TABLE OF CONTENTS Realistic reliability, maintainability and safety (RAMS) objectives need to be set with due regard to the customer's design and operating requirements and cost constraints. In the case of contract development or plant engineering, these are likely to be outlined in a tender document or a requirements specification. Some discussion and joint study with the customer may be required to establish economic reliability values which sensibly meet his or her requirements and are achievable within the proposed technology at the costs allowed for. Over-specifying the requirement may delay the project when tests eventually show that objectives cannot be met and it is realized that budgets will be exceeded. It is not uncommon for safety targets to be overstated due to ill-informed targetting methods. Chapter 22 will address this problem.
When specifying an MTBF it is a common mistake to state a confidence level; in fact the MTBF requirement stands alone. The addition of a confidence level implies a statistical demonstration and supposes that the MTBF would be established by a single demonstration at the stated confidence. On the contrary, a design objective is a target and must be stated without statistical limitations.
Vague statements such as high reliability and the highest quality should be avoided at all costs. They are totally subjective and cannot be measured. Therefore they cannot be demonstrated or proved.
Consideration of the equipment type and the use to which it is put will influence the parameters chosen. Remember the advice given in...
