1. Q: What is ASTM A333 Grade 4?
A:
It is a low-temperature carbon steel pipe designed for low-temperature environments (down to -45°C).
Its chemical composition is primarily carbon, manganese, and silicon, with small amounts of phosphorus and sulfur. It contains no alloying additives and exhibits excellent low-temperature toughness and weldability.
It complies with ASTM A333, which is similar to the domestic standard GB/T 18984 (Seamless Steel Pipe for Low-Temperature Pipes).
2. Q: What is the difference between Grade 4 and other grades (such as Grade 1/6)?
A:
Temperature range: Grade 4 (-45°C) falls between Grade 1 (-50°C) and Grade 6 (-100°C).
Compositional differences: Grade 4 has a slightly higher carbon content than Grade 6 (the latter contains nickel for improved low-temperature performance).
Strength Comparison: Grade 4 tensile strength is ≥415 MPa, higher than Grade 1 (≥380 MPa) but lower than Grade 6 (≥485 MPa).
3. Q: What are the main application areas?
A:
Cryogenic piping systems: Liquefied natural gas (LNG), liquid nitrogen/liquid oxygen transportation, and refrigeration equipment.
Chemical and Energy: Cryogenic separation units in petroleum refining and refrigeration unit piping.
Building Structures: Infrastructure pipelines in cold regions (such as the Arctic Circle).
4. Q: What precautions should be taken during welding and processing?
A:
Preheating requirements: Thick-walled pipes should be preheated to 100-150°C to prevent cold cracking.
Welding consumables: Low-hydrogen electrodes (such as E7018) or matching submerged arc welding wire are recommended.
Post-weld treatment: Slow cooling is recommended to prevent residual stress from affecting low-temperature performance.
5. Q: How can its low-temperature performance be tested?
A:
Impact test: Charpy V-notch impact test at -45°C, with a single specimen absorbed energy of ≥20J (standard requirement).
Non-destructive testing: Ultrasonic (UT) or radiographic (RT) testing for weld defects.
Hardness test: Ensure the post-weld hardness is ≤22 HRC to prevent embrittlement.
