This post provides more suggestions for potentially beneficial ideas to consider when designing for in-service reliability of various types of equipment. As stated in Part 1, most of the ideas are especially applicable to manufacturing or processing equipment that must function continuously over a long service life for the overall system to be economically viable. The engineer may be able to improve his or her design by considering if any of these approaches are practical for the specific application.

1. Think long-term reliability and ways to implement preventative maintenance during design. One way is to be familiar with the different methods of non-destructive testing (NDT), their capabilities and, especially, how physical arrangements can be established during design to allow sufficient access for effective NDT inspections.
2. Realize that many types of failures originate at poor quality welds. This provides another example in which reasonable access is important. Think ahead and, where possible, allow the welder sufficient space to get into a reasonable position to make quality welds. Alternatively, specify the sequence of overall fabrication to permit quality welding.
3. Use a thin corrosion-resistant material alloy metallurgically-clad or electroplated onto a much thicker, substrate metal that has inferior resistance to corrosion. This can be an economical alternative to a single thickness of an expensive, corrosion resistant alloy.
4. Always omit sharp corners and small radii on equipment. Such deficient locations concentrate stresses and often prevent good coverage by coatings. Both mechanical and corrosion failures frequently originate in these areas.
5. Consider where flow “dead legs” may be generated in piping systems during various operating or shutdown conditions. Eliminate these so as to discourage pitting and crevice corrosion as well as MIC.
6. In shell and tube heat exchangers, carefully specify baffle plate hole diameters and spaces between baffles to minimize the chance of flow-induced fatigue failures of tubes. Prior to delivery confirm that these and other specifications are correct during QC inspections of exchangers in the vendor’s fabrication shop. Of course, this assumes such QC inspections are done.
7. Where applicable implement actions to minimize the chances of failure due to erosion or erosion-corrosion (E-C). For example, use sufficient size pipe diameters to prevent too high flow velocities, take large pressure drops in multiple stages rather than at one location, use hard metals to minimize erosion but understand that a more corrosion-resistant alloy is usually more important than alloy hardness in controlling E-C.
8. In very cold temperature applications, assure that the fracture toughness of the alloy selected is sufficient to prevent its brittle failure in service.
9. In high temperature applications, consider the most likely failure modes, e.g., oxidation and associated mechanisms, creep or thermal fatigue, and specify an appropriately resistant alloy or implement other preventative measures.
10. Sometimes a regular, planned in-kind replacement of a component before its useful service life has fully expired is a possible option. This may produce the best economic result especially when regular, effective NDT evaluations are possible and are accomplished to monitor the part’s integrity. The engineer should configure the design so that these  replacements can be accomplished as easily as possible during planned, maintenance shutdowns.

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