Measurement of Creep Deformation in Stainless Steel Welded Joints

Abstract

This article reports early findings of an experimental programme aimed at determining local creep properties of welded joints made from AISI Type 316H austenitic stainless steel. For this purpose, 3 mm thick, flat cross-weld specimens were cut from a pipe and subjected to creep testing at 550°C. In order to determine local creep properties around the weld within the gauge section of the specimens, a full field measurement system based on digital image correlation (DIC) technique has been developed. A purpose built furnace with an optical window was used to allow the gauge section of the specimens to be photographed during testing. The influence of the window opening on the temperature distribution inside the furnace was tested using five thermocouples embedded into a dummy specimen. A digital SLR camera with a 200 mm macro lens and an optical fibre illumination was used to acquire the photos. The gauge section of the specimens was sprayed with a high temperature resistant paint to obtain a speckle pattern, which is required by the DIC. The problems associated with the use of DIC at high temperatures, e.g. image distortion due to convective currents, surface oxidation, etc., and the techniques to overcome these are also discussed in the article. Full field displacement measurements allowed the local creep strain in the weld metal, HAZ and the parent material to be determined