On the plate heat exchanger, a machined nut backed off on the flange bolt that holds the gasket in place. This caused part of the gasket to blow out resulting in ammonia (NH3) to leak into the machine room. The machinery room alarm was activated. Upon inspection, the following failures were found:
- the nuts on the bolts were very loose and only a flat washer was in place with no locking washer on the bolt
- the manufactured nuts did not fit onto the bolts tightly and lock washers were missing on the bolts
- the nuts may have been manufactured with a different pitch than the bolts
- part of the gasket from the flange that holds the ammonia pipe was on the floor from being blown out
- the nuts on the bolts showed a gap that indicated they had loosened off from the time of installation and were no longer at the manufactures torqued specifications of 277ft-lbs
- All the nuts were then taken off the bolts and replaced with new nuts and locking washers
It is highly likely that the missing lock washers did not create a tightening back pressure on the nut after installation which would not maintain the torque specified by the manufacture. The lock washer prevents nuts and bolts from turning, slipping, and coming loose because of vibration. The loose nuts on the flange caused the gasket to blow out and created an ammonia leak.
