Vessels materials strength

If failure is due to external heat applied to the vessel (e.g., from fire), the vessel s internal pressure rises, and at the same time its material strength drops. 

The national pressure vessel codes and standards require that all pressure vessels be subjected to a pressure test to prove the integrity of the finished vessel. A hydraulic test is normally carried out, but a pneumatic test can be substituted under circumstances where the use of a liquid for testing is not practical. Hydraulic tests are safer because only a small amount of energy is stored in the compressed liquid. A standard pressure test is used when the required thickness of the vessel parts can be calculated in accordance with the particular code or standard. The vessel is tested at a pressure above the design pressure, typically 25 to 30 per cent. The test pressure is adjusted to allow for the difference in strength of the vessel material at the test temperature compared with the design temperature, and for any corrosion allowance. 

Because the skirt is an attachment to the pressure vessel, the selection of material is not governed by the ASME Code. Any material selected, however, should be compatible with the vessel material in terms of weldability. Strength for design is also not specified for support material by the ASME Code. Usually, in the absence of any other standard, the rules of the AISC Steel Construction Manual will be utilized. For elevated temperature design, the top three feet of skirt at the attachment point should be of the same material as the shell. 

Vessels of forged or rolled steels and aluminum alloys, metals with reasonably high ductility, are stressed at the final inspection, and in reinspection tests, at a test pressure 1.3 times the maximum allowable working pressure (MAWP), the tank shell is stressed up to 90% of the material strength, which is usually the yield strength... 

Vessels subject to external pressure may fail at well below the yield strength of the material. The geometry of the part is the critical factor rather than material strength. Failures can occur suddenly, by collapse of the component. 

Onizawa, T., et al., 2013b. Development of 2012 edition of JSME code for design and construction of fast reactors (3) development of the material strength standard of modified 9Cr-IMo steel. In Proceedings of the ASME 2013 Pressure Vessels and Piping Conference PVP2013, PVP2013-97611, July 14-18, 2013, Paris, Prance. 

Y. Nagae, T. Onizawa, S. Takaya, T. Yamashita, Material strength evaluation for 60 years design in Japanese sodium fast reactor, in Proceedings of 2014 ASME Pressure Vessels and Piping Conference, 2014, pp. PVP2014—28689. 

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