5.3.4 Interlocks

5.3.4.1 Introduction

An Interlock is a control permissive that exists to prevent or warn an operator against potentially undesired operator commands being issued to the subsea system. Depending on an operator’s access level, he / she may be able to override the interlock in order to perform the desired operation. Interlocks can be categorised into two types: process interlocks and product / system interlocks, though not all customers or SCV’s make this distinction.

5.3.4.2 Process Interlocks

Process interlocks are interlocks which are specific to a particular project dependent on field layout, tree functionality, etc. These are often defined by the customer’s process requirements or by regulatory agencies; e.g., prevention of opening the tree crossover valve if the production master valve and annulus master valve are open.

5.3.4.3 Product or System Interlocks

Interlocks defined by the SCV for the protection of the subsea system; for example, low hydraulic pressure inhibiting opening (pressurising) of a tree valve. These interlocks are typically not able to be overridden by an operator.