Status of Development of the VM12 Steel for Application at High Temperature in Advanced Power Plants

Abstract

Improvement of boiler efficiency is reached by increasing the pressure and temperature of newly designed boilers. Recently developed steel grades such as T/P91 and T/P92 are used in the advanced power plants thanks to their high creep rupture strength resistance which enables maintaining acceptable thickness of the tubes and pipes. Nevertheless their operating temperature range is limited by their oxidation behavior which is lower than classical 12%Cr steels or austenitic steels. For these reasons we have developed a new steel grade which combines good creep resistance and high steam-side oxidation behavior. This new steel, based on chromium content of 12% and with other elements such as cobalt, tungsten and boron, is named VM12. Manufacturing of this grade has been proved by production of several laboratory and industrial heats and rolling of tubes and pipes in several dimensions by different rolling processes. In addition to base metal property investigations — including creep tests and high temperature oxidation behavior — welding, cold bending and hot induction bending qualifications took place. This paper summarizes the results of the investigations and presents the first findings for processing.

Properties of Welded Joints on Superheater Coils Made from New Generation High Alloy Martensitic Steels Connected to Austenitic Creep-Resisting Steels and Supper Alloy Grades, for Supercritical Parameters

“…220 to 260 HV10, in case of steel X10CrWMoVNb9-2 (P92) steel, following welding and heat treatment. In case of X12CrCoWVNb12-2-2 (VM12) steel, in the welded joints can observe the mixture of martensite with a small quantity of bainite [4]. Hardness of parent material, HAZ and welds metal, following welding and heat treatment, has not exceeded 300 HV10, with the maximum difference being not higher than 50 HV10.…”

“…12% Cr and austenitic steels, having approx. 18-25% Cr, as well as nickel superalloys which are to be applied [4]. The calculation results of wall thickness on an exemplary live steam outlet superheater for the following assumed design parameters: design pressure e.g.…”

“…in 640(650) 0 C having the content of 12% Cr, for the steam outlet superheater coils, results in the tube wall thicknesses which are above the technologically acceptable maximum of 10 mm. However, the practice which has been followed so far shows that with the aforementioned exemplary steam parameters the requirements set for live steam and secondary steam collectors are met by steel P92 [1,4]. The stress values, which are admissible for steels such as VM12, TP347FG, SUPER 304H, as well as HR3C, are included in the following documents: standard EN 10216-2, VdTÜV-WB, ASME CODE, SA213, part IIA and material specification for V&M (WBL-439).…”