NRC Equipment Failure Summaries
The NRC has some great reading on their website. In the library section they have 4 statistical studies on the failure results of various pieces of equipment over the past 20 years. They have looked at Pumps, Diesel Generators, Circuit Breakers, and Motor Operated Valves. For example, they have looked at pump failures from 1980-2000, listing the “proximate causes” and the “coupling factors” associated with these pump failures. You can see these reports for yourself here.
There is a lot of good data there (over 200 pages worth for the pumps), giving a statistical analysis of the contributing factors to these failures. Some statistics on the pump failures:
39% were due to Internal Component failures (includes dirt, lubrication, wear and tear), which they attribute to inadequate maintenance.
24% were Design problems (error in specs, incorrect calculations, mounting design).
20% were categorized as Human Error (incorrectly following procedures, poor procedures, inadequate training, accidental action).
These categories add up to 83%. And, after reading these, it is obvious that these are all human performance problems. The other 17% were attributed to Other (setpoint drift), External Environment, and Unknown. A high percentage of these are most likely also due to human error.
This drives home the point that very few equipment failures are due to the equipment just wearing out. Few pieces of gear make it to the end of life region on the Weibull curves, and even the random failures are not due to statistically calculated material failures, but due to the incorrect performance of people. The maintenance tech, operator, inspector, or designer almost always contributes to or intiates the failure.
The NRC does not list the root causes that they determined for these failures. However, a telling example of their conclusions can be seen on page 33 of the pump report, which blames one particular pump failure as being due to “operator inattention to detail.” I can almost read the corrective action for this: “Conduct training with all operators, emphasizing the importance of reading and following all written procedures.” In more common words, “Tell the operators to be more careful.”