Damage description: Compressor valve packing failed to maintain a seal to prevent fluid escape.
INCIDENT OVERVIEW
Ammonia saturated oil leaked from the two-way valve packing of a compressor into the machine room.
The ammonia gases escaped from the leaked oil and triggered the machine room ammonia detector.
INVESTIGATION CONCLUSIONS
The machine room is attached to this facility on the north side of the building. Within the machine room, two ammonia compressors are installed, one 25 horsepower and one 40 horsepower unit. All the ammonia is contained within the machine room, the ammonia chills a calcium chloride brine that is used elsewhere. The 40 horsepower compressor uses pressurized oil to control the operation of the compressor unloaders, a two-way valve allows this oil to be directed to the unloader or to be redirected to the compressor sump. Oil leakage past the valve stem is prevented by packing material that forms a seal by being compressed using a valve stem packing adjustment nut.
FAILURE SCENARIO(S)
Prior to the incident date, the service contractor was on site doing some scheduled general maintenance activities. During these activities, the two-way valve was manipulated by the service technician, this disturbed the seal within the valve stem packing gland allowing oil saturated with ammonia to slowly leak from the valve stem.
FACTS AND EVIDENCE
On Dec. 20, 2019, at 08:10 the head ice technician was notified by the facility security monitoring service that a high ammonia concentration as detected by the machine room detector and that the local fire department was in-route to the facility.
At the site, no machine room entry was made by the Fire Department or the service contractor as the ammonia monitoring equipment was showing the room gas concentration was being reduced by the room exhaust system, once a safer ammonia concentration was reached entry was made by the service technician who located the leaking oil valve and tightened the valve packing and stopping the leak.
CAUSES AND CONTRIBUTING FACTORS
It is likely that the valve packing was disturbed by the service technician manipulating the valve at a prior service, this allowed ammonia saturated oil to escape into the machine room where the ammonia gas was released and eventually set off the room detector.
A possible contributing factor is that the valve packing was not sufficiently compressed after the valve manipulation to prevent any oil leakage.
Photo 1: Compressor unloader oil supply valve (red surveyors tape). Oil was leaking through the valve stem packing gland (arrow)
Photo 2: 40 HP Compressor- Machine #1 (East Unit). Ammonia detector is located above this machine at the ceiling Level.