Creep properties and damage behaviour of component-like tubes of Vm12-materials

Abstract

The gap in the energy supply between current availability and the rising demand for electricity worldwide has to be closed primarily by using modern steam and gas power stations with an increased degree of efficiency and decreased CO2 emissions. Target values for reaching a high degree of efficiency of ≥50% demand increase the steam parameters. The modern creep-resistant steels and their weldments have to have both high creep rupture strength and corrosion resistance.Within the European research programme COST 536, between 2005 and 2009 research and development work in the field of power plant steels had been carried out for conventional applications. The project was focused on the development of appropriate materials, coatings and surface treatments for components in steam power plants with steam inlet temperatures in the turbine of up to 650°C.In framework COST 536, Siempelkamp Pruef- und Gutachter-Gesellschaft mbH (SPG) performed component-like creep tests at pressurized tubes made of martensitic steel VM12. This steel was developed by Vallourec & Mannesmann Tubes with the aim of reaching both sufficient creep strength and increased oxidation resistance and is already used for boiler application in new power plants in Germany.In this paper, the experimental results of uniaxial creep tests, component-like creep tests on tubes with inner pressure and axial loading, metallographic examination and damage characterisation are presented. The tubes are equipped with capacitive high temperature strain gauges for on-line monitoring of strain. All testing data will be implemented as inputs for the numeric FE analysis. The effect of multiaxiality and stress redistribution will be discussed.