High voltage to low voltage
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At our facility, an accident occurred in which process gas was allowed to flow into the nitrogen system. During the hydrogen recovery process, nitrogen was used for purging; however, the nitrogen valve was not closed, and process gas was directly connected to the hydrogen recovery system. Once the hydrogen recovery system started receiving gas, the pressure there reached 2.0 MPa, while the pressure of the low-pressure nitrogen was only 0.8 MPa.
The SOP was not followed properly; in fact, the nitrogen pipeline should have been completely disconnected by installing a blind flange or removing it. It is very dangerous for hydrogen to mix with nitrogen. By the way, don’t the other access points have check valves?
Introducing hydrogen into nitrogen is extremely unsafe. A vent is provided between the two valves, a check valve at the root, and a blind plate is installed between the two valves.
Inspections are not thorough enough; the habit of putting the three-valve assembly into use on-site has developed~~~~ Both management personnel and operators are responsible for this
Such incidents of strict safety management in large chemical plants are relatively rare, while they occur more often in smaller chemical plants
This kind of thing is entirely caused by operational errors; there are many ways to resolve it. Take a good look at the operating procedures – it’s fortunate that nothing serious has happened
Nitrogen is very convenient as a gas for purging during shutdowns or maintenance, but once the system has been made safe, a blind flange must be installed; one should not shy away from taking the extra effort, as this is the only way to avoid creating problems for oneself.
We encountered this once as well: after the subsequent purging, a blind flange was installed directly, and it was removed only when it was time to use it
Inadequate pre-driving process checks are also the most easily overlooked. The temporary replacement pipelines should be removed during the process startup