One of our clients reached out for help with a failure analysis of a fractured component that failed during routine testing. IMR was asked to confirm a preliminary root cause analysis from another test lab the end-user had sent the part to. Additionally, IMR was supplied with swabs from foreign deposits and some additional pieces to analyze.
These swabs, as well as additional particulate samples taken from inside the parts, were analyzed via SEM-EDS to determine composition. The analysis showed embedded particles, primarily composed of alumina, silicon oxide and carbides. Chlorine was also detected.
Pitting was observed on the surfaces near where the particles were collected and the fracture occurred. The part is exposed to high temperature steam in-service in a stagnant area without a lot of flow. Condensation preferentially collects on particles, which can contribute to pitting corrosion. There is also hydrogen in the process steam, which in addition to the pitting, allowed IMR to conclude hydrogen embrittlement as a root cause for failure.
Recommendations to prevent future failure included evaluating the cleaning process as well as inspections of the population of parts for signs of pitting. The client also suggested switching to a component with a thicker wall to lower the local stresses to ensure structural integrity even if embrittlement were to occur in the future.
IMAGE CAPTIONS (LEFT TO RIGHT)
- Pitting on the interior of the bellows
- As-polished embedded particle on inner surface in area exhibiting pitting.
- Representative surfaces showing residual deformation from machining, etched
- SEM Image of one of the pits