corrosion on the top is low, and the carbon steel pipe plus corrosion inhibitor can be considered. This scheme was applied for the first time in a project in China, saving tens of millions of engineering costs.
Mechanical composite pipes and metallurgical composite pipes have their advantages and disadvantages, which are as follows:
(1) The production process of the mechanical composite pipe is relatively simple; the cost is low, but the bonding force is small. It is easy to separate when the pipe is subjected to excessive bending or high temperature, failing the composite pipe; the metallurgical composite pipe has high bonding strength, but the cost is high and production complex.
(2) The bending process of mechanical composite pipes is difficult, and defects such as bulges and bubbles are easy to occur; the production of metallurgical composite pipes is relatively easy, and the bonding strength is better.
(3) After the mechanical composite pipe is transported to the construction site, the cutting can only be carried out in the surfacing area, and the groove cannot be processed outside the surfacing area; the metallurgical composite pipe can be cut at will.
(4) The mechanical composite pipe is suitable for mass production, and the production efficiency of the metallurgical composite pipe made by surfacing welding is low, which is only suitable for small batch production; the production efficiency of the metallurgical composite pipe made of the steel plate by the hot rolling process is high, but the process requirements are high.
The NORSOK M-001 material selection standard stipulates that when the conveying medium is corrosive, the minimum internal corrosion allowance of carbon steel pipes is 3mm, and the maximum corrosion allowance is 10mm. When the corrosion rate is high, the corrosion inhibitor may not be able to effectively reduce the corrosion rate. The anti-corrosion scheme using carbon steel plus corrosion inhibitor easily fails. When the risk of internal corrosion is high, carbon steel is not used, and corrosion-resistant alloy materials are required. Therefore, when the internal corrosion allowance does not exceed 10mm, carbon steel pipes are recommended for subsea pipelines. The grades of carbon steel pipes for subsea pipelines are usually API 5L PSL 2 X65 and X70, mainly depending on the mechanical performance requirements for subsea pipelines.
In general, seamless steel pipes are used for pipes of 2 to 10 inches, high-frequency electric resistance welded steel pipes are generally used for pipes with 12 to 24 inches, and submerged arc welded steel pipes are used for pipes larger than 24 inches. The selection of specific pipe materials also needs to consider the pipe production capacity of the steel pipe manufacturer.
When the internal corrosion allowance exceeds 10mm, it is recommended to use corrosion-resistant alloy composite pipes for submarine pipelines. There is no difference between the base pipe and ordinary carbon steel pipe. The base pipe of mechanical composite pipes is usually seamless steel pipes and high-frequency electric resistance welded steel pipes, and the base pipe of metallurgical composite pipes is usually seamless steel pipes and submerged arc welded steel pipes. The base pipe steel grade is usually API 5L PSL 2 X65 and X70, mainly depending on the requirements for the mechanical properties of the base pipe. The material of the liner depends on the corrosiveness of the medium, generally austenitic stainless steel 316L or nickel-based alloy 625, and the material of the surfacing layer and ring welding seam is generally nickel-based alloy 625. The material of the flat pipe of the submarine pipeline is generally a mechanical composite pipe, and the material of the standpipe and expansion bend is a mechanical composite pipe or a metallurgical composite pipe.
Suggestions on the selection of long-distance and highly corrosive oil and gas field subsea pipelines
For long-distance, highly corrosive oil and gas field subsea pipelines, if corrosion-resistant alloy composite pipes are used throughout the whole process, not only the cost of pipes will be high, but also the efficiency of offshore welding will be greatly affected, which will greatly increase project investment. Different pipelines can be considered in sections of material. In areas with high medium temperatures and a high risk of top corrosion, it is recommended to use corrosion-resistant alloy composite pipes. As the temperature of the conveying medium continues to decrease along the conveying direction, after reaching the critical temperature, the risk of corrosion on the top is low, and the carbon steel pipe plus corrosion inhibitor can be considered. This scheme was applied for the first time in a project in China, saving tens of millions of engineering costs.
