Experimental Analysis of Multi-Pass 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-tube sheet (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 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 tube sheet (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 10 samples. The TTS joint quality was evaluated using multiple inspection methods as per ASME Section IX QW 193.1-191.3 including visual inspection, liquid penetrant testing and macroscopic examination. The experimental findings demonstrated that the three-pass GTAW technique significantly enhance the quality and reliability also extend the life of TTS welds in heat exchangers due to better MLP.