The following incident is a precautionary example of the potential hazards of improperly depressurizing piping to remove a hydrate. During production operations, a control room operator observed a decrease in gas lift pressure supplied through a pipeline to a remote well location. The control room operator notified the onboard platform operators of the pressure drop and the possibility of a hydrate forming inside the 3-inch gas lift piping. The control room operator and platform operators planned to isolate and bleed the pressure to remove the possible hydrate.
The control room operator from his station closed the pipeline shutdown valve (SDV) upstream of the manual flow control valve.
Additionally, the platform operators physically closed the manual isolation valve upstream of the SDV, assumed the hydrate location, and departed the pipeline.
The platform operators then started to relieve the pressure downstream of the hydrate location to atmospheric pressure without properly isolating the pipeline from the bleed point through a ball valve assembly attached to the 3-inch gas lift piping. The ball valve assembly consisted of a threadolet, threaded steel pipe nipples, two 1-inch ball valves inline, and a 90-degree elbow that pointed upward.
With approximately 900 psi trapped behind the valve, the assembly separated from the threadless, striking one of the platform operators under the left armpit area, and causing bruising and swelling. The injured offshore worker was sent for medical treatment and was later released to full duty.
The valve assembly could not be found and is suspected to have fallen overboard after striking the worker.