Why can’t Q235B and Q235C thick plates be used in pressure vessels?
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In GB150-2011, on page P87, it is stated that \"for the steel plates used in container shells, the thickness for Q235B and Q235C shall not exceed 16 mm; for steel plates used in other compressed components, the thickness for Q235B shall not exceed 30 mm, and that for Q235C shall not exceed 40 mm. Why cannot thicker plates be used?\" Is it because the strength is not enough? There is another issue: in NB/T47021, for FM550-1.0, the Q235C flange has a bulge of 6 mm, and its thickness is 44 mm; without that bulge, the thickness is 38 mm. Can it be used in pressure vessels?
The Q235 medium-thick plates that we actually use as frames have too many internal defects; their welding and rolling properties are extremely poor! For pressure vessels? Better not^_^
The Q235 series is a product of the era when materials were scarce; today, the petrochemical industry uses Q245R instead.
Q235B pressure vessels are still in use.
Are you using Q235B?
Enameled kettle pressure vessels cannot be used either!
Why? Are there any restrictions?
Special steels for pressure vessels generally undergo secondary refining processes, ensuring the high quality of the rolled thick plates. Steel in the Q235 series belongs to ordinary carbon steel; it does not undergo any post-furnace refining process. The thickness of such plates is relatively large, and it is difficult to ensure consistent rolling quality. Therefore, when used in pressure vessels, restrictions on thickness are necessary.
Due to limitations in rolling conditions, the performance of thick plates is inferior to that of thin plates. This applies not only to carbon structural steels such as Q235B, but to other materials as well. GB150 imposes restrictions on plate thickness, and there are many additional technical requirements that arise due to the thickness of the plates. For carbon structural steel, since it is not a steel specifically designed for pressure vessels, there are more restrictions. GB150 remains in force due to the needs of the national situation; therefore, it is placed in the last appendix of standard GB150.2, and it is very likely to be completely removed in the next version of the standard. The usage requirements for Q235B material in glass-lined equipment can be relaxed to some extent, but exceeding the specified thickness will introduce additional inspection requirements. Regarding the second question from the poster: for parts with shoulders of size 44, it is obviously not possible to use Q235C; the standard restrictions relate to the thickness of the material used, and have nothing to do with the structure of the part.