How to inspect , replace GT exhaust system components

You don’t have to visit many generating facilities pow-ered by gas turbines (GTs) or attend many user-group meetings to realize that exhaust sys-tems get little or no respect. These relatively simple systems essentially consist of metal components and insulation arranged to direct nomi-nal 1000F gas exiting an engine to a heat-recovery steam generator (HRSG), or stack, while protecting personnel.   

Exhaust systems usually are ignored on rounds, rarely getting more than a passing glance unless an operator hears gas whistling out of a hole, crack, or tear in the ductwork, expansion joint, or between mating faces of adjacent flanges. What’s there to check, anyway?   

However, exhaust systems are not something to forget when an outage approaches. There are inspections you should make before and during an outage to evaluate the condition of system components. While most issues identified can be corrected at least temporarily with weld material and insulation, the wear and tear on these systems—particularly those at plants in cycling service—is consider-able and their lifetimes are limited. Consider yourself lucky to get 15 years out of an exhaust system.   

Purpose of this article is threefold: Help you assess the condition of your plant’s exhaust system, catch up on the latest designs which can help eliminate many of your recurring repair jobs, and gain from one plant’s experience in replacing the exhaust systems on its GTs.