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Welding: Since Hastelloy and austenitic stainless steel have similar weldability, welding can be carried out without special skills once the properties of Hastelloy are understood. Furthermore, it has the same possibilities as welding with dissimilar metals, just like austenitic stainless steel. 1 For welding methods, inert gas arc welding processes such as TIG welding, MIG welding, and plasma welding are more suitable; manual arc welding or electron beam welding can also be used. It cannot be used for gas welding because carburization and oxidation occur. SMAW should also be avoided as it results in a large heat-affected zone. 2 The welding rod to be used should be of the same material as the base metal. The specifications of the welding rods are shown in Table 6. When welding dissimilar metals. Welding rods usually use the same material as that on the Hastelloy side. It is specifically determined based on the welding procedure qualification tests. 3 Pre-welding preparations 1) Before welding, it is necessary to check the misalignment of the plates as well as the type of groove. 2) Whether it is tack welding or actual welding, acetone should be used to remove oils, dirt, and other contaminants from the surface of the base metal at the groove and in its vicinity. 3) The welding rod also needs to be cleaned before welding. 4) In principle, groove preparation is carried out by mechanical methods; when using plasma cutting, a grinding wheel is required to remove the oxide scale or heat-affected zone. The heat-affected zone must be cut away by more than 3 mm. 5) Compared to austenitic stainless steel, the fluidity of molten metal is poorer; therefore, the groove opening should be larger. Table 6 Welding materials for Hastelloy Materials Welding rod name ASME AWS JIS B-2 B-2 SFA-5.14 ER NiMo-7A-5.14 ER NiMo-7 Z3334 Y NiMo-7 BBSFA-5.14 ER NiMo-1A-5.14 ER NiMo-1 Z3334 Y NiMo-1 C-276 C-276 SFA-5.14 ER NiCrMo-4A-5.14 ER NiCrMo-4 Z3334 Y NiCrMo-4 C-22 C-22 SFA-5.14 ER NiCrMo-10A-5.14 ER NiCrMo-10 C-4 C-4 SFA-5.14 ER NiCrMo-7A-5.14 ER NiCrMo-7 GGSFA-5.14 ER NiCrMo-1A-5.14 ER NiCrMo-1 Z3334 Y NiMo-7 G-3 G-3 SFA-5.14 ER NiCrMo-9A-5.14 ER NiCrMo-9 G-30 G-30 SFA-5.14 ER NiCrMo-11A-5.14 ER NiCrMo-11 4 Welding procedures 1) Care should be taken during tack welding just as it is done during actual welding. It is necessary to completely remove adhering substances such as scale and harmful defects generated during tack welding. 2) If backside protection with an inert gas is not provided, the weld on the reverse side will be severely oxidized, resulting in poor weld formation. Use a back protection tool depending on the shape of the base material. 3) Flat welding should be preferred for the welding position. If flat welding proves difficult, vertical or overhead welding can be used; bottom welding should be avoided. 4) Preheating is not required; the temperature between layers should be kept below 150°C as much as possible. On each layer, oxidation scales and the like should be removed using a stainless steel brush or a soft grinding wheel. 5) To control the welding heat, the welding rod should not swing back and forth during movement; it should move in a straight line as much as possible. 6) Due to the possibility of high-temperature solidification cracking, attention should be paid to crater treatment. Representative welding condition examples are shown in Table 7. Table 7 Welding processes for Hastelloy Welding method: TIG welding Welding position: Flat welding Ar flow rate (welding torch): 10–15 l/min (back side); 5–10 l/min Current/polarity: DC/positive polarity Welder qualification: JIS TN-FVH Diameter of tungsten electrode: 2.4–3.2 mm Interpass temperature: Below 150°C Diameter of welding rod, current (A), and thickness of base metal plate (mm): 1.6 – 50: 1.6–3.0; 2.4 – 80: 3.0–6.0; 3.2 – 100: 6.0–12.0 Post-weld heat treatment: Except for Hastelloy B and C, other Hastelloys can be used in their welded state, unless special circumstances apply. Solid solution treatment is used for post-weld heat treatment. 6 The inspection of welds involves the assessment of welder qualifications and welding procedure qualification, with the test results recorded in WQR and PQR. Although welds can be inspected in the same way as with stainless steel, penetrant testing and radiographic testing can be used as non-destructive testing methods, whereas magnetic particle testing or ultrasonic testing cannot be used.