PRCI Report 215

L51744e

Battelle Memorial Institute

Need: Fittings (elbows, tees, caps, and reducers) are the most common components used in pipelines that are typically furnished in a heat-treated condition, such as normalized, normalized and tempered, or quenched and tempered. Recent industry experience has shown that heat-treated pipeline components, particularly high yield strength fittings, have been produced using different manufacturing processes, various starting materials, and several methods of testing the finished products. In addition, serious questions have been raised concerning the quality assurance/quality control methods employed recently.

Result: The objective of this study was to establish guidelines that could be used to predict the properties of heat-treated fittings. Such guidelines then could be used to aid in the selection of steel compositions that would result in the required minimum strength properties of heat-treated fittings produced in accordance with the requirements of MSS SP-75, Specification for High Test Wrought Butt Welding Fittings. A second use of those guidelines would be to estimate the properties of a fitting based upon hardness measurements and the composition of the steel.
A review of the steels that have been used to produce heat-treated fittings, revealed that, because those steels possessed insufficient hardenability, their properties could not be calculated based upon established metallurgical relationships developed for through hardening steels. Consequently, attempts were made to establish empirical correlations between the strengths of heat-treated fittings and their chemical compositions based upon test reports obtained from actual fittings. Information from 54 test reports were reviewed in support of these attempts.

Benefit: The approach taken to satisfy this objective involved two tasks. Task 1 was to determine the pressure capacity requirements for fittings as a function of the pressure capability of the matching pipe. Task 2 consisted of defining the chemical composition requirements, heat treatment procedures, and mechanical properties required to achieve the pressure capacity of the heat-treated fittings.