It is pretty standard practice to hook up a compressed gas cylinder to a process. In fact, many “blanket systems” on a small vessel will use a Nitrogen CG cylinder to provide the blanketing gas. However, it is even more common to find this setup done improperly. In this article, I will offer a RAGAGEP to follow that explicitly covers this practice. First things first, my RAGAGEP states: (emphasis by me)
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5.8.2 Check valves Compressed gas containers should NOT be attached to a process where the container can be contaminated by the backflow of other process materials. In cases where such a possibility could exist, design consideration shall include the use of check valves and/or traps for this purpose. These check valves and/or traps shall be checked and maintained on a regular schedule to ensure proper operation. |
A quick 30-second check can tell us if our connection is protected! But notice the last sentence/requirement… the check valves and/or traps MUST be in our PM/MI program so that they are checked and maintained on a regular schedule to ensure proper operation.
Of course, it should go without saying that these compressed gas cylinder arrangements will need an MOC and a PSSR; however, this article is to provide some basis for the set-up/design of this connection. The PSSR should confirm there is a check valve or trap capable of preventing backflow scenarios AND that the device(s) is in the PM/MI program inspection/testing program based on the manufacturer’s recommendations.
For more Compressed Gas Cylinder safety, check out the latest CGA P-1, SAFE HANDLING OF COMPRESSED GASES IN CONTAINERS, 13th edition
PLEASE NOTE: this does not apply to Gas Fire Suppression systems like CO2 systems. This applies ONLY when there is a path for backflow from the process to the cylinder. NEVER assume the cylinder pressure (always higher than process pressure) as a safeguard. I know this used to be the fall-back safeguard, but in 2010, the RAGAGEP changed and now requires a check valve or trap.