Inconel 600 is a type of nickel-based alloy commonly used in applications involving high temperatures and corrosive environments, such as reactors in the chemical industry. Welding of Inconel 600 chloride reactors typically requires adherence to specific welding precautions to ensure welding quality and component performance. Here are some general guidelines that may apply to the welding of Inconel 600 chloride reactors:
- Welding Methods: The welding of nickel-based alloys commonly employs shielded metal arc welding (SMAW) and tungsten inert gas (TIG) welding. TIG welding provides stable welding quality, good weld bead formation, and minimal spatter and slag.
- Groove Shape: For a shell thickness of 18mm, an X-shaped groove is used. The molten metal flowability in nickel-based alloy welding is poor, resulting in shallow penetration. Increasing welding current does not improve flowability or penetration depth. To ensure full penetration and prevent incomplete fusion at the groove edges, a larger groove angle and smaller root gap are necessary. A larger groove angle is beneficial for welder’s operation, preventing incomplete fusion at the groove edges, and reducing stress during metal solidification to prevent crystalline cracks. It’s best to use a planing machine for groove preparation; if plasma is used, the contaminated surface must be ground without causing overheating.
- Pre-Weld Cleaning and Welding Protection: To achieve high-quality weld joints in nickel-based alloy welding, two important conditions must be met: First, both the base material surface and welding wire surface must be clean to prevent contaminants from melting into the weld seam; second, effective protection using argon gas is crucial to shield the high-temperature molten pool and welding zone from oxidation. Contaminants refer to substances containing S, P, Si, and other low-melting-point materials. S, P, Si can form low-melting eutectics with nickel, causing weld metal embrittlement and crystalline cracks. Oxide films with higher melting points on the base material surface can lead to slag inclusion in the weld metal and even hinder the normal welding process. Grease on the base material surface can be removed using acetone, while dense and firm oxide films should be ground away using a stainless steel wire brush. The simplest cleaning process involves grinding the groove and the adjacent 25mm area to remove oxide films, followed by acetone cleaning to eliminate oil and dust. During welding, the molten pool and the hot end of the welding wire should always be protected by argon gas shielding. Welds with temperatures above 300°C also require a trailing shield. For multi-pass welding, each layer must be protected, and protection effectiveness can be judged by the color of the weld bead surface, with silver-white being optimal. The argon gas circuit should be regularly checked to ensure pure and dry shielding gas, especially for long-unused trailing shields, which should be dried before use.
- Welding Process Parameters: During welding, strict control of welding line energy is necessary, achieved by reducing welding current or increasing welding speed. Small current welding is preferred due to the poor thermal conductivity of nickel-based alloys. High currents can cause overheating of the weld and heat-affected zone, resulting in coarse grains and increased susceptibility to heat cracks. Moreover, high currents can cause the evaporation of deoxidizing agents Ti, Mn, Nb from the weld metal, leading to porosity and a decrease in joint mechanical properties and corrosion resistance. For TIG welding, the line energy should not exceed 15 kJ/cm, and the interlayer temperature should not exceed 150°C. Due to the low content of impurity elements such as S, P, Si in the base material and welding materials, proper pre-weld cleaning and control of welding process parameters can prevent the occurrence of defects such as excessive porosity and cracks during actual welding.
- Considerations During Welding:
- 5.1 Arc initiation should be within the groove or on the tack plate. In multi-pass welding, the juncture of adjacent layers should be staggered.
- 5.2 The root pass should have a certain thickness, and welding parameters should be adjusted appropriately to achieve a raised cross-sectional weld bead, reducing constraint. Otherwise, crystalline cracks can occur. Similar raised cross-sectional weld beads should be achieved for other layers, in contrast to the flat or concave cross-sectional weld beads common in welding of ordinary low-alloy steels or stainless steels.
- 5.3 Welds in contact with corrosive media should ideally be the final welds, reducing the number of times the weld is subjected to heat and enhancing corrosion resistance.
- 5.4 Remove surface oxidation colors from welds and the heat-affected zone while still hot.