Rules for Substitution of Pressure Vessel Materials
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Under what circumstances can materials be substituted for each other during the production process?
Higher-grade materials can replace lower-grade ones; for example, Q345R can substitute for Q235R
The statement above is worth paying attention to – it’s not possible to use a higher-grade material in place of a lower-grade one, such as high-strength steel in place of low-strength steel. The issue of material substitution has been discussed many times; you can check the relevant links
High replaces low, thickness replaces thinness. In short, good generation gaps are acceptable, but it is also necessary to consider whether the properties of the medium and the results of process evaluation permit it.
Principles for material substitution: The general principle is to use better materials in place of inferior ones, and the following factors should also be taken into consideration: 1) Whether the strength grade of the substitute material affects the classification of the container. 2) Compatibility of the material with the working medium. Such as stress corrosion, intergranular corrosion, etc. 3) Whether the allowable stress of the substitute material at the specified temperature meets the requirements of the original design. 4) Will the substitute materials result in changes such as those to the welding materials or welding process? 5) Will alternative materials introduce requirements such as changes to heat treatment conditions, non-destructive testing, and welding test plates?
The discussion on the 5th floor was quite comprehensive; it can’t be said that replacing something inferior with a superior option is always a good thing. Sometimes it can affect the relevant technical indicators
The principle is to prefer the better option over the worse one. For details, see Article 27 of the Compliance Regulations.
It’s not enough to simply use alternatives in accordance with the standards; relevant procedures for substituting materials must also be carried out before manufacturers can do so
Article 27: In principle, manufacturing or on-site welding units of pressure vessels must obtain prior approval for material substitutions of the main pressure-bearing components from the design unit, and the modified parts must be detailed in the as-built drawings. When there is experience in using the material at the manufacturing facility and the performance of the substitute material is superior to that of the original material (applicable only to 16MnR, 20R, Q235 series steel plates, 16Mn,
The substitution of the main stressed components must be approved by the original design agency. Hehe
It is also necessary to consider whether setting up a company PQR can provide effective coverage
The statement on the second floor is not appropriate; Q345R cannot always be used as a substitute for Q245R. It depends on the specific medium involved. For example, when the medium contains H2S, Q245R should be used, and in such cases Q345R cannot be used as a substitute
Of course, using alternative materials constitutes a significant change in the design, and it needs to be considered carefully during the design and manufacturing processes. If substitution is indeed necessary, it should be handled in accordance with what was mentioned on floor 5.
It cannot be generalized; one cannot consider only strength – the material itself also needs to be taken into account, especially its compatibility with welding to attachments, heat treatment, and so on.
Yes, sometimes in stress-corrosion environments, Q345R is even inferior to Q235B.
Additional note on the points mentioned for the 5th floor: The impact of design conditions, the suitability of manufacturing processes, the differences between substitute materials and the materials specified in the original design standards, the thermal stresses arising from the use of steels from different organizations in place of one another as well as the welding issues associated with such mixed steels, and the cost-effectiveness of substitute materials should also be taken into consideration.
I agree with the view from the fifth floor; under special circumstances, some conditions can indeed be negotiated.