Examination of welds made of 7CrMoVTiB10-10 (T24) to identify stress corrosion cracking occurring during operation

Reiner Zielke, RIF e.V., Dortmund, Deutschland
Hans-Georg Rademacher, RIF e.V., Dortmund, Deutschland

Introducing T24 as material for membrane walls which contact water, many leakages were identified during the commissioning phase of coal fired power plants. All the damage identified was located in the heat affected zone (HAZ) of the welds. A detailed analysis of the root cause identified stress corrosion cracking, which occurs under unfavorable operating conditions, as the main problem. To determine the operating parameters that lead to cracking, an experimental setup was developed that allows simulating the load and water chemical conditions in the commissioning phase. In addition to that, sensors to determinate the crack initiation and to monitor the damage evolution were installed. This test set-up allows extensive and systematic studies. With the measurement systems installed it is expected to obtain information to understand the damage mechanism.

In this contribution, the experimental set-setup, the measurement systems used and also some experimental results are presented. To obtain more information about the exact time of the crack initiation and crack propagation new measurement systems are implemented. These are acoustic emission sensors to detect crack initiations and propagations as well as digital image correlation, which is used for the optical analysis of the strain distribution on the sample. With this technique it is possible to control the external (integral) strain measurement and to identify other areas on the sample in which cracks are initiated.

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