Experimental Analysis of Multipass GTAW Techniques for Tube-to-Tubesheet Welding in Heat Exchangers

The efficiency, quality, and reliability of shell and tube heat exchangers are significantly influenced by the design and execution of tube-to-tubesheet (TTS) welding. The key factor includes the selection of materials, welding process, and accuracy of dimensional specifications. There are three commonly used TTS joint designs such as the expanded joint (no welding), seal-welded joint (single pass welding with or without expansion), and strength-welded joint (two pass welding followed by expansion) as per the American Society of Mechanical Engineers (ASME) Section VIII Div. 1 UW-20. An extensive literature review revealed a strong reliance on various welding processes but the designs were limited to traditional joint configurations. In the proposed study, an attempt was made to investigate TTS welding using the gas tungsten arc welding (GTAW) process with a three pass or three layer technique following the inspection standard (ASME Section IX QW 193). Experimental investigations were conducted on a 50 mm thickness carbon steel tubesheet (SA 516 Gr. 70 N) and 19.05 mm outside diameter (OD) with 2.11 mm thickness of carbon steel tubes (SA 179) using a GTAW welding machine for ten samples. The quality of the TTS joint was assessed through various inspection techniques in accordance with ASME Section IX QW 193.1-191.3, encompassing visual inspection, liquid penetrant testing, and macroscopic examination to identify the minimum leak path (MLP). The experimental findings demonstrated that the three pass GTAW technique significantly enhances the quality and reliability and also extends the life of TTS welds in heat exchangers due to better MLP.