Questions regarding the HG/T20581 table for selecting materials resistant to hydrogen corrosion in a hydrogen atmosphere
Thread Content
Hello, teachers! Regarding HG/T20581, page P68, “Figure 7.8.3 Limitations on the use of carbon steel and pearlitic heat-resistant steel in hydrogen atmospheres”, I have the following questions. I would appreciate it if the knowledgeable teachers could provide answers. Thank you! 1. The application range of carbon steel is below the thick horizontal line. Why are black dots marked above the horizontal line? Are the black dots unnecessary? There is a blank circle below the horizontal line; is this blank circle unnecessary? 2. What do the half-white and half-black dots represent? It says “see notes” on the diagram, but the notes don’t mention this symbol either. 3. “Note: For 0.5Mo steel, see the appendix and Figure 2.” Where are the appendix and Figure 2?
There’s nothing that can be done about it – HG refers to API RP 941, but not in its entirety; the standard only includes one diagram. If one looks at API RP 941, it becomes clear that this diagram comes with annotations, which explain that the points and numbers on the diagram represent data and usage examples provided by various engineering companies. As for the black markings on the curve indicating safety, they are there because the curve is derived from regression analysis of discrete engineering examples, resulting in a smooth trend line. There’s also the 0.5Mo material; there is no corresponding grade for this in China, while abroad it is likely the SA204 material. Therefore, HG, as the domestic standard, does not include this curve at all. The attachment shown in the diagram probably refers to Appendix A of API RP 941, so it certainly cannot be found in HG. If you want to learn more, it is recommended to consult the API RP941 standard, as it provides a more direct way to understand the subject. If you are interested in learning further, you can take a look at API TP 941 for additional information.
Thank you for your detailed answer! I’ve learned something