A major plant upgrade to the ammonia refrigeration machinery room was completed in September 2019. This upgrade included new:
- compressors
- heat exchangers
- pressure vessels
- pressure piping
- controls
The refrigeration system was in operation for 3 months and on January 4, 2020, @ 0800 the shift engineer observed a reading of 12 ppm on the ammonia leak detector monitor.
The first stage ammonia alarm and high-speed fan were not activated due to the small amount present. The shift engineer notified the on-site chief engineer who donned PPE and located the leak. The compressor was isolated, pumped down, and locked-out. The chief engineer notified the refrigeration contractor, who made repairs by replacing the NPS ¾ inch close threaded nipple. The refrigeration technician observed a loose cut thread on the NPS ¾ inch close nipple pipe fitting that was installed adjacent to the compressor discharge header to connect the relief valve.
It is very likely that the leak, at the NPS ¾ inch close threaded nipple, resulted when the nipple did not engage properly and vibrations from the operating compressor caused further disengagement.
NOTE: Ignore the red arrow, as it is not pointing to the LOPC point
Normal Pipe Size¾ close nipple upstream of elbow
Source: https://www.technicalsafetybc.ca/sites/default/files/2021-01/D%2016279%20962261%202020-DE-03.pdf