Papers by Keyword: T23

Abstract: Increased efficiency and emission reduction in modern power plants lead to the use of new advanced materials with enhanced creep strength, with the objective to increase the steam parameters of power plants. With over ten years on market and wide experience related to its use, ASTM Grade 92 is becoming one of the most required materials when high service temperatures are reached (max. 610°C). Its composition, with 9%Cr and 1.5%W, gives rise to martensitic microstructures which offer very high creep strength and long term stability. The improved weldability and creep-strength between 500 and 580°C of the low alloy ASTM Grade 23, as well as a cost advantage over higher Cr materials in this temperature range, make it one of the possible candidates to meet the stringent requirements of modern power plants. Air Liquide Welding (ALW) has optimized and distributes a complete product family for the welding of Grades 23 and 92. TenarisDalmine (TD) focused on the development of Grade 23 tubes and pipes and is working on the development of Grade 92. A deep characterization work of the microstructural evolution and long term creep performances of these high temperature resistant materials was thus undertaken by ALW and TD, in collaboration with the Centro Sviluppo Materiali (CSM). The joint characterization program consisted in the assessment of welded joints creep properties. Welded joints were produced using the gas tungsten (GTAW), shielded metal (SMAW) and submerged arc welding (SAW) processes. Mechanical and creep properties of weldments were measured both in the as welded and post weld heat treated conditions and proper WPS’s were designed in a manner such that industrial production needs were satisfied. Short term creep resistance of cross weld specimens was measured to be within the base material acceptance criteria. Long term base material and cross weld creep performance evaluation are now in progress.

Abstract: This paper describes the evaluation of the creep behavior with two types of matching filler metals for 2.25Cr-1.6W(T23)/Mod. 9Cr-1Mo(T91) dissimilar weld joint. Through the welding procedure qualification tests prior to the creep tests, optimum PWHT holding times at 745±5oC were determined as 30minutes for T23 matching filler metal and 60minutes for T91 matching filler metal. It was also confirmed that carbon migration across the weld interfaces and the softened area at HAZ occurred during PWHT. Creep rupture tests were carried out at 575-650oC and 70-220MPa for two dissimilar metal welds manufactured by an optimum PWHT condition. From the comparison of creep rupture strength, it was shown that the creep strength of the welded joint including T23 matching filler metal was similar to that of T23 base material and somewhat higher than that of the welded joint including T91 matching filler metal. From metallurgical study on the crept specimen, the creep damage of T23/T91 dissimilar weld joints could occur at T23 side IC HAZ and near the T23/T91 weld interface simultaneously. However, the final failure locations seemed to depend on the filler metal and the cause of this phenomenon might be regarded as the additional effect of carbon migration across the weld interfaces. It is thought that the dissimilar weld including T91 filler metal which failures at T23 side CG HAZ subject to both metallurgical notch and carbon migration become more susceptible to creep damage than that including T23 filler metal in which the carbon depletion occurs at the T23 filler metal with higher creep strength than T23 HAZ. T23 filler metal can therefore be proposed for matching filler metal of T23/T91 dissimilar weld joints