An Overview Of Reliability Engineering Principles

Reliability is the probability of equipment or processes to function without failure when operated correctly for a given interval of time under stated conditions. Equipment and processes failures waste money on unreliability problems. The business issue of reliability is control of failures to reduce costs and improve operations by enhancing business performance with affordable levels of reliability. Reliability numbers by themselves lack motivation for improvements. However, converting unreliability into monetary values, causes numbers to spring to life and guides actions for making cost effective changes, by using actual plant data for costs and failures. Reliability engineering tools are discussed which assist plant improvement programs for reducing the high cost of unreliability. Reliability Definitions Reliability has many definitions. For things that cannot be repaired: Reliability is the duration or probability of failure-free performance under stated conditions. For things that can be repaired: Reliability is the probability that an item can perform its intended function for a specified interval under stated conditions. For those who wish simplicity, a single word definition is: dependability. The Motivation For Improving Reliability Enhancing reliability satisfies customers with on-time delivery of products through increased production equipment reliability and reduced warranty problems from products that fail early. Higher reliability reduces the cost for equipment failures that decrease production and limit gross profits from plants operating at maximum capacity as with commodity products and high demand proprietary products. Boosting reliability improves business performance. The clear reason for improving reliability is spelled with one word: money. We speak of reliability, but we measure failures. Failures demonstrate evidence of lack of reliability. Reliability problems are failures, and failures cost money in an economic enterprise. Failures in most continuous process industries are measured in downtime for the process. Similarly, cutbacks in output are also failures to achieve the desired economic results from the process or equipment. Most people comprehend loss of reliability from equipment downtime. Fewer people can define when a cutback in output grows into a demonstrated failure. Definition of failure, which leads to a need for reliability improvements, is a vital: failures galvanize organizations into action for making improvements. Funding for reliability improvements must come from the cost of unreliability. At the heart of reliability improvements is the need to find affordable business solutions. Good reliability engineering work for business is the never ending search for affordable improvements resulting in larger profits by cleverly solving nagging problems. Good reliability engineering is not the search for perfection but rather a search for effective business solutions to failure problems. Reliability numbers (a value between zero and one) lack a motivation for making business improvements. However, reliability numbers spring to life when converted into monetary values expressing the cost of unreliability. Annualizing losses by means of the cost of unreliability immediately identifies for everyone the amount of money that can be spent to correct reliability problems. Clever solutions minimizing expenditures for corrections is the basis for hero awards in industry. Throwing money at reliability problems in the form of hardware and software may satisfy the angst, but does little for solving root cause(s) of problems/losses for the business enterprise. Reliability requirements for businesses change because of competitive conditions and business risks. Reliability values are not fixed and immutable, but change with business conditions. Different business conditions require use of different reliability engineering tools for solving business problems. You don’t need the best reliability in the world for your business—you just need an improvement over your fiercest competitor so your business is the low cost provider. Motivations for reliability improvements are driven by the cost of unreliability and how unreliability affects the bottom line for the business. Reliability As An Art And Science The world became more complicated in the late 1920s and early 1930s as telephones and electron vacuum tubes grew in demand. Higher demands for these new products required making them more economically and improving their reliability. These two new technologies spurred early reliability studies. During World War II, airborne radios delivered into remote theaters of war had appalling reliability. Only ~17% of them worked upon arrival into the battle zone. War efforts also produced a new weapon of terror--the V-1 rocket. The V-1 rocket had a demonstrated reliability of 1 success out of 11 attempts for a calculated reliability of 9.1%.—this was a great result for frontier technology but a terrible success rate considering the consumption of limited resources. Robert Lussor, an electrical engineer, is generally acknowledged as the individual who first quantified reliability studies of V-1