The platform was in the process of commencing their annual shutdown. Stage one of the flushing operation had been completed using high water wells to coarsely flush the process of oil. The 1st Stage separator oil compartment had been drained and the vessel depressurised for 36 hours.
The task in hand was to complete the flushing programme using firewater through the tree, flow lines and manifold into the 1st Stage separator. The residual oil was then removed via a platform utilities hose connected by an instantaneous coupling at the top of the separator to an open outlet at the open hazardous drains.
During the flushing operations, the hose became detached at the instantaneous coupling connection point. The sudden depressurisation of vessel caused gas break out from the fluids, oily water, released to the atmosphere and activated multiple gas heads with the area.
The gas heads cleared almost instantaneously however their activation resulted in GPA and a level two surface process shutdown.
Investigations identified that the instantaneous coupling was not correctly engaged as the lugs on instantaneous coupling clashed with the bolts which were in place to secure the flanged connection point for the hose on top of the vessel and/or the fact lugs on instantaneous coupling female section were stiff to locate securely onto the male section as no formal inspection or maintenance was carried out on hose.
The use of a high integrity coupling for operations of this type.