Application of Reliability Engineering To Offshore Production Equipment
Authors: Howey R.A. , Gaarder O.H. 
Published: December 2007

A reliability study was performed on a subsea completion system using an event-consequence approach. The application of reliability-study information to the economics of offshore equipment design represents a new and useful tool for the oil industry.

Introduction

Although many papers have been written concerning the different types of reliability studies, few have given concrete examples. This paper shows where the eventconsequence approach fits in the range of possible types of reliability studies. Specific examples are used to give the steps that are required in completing an eventconsequence study and the types of results that can be obtained. Based on experience with the subsea completion-system study, a method for choosing the optimum reliability-study approach is presented.

Definitions of Reliability-Study Approaches

One can conveniently differentiate among three levels of reliability analyses: hazard analysis, traditional reliability analysis, and event-consequence analysis.

Hazard Analysis

Hazard analysis is defined as a qualitative evaluation of hazards to the environment of the equipment (system) under consideration. This definition seems to have become generally accepted as far as the oil industry and its regulatory governmental agencies are concerned. The steps taken in performing such an analysis are as follows:Define the system (equipment) to be considered.Define the hazards, such as oil and gas pollution, to life safety.Determine qualitatively what has to fail for a particular hazard to occur. particular hazard to occur.Categorize the hazards as major, minor, or insignificant, depending on type and/or quantity of hazard, and how many levels of redundant safety systems must fail for the hazard to occur.

This type of analysis is a "top-down" approach in that hazards such as personal injury, fire, and pollution are listed before asking, "What failures can cause these hazards?" The basis of such an analysis is the hope that the analyst will find all components that will cause the hazards. This top-down approach normally uses a "matrix" that lists failures vs effects, but it turns out to be only a qualitative tool. Thus, without an organized method of examining all components, and without a consistent standard for specific types of equipment, the matrix approach will cause inconsistent and vague results.

Hazard Analysis - API Recommended Practice. The American Petroleum Institute has found a very effective means for system-hazards analysis in the development of API "Recommended Practice 14C." It is effective in that it assumes all components in hazardous service need to be reviewed. Thus, this is a "bottom-up" analysis. "Recommended Practice 14C" also achieves consistent results in that it recommends specific types of safety devices for nine major components that make up most of the hazardous process flows on platforms. This standard states specifically that equipment will have two levels of protection independent of the normal control devices. protection independent of the normal control devices. Thus, quality is built into the design. The technique of setting specific requirements for specific equipment will assure a safe design and reduce safety design time from that required by the matrix approach.

JPT

P. 339