Instrumentation And Control Hazop: A New Application Of Technology For The Auger Tension Leg Platform
Authors: Forster L.D. , Brown W.H. 
Published: October 2008

The structured Hazard & Operability (HAZOP) methodology was adapted to review the instrumentation and control systems for Shell's Auger Tension Leg Platform (TLP). The TLP is scheduled for installation in the Gulf of Mexico in late 1993. The HAZOP methodology is a very flexible approach used to identify potential problems. It utilizes a team of specialists and a list of guidewords which are used to stimulate the creative thinking of the specialists to evaluate potential deviations from the original design intent and the impact of the deviation on the entire system. The most common application of the HAZOP technique is the review of process units. This study supplemented the results of a process HAZOP Study conducted earlier in the design of the TLP. Several improvements to the instrumentation system were implemented as a result of this analysis. The platform instrumentation and control system consists of an extensive host computer - programmable logic controller system which interfaces with electronic monitoring equipment and conventional electrical, hydraulic, and pneumatic control equipment. Twelve platform systems were selected and analyzed during the 9 month period from December 1991 to August 1992. Selected systems included ballast and bilge controls, fire and gas detection systems, and two gas compressor systems among others. Although somewhat time and resource intensive, ways were found to introduce efficiencies into the process, resulting in a cost effective means of reducing potential hazards and operational difficulties.

INTRODUCTION

The Auger TLP, to be installed in 2860 ft. of water, combines marine, utility and power generation systems with a drilling rig and a process facility, capable of handling peak production of approximately 46,000 barrels of oil per day and 125 million cubic feet of natural gas per day. An overview of the TLP is shown in Figure 1. Many innovations were utilized throughout the design, some to save cost, but mostly to ensure the viability, effectiveness, and safe operation of the platform in this water depth, the deepest yet for oil and gas production.

Personnel safety, preservation of the environment, and minimization of risk of loss of investment were high priority objectives in the design of the TLP. Steps were taken throughout the design to ensure that these objectives would be met.

The Auger mechanical systems were subject to process HAZOPS earlier in the design phase of the platform. In these HAZOPS, the instrumentation systems were considered to be black boxes.

The first phase consisted of applying the HAZOP methodology to the platform instrumentation and control systems. Although the instrumentation and control systems are comprised of industry standard building blocks, when taken as a whole they result in a complex network consisting of 40-plus Programmable Logic Controllers (PLCS) interfacing with more than 3500 wired end devices, a four unit host computer system with twelve operator work stations located in a central control room and at strategic locations on the platform. Figure 2 gives an idea of the number of systems involved in this facility.