Subsea Intervention Workover ControlSystems - FIRST EDITION

Abstract

This document provides the requirements for the design, manufacture, and testing of intervention workover control system (IWOCS) equipment.

Blowout prevention (BOP) control systems are outside the scope of this Recommended Practice and typically are not connected to the IWOCS.

Some requirements in this document are specific to the execution of end user–defined safety functions.

It is the end users’ responsibility to define the safety functions (i.e. timed sequence of events to operate a safety class device) as an input to this document.

This document defines “safety class control functions” used to operate safety class devices.

Annex A provides guidance on the determination of safety class control functions based on the end user–provided safety functions.

This document identifies the IWOCS equipment typically used in a thru-blowout preventer intervention riser system (TBIRS) and an open-water intervention riser system (OWIRS); see API 17G for more details on these systems and associated components.

The IWOCS equipment described in this document may be used for other system types.

Table 1 lists equipment typically controlled by an IWOCS.

Refer to Figure 1 and Figure 2 for example IWOCS block diagrams for both system types.

IWOCS equipment may be configured in one of the control system architectures listed below.

It is not the intent of this document to mandate the type of control system architecture used for a given application.

― Direct hydraulic control system (see 3.1.2 for definition);

― Discrete hydraulic control system (see 3.1.3 for definition);

― Electro-hydraulic (EH) control system (see 3.1.4 for definition);

― Multiplex (MUX) control system (see 3.1.7 for definition).

The IWOCS equipment may be deployed using one of the methods listed below (see Figure 3 for typical deployment methods).

It is not the intent of this document to mandate the type of deployment method used.

All normal class and safety class control functions (see 3.1.8 and 3.1.12, respectively) need to conform to the requirements given within this document regardless of deployment method.

― Dependent Riser Based Deployment Method: The dependent riser deployment method supports the umbilical’s weight by attaching it to an existing riser (e.g., drilling marine riser or open water riser).

Deployment and recovery of the IWOCS using this mode is often dependent on the riser to which the IWOCS is attached.

― Independent Riser Based Deployment Method: The independent riser deployment method supports the umbilical’s weight using a dedicated riser for the IWOCS.

This dedicated riser may be a wire, cable or the umbilical itself.

The independent riser deployment method may use a launch and recovery system (LARS) and sheave to overboard the umbilical during deployment and retrieval.

Deployment and recovery of IWOCS using this mode is often independent of other risers on the vessel or rig.

― ROV Based Deployment Method: The ROV based deployment method is very similar to the independent riser method; however, it uses a ROV winch, sheave, and LARS arrangement to deploy and recover the ROV and its umbilical.

The ROV based deployment method may additionally use a ROV skid (i.e., belly skid) for additional functionality if required.