Some Experiences in the Creep Testing of Piping Elbows

Abstract

Although the analysis of high temperature piping systems subject to creep is fairly well established basic experimental information on the behaviour of real piping systems at high temperature is lacking. The majority of creep tests conducted on piping components have been concerned with specific geometries relevant to particular applications. The aim of the series of tests undertaken at the University of Strathclyde has been to examine a range of geometries which would arguably be more useful in benchmark applications and design studies. To this end two test programmes were initiated providing seventeen piping elbow assemblies each consisting of a straight—bend—straight configuration. For each the nominal tube diameter was chosen to be 152 mm (6 in) with a nominal bend radius of 229 mm (9 in) attached in two tangent straights of an equal length of 610 mm (24 in). Two different wall thicknesses were selected, 71mm (0–28 in) and 3–6 mm (0–14 in) and three different bend angles, 45°, 90° and 180° (the overall geometries are shown in Fig. 1). The pipe material was Type 316 stainless steel with a nominal test temperature of 570°C. The loadings were either in-plane bending (opening or closing) or out-of-plane bending, or indeed some combination, in forward creep or under relaxation conditions.