Practical Reliability Engineering, 5th Edition

6

Reliability Prediction and Modelling

6.1 Introduction

An accurate prediction of the reliability of a new product, before it is manufactured or marketed, is obviously highly desirable. Depending upon the product and its market, advance knowledge of reliability would allow accurate forecasts to be made of support costs, spares requirements, warranty costs, marketability, and so on. However, a reliability prediction can rarely be made with high accuracy or confidence. Nevertheless, even a tentative estimate can provide a basis for forecasting of dependent factors such as life cycle costs. Reliability prediction can also be valuable as part of the study and design processes, for comparing options and for highlighting critical reliability features of designs.

If a new engineered system is being planned, which will supersede an existing system, and the reliability of the existing system is known, then its reliability could reasonably be used as a starting point for predicting the likely reliability of the new system. However, the changes that will be introduced in the new system will be likely to affect its reliability: for example, more functions might be controlled through software, novel subsystems or components might be included, and so on. Some of these changes could enhance reliability, others might introduce new risks. There will also be programme and management aspects that would influence reliability, such as commitment and resources applied to achievement of quality and reliability ...