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The quantity and frequency of non-destructive testing (NDT) across the life cycle of a missile inventory must be carefully considered. This paper provides a process for optimizing the quantity of missiles subject to NDT across the life of the missile inventory. This process ensures that the program does not exceed the minimum test quantity necessary to ensure that the inventory continues to meet the user's reliability requirement based on the predicted failure probability and annual test quantity. The methodology takes into account the age distribution of the inventory, tested/untested populations, removal of failing hardware, and items with multiple tests through the system life. The analysis also provides an estimate of the minimum and maximum test time that missiles will be exposed to across the projected life of the inventory. The paper provides an example of the process as applied to a representative Army missile system. This example demonstrates the practicality and simplicity of the process. The affect of varying levels of NDT on the inventory reliability is readily apparent in graphical form that facilitates the Reliability Engineer in presenting options to the Program Manager for making sustainment decisions. Overall, the U.S. Army Stockpile Reliability Program (SRP) has repeatedly demonstrated successes in identifying trends, ensuring readiness, and justifying missile shelf life extensions. However, under the current era of decreasing defense budgets, and expectations to push the life of existing missile systems out without replacement, NDT costs should be minimized while simultaneously minimizing the wear of those tests on the inventory. The approach outlined in this paper can be used to accomplish this on either the existing NDT program for a fielded system, or by the Program Manager developing a SRP program plan for a new missile system. |
