L51758 Non-Destructive Assurance of Quality of Heat-Treated Fittings

Sometimes heat treated components fail to pass the specified minimum mechanical requirements (yield strength, Charpy V-notch toughness). The influence of the complete heat cycle on the end results is not well understood and without a N.D.T. method for determining these properties the pipeline companies have difficulty in determining acceptable and non-acceptable individual components. In the quality control process for heat treated components, it is important to have a non-destructive testing technique available for predicting the yield strength and, if necessary, Charpy V-notch properties. In order to quantify the influence of the thermal cycle on the essential mechanical properties of plate material FeE355 and evaluate a promising N.D.T method for predicting yield strength and toughness, five heats of plate material FeE355 received ten different normalizing heat treatments (combinations of three different austenitizing temperatures and 4 heating/cooling rates). The heat treatment conditions were chosen to obtain a wide range of ferrite grain sizes/yield strengths. Together with the as-delivered conditions 55 conditions of plate material FeE355 were examined. Theexamination included:- Ferrite grain size measurements directly on the outer surface of the material (after removal of the decarburized zone) by means of replicas.- Tensile tests at 20°C, in twofold for all 55 conditions.- Charpy V impact tests at three temperatures, each in threefold for all 55 conditions.- Ferrite grain size measurements on cross sections of one of the threaded ends of all 110 tensile specimens.