Determining outage scope and major component replacement using a risk based approach

The boilers of many units at power stations in South Africa have exceeded their original design life and code criteria alone cannot give sufficient guidance in terms of inspections and replacement of major components. The operations strategy for the boilers is to operate from one outage to another with minimal disruptions due to failures. The outage philosophy is currently a general overhaul every six years, with a smaller outage to replace the boiler burner equipment every three years. The current outage scope is essentially an inspection scope of work. The actual work is based on the findings of the inspections. A study was conducted at a power station to evaluate the boiler inspection data from previous outages. The objective of the study was to establish a risk-based model for reviewing the boiler and piping systems in a consistent manner to determine the inspection scope. The inspection data should be captured in a database from where analysis can be performed to determine the next outage scope. This work reports the findings of the study that was done to determine the damage of water tubes of a furnace as a function of usage and other parameters. A risk-based approach is then presented for targeting inspections for the most critical equipment.