Subsea Isolation Valves SSIV

Subsea pipeline emergency isolation valves for offshore facilities are provided where a risk analysis indicated topside isolation may be considered vulnerable. They should be protected from ship impacts, anchor dragging, flammable liquid spills and heavy objects that may be dropped from the offshore facility. 

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Isolation - It has been shown that the addition of isolation valves at periodic intervals is not as cost effective as prevention measures such as thickness inspections or tests. However all pipelines should be provided with a means for emergency isolation at it entry or exit from a facility. Offshore facilities may be particularly vulnerable to pipeline incidents as the Piper Alpha disaster has shown. In that accident a contributing factor to the destruction was the backfeed of the contents of the gas pipeline to platform once the topside isolation valve or piping lost its integrity. Further isolation means (i.e., a subsea isolation valve SSIV) were not available. 

A description is presented in Figure 1.3, where the limits of the pipeline can be seen in relation to the pipeline riser and subsea isolation valve (SSIV) an assumption may be made that this condition is replicated at each pipeline end. 

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