Pressure Vessel Loads
The forces applied to a vessel and its structural attachments are called loads, and the first requirement in vessel design is to determine the loads and the conditions to which the vessel will be subjected in operation.
The major loads acting on a pressure vessel are caused by:
1. Internal pressure
2. External pressure
3. Weight of vessel and contents (including internal components that transmit
loads to the pressure vessel)
4. Wind and seismic forces
5. Connecting piping and the weight of external appurtenances (platforms, etc.)
6. Differential thermal expansion (or temperature gradients)
7. Cyclic forces
These forces must be considered during design in order to prevent failure from any of the failure modes mentioned earlier.
The loads are usually static, or the amplitude and frequency of their fluctuations are such that they can be considered to be so. However, cyclic loads of sufficient magnitude can result in a fatigue failure, and it may be necessary to consider them in the design of a pressure vessel. For example, pressure fluctuations that exceed 20% of the design pressure and cyclic temperature gradients greater than 50°F between adjacent locations can cause fatigue.
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