Lifetime assessment of complex industrial systems - A framework for renewal strategies

Sammanfattning: For technical systems in the electricity and paper and pulpindustries, asset management is emerging as a new approachaddressing how to exploit physical assets with long operativelives in the most profitably way. An important problem forasset management staff is knowing when to carry out areplacement or renewal. This is a difficult question whichrequires taking into consideration parameters of totallydifferent natures?e.g. reliability data, operatingcosts, condition information from technical systems, theenvironment and rules and regulation. An incorrect estimate ofa residual lifetime can result in a premature renewal withaccompanying high capital costs. If, however, renewal isdelayed, a breakdown may occur which can cause major damage totechnical equipment and a loss of income due to outages.This work presents a formal model that calculates expectedcosts of different long-term strategies when managing technicalsystems. It is shown that with relatively few inputs, which inmany cases are easy to collect or estimate, a good picture canbe developed that shows the amount of resources a company willneed in the future in terms of renewals of their technicalsystems. The foundation for this work is a case study and aliterature review; the objective was to study what methods andmodels are in use today when estimating residual lifetime oftechnical systems. Also, aspects that influence long-term assetmanagement were investigated. Lessons learned from the casestudy and literature review were then used to develop a dynamicmodel, the Dynamic Lifetime Analysis model (DLA model).This model is based on a probabilistic and dynamic riskanalysis of a technical system, linking different aspects ofrisk management strategies to specific characteristics of thephysical system. Furthermore it is shown how this model,coupled with specific value judgments, can be used to designoptimal long-term strategies. When taking more than onetechnical system under consideration the model shows that it isnot always the most effective, from a system viewpoint, torenew it too close to a possible breakdown. If there is aperiod predicted to incur high investment, it can, at times, bebetter to do an early renewal thereby maintaining resources ata constant level. The thesis also describes how to work withlong-term strategic decisions in a structural manner in orderfor the actors on a deregulated market to stay competitive.Key Words:Residual lifetime estimation, Assetmanagement, Maintenance, Technical systems in power and pulp-and paper industries, Long terms renewal strategies.