Cause analysis of cracks in high-pressure elbows
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Recently, during a shutdown for maintenance in our company’s synthesis workshop, three cracks were found on the elbow from the soft water heater outlet to the water cooling section, with air leaking from these cracks; accordingly, this elbow was replaced. It has been found that this elbow has only been in use for two years. I would like to ask my colleagues: what is the cause of these cracks? As a supplementary note, no significant air leakage was observed during the production of this system.
There may be three reasons: 1. An inherent manufacturing defect； 2. Medium erosion, mechanism corrosion ； 3. Stress concentration.
It is mainly caused by manufacturing defects – there are internal quality issues with the elbow itself during its bending process. If it is indeed a high-pressure pipeline, then this elbow must undergo ultrasonic and magnetic particle testing during construction
Gas-liquid entrainment scouring on elbows causes significant thinning. But the problem with the moderator’s unit seems to be a manufacturing defect; is there no product certification?
It would be best to have photos for easier analysis. Cracks can be caused by several factors: 1. Quality issues with the elbow itself, such as material-related problems; 2. Stress corrosion cracking. Erosion is less likely to be the cause, as the destructive mode of erosion is perforation following thinning of the material
Manufacturing defects are essentially quality issues. It is recommended to conduct mechanical property tests
Stress concentration, fatigue from frequent vibrations, material issues, defects in pipe fitting fabrication
To determine the shape of the crack: 1. Transverse crack; 2. Longitudinal crack; 3. Whether it is located in the middle or at either end of the elbow. Further analysis is then needed to consider factors such as media erosion, corrosion mechanisms, stress concentration, etc.