2021 RETA Breeze March-April

not uncommon and can have many causes: vibration, mechanical stress, excessive pressure or liquid hammer, improper application or material, or improper installation methods being the usual suspects. However, it is important to note that the failure of these pipe nipples is not the root cause, but rather a symptom of another issue. Closer examination of the following photographs provides clues that point to the root cause. On each of the examples to the right note that there is a relatively heavy concentration of unsupported weight at the end of a relatively long and comparatively light pipe nipple. If one goes back to the photos of the failed nipple, a closer examination reveals the presence of ratchet marks around the circumference of the nipple. The photo below is an example of an unrelated failed pipe nipple that more clearly illustrates what these marks look like:

Findings

Overload Region

Ratchet Marks

Beach Marks

The presence of these marks indicates that fatigue cracks initiated in a variety of locations and propagated through the material. Multiple crack initiation regions indicate that the forces acting on the pipe were multidirectional as would be expected if vibration was present. The fatigue cracks all originated at the thread roots, which is expected

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