Rodrigo Sampaio Lopes’s research while affiliated with Federal University of São João del-Rei and other places

Maintenance policies must consider system reliability and the risk of accidents in systems where equipment failures represent a risk. In this context, this work proposes an age replacement policy with Bayesian imperfect repair and considers the “as low as reasonably practicable” (ALARP) principle. The policy determines the age of replacement that minimizes the long-run cost per unit time when the failure rate is ALARP. The model also supposes that failures are either minimally or perfectly repaired, depending on the skill of the maintainer. Numerical applications are performed with and without the disproportion factor in ALARP, both for infinite and one-replacement-cycle horizons. The results show that considering imperfect repair leads to an increase in replacement costs and a decrease in the optimal replacement age when considering the ALARP principle. The model applies to situations where there are conflicts of interest between maintenance management and risk; that is, cases where the aim is to reduce the cost of replacing equipment and minimize the risks. Maintenance policies must consider system reliability and the risk of accidents in systems where equipment failures represent a risk. In this context, this work proposes an age replacement policy with Bayesian imperfect repair and considers the “as low as reasonably practicable” (ALARP) principle. The policy determines the age of replacement that minimizes the long-run cost per unit time when the failure rate is ALARP. The model also supposes that failures are either minimally or perfectly repaired, depending on the skill of the maintainer. Numerical applications are performed with and without the disproportion factor in ALARP, both for infinite and one-replacement-cycle horizons. The results show that considering imperfect repair leads to an increase in replacement costs and a decrease in the optimal replacement age when considering the ALARP principle. The model applies to situations where there are conflicts of interest between maintenance management and risk; that is, cases where the aim is to reduce the cost of replacing equipment and minimize the risks. Keywords: maintenance; replacement; risk; safety; reliability; ALARP

We model a maintenance policy with fixed periodic structure that is a hybrid of periodic inspection and opportunistic replacement. The policy is applicable to geographically remote systems such as offshore wind farms. The policy has three phases. Initially, there is an inspection phase to identify early defects. This is followed by a wear out phase during which corrective replacements are performed. Preventive replacement occurs at the end of this phase. The novelty of the model is an opportunistic phase, which overlaps with the latter part of the corrective phase, when preventive replacement is executed early if an opportunity arises. In this way, we model the reality in which remote systems with high logistics costs and restricted access may benefit from opportunistic visits for maintenance. Using a numerical example, we analyse the behaviour of the decision variables for a range of values of the parameters common to such systems. These parameters relate to: component heterogeneity; restricted access; default (failure to execute a planned action); arrival of opportunities and other standard parameters in a maintenance cost model. Specifically, our results indicate when opportunities can have a significant impact on the cost-rate of the optimum policy, but that leveraging opportunities cannot achieve a very high availability. Generally, we demonstrate that maintenance planning should be flexible when factors beyond the control of the maintainer impact maintenance effectiveness.

The energy systems are composed of several protection systems that have the function of isolating a fault and protect critical components. The necessity of providing maintenance of protection systems for substations and transmission networks is a challenge for maintenance managers because they schedule maintenance actions that have different consequences. In this chapter, we describe the decision problem to establish the frequency of inspection and replacement actions for the circuit breaker. We propose a multi-criteria model considering the preference of the decision-maker about the risk and cost criteria and addressing the veto for alternatives. The steps to implement the model are applied to a circuit breaker in a pilot substation in Brazil. The results show the advantages of considering more than one criterion and the preference of the decision-maker defining a combination of maintenance actions considering risk and cost.KeywordsMaintenanceProtection systemsDelay-timeDefect inductionMCDMMAUT

We study an inspection and replacement policy for a system when maintenance actions are executed at times or “visits” with a fixed, periodic schedule. Then, the novel focus of the paper is not when to schedule maintenance but what maintenance to schedule at known times. Violations (defaults) may occur because time or resource is limited. The model is motivated by maintenance policy typically used for high-value, engineered systems e.g. windfarms, transportation systems, manufacturing lines. This motivation underlies the importance of the work. Inspections are modelled using the delay time concept. System lifetime is heterogeneous, so that early defects, due to say poor quality parts or installation, may occur. There is a lag between failure and corrective replacement and so we model the cost of downtime. We determine the cost-rate, system reliability and average availability of a policy with an initial inspection (preventive maintenance) phase followed by a wear-out (corrective maintenance) phase. A numerical example illustrates and investigates characteristics of the policy. Results indicate that the scheduled time for preventive replacement and the effective visit-frequency have the largest effect on policy performance. The policy is scalable to multi-component systems in a way that facilitates the study of grouping policies.