Dr. Krishnan Sivaraman

Abhishek Singh

Abstract

L&T Heavy Engineering is amongst very few global manufacturers licensed to manufacture critical high pressure equipment like Urea reactors, Urea strippers, Carbamate Condensers & Carbamate Separators for urea service under various Process licensors. Inside surface of these vessels are lined with liner materials to prevent direct contact of corrosive hydrocarbon fluid with substrate base metal. The most commonly used liner materials for such application are urea grade SA240 TP310 MoLN & SA240 TP316 L-UG etc. Thickness of these liner materials varies between 5 to 8 mm depending upon the operating conditions. Out of these equipment Urea Rector involves huge amount of liner welding of the order of ~150-200 kg per equipment. Major part of this weld deposition is attributed to liner circumferential & longitudinal seams. Hitherto, this liner welding is carried out by manual Gas Tungsten Arc Welding (GTAW) process which fairs very low in productivity & thus higher cycle time. To meet stringent corrosion properties liner welding calls for clean & slag free welding process along with dust free atmosphere, hence GTAW process is best suited for this application. However, in order to improve productivity & to reduce cycle time, we took up the challenge of exploring variants of GTAW which will yield higher productivity while at the same time comply with stringent quality requirements. Thus the idea of implementing semi-automatic GTAW welding was conceived which is expected to improve productivity drastically for such liner longitudinal & circumferential seam welding. The paper captures the challenges faced during trial & development of semi-automatic GTAW and its implementation for the first time in Urea reactor

Keywords- Semi-Automatic GTAW, Liner welding, Urea Reactor