Credibility of administrative controls to prevent a blocked outlet scenario for PSV Sizing

Can an overpressure scenario of a blocked outlet be avoided if the valve is a LO (Locked Open) valve?

It agrees with common logic that the scenario should not be applicable since the valve will be locked open with a padlock. There would be no possibility of overpressure because the valve will always be kept open and there will be a continuous flow of fluid. However, this is only partly true because –
“The credit for administrative control shall only be considered if the potential overpressure does not exceed the corrected hydrotest pressure value”.

Hence, even though the valve is provided with LO, there is always a chance for failure of administrative control, i.e. inadvertent closure of the valve due to an operator error.
Therefore, always check if the corrected hydrotest pressure value is above the expected pressure encountered during an overpressure scenario and the line can handle the excess pressure.

While taking the credit of hydrotest pressure, one should ensure that the line will be hydrotested and proper records shall also be maintained.


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