International Research Journal of Engineering and Technology (IRJET)
e-ISSN: 2395-0056
Volume: 12 Issue: 08 | Aug 2025
p-ISSN: 2395-0072
www.irjet.net
Orbital Fillet Welding of SS321 Thin Tubes without Electrode Adaptor E Alluraiah1, R Thirupathi2, L Sree Vardhan3, 1Senior Research Fellow, Centre for Advanced Systems, DRDO, Hyderabad, India 2Technial Officer-A, Centre for Advanced Systems, DRDO, Hyderabad, India 3Scientist-F, Centre for Advanced Systems, DRDO, Hyderabad, India
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Abstract - Autogenous fillet welding of tube-in-tube of MIL
automated. The minimum dwell time that can still be controlled manually corresponds to arc welding (approximately 0.3 seconds). Heat sources more intense than arcs have shorter dwell times; therefore, they must be automated.
Grade SS321 stainless steel tubes with 4mm to 13mm internal diameter and 6mm to 16mm outer diameter, were joined using Orbitalum® OW 38S weld head and ORBIMAT 180 SW orbital welding machine, without electrode adaptor. Macrostructure and strength of the welded joints were investigated. Fillet welds with smooth contour and good penetration were achieved. The welded joints withstood required pneumatic pressure of 430 ksc and hydraulic pressure of 525 ksc. Welded joints yield strength and tensile strength were between 92% to100% of the base metal. Percentage of elongation achieved was 58% to 100% of the base metal.
Orbital welding is a technique whereby the welding tool is rotated through 360° around a static workpiece. Originally developed to solve the problem of operator error in Tungsten Inert Gas (TIG) welding [2,5], and allow for a uniform weld around pipes and tubes, which can be difficult to achieve with manual welding processes. The orbital welding process can create high quality repeatable welds with the use of a computer, meaning that there is little need for intervention from a welding operator. The process is used for two main applications; tube-to-tube / pipe-to-pipe joining and tube-to-tube sheet joining, with pulsed current [3].
Key Words: Orbital welding, fillet, NDT, stainless steel tube, strength.
1.INTRODUCTION
MIL Grade SS321 type tubes of different diameters and thickness are used for the manifold preparation required for defence applications. Only square butt weld joints are designed without beveling for the similar diameter tubes, keeping design criteria in view. For dissimilar diameter joints, threaded type lock-tight joints are designed. Tungsten electrode is fixed to the adaptor to weld orbital fillet joints. In this current study, dissimilar tube diameters, ID of bigger tube matching with OD of smaller tube are taken up to weld by orbital TIG welding process, without the adaptor and to evaluate the joint strength and its integrity. The combination of tubes is 4/6 mm (ID/OD), 6/8 mm, 8/10 mm, 10/12 mm, 9/12 mm and 13/16 mm. The critical parameters were optimized [6,7] by trial and error method, and welding was performed in 5G position, maintaining an overlap of 1mm, 2mm and 3mm, respectively in each type of ID/OD combination. To qualify the weld joint, radiographic inspection, macrostructure, hydraulic proof pressure testing, pneumatic proof pressure testing, and tensile properties [4] were evaluated and reported.
Welding in the aeronautics industry is experiencing exciting developments. The widespread application of computers and the improved knowledge and design of new materials are shaping the way welding is implemented and process and product are being designed. Welds are replacing rivets in a variety of components in both military and commercial airplanes, to improve both cost and structural integrity. Diffusion, laser, and electron-beam welding are preferred in commercial aircraft, while electron-beam welding is continually gaining ground for the joining of titanium alloys in military airplanes. In large commercial airplanes, laserbeam welds are poised to replace rivets in large parts of the fuselage. Some new processes developed for the space industry also show promise for the aeronautics industry. These include friction stir welding and variable polarity plasma arc welding, which are already being used for critical applications in rockets. The penetration is measured as the ratio of depth to width of the weld cross section increases dramatically with the intensity of the heat source. This makes the welding process more efficient and allows for higher welding speeds. more efficient process requires less heat input for the same joint, resulting in a stronger weld, as a smaller heat source moving at a faster speed also implies a much-reduced dwell time at any particular point. If the dwell time is too short, the process cannot be manually controlled and must be
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2. EXPERIMENTAL PLAN 2.1 Parent Material The parent material is MIL Grade SS321 tubes of different ID/OD. Tubes, each 150 mm in length were cut using special
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