Effect of tempered bead techniques on maximum HAZ hardness for in service pipeline welding

摘要

This research intends to investigate the main factors of tempered bead techniques affecting on maximum HAZ hardness for in-service pipeline welding. Tempering parameters to be considered are the overlap ratio, weld bead sequences, and subsequent welding processes. This research consists of two parts of experimental procedure. Firstly, critical HAZ hardness (< 350 HV) in the first weld bead was estimated using computational simulation. Secondly, welding experiments were conducted with tempered techniques. Experimental setup included the used material of API 5L Gr. B pipe steel with nominal size of DN 200, wall thickness of 8.18 mm, and water piping How of 18.77 m~(3)/hr. As a results, it suggested that the overlap weld ratio of 50h and 75%, weld bead sequences, as well as subsequent SMAW processes, were proficient of reducing significantly maximum HAZ hardness at the weld root. Nevertheless, in the case that the weld root was built up, maximum HAZ hardness was slightly changed with different weld bead sequences.