Special Equipment Requirements for Pressure Vessels Including Exchanger Shells, Channels, etc

20 Special Equipment Requirements for Pressure Vessels (Including Exchanger Shells, Channels, etc.) 

When pressure vessels are subjected to low temperatures, i.e. below 0 °C, materials and fabrication practices, e.g. post-weld heat treatment, should be selected to minimize the risk of brittle fracture. 

Requirements for material selection depend upon the minimum design temperature. However, where this minimum design temperature is not a normal continuous operating condition, for example, if it arises as a result of autorefligeration due to rapid depressurization, the fiiU range of temperatures and coincident pressures should be evaluated in order to determine the appropriate conditions for material selection. 

The use of post-weld heat treatment can extend the use of carbon steel to temperatures lower than would be acceptable for as-welded vessels. However, unless post-weld heat treatment is required for process reasons, it should be specified only when the requirement cannot be met by using carbon steel in the as-welded condition. 

Carbon steel should normally be selected for pressure vessels, and an appropriate corrosion allowance applied where total corrosion is not expected to exceed 6 mm over the design fife of the vessel. Where the corrosion rate is predicted to exceed this, the various alternatives should be evaluated. These may include, but should not be limited to, the following  

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