A comparison of induction heating and ceramic pads for localised post-weld heat treatment of friction taper hydro-pillar welds in thick-walled steam pipe

Abstract

The WeldCore® friction taper hydro-pillar (FTHP) welding platform provides integrated coring of 8 mm diameter creep condition monitoring specimens and automated welding of the hole in thick-walled steam pipe. The FTHP welds should be restored as closely as possible to their original material condition, and are therefore given a post-weld heat treatment (PWHT) that is usually done using flexible ceramic heating pads wrapped around the pipe. However, it may often be more desirable to perform localised induction heating using a ‘pancake style’ coil placed only directly at the weld location. This approach to localised induction heating is not a qualified procedure for thick-walled pipe and there is a scarcity of published literature on this topic. Hence this paper compares flexible ceramic pads and induction techniques for PWHT of FTHP welds in A106 Gr B pipe, 406 mm in diameter and with 20.4 mm wall thickness. The comparison considers metallography, microhardness, tensile and U-bend tests and concludes that both techniques are equally good in PWHT.