Seismic load analysis


A pump intended to operate in critical service and environmentally sensitive areas
may require seismic load analysis to ensure its safe continuous operation in the
event of seismic activity, or earthquake.


Years ago, a typical specification for a pump placed in a seismic category, e.g.,
Category 1B, required that the pump maintained its operating function both during
and following the Design Operating Earthquake (DOE). Minor damage caused by
seismic forces arising from a DOE event was permitted provided the damage did
not impair the pump’s operating function.


It was also required that the pump shall not rupture leading to the leakage of the
pumped fluid resulting from the Design Operating Earthquake (DOE), or Design
Contingency Earthquake (DCE). Additionally, the mounting of the equipment and
its components were to resist the sliding and overturning effects of seismic forces
arising from a DOE, or DCE event.


The seismic load analysis was done using conventional mathematical and
analytical techniques because the simulation of a model pump in a seismic
condition was impractical. The analysis was similar to the conventional structural
and rotor dynamics analysis, but with the addition of seismic forces. The seismic
force was a function of the design acceleration as specified in either DOE, or
DCE, and ranged from 0.71g to 0.83g (where g is the acceleration due to gravity.)
The stresses used in the analysis were the combined operation loads and
seismic forces.


In one example where seismic loads were included, the standard design of a  
multistage horizontal pump was found to be deficient under seismic loads. The
pump required the addition of stiffening ribs on the casing, and an increase in the
size of its hold down bolts. The analysis showed the rotor was well damped and
had no critical speed issues.


The industry standard for seismic analysis undergoes periodic changes and
varies depending on specific regions. Readers are advised to check for, and use,
the current standard when doing the analysis.



R: 0910-SELO
C: design
F: seismic analysis
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