PT Arun operates 21 GE Model MS-5002 B/C gas turbines as mechanical drive with a total power of 514 MW, and a total of 2.7 million hours of accumulated operation. The first generations of simple cycle gas turbines were designed at 1700 F (927 C) firing temperature using first stage buckets design cast from IN-738LC and coated with a conventional 2-phase platinum aluminide coating (Pt-Al). Since 1989, the output power was increased by raising gas turbine firing temperature to 1770 F (965 C). This uprate was implemented by using first stage buckets cast from GTD-111 DS and coated with GT-29 Plus.
Metallurgical examination of these coatings at various operating hours have been performed to check their performance and the cause of coating degradation. These results are considered for future coating selection.
In the last two years PT Arun has explored a new single phase NiCoCrAlY coating and a single phase Pt-Al diffusion coating using chemical vapor disposition process as an alternate to GT-29 plus coating replacement. Both of these coatings are used at PT Arun and have accumulated 32,400 hours for NiCoCrAlY or GT-33 and 2880 hours for single phase Pt-Al or MDC-150L coating as of June 1996. The information regarding qualification of these alternate coatings (zero running hours) will be discussed in this paper.