What are the commonly used materials for straight seam steel pipes?
Carbon steel (Q235, Q345), low alloy steel (X42-X80), and stainless steel (304, 316L) are the mainstream materials. The X series meets the API 5L standard and is used for high-pressure oil and gas pipelines; stainless steel is corrosion-resistant but expensive. Nickel-based steel (such as L245N) is commonly used in low-temperature environments.
How to choose materials according to the application environment?
L360M steel resistant to H2S is required in acidic environments; duplex stainless steel 2205 is used for offshore platforms; P91/P92 alloy steel is selected for high-temperature pipelines. Materials that meet the impact energy standards at -40℃ are required in cold zones. Cost and life need to be balanced, for example, Q235B can be used for municipal water supply.
What is the effect of carbon equivalent (Ceq) on weldability?
When Ceq exceeds 0.45%, the risk of cold cracking increases significantly, and preheating or post-heating is required. The calculation formula includes the content of elements such as C, Mn, and Cr. The Ceq of X70 steel is usually controlled at 0.38-0.43. High Ceq materials require low hydrogen welding rods and strict process evaluation.
Why are X series steels commonly used in oil and gas pipelines?
The X series (such as X65) achieves high strength (yield ≥ 450MPa) and high toughness through microalloying and controlled rolling processes. Its sulfur and phosphorus content is ≤0.025%, meeting the DWTT test requirements of API 5L. Compared with ordinary steel, it can reduce weight by 20% and reduce laying costs.
In which fields is stainless steel straight seam steel pipe irreplaceable?
The food and pharmaceutical industry requires 316L grade sterile pipelines; chemical reactors are resistant to hydrochloric acid/nitric acid corrosion; and nitrogen-controlled stainless steel is used in the primary circuit of nuclear power. Its surface finish Ra≤0.8μm, and there is no magnetic interference with precision instruments.
