Computational Aspects of Generic Risk Based Inspection Planning

for the 2 ASRANET Colloquium KEYNOTES Risk based inspection planning, fatigue deterioration, Bayesian decision theory, structural reliability ABSTRACT Engineering systems are ideally designed to ensure an economical operation throughout the anticipated service life in compliance with given requirements and acceptance criteria. Such acceptance criteria are typically related to the safety of personnel and risk to environment. Deterioration processes such as fatigue crack growth and corrosion will always be present to some degree and depending on the adapted design philosophy in terms of degradation allowance and protective measures the deterioration processes may reduce the performance of the system beyond what is acceptable. In order to ensure that the given acceptance criteria are fulfilled throughout the service life of the engineering systems it may thus be necessary to control the development of deterioration and if required to install corrective maintenance measures. In usual practical applications inspection is the most relevant and effective means of deterioration control.Engineering systems are ideally designed to ensure an economical operation throughout the anticipated service life in compliance with given requirements and acceptance criteria. Such acceptance criteria are typically related to the safety of personnel and risk to environment. Deterioration processes such as fatigue crack growth and corrosion will always be present to some degree and depending on the adapted design philosophy in terms of degradation allowance and protective measures the deterioration processes may reduce the performance of the system beyond what is acceptable. In order to ensure that the given acceptance criteria are fulfilled throughout the service life of the engineering systems it may thus be necessary to control the development of deterioration and if required to install corrective maintenance measures. In usual practical applications inspection is the most relevant and effective means of deterioration control. During the last 15 to 20 years reliability based and risk based approaches have been developed for the planning of inspections. These approaches take basis in the Bayesian decision theory to minimize overall service life costs including direct and implied costs of failures, repairs and inspections. Application of these methods was however restricted due to the significant numerical effort required, but this drawback was overcome by the generic approach to Risk Based Inspection Planning (RBI), as first presented by Faber et al. (2000). The generic approach not only allows for a wider application of RBI in practice, but also provides the means for inspection planning of systems, Straub and Faber (2002) and has recently been implemented by the industry as reported by Faber et al. (2003). The paper presents the detailed methodology of the Generic RBI with a special focus on the computational aspects of the procedure. Thereby it is distinguished between a) the calculations of the generic inspection plans that are pre-fabricated and b) the evaluation of the specific inspection plans based on the generic plans. Crucial issues which are discussed in the paper are the balance between computation efforts and the accuracy of the applied numerical methods, the determination of an appropriate interpolation scheme as well as the quality control of the calculations.