RBI application in a CHP plant

Risk-based inspection (RBI) has become common approach to support asset management in e.g. refineries, chemical industry in general and a few other industrial sectors. Although there are regionally established traditions to use RBI also in power plants, recently the interest has been spreading to include a widening base of common power plants. This is partly due to increasingly established standard practices, tools and availability of the techniques also for smaller scale users, and partly due to the generally established benefits and needs for safety and optimization of resources. In this paper we show how RBI was applied in a small scale for the main steam line of a CHP (combined heat and power) plant in Finland. The experience showed some typical features of initiating RBI, for example how important and beneficial (although at first somewhat tedious) it is to systematically gather and handle the required background information of design, fabrication, inspections, maintenance and operational history for RBI of an ageing plant. In the case of the example plant, the steam system had been significantly modified because of process changes, and the level of documentation was not equally thorough everywhere. Existing conventional guidelines and experience were found to be useful to support relatively lean RBI by suggesting typical areas of elevated probability of failure and therefore recommended areas to be inspected, for example at welds of large branches, locations of high strains in thermal system displacement or deviations in the function of the piping supports. Observed indications in the inspections were largely consistent with expectations and only resulted in repairs within the planned outage period. The resulting risk-based (or -informed) inspection and action plans are the main outcomes of the RBI exercise, aiming to produce the best justification and return on the maintenance investment, and to support safe operation and long-term lifecycle performance of the plant.