Yasuoki Tomita

A Review of Damage Accumulation Rules Applied to Maintenance Scheduling of Advanced Industrial Gas Turbines

Land based gas turbines are utilized to provide electric power on a continuous basis or just to satisfy peak consumer demand for a short operating period during each day. A unit that is operating on a continuous basis will incur few start and stop thermal cycles, and is typically referred to running in a baseload mode (BL). However, a unit that is operating to meet daily peak loads will accumulate an increased number of start and stop thermal cycles, and is typically referred to as operating in a daily start and stop mode (DSS). Gas turbine units are also operated with a weekly start and stop (WSS) cycle due to a different customer power demand. Hot parts in engines running in BL, WSS and DSS accumulate different levels of fatigue damage because thermal cycles vary significantly within the same actual operating hour period; e.g., the DSS engine will accumulate the most fatigue damage during the same operating hour period. Material testing has shown that an interaction of creep and fatigue damage produces a reduction in the fatigue life of a component. Different criteria and maintenance scheduling philosophy are used within the industrial gas turbine industry to account for the interaction of the creep and fatigue damage in engines. The purpose of this paper is to document how a maintenance scheduling philosophy has been developed that takes into account actual differences in engine usage on the capability of gas turbine hot parts and how current maintenance schedule intervals are being revised for Mitsubishi’s customers.Copyright

OEM’s Approach to Maintain High Reliability of Hot Gas Path Parts

The reliability of gas turbine (GT) Hot Gas Path components requires both design and metallurgical expertise. There are numerous repair facilities around the world with general metallurgical expertise. However, the maintenance process can be noticeably improved through a feedback approach that incorporates the original part design know-how and the fleet wide experience gathered from operational data. A lot of users apply daily start-stop cycles so these peaking operations will impose more severe duties on the hot gas path parts (HGPPs). For this reason, we have achieved high GT reliability, low fall out rate, and improved repair processes utilizing our in-house verification plant (combined power plant of G class GT). For service units, the Remote Monitoring concept [1] was developed to provide an extra level of protection and diagnostics for power generation equipment and it has also facilitated correlation between HGPPs distress and operational profiles. The use of historical operating data, including number of cycles, trips, and rapid load changes can reveal valuable information on the HGPPs distress and assist repair process improvement. Fleet database can give lots of feedback on the reliability and durability of the repaired components. This paper describes our own process of improving HGPP design and feedback to the maintenance. This process includes analysis of thermal barrier coating (TBC) degradation, careful application of life assessment techniques on substrate metallurgy, and analysis of operational data to improve design and repair techniques for increasing fleet availability.Copyright