Analysis of Failure in Corrugated Metal Pipe Under Acid Pickling Due to Grain Boundary Cracking

As a flexible pressure resistant pipe fitting, corrugated metal pipes can be used to compensate for the mutual displacement of pipes, machines, and equipment connection ends, absorb vibration energy, and play a role in vibration reduction, noise reduction, etc. However, the processing technology of corrugated pipes is complex and requires multiple processing steps from raw materials to finished products, including physical and chemical treatment engineering. If the processing technology is slightly improper, it will bring defects to the corrugated pipes, thereby affecting their performance and even catastrophic consequences. A corrugated metal pipe broke during the ultrasonic cleaning process before use, resulting in the product being scrapped. In order to identify the causes of cracking in corrugated metal pipes and guide the improvement of product production processes, a study was conducted on the metal pipes used in the production of corrugated metal pipes, as well as the semi-finished and failed corrugated pipes produced in various stages, through mechanical properties, hardness, microstructure, and fracture analysis. The results show that the corrugated pipe material used meets the requirements of the process documents. During the physical processing, residual stress is inevitably generated at the peaks and valleys. At the same time, during the pickling process, due to improper process control, grain boundary cracks appear on the surface of the corrugated metal pipe after pickling. The residual stress at the root of the grain boundary cracks overlaps with the impact force generated during ultrasonic cleaning, leading to local instability and cracking.