Risk Analysis, Vol. 26, No. 1, 2006 DOI: 10.1111/j.1539-6924.2006.00705.x Risk-Based Integrity and Inspection Modeling (RBIIM) of Process Components/System Faisal I. Khan, 1* Mahmoud M. Haddara, 1 and Subrata K. Bhattacharya 1,2 Process plants deal with hazardous (highly flammable and toxic) chemicals at extreme con- ditions of temperature and pressure. Proper inspection and maintenance of these facilities is paramount for the maintenance of safe and continuous operation. This article proposes a risk-based methodology for integrity and inspection modeling (RBIIM) to ensure safe and fault-free operation of the facility. This methodology uses a gamma distribution to model the material degradation and a Bayesian updating method to improve the distribution based on actual inspection results. The method deals with the two cases of perfect and imperfect inspec- tions. The measurement error resulting from imperfect inspections is modeled as a zero-mean, normally distributed random process. The risk is calculated using the probability of failure and the consequence is assessed in terms of cost as a function of time. The risk function is used to determine an optimal inspection and replacement interval. The calculated inspection and replacement interval is subsequently used in the design of an integrity inspection plan. Two case studies are presented: the maintenance of an autoclave and the maintenance of a pipeline segment. For the autoclave, the interval between two successive inspections is found to be 19 years. For the pipeline, the next inspection is due after 5 years from now. Measurements taken at inspections are used in estimating a new degradation rate that can then be used to update the failure distribution function. KEY WORDS: Failure modeling; integrity assessment and evaluation; quantitative risk assessment; risk- based inspection; risk-based maintenance 1. INTRODUCTION Maintaining the integrity of a large number of aging process components is a subject of prime im- portance to process companies all over the world. In Canada, there are more than 250,000 km of pipelines carrying natural gas, crude oil, and petroleum prod- ucts (Pandey, 1998). To protect the public, the fi- 1 Faculty of Engineering & Applied Science, Memorial University of Newfoundland, St John’s, NL, A1B 3X5, Canada. 2 Department of Ocean Engineering, Indian Institute of Technol- ogy, Chennai, 600 036, India. ∗ Address correspondence to Faisal I. Khan, Faculty of Engineering & Applied Science, Memorial University of Newfoundland, St John’s, NL, A1B 3X5, Canada; fkhan@engr.mun.ca. nancial investment, and the environment against the consequences of failures occurring to these sys- tems, an assessment of the condition of existing in- frastructure (major process units, pipelines, etc.) is necessary. The condition assessment quantifies the degradation of the material and provides a basis for the decision-making process regarding preventive maintenance and/or replacement. With limited main- tenance resources, it is essential that the available funds be spent where they are most effective in re- ducing potential risks (Concord, 1993; Pandey, 1998). The traditional methods of assessing the condi- tion of process systems are based on a deterministic load-resistance methodology in which the integrity of the components is evaluated by comparing the 203 0272-4332/06/0100-0203$22.00/1 C  2006 Society for Risk Analysis