Karsten Niepold

Integrated Weld Quality Concept—A Holistic Design Approach for Steam Turbine Rotor Weld Joints

The today’s energy market requires highly efficient power plants under flexible operating conditions. Especially, the fluctuating availability of renewables demands higher cycling of fossil fired power plants. The need for highly efficient steam turbines is driven by CO2 reduction programs and depletion of fossil resources. Increased efficiency requires higher steam temperatures up to 630°C in today’s units or even more for future steam power plants. The gap between material properties in the hot and cold running parts of a steam turbine rotor is widened by increased live steam temperatures and the increased demand for flexibility. These technical challenges are accompanied by economic aspects, i.e. the market requirements have to be met at reasonable costs.The welding of steam turbine rotors is one measure to balance required material properties and economical solutions. The rotor is a core component of the steam turbine and its long-term integrity is a key factor for reliable and safe operation of the power plant. An important aspect of weld quality is the determination of permissible size of weld imperfections assessed by fracture mechanics methods. The integrity of rotor weld joints is assured by ultrasonic inspection after the final post weld heat treatment with respect to fracture mechanics allowable flaw sizes. This procedure usually does not take credit from the quality measures applied during monitoring of the welding process.This paper provides an overview of an holistic design approach for steam turbine rotor weld joints comprising the welding process and its improved online monitoring, non-destructive evaluation, material technology, and its fracture mechanics assessment. The corresponding quality measures and their interaction with fracture mechanics design of the weld joint are described. The application of this concept allows to exploit the potentials of weld joints and to assure a safe turbine operation over life time.Copyright

The Role of Rotor Welding Design in Meeting Future Market Requirements

The demand for current and future steam turbine components is driven by higher efficiency but also by higher plant cycling needs and optimized cost balance. An increase in efficiency increases the demand for higher life steam temperatures of up to 620/630°C for today’s units and of even up to 720°C for future steam power plants. The gap between required material properties in the hot and cold running parts of a steam turbine rotor is widened by the increased live steam temperatures and the increased demand for flexibility and adaptability to current and expected future energy market conditions. Besides further material development, welding is one measure to realize such contradictory rotor characteristics. Whereas 720°C is more a future related task, solutions for 560°C / 620°C apply already welded rotors.The paper discusses from a perspective of a steam turbine manufacturer the technical features to enable flexible high efficient rotor components with a focus on advanced welding technologies suitable for different large steam turbine components and what further steps for new welding technologies are under way.Copyright

Integrated Weld Quality Concept: A Holistic Design Approach for Steam Turbine Rotor Weld Joints

The today’s energy market requires highly efficient power plants under flexible operating conditions. Especially, the fluctuating availability of renewables demands higher cycling of fossil fired power plants. The need for highly efficient steam turbines is driven by CO2 reduction programs and depletion of fossil resources. Increased efficiency requires higher steam temperatures up to 630°C in today’s units or even more for future steam power plants. The gap between material properties in the hot and cold running parts of a steam turbine rotor is widened by increased live steam temperatures and the increased demand for flexibility. These technical challenges are accompanied by economic aspects, i.e. the market requirements have to be met at reasonable costs.The welding of steam turbine rotors is one measure to balance required material properties and economical solutions. The rotor is a core component of the steam turbine and its long-term integrity is a key factor for reliable and safe operation of the power plant. An important aspect of weld quality is the determination of permissible size of weld imperfections assessed by fracture mechanics methods. The integrity of rotor weld joints is assured by ultrasonic inspection after the final post weld heat treatment with respect to fracture mechanics allowable flaw sizes. This procedure usually does not take credit from the quality measures applied during monitoring of the welding process.This paper provides an overview of an holistic design approach for steam turbine rotor weld joints comprising the welding process and its improved online monitoring, non-destructive evaluation, material technology, and its fracture mechanics assessment. The corresponding quality measures and their interaction with fracture mechanics design of the weld joint are described. The application of this concept allows to exploit the potentials of weld joints and to assure a safe turbine operation over life time.Copyright