Analysis of transverse cracks in fluorinated rubber elbows
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This post was last edited by green0031 on 2018-9-4 at 10:03. The elbow is made of steel with a PTFE lining; the medium used is a mixed acid (nitric acid, sulfuric acid, hydrochloric acid). The temperature is below 100 degrees. It is located at a point where a horizontal pipe section turns into a vertical one, at a height of 4 meters above the ground. Photos are provided below: The cracks are situated near the center of the elbow’s steel structure, and there are two transverse cracks that run through it, each less than 1 millimeter wide and not continuous at either end. Could everyone help analyze this? What might be the likely cause of the cracks? Could it be temperature-induced tensile stress combined with the fact that that area is a weak point? If so, how can we take preventive measures?
Based on the shape of the crack, it can be preliminarily inferred that the material has degraded
If possible, the samples should be subjected to performance tests in accordance with the requirements specified in the elbow warranty document; at the very least, tensile testing and metallographic analysis should be carried out. Preliminary judgment: There is a significant issue with the material itself; it is suspected that the elbow was not heat-treated after being manufactured.
A bellows can be installed to absorb expansion stresses.
“There are transverse cracks with a width of less than 1 millimeter that run through the material at both ends, where they are discontinuous. ”What does that sentence mean?
In other words, the depth of the crack has basically reached the surface of the inner PTFE sleeve
It seems that the cracks propagate from the outside inward; they are likely fatigue cracks resulting from the original defects under the effects of temperature and other stresses.