A longitudinal crack and window opening type failure occurred in neutral zone that is applied to least plastic deformation in the bent TP347H tube during operation. From the analysis of residual stress and plastic deformation during the tube bending, there is low creep strength and high residual stress in neutral zone as compared other regions like intrados and extrados. Therefore, failure occurred in neutral zone due to stress relaxation concentrated in grain boundary during operation.

The inspection and evaluation of defects in the welds of P92 high temperature reheater header with a diameter of about 1000mm and a wall thickness of about 100 mm have been done by means of hardness test, nondestructive testing on the surface, ultrasonic testing, metallographic and component sampling. By analyzing the results of on-site test and samples removed from the component, it is found that cracks existing in the welds are hydrogen induced delayed cracks. During the welding process and post-heating treatment (hydrogen bake-out), dehydrogenation was insufficient. This fact, combined with welding residual stresses resulted in the observed hydrogen induced cracking.

During commissioning of recently built modern, and highly efficient coal-fired power plants, cracks were detected after very short time of operation within the welds of membrane walls made from alloy T24. The root cause analysis revealed transgranular and mostly intergranular cracks adjacent to the heat affected zone beside weld joints. At that time, the degradation mechanism was rather unclear, which led to an extended root cause analysis for clarification of these failures. The environmentally assisted cracking behavior of alloy T24 in oxygenated high-temperature water was determined by an experimental test program. Hereby, the cracking of 2½% chromium steel T24 and 1% chromium steel T12 were determined in high-temperature water depending on the effect of water chemistry parameters such as dissolved oxygen content, pH, and temperature, but also with respect to the mechanical load component by residual stresses and the microstructure. The results clearly show that the cracking of this low-alloy steel in oxygenated high-temperature water is driven by the dissolved oxygen content and the breakdown of the passive corrosion protective oxide scale on the specimens by mechanical degradation of the oxide scale as fracture due to straining. The results give further evidence that a reduction of the residual stresses by a stress relief heat treatment of the boiler in combination with the strict compliance of the limits for dissolved oxygen content in the feed water according to water chemistry standards are effective countermeasures to prevent environmentally assisted cracking of T24 membrane wall butt welds during plastic strain transients.