Achieving Cleanliness Levels During Fabrication, Assembly, and Testing of Subsystems and Hydraulic Tubing Network for the Zinc Subsea Production System

Abstract

Abstract The Exxon Zinc Subsea Production System utilizes an electrohydraulic controlsystem to perform various equipment functions subsea, and to provide status ofequipment and well conditions to the Alabaster host platform. The hydraulicfluid utilized is water-based Marston Bentley HW 525 with a cleanlinessrequirement of NAS 1638 class 8 or better. This cleanliness level is requiredfor the proper operation of subsea valves over the duration of systemoperation. This paper discusses the methodology, procedures and equipmentrequirements to achieve and maintain this cleanliness level. It addresses thesurface equipment that stores and supplies the control fluid, the hydraulicumbilicals that carry the fluid to Zinc, the subsea hardware, and variousrunning tools that could interface with the subsea hydraulic network. Componentcleaning, clean room operations, hydrostatic testing and system flushing arediscussed. The cleanliness monitoring QC steps during system integration andtesting are also presented. Introduction The Exxon Zinc Project is a Subsea Production System located in the Gulf ofMexico - Mississippi Canyon area. The project includes a ten-well subseatemplate and manifold production system situated in 1,460 feet of water tiedback to the Alabaster platform 6 miles to the west in 468 feet of water. Gasproduction is achieved through three flowlines. Well control is achievedthrough an electrohydraulic control system via separate electrical andhydraulic umbilicals. The flowline and umbilical connections at Zinc are byremote diverless methods. The multiplexed control system incorporates a subseacontrol skid which houses the control pods. A hydraulic tubing networkinterconnects the control skid pod bases with the ten tree locations, and thepigging valve manifold interface. There are approximately 2,000 feet of tubingin the control skid and 14,000 feet in the manifold tubing network. Thisconsists of 3/4" OD × 3/8" ID super austenitic stainless steel tubingand fittings preassembled and socket welded into place. In addition to the above, there are tubing runs within each control pod, subsea tree and the pigging valve assembly. This tubing interconnects thevarious control valves and subsea gate valve actuators. Hydraulic fluid issupplied to the control skid through a nineteen hose hydraulic umbilical. TheNYLON hoses, are arranged concentrically and protected by layers of medium andhigh density polyethylene and jacketed armor wire.