ABSTRACT
In this paper we carry out a study to support maintenance policies in the natural gas distribution system in the City of São Paulo, Brazil. The selected maintenance policy (preventive, inspection, and corrective) and its cost is one of the main concerns for asset decision-makers in utilities such as natural gas distribution companies. Maintenance activities in utilities have a number of special features: (1) Usually there is a contractual agreement between operating company and Governmental Regulatory Agency with strict clauses in terms of reliability; (2) Life-span of assets is long, usually more than 10 years; (3) The property of assets belongs to Governmental Agency, not to the concessionary. In addition, there is a natural pressure for increase in financial return from investors. Then, managers must face and solve a puzzle: High values of reliability and availability in the delivery natural gas to costumers and at the same time control cost to generate return for investors.
The methodology is composed of (1) A study of current maintenance policies, especially preventive and inspections, (2) Reliability modeling of time-to-failure of hundreds of components in order to know indicators such as MTBF, probability of failure, etc., (3) Modeling of the randomness of the time-to-maintenance, (4) Model to estimate the optimal interval of preventive maintenance in terms of cost, (4) Model to estimate the failure risk level for different replacement intervals.
With the result of this study a number of changes have been implemented in field such as (1) increase in interval of preventive maintenance to save cost, (2) reduction of interval or preventive maintenance to reduce risk, (3) Elimination of some inspections actions, (4) Reduction in the stock of spare part. As a result, it has been reported savings of US$ 2 million in maintenance cost over the last year without increase in risk of failure.
