Design And Functional Requirements

The preceding sections provided the procedures for determining the seismic response of pumping equipment. However, in order to determine the acceptability of these results, they have to be combined with the pump's normal operational loads and compared to predetermined stress limitations. In accordance with the ASME code, the customer's design specification shall advise the applicable load combinations and allowable stress values.

Typically, the pump load combinations can be divided into four levels or service limits. Table 1 lists these service limits in ascending order dependent upon the magnitude of component deformation resulting from operation at the prescribed condition. In addition, Table 2 lists the ASME code allowable stress limits for each of these conditions. If no allowable stress limits are specified in the customer's design specification, no allowable stress increases should be used for the increasing load combinations, including those for OBE and SSE operation.

In addition to the specific requirements for stress levels or functionality of pressure containing components, the following items should be addressed as part of any seismic qualification of pump-motor assemblies:

• Secondary stress loading caused by differential movement of connected components should be determined.

• Displacements and deflections should be measured during testing or calculated, if qualified by analysis, in order to assure they are not excessive.

• Loads to be used in the design of the pump-motor assembly foundation and anchorage should be established.

• Seismic loads must be added to other normal shaft loads in order to verify stress levels, bearing loads, running clearances and possibly coupling misalignment.

• For electric motors, deflections or component dislocations should be closely monitored in order to assure that

TABLE 1 Typical load combinations and stress limits

Plant Condition

Design/ Normal







PD + SL +

PD + SL +


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