Reliability Tip:

Why do Random Failures Occur?

When machinery is designed, the design engineers use a set of assumptions about the service and loads that the machine will experience over its life. These loads will create stress on the components that make up the machine. Each component is then designed to have the appropriate “resistance” to this stress so that the machine will experience a long and happy life. However, when the stress on a machine component exceeds its resistance to stress, component damage and eventual failure will occur.

Unfortunately, in the real world, we often give the machine a “double whammy” – we do things to both increase the stress and decrease the resistance to stress.

Stress will be increased when:

• We operate the machine beyond its capabilities (e.g., operating two pumps when only one is required, causing a “dead head” condition)
• We subject it to excessive conditions (e.g., poor lubrication practices cause the bearings to wear prematurely, failing to clean the machine causes it to overheat)
• We use poor installation practices (improper alignment tolerances, insufficient foundation mass).

Resistance to stress will be decreased when:

• We fail to use precision methods during machine repair (not torqueing fasteners properly or in the correct sequence, or not ensuring fits and clearances are within tolerance)
• We use inferior materials during repair (used parts, cheaper foreign materials)
• We allow corrosion or erosion to occur, causing material loss

So, to have high reliability, we need to pay attention to the little things that will keep stress low and resistance to stress high.

Additional information here.

Additional information here.