RAM Analysis of a Moderate Sized Chemical Plant

Recently, there was a request for a "reliability analysis" of a moderate sized chemical plant. The situation was one in which the plant was in a "sold out" position and more product could be sold if it could be made.

Plant management viewed "reliability" as the primary barrier to increased production. During the initial discussions, plant representatives described elements of reliability, availability and maintainability as the issues they grouped under the single heading "reliability" where they had concerns. As a result, a comprehensive RAM (reliability, availability, maintainability) analysis was recommended.

The analysis found that there were some opportunities associated with "reliability" problems. A number of pieces of unspared plant equipment had marginal reliability that allowed random and not infrequent failures. When combined, the overall plant experienced frequent outages. Considering the amount of time needed to make repairs and bring the plant back on line and product on specification, these outages cost a significant amount of production.

Expert Analysis

Analysis of availability showed that a significant portion of down time resulted from scheduled outages for maintenance and internal inspection. Availability loss to scheduled outages is controlled by two factors.

The first factor(s) can be best described as "run-limiters". Run-limiters are systems or devices that determine how long a plant can operate without a shutdown. In some cases, maximum run-length is determined by regulatory limits (e.g. annual boiler inspections). In other situations, the wear and tear on a single component sets the run-length. In these cases, steps can be taken to make the run-limiting device more robust to allow longer runs between outages.

The second factor that controls availability loss due to scheduled outages is the "duration-setter(s)" or the system of device that determines how long the outage will last. Here a variety of approaches are available for reducing the critical path duration of the outage, But one must always be sensitive to the fact that there are frequently a number of near-critical work paths and to make sure that all competing paths have been addressed.

Finally, maintainability is an area that frequently escapes review but often provides an opportunity for improvement. Maintainability is defined as a measure of the ability to restore inherent reliability in a ratable period of time. While dedicated craftsmen frequently work until their product is reliable, their work plan is frequently not ratable (meaning that the work cannot be completed in a specified period). It is possible to make all work ratable by moving uncontrollable tasks outside the outage period. In one example, you replace the complete system during the outage and rebuild the removed system at your leisure once the outage is over.

Selectively addressing the least costly opportunities in each area can significantly increase unit output with a small investment by :

• Improving reliability by upgrading marginal equipment or adding redundancy.
• Lengthening run-length by making "run-limiters" more robust and by addressing "duration setters".
• Improving maintainability by making all tasks ratable so they can be completed on a known schedule.

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