Do Pressure Relief Right Consider nine pointers to develop a suitable design

摘要

A REFINER hired me to review project drawings from one of the country's largest engineering firms.I was aghast that one drawing showed two pressure relief valves(PRVs)in series.The only defense I heard was that the refiner had signed off on it.A year later,I worked with a vendor of a twin-seal block valve investigating a mysterious failure of its valve in a refinery tank farm; we found that two PRVs in series accounted for that failure.Pressure relief work is fairly intricate.Generally,companies set up"survey"teams that create their own,often flawed,design principles.I've worked on a few of these teams,so let me share some of what I've learned.First,let's look at the 3% pressure drop rule stated in API-520"Sizing,Selection,and Installation of Pressure-Relieving Devices,Part II-Installation."You should follow that rule.There may be wiggle room,as this video,https://bit.ly/3jANF2L,reveals,but even its presenter warns you shouldn't deviate unless you've got a good lawyer.