1. Core positioning and industry application of EH36 steel
As a key material in the field of shipbuilding and marine engineering, EH36 steel has the core characteristics of high strength, low temperature toughness and crack arrest performance. According to the International Association of Classification Societies (IACS) specifications, EH36 steel plates must meet the requirements of -40℃ impact toughness, tensile strength range of 490-630MPa, yield strength of not less than 355MPa, and elongation ≥21%. This type of steel is widely used in key parts such as decks, hatch coamings, torsion boxes, etc. of ultra-large container ships, and its performance is directly related to the structural safety of ships under extreme sea conditions.
2. Detailed explanation of LR certification process
Lloyd's Register (LR) certification is the core threshold for EH36 steel to enter the international market. The certification process covers the following key links:
Technical document review
Technical documents that meet LR specifications must be submitted, including chemical composition reports (C≤0.18%, Mn 0.90-1.60%, P≤0.025%, S≤0.025%), mechanical properties test data (such as -40℃ impact energy ≥34J) and production process documents.
Factory audit and witness test
LR experts need to conduct on-site audits of the production process, focusing on the stability of the thermomechanical rolling (TMCP) + tempering process, and witness sampling tests to ensure that the thickness direction performance of the steel plate (such as the lamellar tearing resistance of Z35 grade) meets the standards.
Certification mark and continuous supervision
After passing the certification, the steel plate must be marked with the LR classification society mark and furnace batch number, and each subsequent batch must be subject to regular sampling to ensure quality consistency.
3. E36 steel testing standard system
The testing of EH36 steel needs to follow a multi-dimensional standard system:
Chemical composition control
According to GB/T 712-2011 and ISO 4995:2018 standards, the carbon equivalent (Pcm value) needs to be strictly controlled to reduce the risk of welding cracks, and micro-alloy elements such as Nb, V, and Ti are added to refine the grains and improve low-temperature toughness.
Mechanical property verification
Full-thickness tensile test (ensuring yield strength ≥355MPa), Charpy V-notch impact test (absorbed energy ≥34J at -40℃) and CTOD crack tip opening displacement test (meeting BCACOD standard) are required.
Non-destructive testing requirements
According to NB/T 47013.3 standard, steel plates need to be ultrasonically inspected one by one, and the qualified level is not less than level Ⅲ to ensure that there are no defects such as interlayers and cracks inside.
Surface quality control
A thin layer of iron oxide is allowed, but the depth shall not exceed the negative deviation of the thickness. The minimum thickness after grinding shall not be less than 93% of the nominal thickness, and the total grinding area shall not exceed 2% of the total area.
4. Core differences in ship steel standards
There are slight differences in the standards of EH36 steel for different classification societies:
China CCS standard: Implement GB/T 712-2011, emphasize -40℃ impact toughness and Z-direction performance classification (Z15/Z25/Z35).
US ABS standard: Refer to ASTM A131 specification, control sulfur and phosphorus content more strictly (P≤0.020%, S≤0.020%), and require a crack sensitivity coefficient (Pcm) calculation report.
European BV/DNV GL standard: In addition to conventional mechanical properties, fatigue performance test requirements are added to ensure long-term reliability under alternating loads.
5. Development trend of detection technology
With the trend of large-scale ships, EH36 steel detection technology is developing towards high precision and intelligence:
Automated flaw detection system: Phased array ultrasonic technology (PAUT) is used to replace traditional ultrasonic detection to improve defect recognition rate.
Big data quality traceability: Record the data of the entire life cycle of steel plates through the Internet of Things technology to achieve rapid traceability of quality problems.
Green detection technology: Develop low-radiation and pollution-free detection methods to meet the environmental protection requirements of the shipbuilding industry.
Conclusion
The detection of EH36 steel needs to be based on LR certification, integrate the standards of multinational classification societies, and ensure that it meets the stringent requirements of the shipbuilding industry through comprehensive control of chemical composition, mechanical properties, non-destructive testing and surface quality. With the iterative upgrade of detection technology, the quality control of EH36 steel will be more accurate and efficient in the future, providing solid protection for global shipping safety.