General

Arrangements for high-rate emergency depressuring and low-rate operational depressuring required in oil refineries, chemical plants, gas plants and exploration and production facilities may differ, therefore due care and attention shall be given to these when applying the typical depressuring systems. On Exploration and Production, high rate emergency depressuring system should consist of an actuated ball valve (ABV) and a rate adjusting device. For a process system where it's components are not sensitive to the depressuring rate, a restriction orifice may be used as a rate adjusting device. But for a sensitive process component a combination between an ABV and a control valve with a controller may be considered.

High-rate emergency depressuring valve

The valve actuator shall have a spring-to-open action and be sized such that it is capable of full operation from open to close or close to open with an air pressure signal of 4.2 bar (ga) at the maximum upstream pressure and the minimum downstream pressure. The actual capacity (Cv factor) of the valve should not be less than the calculated value.

In certain applications, for operational reasons, we can decide to install a restriction orifice plate in series with the depressuring valve. The Cv value obtained in the blow down study should be used as a sizing base for the restriction orifice.

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