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Design Basis for Planned Shutdowns

  • 1. GTs would be taken out of service for inspection/overhaul for 25-26 days a year.
  • 2. HRSGs would be shut down for 14 days every 3 years for statutory inspection.
  • 3. BFW pumps: overhaul—240 hours every four years; minimum flow valve—48 hours every six months; seal change—72 hours every two years.

Reliability Engineering in New Projects 259

Schematic Drawing of Power Plant

Figure 34.1 Schematic Drawing of Power Plant

The HRSGs would be shut down at the same time as the corresponding GT. Hence, the HRSG down time need not be considered.

Analysis Technique

We appointed a well-known reliability consultancy firm to carry out the analysis. They planned to use Fault Tree Analysis (FTA) to model the system. While building the model, they worked closely with the project team members to ensure that the model represented the process flow scheme and that limitations in different scenarios were correctly represented. They used data from published generic sources such as IEEE Std. 500i, OREDA IIii, OREDA Шт and NPRDiv and applied error factors to the data to give 90% confidence limits. The software package had a built in Monte-Carlo simulator to enable probabilistic predictions. Appendix 34-A has more details about FTA.

Once the model was built, we could play tunes on it. The sensitivity of the final output to various changes could be checked. These included the addition or removal of individual items of equipment or in their configuration, changes in their reliability parameters, or shut down durations. This permitted us to find the most cost-effective configuration.

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