|The RA253 material is special for high temperature service. The crack was located in a fired rotary kiln that operated at very high temperatures between 500 to 900 C. Cracks which appear to be shaped like the branches of a tree, or roots, signal a metallurgical change in the material that usually indicate that it can no longer serve its intended purpose.
|There were several cracks such as the one above, and a couple were patch welded to keep product from leaking out (Figure 2). Within several months the repair started leaking again, and to no surprise, the new crack had the same branch-like appearance as the first crack.
The basic failure mechanism had occurred on an intergranular scale, the crack(s) actually following the grain boundaries of the material. If the problem were strictly structural, the crack would essentially be straight.
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