DIFFUSIBLE HYDROGEN CONTENT IN SUBMERGED ARC WELDING (SAW) - A NEW METHOD FOR HYDROGEN DETERMINATION

摘要

A knowledge of safe weld metal hydrogen levels compared with actual levels checked in welds are very important for heavy industries. The need of post-weld de-hydrogenation heat treatment and the minimum preheat and interpass temperature requirements to avoid cold cracking of weld metals have to be reasonably well established. Tests have been carried out to check hydrogen content in SAW of 2,25Cr 1Mo heavy section Steel coupons. A new electrochemical method has been employed; this method is a very fast one (10-20 min. for every test). Measures of diffusible hydrogen according to AWS A4.3-86 have been carried out for comparison. Different preheat and interpass temperatures, two different weld metals and welding procedure specifications have been investigated. Hydrogen has been checked in 3 different conditions: a) As welded b)After De-hydrogenation Heat Treatment (DHT,350℃×4h) c) After Intermediate Stress Realiving (ISR, 620℃×1h) Measurements are compared with theoretical considerations: outgassing factor as a function of hydrogen diffusion coefficient and time of heat treatment are calculated and reported in this paper. Safe weld metal hydrogen levels have been checked by mechanical tests and a hydrogen induced cracking test (electrochemical method) has been carried out according to ASTM STP 962.