CLADDING TECHNOLOGY SHANXI CO., LTDTIG Welding of Pure Nickel and Pure Nickel with Various Steels
Literature Overview
This 1993 study by Yu Lirong, published in the Welding journal and conducted at the Jiangsu Chemical Equipment Manufacturing and Installation Company, provides practical guidance on the TIG welding of pure nickel and dissimilar joints between pure nickel and various carbon and alloy steels. The study addresses a critical need in the chemical processing industry, where nickel-based alloys are extensively used for corrosion-resistant components in pressure vessels, heat exchangers, and piping systems.
Core Technical Points
Pure nickel (Ni) offers exceptional resistance to alkaline corrosion and is widely used in chemical processing equipment. However, welding pure nickel and nickel-steel dissimilar joints presents several challenges:
- High thermal conductivity of nickel, requiring higher heat input for penetration
- Susceptibility to hot cracking due to the low melting point of nickel-sulfide eutectics
- Dilution effects in dissimilar joints, which can compromise the corrosion resistance of the nickel side
- Thermal expansion mismatch between nickel and steels, leading to residual stresses and distortion
The study provides practical welding procedures for various nickel-steel combinations, including nickel-carbon steel, nickel-low alloy steel, and nickel-stainless steel joints.
Welding Parameters and Filler Metal Selection
| Base Metal Combination | Filler Metal | Welding Current (A) | Travel Speed (mm/min) | Shielding Gas |
|---|---|---|---|---|
| Pure Ni to Pure Ni | Ni-100 (ERNi-100) | 120–180 | 30–50 | Argon |
| Ni to Carbon Steel | Ni-82 (ERNi-82) | 150–220 | 25–40 | Argon |
| Ni to Low Alloy Steel | Ni-82 (ERNi-82) | 160–240 | 25–40 | Argon |
| Ni to Stainless Steel | Ni-625 (ERNi-625) | 140–200 | 30–50 | Argon |
The selection of filler metal is critical for achieving a sound weld with acceptable mechanical properties and corrosion resistance. Nickel-rich filler metals (such as ERNi-100 and ERNi-82) are recommended for nickel-steel joints to minimize dilution and maintain the corrosion resistance of the nickel side. The use of Ni-82, which contains approximately 82% nickel and 18% iron, provides a good balance between weldability and corrosion resistance for nickel-carbon steel joints.
Defect Analysis and Countermeasures
The study identifies several common defects in nickel-steel TIG welds and provides countermeasures:
- Hot cracking: caused by the low melting point of nickel-sulfide eutectics, mitigated by using low-sulfur filler metals and preheating the base metal
- Porosity: resulting from hydrogen pickup, prevented by using dry filler metals and adequate shielding gas coverage
- Lack of fusion: due to the high thermal conductivity of nickel, addressed by increasing current and reducing travel speed
- Cracking in the HAZ: caused by thermal expansion mismatch, reduced by using compatible filler metals and post-weld heat treatment
The study emphasizes the importance of preheating and interpass temperature control for nickel-steel joints. Preheating to 150–250°C reduces the cooling rate and minimizes the formation of brittle phases in the HAZ. The interpass temperature should be maintained below 250°C to prevent excessive grain growth and softening of the weld metal.
Relevance to Cladding and Pressure Vessel Applications
Pure nickel and nickel alloys are extensively used in the chemical processing industry for pressure vessels, heat exchangers, and piping systems that handle aggressive chemicals such as caustic soda, ammonia, and organic acids. The TIG welding techniques described in this study are directly applicable to the fabrication of nickel-clad pressure vessels and dissimilar material joints in chemical processing equipment.
For cladding applications, the study provides guidance on the selection of filler metals and welding parameters for achieving a sound bond between nickel and carbon steel base metals. The use of Ni-82 filler metal is particularly recommended for nickel-clad carbon steel pressure vessels, as it provides adequate corrosion resistance while maintaining good weldability.
Study Insights and Reflections
This practical study provides valuable guidance for engineers and welders involved in the fabrication of nickel-based components and dissimilar material joints. The emphasis on filler metal selection, preheating, and interpass temperature control highlights the importance of process parameters in achieving sound welds with acceptable mechanical properties and corrosion resistance.
The study also underscores the challenges of welding nickel with steels, particularly the susceptibility to hot cracking and the need for careful control of the welding environment. The practical recommendations provided in the study are directly applicable to the fabrication of pressure vessels and heat exchangers in the chemical processing industry.
This work contributes to the practical knowledge base for welding nickel-based alloys and dissimilar material joints, providing engineers with the information needed to design and fabricate reliable components for aggressive chemical environments.