Metallographic examination of new “untested” elements revealed that the units were supplied with the sheath in an annealed state.
The following example illustrates some of our contributions to this business sector:
- Repeated, explosive failures of heating elements in commercial coffee vending machines led to the evaluation several failed heating elements. The inconel-sheathed, resistance elements burst after only a short service life when the machine began to heat water. No corrosion damage was seen which might have allowed water to seep into the element. Metallographic evaluation found the elements to have a uniform, fine-grained microstructure with no obvious defect. Examination of the element exterior did not find any cracks or obvious manufacturing defects that would explain the failure. A discussion of the problem with the vending machine manufacturer found that, as part of their quality control, each new element was tested by powering it until it became orange-hot to assure the element was operational. Immediately afterward the hot element was then plunged into cold water. Metallographic examination of new “untested” elements revealed that the units were supplied with the sheath in an annealed state. The annealed structure allowed for normal expansion when the element was used. Quenching had rendered the sheath hard and relatively inflexible. During initial heating the sheath would crack and allow water to seep into the element. During a subsequent heating cycle the element would burst from steam pressure.
The above example is only a sample of our work in this area. We would be pleased to provide any additional information you may require. We also invite you to review examples on our website of work that we have performed in support of other business sectors.
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