Design procedures for production tubing strings are conceptually similar to other structural designs; a combination of safety factors and other implicit conservatism are used to assure the safety of a design. Because design procedures for tubing strings have been developed over a long period of time, it is not obvious that these procedures would lead to consistent reliabilities for various modes of failure in a string, e.g., triaxial failure, tubing collapse, or tension failure. In this paper, probabilities of failure for joints in an example (steel) tubing String design are calculated and compared. In these calculations, the loading conditions are assumed to be known. The conditional probabilities of failure can vary widely depending on the location of a joint in the string and its controlling mechanism of failure. The calculated reliabilities are also compared to the case where the string is designed with Corrosion Resistant Alloy joints. The results of such studies can be used to develop reliability- based design criteria for tubing strings.

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