Sometimes for dow service pumps or other critical service pumps there is a small bore bypass given in suction/ discharge piping from pump. This bypass serves the purpose of avoiding termal shock to pump casing while startup as the casing will be warmed up by keeping main line shut and bypass working.Once the pump is warm main line will be started. What happens if the pump is to be removed for maintainance in the sense is
there any instruction in the pump manual that as soon as the main line flow
and bypass are stopped the bolts at pump nozzle flanges should be loosened
immediately ?This is because till the pump is removed for maintainance loads like spring hanger loads should not get transferred to pump nozzle flanges . If the bolts are to be loosened in this
fashion then we need not check the loads on pump nozzles when it is acting as
standby in the thermal case made for standby. This is because as the pump will remain hot thro' the bypass even when it is not running . In such case the fluid in bypass may remain stagnant but heat transfer should ensure that this fluid is warm and
does not attain ambient conditions. We can consider some temp. drop and model
the standby case, which should be much better than modeling the pump at
ambient in standby case. API or any code for pump is not clearly making any
distinction that the allowable mentioned by the codes are during service Or
we have to limit the induced loads on pump nozzles as per code requirements
in sustained case as well ? We do not check sustained case loads in case of
pumps. Sometimes this standby case loads force us to put expansion joints. When checked with maintainance people who have worked in such plants they quote that it is very rare that a pump will remain cold and in the circuit not for very long time. The pump removal is well planned and cold pump can not remain connected to piping for long. Rather most of the times it is removed when the piping is hot or at temperature which can be handled. This means there is no need to check loads in a case with pump as standby and at ambient and other pumps running at that time ? Can somebody advice ? Has anybody checked with pump manufacturer ?
Regards,
Sunil Godbole