reliability engineering

A density figure-of-merit metric often referred to as the average or expected value. In the simplest form it appears as arithmetic S(time)/S(events) or in complicated situations as a statistic metric. It applies to mean life (ML), mean down time (MDT), mean maintenance time (MMT), mean time between failures (MTBF for repairable items), mean time to failures (MTTF for replacement items), mean time between maintenance (MTBM), mean time between maintenance scheduled (MTBMs), mean maintenance time unscheduled (MMTu), mean maintenance time scheduled (MMTs), mean time between overhauls (MTBO), mean time between unscheduled removals(MTBRu), mean time to restore (MTR), mean time between downing events (MTBDE), and so forth. The units will be time/metric, e.g., hours/failure. The reciprocal of the metric provides an incident rate, e.g., failures/hour.

Specific questions to ask the design engineers during a review specifically for reliability using failure data from operations and maintenance are: 1) show the calculated availability for the system based on a RAM model, 2) show the calculated number of failures during the specified mission time between turnarounds based on a reliability and maintainability (RAM) model, 3) show details of FEMA studies, 4) show details of FTA calculations, 5) show the calculated mean times between downing events, 6) show the calculated the mean time between cutbacks from full production capability and losses thus incurred, 7) show the QFD matrix and details, and 8) show the calculated cost of unreliability.

A tactical job for rapidly repairing equipment to operable conditions by studying operating and repair manuals. Acquires failure data and prepares maintenance plans of restoring equipment to operable condition in a minimum amount of time. Prepares general diagrams, charts, drawings, and spare parts requirements for maintenance planners. Makes recommendations for improving the repair cycle. Provides manning level forecast for supervisors and estimates the duration of outages. Determines the cost advantages of alternatives for developing action plans to comply with internal/external customer demands for timely repairs of processes/equipment. The purpose of these activities is to restore equipment to service in a timely manner.

Management communicates with their staffs through important policy statements. Management policies are general and relate to procedures and rules which are specific for implementing policies. Written statements of policy regarding reliability are decisive documents about avoid system failures in the same way as safety policies address the need for absence of human injuries, quality policies address the need for absence of product discrepancies, environmental policies address the need for avoiding spills and releases. Management needs to also say by a policy statement a reliability policy which may read like this: We will build an economical and failure free process which will operate for 5 years between planned outages. This statement will clearly communicate that failures to the process (which is the money machine) are to be abhorred and avoided!

Events/incidents are single events or occurrences that happen, especially one that is particularly significant, that results in a failure from a non-aging mechanism for reliability purposes.

Highly accelerated life test (HALT) is an offspring of older environmental stress screening (ESS) tests and it is a testing process for ruggedization of pre-production products by heavily stressing the product to identify failure modes quickly and to verify weak links in the system.

Weibull analysis is the tool of choice for most reliability engineers when they consider what to do with age-to-failure data.

If you've got one piece of failure data and nothing else, you're a poor person without much hope.

The probability of survival and of failure of components or equipment is under the condition of chance failure which means a constant instantaneous failure rate where the die-off rate is the same for any surviving (unfailed) population.

The potential or actual probability of a system to perform a mission for a given level of performance under specified operating conditions defined as the product of reliability*availability*maintainability*capability. Many variants of the effectiveness equation exist, e.g., OEE, and others.

The critical items list is a top level summary of problems/cost used for discussions with management about key reliability issues. The summary list converts technical details to a summary of costs and time while placing the issues into a Pareto distribution explained in terms of money and the vital few problems to be solved for competitive reasons.

A fundamental frequency distribution that produces a symmetrical bell-shaped diagram based on the Gaussian distribution to form a normal law of errors.