Risk based inspection : developing empirical formula to calculate inspection coverage

Abstract

The Risk Based Inspection (RBI) method prioritizes the process equipment, by calculating separate likelihood and consequence values for each piece of equipment. The combination of likelihood and consequence can be evaluated in a variety of ways to indicate critical equipment for action. Using the tools of Risk Based Inspection, it has been confirmed that equipment can be operated safely for a period of time, if inspections closely monitor the condition to eliminate uncertainties inherent in predicting the damage rates such as corrosion and erosion. The developing RBI tools for the Oil and Gas industries show promise as being effective and practical for decision making regarding equipment inspection (Conley and Reynolds, 1997). A Risk-based inspection approach helps in designing an alternative strategy to minimize the risk resulting from failures. Adapting a risk-based maintenance strategy is essential in developing cost-effective maintenance policies (Bertolini et al., 2009) On the Norwegian Continental Shelf (NCS), some of the production and process facilities are reaching to the end of their design life and need of inspection activities is more critical. Stricter environmental and safety regulations and barriers coupled with increasing emphasis on cost reductions have been forcing the industry to use development inspection techniques and materials (Santos and Hajri, 2000). These returns to the questions: how much is the inspection coverage? In this study, the Technical Condition (TC) of a sub-system in a production and process facility is evaluated based on findings and historical data. Wall thicknesses of piping components inherently decrease due to degradation mechanisms such as corrosion and erosion. The minimum wall thickness is defined based on the standards and regulations. Based on the TC, reports are made for future inspection purposes as well as to present to the asset owner (Operator Company). The report recommends number of inspection that has to be carried out annually based on The TC. Based on the remaining design life of the process facility, finding rate, criticality of the system, materials specification changes, degradation rate, unexpected degradation behaviours and the experience of the inspection planners, the thesis suggests an empirical model for inspection coverage by using risk based inspection strategy and previous inspection data to be used on an aged platform. The thesis also discusses about developing an inspection model as well as validating it based on past inspection data (Santos and Hajri, 2000).