Steel flat products for pressure purposes - Technical delivery conditions - Part 5: Weldable fine grain steels, thermomechanically rolled
1Key Takeaways
This document specifies the requirements for flat products for pressure equipment, made of thermomechanically rolled weldable fine grain steels as specified in Tables A.1 and B.1. The steels are not suitable for hot forming. Until now, no sufficient data for the standardization of the elevated temperature properties of…
2Expert Interpretation
An in-depth analysis of the ISO 9328-5:2018 standard's technical requirements for thermomechanically rolled fine-grain steel plates for pressure vessels, covering chemical composition, mechanical properties, low-temperature toughness requirements, and key welding process control points. A detailed analysis compares the delivery requirements of typical steel grades like P355ML2 and PT550M with those specified in the ASME/EN standard.
Analysis of core requirements of the standard
| Technical parameters | European system (Annex A) | ASME system (Annex B) |
|---|---|---|
| Strength classification basis | Yield strength(ReH) | Tensile strength(Rm) |
| Typical steel grades | P355M/ML1/ML2 | PT440M/ML1/ML3 |
| CEV maximum value | 0.39-0.47 | 0.37-0.45 |
Key Performance Indicators
1. Chemical Composition Control
The standard stipulates that Thermomechanically rolled fine grain steel must meet the following requirements:
- Als content ≥ 0.020% (or acid-soluble aluminum ≥ 0.015%)
- Total V+Nb+Ti ≤ 0.15%
- P and S contents ≤ 0.025% respectively
2. Mechanical Property Requirements
Take P355ML2 as an example:
- Yield strength of 50mm thick plate ≥ 345MPa
- -50℃ impact energy ≥ 27J (optional 40J)
- Elongation A ≥ 22%
Key Points of Technological Evolution
- Main Changes in the 2018 Edition:
- The term "product thickness" is changed to "nominal thickness"
- Updated ordering example content
- Boron content requirement (B≤0.0010%) is added to Table B.1
- Differences from the 2011 Edition:
- Refined phosphorus and sulfur control requirements
- Supplemented simulated post-weld heat treatment test clauses
Implementation Recommendations
1. Material Selection Principles
- When the design temperature is ≤-40℃, ML1/ML2 series is preferred.
- The carbon equivalent value (CEV) of pressure-bearing parts needs to be specially controlled.
2. Welding process control
When the P parameter value exceeds 17.3:
- A simulated post-weld heat treatment test is required.
- Develop welding procedure qualification in accordance with EN 1011-2.
- Strictly control the diffusible hydrogen content.