We can consider Risk-Based Maintenance (RBM) as an evolution of RCM (Reliability-Centered Maintenance), RCM is based in the equipment condition and the importance of equipment to system, but it is limited because it doesn’t solve the quantification of failures. (1)
Due this ability to quantify problems join its simplicity to implant, RBM has been successfully applied in Oil & Gas, petrochemical plants, power generation y distribution networks, etc... And it achieves important savings.
API RP 580 Standard defines risk as the combination of the probability of an event occurring during a time period and the consequences associated with the event. In mathematical terms:
Risk = Probability X Consequence
We can obtain and economic value (if the consequence is valued) or a classification by a risk matrix.
API consider the Risk-Based Inspections (RBI) as the next generation of inspection interval settings, focuses attention specifically on the equipment and associated deterioration mechanisms representing the most risk to the facility. It recognizes the ultimate goal of inspection is the safety and reliability of facilities. (2)
F.I. Khan and M.M. Haddara propose an RBM methodology (3) that is broken down into three modules:
- Module I: Risk estimation, including a failure scenario development, a consequence assessment and a probability failure analysis, it can be conducted using Fault Tree Analysis (FTA).
- Module II: Risk Evaluation, setting up acceptance criteria and applying these criteria to the estimated risk for each unit in the system.
- Module III: Maintenance planning, optimizing the maintenance plan to reduce the probability of failure, reducing the total risk level of the system.
In this module, we can use the measures to control and mitigate risks propossed in the ISO 17776 Standard, as prevention, la detection and control. (4)
Norsok Standard Z-008 (5) not only does RBM propose to design and update maintenance programs but proposes it to prioritizing maintenance activities and evaluates spare parts quantity and location.
We find in RBM a more simple methodology than RCM, it also requires an initial reliability study but include an economic risk assessment, so it allows doing financial analysis and makes easier to choose timed based and on-condition tasks as well as complex actions as spare parts quantity and location, re-design of equipment or changes in the process.
(1) Zhao M-X., Su J., Liu S-G. Risk assessment based maintenance management for distribution network. Journal of international council on electrical engineering Vol.2, No 1, pp. 84-89, 2012.
(2) Risk-based Inspection. API Recommended Practice 580. 1st Edition, May 2002.
(3) Khan F.I., Haddara M.M. Risk-based maintenance (RBM): A quantitative approach for maintenance/inspection scheduling and planning. Journal of loss prevention in the process industries 16 (2003) 561-573.
(4) ISO 17776:2000 Petroleum and natural gas industries- Offshore production installations - Guidelines on tools and techniques for hazard identification and risk assessment. 1st Edition 2000-10-15.
(5) Norsok Standard Z-008 Edition 3, June 2011. Risk based maintenance and consequence classification.