Proper design and fabrication, heat treatment and inspection practices play a vital role in achieving good quality and performance of low alloy steel piping. These materials have narrower fabrication windows as the alloy content goes up and non-adherence to correct execution practices may lead to leakage by delayed hydrogen cracking, stress corrosion cracking or fatigue resulting in unplanned shutdowns and costly repairs.
This paper describes details about strengths and weaknesses of support design and fabrication practices for such attachment welds. The paper discusses various precautions to be taken during the design and fabrication stages for low alloy steel supports attachment welds. It will discuss heat treatment cycles viz. preheat, interpass, dehydrogenation treatment (post heating) and post weld heat treatment (PWHT). The control of consumables, welding environment conditions, and the weld heating cycle is essential to prevent hydrogen assisted cold cracking in high hardness microstructures in weld and HAZ, and for achieving successful relief of residual welding stresses.