Column Equipment

Get the Parts Part Right

EP Editorial Staff | September 12, 2018

By Drew D. Troyer, CRE, Contributing Editor

Early-life failures plague industries that depend upon asset-intensive processes. Early-life failures are those that occur shortly after startup of new, recently rebuilt, or recently repaired machines. While there are many causes for early-life failures, they can be classified in terms of bad parts or bad workmanship, both traceable to a lack of planning and control. Saving the workmanship issue for another time, this month I’m focusing on installing the right parts, in the right condition, in the right way to avoid early-life failures. In short, let’s look at managing stores.

Stored parts are susceptible to three primary static degradation mechanisms: corrosion, fretting (or false brinelling), and oxidation.

Corrosion, which includes rust, is a chemical attack on component surfaces. Metals are affected in various ways by chemicals. Water, though, is the most common chemical agent that parts encounter. It directly corrodes iron and steel surfaces, causing rust. It also increases the corrosive potential of acids that attack brass, bronze, and other metals.

Fretting is referred to as corrosion in some references and wear in others. The result is the same: material degradation. Fretting occurs when the contact points of stored equipment are subjected to high-frequency, low-amplitude vibration. Stressing those contact points over and over again ultimately leads to material fatigue. Imagine, for example, bending a wire in the same spot repeatedly. Eventually, fatigue sets in and the wire breaks.

Oxidation attacks elastomers, lubricants, and other chemical materials. It occurs when oxygen ions attack the molecules in such material, resulting in changes and degradation. For example, when oxygen ions attack lubricating oils, sludge and/or acid are formed, depending upon the nature of the attacked molecule.

Stored parts are susceptible to static degradation from corrosion, fretting, and oxidation. Installing degraded parts can lead to early-life equipment failures.

Because static degradation can be difficult to identify and assess, it’s a major challenge for plant personnel. Unlike dynamic-failure mechanisms that reveal themselves in various ways, including vibration, noise, heat, and wear particles, static-degradation mechanisms are silent killers. So, we must take extra care to store parts in clean, dry, cool areas and, in turn, avoid installing problems on our machines. We also must be proactive in storeroom-management practices and ensure that we have required parts when we need them. (One of my upcoming e-newsletter articles will address best practices.)

It’s also imperative to employ a range of metrics to see how we’re doing. Consider these:

• percentage of planned jobs with complete and accurate parts kits

• percentage of planned jobs requiring expedited parts

• percentage of inventory value that’s obsolete or visibly unsuitable for use.

• percentage of repair jobs that require follow-up action within X days after repair (30 days is a reasonable timeframe)

• annual inventory turns (two each year is a good goal)

• inventory value as a percentage of replacement asset value (RAV).

Keep in mind that reliable maintenance and repairs depend on the harmonious union of qualified craftspeople equipped with the right tools, parts, and plans. Don’t let the controllable elements of parts quality and condition be your site’s Achilles heel. EP

Based in Tulsa, OK, industry veteran Drew Troyer is principal with Sigma Reliability Solutions. Email Drew.Troyer@sigma-reliability.com.

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