1970-02-01

Methodology to Define, Monitor and Control Life-Limited Components During Storage 700604

This paper summarizes the multiplicity of technical methods employed by industry and government agencies to define, monitor and control life-limited aerospace components during storage. Recommendations are made concerning these methods that will assist the reader in the selection of the methodology to meet his particular program requirements. A life-limited component is one whose reliability or performance will deteriorate below acceptable limits due to either calendar aging or to usage before its service life is completed.
With the stretch-out of many aerospace programs, the lives of many components may be approached or exceeded during the extended storage periods. Means must be found to extend and recertify the lives of affected components to prevent costly replacement programs. The methods described are discussed relative to components/systems in storage. However, these same methods can also be utilized either to insure that a new design will meet life requirements or to monitor and control life-limited components in service. Application of these methods to other than storage is discussed.
The paper describes seven methods that can be employed to determine, confirm, and/or extend/recertify component lives. These methods include testing, surveillance, inspection, refurbishment, analysis, similarity, and waiver. Case histories are employed to illustrate the use of the methods. In addition, the management controls to monitor and control life-limited components are briefly discussed. A tabulation of the life limits applied to identical or similar components/systems by various organizations is presented to allow the reader to compare some of his estimated component lives with the estimates of others.
The information contained in this paper is from a study of programs for evaluation of component life conducted by the Martin Marietta Corporation for NASA-MSFC. Over 130 pertinent documents were reviewed and studied. Forty organizations were visited to obtain component life data.

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