Abstract
	This article presents the results of weldability tests performed on T23, T24 and T25 steels. Based on these test results a suitable preheating temperature was calculated for welding the said steels of 6 to 20 mm thickness. Further, this article deals with hardening of weld joints in perspective steels T23 and T24 during extensive exposure at operating temperature 500 °C. The extent of secondary hardening depends on application of tempering after welding. Non-tempered weld joints undergo an unacceptable increase in hardness during exposure at operating temperature. Based on test results a suitable temperature profile was calculated for welding membrane walls from T23 and T24 steels.