PERFORMANCE OF WELDED JOINTS IN LOW-ALLOY STEELS T/P23 AND T/P24 FOR CHALLENGING HIGH-TEMPERATURE APPLICATIONS

Increasing thermal loads, temperatures and pressures in boilers and steam systems is attractive to improve the efficiency and operational economy of power and process plants. The adoption of new high strength, modified 2% Cr steels can be an option, provided that these will perform for the required component life. Challenges have arisen when using new high strength T/P23 and T/P24 steels for waterwalls, superheaters and steam lines. This paper reviews the recent understanding of the applicability and limitations of these steels in welded components. A range of causative reasons are proposed for the not entirely successful application of the P/T23 and P/T24 particularly in waterwalls and steam lines. The complexity of optimising weld properties is demonstrated in view of unforgiving material response especially at weld defects, as well as of high weldment hardness and limited ductility. Selection of filler metal type and composition is elucidated with respect to propensity to low weld metal ductility, such as low creep ductility damage or reheat cracking. The role of structural rigidity and actual constraint conditions in real components is discussed, as it comes to adopting filler metals with the aim of either increasing weld creep strength or ensuring adequate creep ductility, as well as to whether to conduct or omit the subsequent PWHT. One of the most persistent remaining challenging issues concerns welded thick-wall applications for high temperature headers, steam pipes or turbines, where the weld metal tends to show very limited creep ductility. More recently, setbacks have been seen in the attempts to use T24 in welded water walls of large boiler plants. Multiple causes have been proposed for the observed early waterwall cracking, and again, the problems concentrate on welds that tend to exhibit reduced creep ductility.

AUERKARI Pertti;  HOLMSTROM Bjorn;  NEVASMAA Pekka;  SALONEN Jorma; 

2015-01-19

Forschungszentrum Jülich

JRC92100

978-3-95806-000-5,   

1866-1793,   

https://publications.jrc.ec.europa.eu/repository/handle/JRC92100,