Detailed Hot Section Mapping of Siemens SGT-600Jenny Sundberg & Mats, Blomstedt, Siemens Industrial, Turbomachinery AB, SE-612 83 Finspong, Sweden

ABSTRACT
The 25-MW Siemens gas turbine SGT-600 (previously known as GT10B) is a mature product, which recently passed five million operating hours. The first engines were introduced in the mid-eighties, and currently over 230 SGT-600 have been sold. A four-year development project has been performed with the aim of enhancing knowledge of the SGT-600 lifing status, by mapping engine temperatures. The project started with an update of the models performed in 3D for CAD, aero, cooling and stress. Next, a thermo-crystal engine test at full load took place. 1741 thermo-crystals were used, measuring the gas temperature profile throughout the whole turbine and metal temperature distribution for blades 1-4 and vanes 1-2. The results were used to calibrate the aero, secondary air system and cooling models, in order to achieve more reliable stress calculations at full load.

These models were also used as a base for sensitivity analysis concerning ambient temperature and power turbine matching. A second engine test using thermocouples was also performed. It covered a large number of cases, for example part and peak loads, start and stop cycles and effect of the combustor bypass system. The results were used to validate 3D calculations for the tested cases. The combination of computational models, measurements and field experience from the fleet has resulted in a substantial bank of knowledge of the lifing status of the SGT-600 turbine. One outcome of the project is that blade 3 turned out to have 50% longer life than was previously predicted. This and other conclusions will result in updated cycle-based maintenance plans, performance and design optimization, improvements of the Condition Based Maintenance product and possible extensions of the Time Between Overhaul.

INTRODUCTION
The SGT-600 was originally designed by the Swiss company Sulzer Escher Wyss and the machine was then known as Type 10. The first unit was in commercial operation in 1988. The rating was 22MW, which was considered as an introductory level. In 1990 this engine was transferred to Siemens Industrial Turbomachinery AB (at that time ABB Stal) where the first design change was to introduce a Dry Low Emission (DLE) burner with 25ppm NOx dry @15%O2 on gas, which now is standard (conventional burner is available as an option). The machine was then called GT10A.

A mature rating of 24.5 MW was introduced in 1992 (34.2% efficiency) and – excluding some minor changes – the rating has been the same since then. The machine was referred to as GT10B. Within the Siemens family the name of the machine today is SGT-600.

SGT-600 gas turbine

This twin-shaft machine is used both for Power Generation (PG) and Mechanical Drive (MD)applications. Over 230 units have been sold and the split between PG and MD is close to 50/50. The total accumulated operating hours is more than 5 million, whereof 80% is with DLE. The fleet leader is at the level of 140 000 hours. This machine is now a well established product on the market with a high Reliability Factor(>99 %), Availability Factor (>97 %) and Mean Time Between Failure (>2000 h).

The AF, RF and MTBF figures are very important for a plant and every effort should be made to increase this further. This requirement, together with new state-of-the-art measurements and computational models, motivated extensive mapping to know the stresses of the machine for all operating conditions. The aims were among other things to optimize both cyclic and time-based maintenance programs. Consequently, new levels of AF, RF and MTBF are foreseen.

The hot-section mapping project was initiated in October 2004. An overview of the project is seen in Figure 2. The project started with an update of models performed in 3D for CAD, aero, cooling and stress. The project covered cyclic and creep lifetimes for turbine blades 1-4, turbine vanes 1-2 and CT discs 1-2. In 2005 a thermo-crystal engine test at full load took place. The results were used to calibrate the aero, secondary air system and cooling models, in order to achieve more reliable stress calculations at full load. A second engine test using thermocouples was performed in 2006. It covered among other things part and peak loads, start, stop and trip cycles and the effect of the bypass system. The results were used to validate 3D calculations for the tested cases.

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