Recent articles on the internet have indicated that the littoral combat ship Milwaukee broke down at sea. The articles were written shortly after the event and only had limited information about the event. Breakdowns like this can be simple to investigate – or extremely complicated. We at Kevin Kennedy Associates are not involved in the investigation, but if one was to investigate a break down of this type, a number of issues come into play. The issues that would have to be considered as part of the failure analysis would include and not be limited to
- the location of the filter that is collecting the metal filings.
- the type of metal (aids in determining the source of the metal).
- design related issues
- were the failed components designed to meet the operating environment?
- was the type of design appropriate for this particular application?
- were the proper steels used for the application?
- were there any required heat treatments or surface hardening required for any of the components?
- did someone skip performing an engineering analysis?
- manufacturing related issues
- did the damages components meet the design requirements as spelled out in the design specifications and design documents?
- do the parts reflect the dimensions, surface finish, surface hardness, etc. as called out in the detailed part drawings?
- do greater loads exist during operations than anticipated?
- was the correct steel and applicable heat treatment used based on the design drawings?
- operational related issues
- was the system properly flushed after initial assembly?
- was the combat ship operated outside of the expected operating conditions?
- was the system filled with the proper lubricants?
This list in not comprehensive by any means, but it is clear that a thorough failure analysis investigation can touch on many different issues. Now, not every single component has to be examined for every design and manufacturing detail, but enough have to be examined to evaluate potential failure modes. For example, the schematic below outlines the thought process one might use to work their way through the investigation. It includes determining where the metal chips came from, considering potential failure modes (hypotheses), and then collecting data for analysis to determine if it supports one of the proposed hypotheses or not. If not, one goes back and develops additional hypotheses, or collects more data for evaluation.
As you will note in our future articles on failure analysis, there will always be issues that relate to the design, manufacture, and use of the component or system. When components or systems fail, it will often be the result of a poor design, improper manufacturing, or usage that falls outside of the expected range. The operational related issues take time to evaluate and understand.