Occasional loads

The allowable stress for occasional loads of short duration, such as surge, extreme wind, or earthquake, may be taken as the strength reduction factor times 90% of the yield strength at temperature times Mj for materials with ductile behavior. This yield strength shall be as listed in ASME BPV Code Section II, Part D, Table Y-l (ensure materials are suitable for hydrogen service see API 941), or determined in accordance with para. 

Drums will normally be received in 80 drum loads with occasional loads of up to 100 drums and a storage layout which allows for access around such a load for inspection for leakage, stocktaking, etc., is desirable. 

This hypothetical problem serves to illustrate how categories and types of loadings are related to the stresses they produce. The stresses which are required for equilibrium of the vessel are primary stresses. The stresses due to pressure and wind are primary general membrane stresses since even if yielding occurred, redistribution of stresses would not be possible. These stresses should be limited to the Code allowable stress values, where increases for occasional loading may be allowed for certain sections of the Code. 

For occasional loads, the vessel may experience some or all of these loadings at various times but not all at once and not more or less continuously. Therefore a temporarily higher stress is acceptable. 

Occasional loads—Short-term duration variable. 

As the term is used here, inertia loads are different from shock loads. Inertia loads are the occasional loads imposed on the chain by imusual, and often unexpected, events. They may come from starting a heavily loaded conveyor or a drive with a large flywheel. Or they may be caused by a sudden momentary jam in the driven machine or conveyor. The drive or conveyor designer should calculate expected starting loads and be sme that they are never more than the yield strength of the chain. 

The stresses on a piping system define the service conditions of the piping systan and are a function of the loads on that system. The sources of these loads are internal pressnre, piping system dead weight, differential expansion due to temperature changes, wind loads, and snow or ice loads. Loads on a piping system are classified as sustained or occasional loads. 

Occasional loads are those loads that act on the system on an intermittent basis. Examples of occasional loads are those placed on the systan from the hydrostatic leak test, seismic loads, and other dynamic loads. Dynamic loads are those from forces acting on the system, such as forces caused by water hammer, and the energy released by a pressure relief device. Another type of occasional load is caused by the expansion of the piping system material. An example of an expansion load is the thermal expansion of pipe against a restraint due to a change in temperature. 

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