Page 14 - Temporary Isolation of Relief Devices - CCPS Safe Work Practice
P. 14
Strategies and Effective Practices
to Manage and Mitigate Hazards
WARNING: Some pressure safety valve outlets are not rated for the inlet design pressure. Therefore, if there are both
inlet and outlet isolation valves to be closed, the procedures should specify for the inlet valve to be closed first and
then the outlet valve to be closed (see Figure 1).
Note that closing a PRD’s outlet isolation valve is usually necessary to prevent backflow of process fluid from other
venting or PRD lifting events in the vent header.
g Captive key interlocks are a highly effective method to manage proper PRD isolation valve sequencing, such as in
this circumstance.
g When putting the PRD back into service, the reverse order should be performed – open the outlet isolation valve
first and then the inlet valve.
g Use the most up-to-date P&ID as the primary means of determining the location of each isolation valve required to
safely isolate the PRD.
g Follow the site Locked Valve procedure to close all necessary isolation valves. This should include having an
authorized site person unlock the necessary valves, close them, and lock and tag them in the closed position so
they cannot be accidentally reopened during the job duration.
g Enter the isolated valves locked closed status into the site’s Locked Valve register.
g As a best practice, the Panel Operator can keep trend of pressure and other key process parameters on the main
display panel, for effective monitoring.
g If the governing pressure code requires it, station a watch person with continuous communication to the control room
to monitor the operating process that has its PRD isolated to enable quick response to an overpressure upset.
g The watch person must have training in recognizing an overpressure condition is occurring and response
procedures to effectively mitigate the condition.
Figure 1 – Pressure Safety Valve with Locked Open Inlet and Outlet Isolation Valves
11 SAFE WORK PRACTICE, TEMPORARY ISOLATION OF RELIEF DEVICES
