Analysis of cracks in low-temperature superheater tubes
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The image above shows the tubes of the low-temperature superheater; the material of these heat exchange tubes is 12Cr1MoVG, with a diameter of 38x4. The tubes undergo stress-relief annealing at 700°C. Process conditions: Flue gas temperature is 630°C, saturated steam pressure is 2.36 MPa with a temperature of 223°C. The exit temperature of the low-temperature superheater is 270°C, while that of the high-temperature superheater is 230°C. Approximately 2 months after installation following replacement, the aforementioned pipe cracking occurred. The inner and outer surfaces of the pipe were smooth, with no signs of wear or cavitation. Based on the appearance of the cracks, it is uncertain whether the failure was caused by residual stresses from the pipe’s processing not having been fully relieved, or if there are other underlying causes
Based on the description, it is likely that the brittle fracture was caused by residual stresses in the pipeline not having been fully relieved. However, other possible causes cannot be ruled out, such as material defects, design or installation errors, abnormal operating parameters, etc. Further analysis is needed to determine the specific cause. .
Is there any over-temperature phenomenon? It seems to be caused by over-temperature.
In the first image, the cracks on the pipe appear to be defects in the pipe material itself, with no radial cracks at either end of the fissures.
For the material and specifications you mentioned, heat treatment is not required; even if heat treatment is carried out, it is high-temperature tempering, not stress-relief treatment. The defects may be caused by substandard welding materials or improper manufacturing processes.