The production wing valve (PWV) of a subsea gas condensate producer failed during valve testing. The valve was flushed with various fluids and operated several times. This did not affect the leak rate. The valve was leaking in closed position 2,3 times higher than the API leak criteria for SCSSVs internal leak (0,4 Sm3/min).

The well has a typical horizontal X-mas tree solution and 5 ½” tubing.

As a risk compensating mean the operator has added the manifold branch valves (MPVs) to the ESD/PSD sequence to compensate for the leak in the PWV.


In the study the effect of the PWV failure and the compensating means were analysed in terms of blowout probability and the ability to isolate ruptured flowlines.

Further, also the effect of a failed production master valve (PMV), a failed tubing retrievable surface controlled subsurface safety valve (TRSCSSV), and a failed X-over valve (XOV) were analysed.

A fault tree model of the specific well was been established. The majority of failure data used for the analyses stems from WellMaster, Oreda and SubseaMaster.