Traditionally operations and maintenance personnel have used gas detectors to check the fuel pig tail flanges for leaks during the startup process. This is to ensure that no fuel is present that could cause a fire in the compartment. An less risky alternative to this process is to perform a soapy water check while the unit is on crank. A pressurized garden sprayer is filled with soapy water and while the unit is being cranked and sufficient air pressure is present the entire unit is sprayed down with the soapy water mixture. Not only will this produce evidence of leakage at the fuel flanges but will reveal any air leaks on the can bases, the wrapper four way joints, the primary fuel covers or anywhere else air can escape.

Since this a relatively simple and safe procedure TGM® recommends performing this check prior to any maintenance being performed (after the unit is shut down and just before the LOTO is initiated). Any and all air leaks can be identified and they can be addressed during the scheduled maintenance cycle if feasible.

There have been several TIL’s released on the care and quality of the flexible metal hoses for CT’s. The end user has gotten into the practice of having the flexible metal hose pressure checked during the hot gas path cycle. If the soapy water checks are performed prior to any work being performed and any of the flexible metal hoses are leaking then why bother to have them pressure checked. This approach can save expensive labor cost by eliminating a test on a hose that will fall out. Plus wouldn’t it be better to know you have a leak at the wrapper four way joint before it is removed to perform a hot gas path than finding out during the inspection at start up?

Thermal Barrier Coatings (TBCs) protect the first several rows of hot gas path parts from the high combustion temperatures in many advanced large frame turbines. Not all coating applications are equal, and some can even reduce the efficiency of your unit.
TBCs are designed to reduce the temperature of the buckets and stators while providing resistance to corrosion and reducing oxidation of the component. TBCs form aluminum-oxide and chromium-oxide scales and act as a physical barrier to reduce component temperatures, extending the life of the parts. These TBCs are subjected to mechanical stresses, and spallation (coating separation) can occur. If a significant amount of TBC has separated from the metal, the parent metal will be exposed to the hot combustion gases and component degradation will be accelerated.
Hot gas path components should be inspected for TBC spallation at every Hot Gas Path or Major outage. Streaks of brown lines that appear to be coming from the cooling holes are a good sign that the component is receiving adequate cooling air, and spallation is at a minimum. When receiving components from the repair shop it is important to carefully inspect the components for an even coat of TBC. Also inspect the cooling air passages for debris and proper sizing to ensure that proper air flow can pass through the tiny passages for designed cooling.