The Special Requirements for SMLS Pipes for High-pressure Hydrogen Transportation

High-pressure hydrogen transportation places very strict requirements on SMLS pipes because hydrogen has some special physical and chemical properties, such as:
Hydrogen embrittlement: Hydrogen atoms can penetrate into the metal lattice, causing the mechanical properties of the metal material to deteriorate, such as reduced strength, toughness and plasticity, making it prone to brittle fracture.
Hydrogen leakage: Hydrogen molecules are small in size and can easily leak through tiny pores or defects in metal materials.
Flammable and explosive: When hydrogen is mixed with air, it is easy to burn or explode within a certain concentration range.
Therefore, seamless steel pipes used for high-pressure hydrogen transportation must have the following special properties and requirements:
 
1. High strength and high toughness
Withstand high pressure: High-pressure hydrogen transmission pipelines need to withstand high internal pressure, so the steel pipes must have sufficient strength to prevent bursting.
Resist hydrogen embrittlement: Hydrogen embrittlement will cause the toughness of the material to decrease, making it prone to brittle fracture. Therefore, the steel pipe needs to have higher toughness to improve its resistance to hydrogen embrittlement.
 
2. Good resistance to hydrogen embrittlement
This is one of the most important requirements for seamless steel pipes for high-pressure hydrogen transportation. In order to improve the hydrogen embrittlement resistance, the following measures are usually taken:
 
Choose the right steel grade: Choose steel grades that are less sensitive to hydrogen embrittlement, such as low-alloy high-strength steel, austenitic stainless steel, etc. Some data have proposed a seamless steel pipe for high-pressure hydrogenation equipment, whose chemical composition has been specially designed to improve the corrosion resistance of wet hydrogen sulfide, thereby indirectly improving the hydrogen embrittlement resistance. There are also materials that clearly require in the standard that furnace butt welding (FBW) cannot be used for hydrogen pipeline welding. This may be because FBW welding is more prone to defects, thereby increasing the risk of hydrogen embrittlement. There is also information showing that the pipeline materials are mainly low-strength pipeline steels such as X42, X52, and X56, which are commonly used hydrogen embrittlement-resistant steels.
 
Controlling the microstructure of steel: Refining grains and reducing grain boundary segregation can improve the steel's resistance to hydrogen embrittlement.
Control the impurity content of steel: Reducing the content of impurities such as sulfur and phosphorus in steel can reduce the occurrence of hydrogen embrittlement.
Surface Treatment: Metal surface coatings can be used to inhibit hydrogen embrittlement of steel pipes.
 
3. Good sealing performance
Prevent hydrogen leakage: Hydrogen molecules are small and can easily leak through tiny pores or defects in metal materials. Therefore, the steel pipe needs to have good sealing performance to prevent hydrogen leakage and ensure transportation efficiency and safety.
Seamless structure: Seamless steel pipes have no welds, which avoids possible leakage problems at the welds, and are therefore more suitable for high-pressure hydrogen transportation.
 
4. Good welding performance
If welding connection is required, the steel pipe needs to have good welding performance to ensure the quality and reliability of the weld. Some data indicate that the optional welding methods include double-sided submerged arc welding (DSA), fusion welding (EFW), electric resistance welding (ERW), flash welding (FW) and seamless steel pipes. This shows that for hydrogen pipeline welding, it is necessary to select a suitable welding method.
 
5. Corrosion resistance
Hydrogen transmission pipelines may need to operate in humid environments or environments containing other corrosive media, so the steel pipes need to have certain corrosion resistance.
 
6. Other requirements
Dimensional accuracy: In order to ensure the quality of pipeline connection and installation, the steel pipe needs to have a certain dimensional accuracy.
Surface quality: The surface of the steel pipe should be smooth and free of defects to reduce the risk of hydrogen leakage.
 
Conclusion
 
High-pressure hydrogen transportation places very strict requirements on seamless steel pipes, including high strength, high toughness, good resistance to hydrogen embrittlement, good sealing performance, good welding performance and corrosion resistance, etc. When selecting seamless steel pipes for high-pressure hydrogen transportation, it is necessary to strictly follow the relevant standards and specifications, and carry out necessary inspections and tests to ensure the safe and reliable operation of the pipeline.

Read more: The Requirements for Welding Hot-rolled Seamless Steel Pipes