A few months after start-up a plant was having problems with high refrigeration condensing pressure. The first step was to get an analysis of their propane refrigerant. The analysis came back with 13 mol% methane in the vapor space of the accumulator. Not believing that analysis could be right with that much methane, a second analysis was requested and it came back even higher. The first suspicion was the quality of propane being delivered, but that was quickly verified and dismissed. The recommendation was to blow down the accumulator vapor space and top off with good propane. Unfortunately the problem returned a short time later. One of our incredible RCE engineers finally figured out that the PSV on chiller (for tube rupture) did NOT have a back flow preventer on the pilot line. So when the plant had flaring incidents flared gas was back-flowing into the chiller since it normally operates at a very low pressure. Hence the source of the methane was inlet or residue gas that was being flared. A backflow preventer was added to the PSV and no further issues have occurred.
