1. What is the basic definition of GB/T 712 EH36 steel pipe?
EH36 is a high-strength hull structural steel specified in the Chinese national standard (GB/T 712-2023). It belongs to the E-grade quality grade and is suitable for use in low-temperature environments of -40°C. Its naming convention is as follows:
"E" indicates extreme low-temperature toughness (meets -40°C impact resistance);
"H36" indicates a minimum yield strength of 355 MPa (36 kgf/mm²) or greater.
This material achieves a combination of high strength and extreme low-temperature toughness through microalloying and the controlled rolling and controlled cooling (TMCP) process, making it a core material for polar vessels and deep-sea equipment.
2. What are the main applications for EH36 steel pipe?
Polar vessels: The hull structures of icebreakers and tankers navigating the Arctic route must withstand temperatures below -40°C.
Deep-sea equipment: Components subjected to high stress and low temperatures, such as semi-submersible drilling platforms and deepwater jackets.
LNG carriers: Due to its excellent low-temperature toughness, it is suitable for the peripheral support structures of liquefied natural gas (-162°C) storage tanks.
3. What technological breakthroughs does EH36 offer compared to conventional marine steels (such as AH36)?
Low-temperature performance: -40°C impact energy (KV2) ≥ 34 J, more stringent than AH36 (-20°C).
Alloy optimization: Adding Ni (nickel) and Cu (copper) improves low-temperature toughness while controlling the P and S impurity contents (≤0.025%).
Process upgrade: Using TMCP (thermomechanically controlled process) instead of traditional normalizing to refine grain size and reduce welding sensitivity.
4. What special considerations are required when processing and welding EH36 steel pipe? Welding Process: Ultra-low hydrogen welding consumables (such as AWS E10018-G) must be used, with a preheat temperature of 100-150°C (higher for plate thickness > 25mm).
Cold Forming Limitations: The bending radius must be ≥ 3 times the wall thickness to avoid microcracking caused by cold working.
Post-weld Treatment: Dehydrogenation treatment (250-350°C x 2h) is performed on thick plate welds to prevent delayed cracking.
5. How is the compliance of EH36 steel pipe verified? What are the key inspection items? Marking Verification: The steel pipe surface must be clearly marked with "EH36," the GB/T 712 standard number, the heat batch number, and the manufacturer's information.
Certificate Review: The Material Certificate (MTC) must include:
Chemical composition (e.g., C ≤ 0.16%, Ni ≤ 0.40%);
Mechanical properties (yield strength ≥ 355 MPa, tensile strength 490-620 MPa);
-40°C impact test data (average of three specimens ≥ 34 J, single specimen ≥ 24 J);
Non-destructive Testing: Full-scale ultrasonic testing (UT) is performed to ensure the absence of internal defects. Critical welds require radiographic testing (RT).
