Specialized Filler Metals in Heavy Industrial Weldings
March 26, 2024
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Specialized Filler Metals in Heavy Industrial Weldings

Welding exotic alloys — titanium, Inconel, Hastelloy, Monel, and super-duplex stainless steels — is not simply a matter of joining two pieces of metal together. It demands a precise understanding of metallurgy, material science, and the specific behaviour of each alloy under the heat of the welding arc. These materials are used in the most demanding industrial environments precisely because of their exceptional properties: extreme temperature resistance, corrosion resistance, or strength-to-weight ratio. Preserving those properties through the welding process requires careful filler metal selection, strict process controls, and an uncompromising approach to contamination.

This article covers the key exotic alloys encountered in heavy industrial welding, the specific challenges each presents, the correct filler metal approach, and the ESAB products available for each application. For a broader overview of filler metal selection across common structural materials, see our Welding Consumables Selection Guide.

What Are Exotic Alloys and Where Are They Used?

The term "exotic alloys" is used informally to describe materials that fall outside standard carbon and stainless steels — typically nickel-based superalloys, titanium alloys, and high-performance copper-nickel alloys. They appear in industries where conventional materials cannot meet the service requirements:

  • Aerospace and defence — gas turbine components, aircraft structural parts, missile housings, and military vehicles where high strength, low weight, and extreme temperature performance are required
  • Oil and gas — offshore structures, subsea pipework, valves, and process equipment in highly corrosive environments including sour service (H₂S) and chloride-bearing media
  • Chemical processing — reaction vessels, heat exchangers, distillation columns, and pipework handling aggressive acids and oxidising media
  • Power generation — boiler components, recovery boilers, and turbine parts subject to extreme temperatures and pressures
  • Marine engineering — seawater-resistant structures, propeller shafts, and desalination equipment
  • Medical and pharmaceutical — implants, surgical instruments, and process equipment where biocompatibility and corrosion resistance are paramount

Inconel and Nickel-Chromium-Molybdenum Alloys

Properties and applications

Inconel is a family of nickel-chromium superalloys (the most common being Alloy 625, UNS N06625) characterised by outstanding resistance to oxidation and corrosion at elevated temperatures — up to 980°C in some service conditions. When heated, Inconel forms a stable, thick oxide layer that resists further attack, making it the material of choice for gas turbine components, power boiler tubes, engine exhaust systems, aircraft ducting, and chemical processing equipment subject to extreme thermal and corrosive loading.

Welding challenges

The primary concern when welding nickel-chromium-molybdenum alloys is hot cracking and the formation of detrimental intermetallic phases at grain boundaries. The composition must be carefully controlled to avoid niobium segregation (in Alloy 625) and to maintain a fully austenitic, crack-resistant microstructure. Heat input must be controlled precisely — excessive heat input leads to grain growth and loss of corrosion resistance in the heat-affected zone (HAZ).

ESAB filler metal recommendations

ESAB's Exaton Ni60 (MIG/TIG) is suitable for joining nickel-chromium-molybdenum nickel alloys — including Alloy 625 (UNS N06625) — and for dissimilar joining of stainless steels to nickel alloys for high-temperature service. Applications include cryogenics, power generation, marine seawater applications, and chemical processing. For overlay welding on carbon and low-alloy steels in oil and gas applications, Exaton Ni60 Overlay is specifically engineered for hot wire TIG, mechanised TIG, and MIG cladding.

For the most demanding applications requiring maximum corrosion resistance in both oxidising and reducing media — including Hastelloy C-276 (UNS N10276) and C-22 (UNS N06022) type alloys — Exaton Ni59 (Ni-Cr-Mo, UNS N06059) provides excellent thermal stability and outstanding resistance to intermetallic precipitation during welding.

Hastelloy Alloys

Properties and applications

Hastelloy alloys (primarily the C-series: C-276, C-22, C-2000) are nickel-molybdenum-chromium alloys engineered for exceptional resistance to a wide range of highly corrosive environments — including hydrochloric acid, sulphuric acid, chlorine, and other aggressive media where austenitic stainless steels fail. They are extensively used in chemical processing, pharmaceutical manufacturing, pollution control equipment, and waste treatment facilities.

Welding challenges

Hastelloy alloys are susceptible to carbide precipitation in the HAZ if heat input is not carefully controlled, which can impair corrosion resistance. Interpass temperature must be closely managed. Contamination from carbon steel tooling, scale, or surface oxides can introduce defects — dedicated tooling and thorough pre-weld cleaning are essential. The filler must precisely match or exceed the corrosion resistance of the base material, particularly for immersed service in aggressive media.

ESAB filler metal recommendations

Exaton Ni59 is the primary recommendation for welding Hastelloy C-type alloys. The alloy's Nb-free composition and exceptional resistance in both oxidising and reducing chloride-bearing media make it the most versatile option for this alloy family, including dissimilar joints to super-austenitic and super-duplex stainless steels.

Titanium Alloys

Properties and applications

Titanium and its alloys are prized for their exceptional strength-to-weight ratio — comparable to steel at roughly half the density — combined with outstanding corrosion resistance in seawater, chlorides, and many industrial chemicals. They are used extensively in aerospace structures, medical implants, offshore oil and gas equipment, desalination plants, and marine hardware.

Welding challenges

Titanium is highly reactive at elevated temperatures and will absorb oxygen, nitrogen, and hydrogen from the atmosphere — even trace levels of contamination cause severe embrittlement of the weld and HAZ. This makes atmospheric shielding the single most critical factor in titanium welding:

  • Primary shielding must cover the weld pool completely — pure argon (99.999%) is required
  • Trailing shields must protect the weld until it has cooled below approximately 300°C — a colour change from bright silver to straw yellow indicates the acceptable limit; blue, grey, or white colouration indicates contamination and the weld must be rejected
  • Purging is required on the back face of all butt joints
  • The work area, tooling, and the welder's gloves must be scrupulously clean — oil from fingerprints is sufficient to contaminate a titanium weld

TIG (GTAW) is the preferred process for titanium welding due to the precise arc control it offers and the ease of applying supplementary shielding. For full guidance on TIG filler metal selection across titanium and other precision alloys, see our TIG Filler Metals Guide.

Monel Alloys (Nickel-Copper)

Properties and applications

Monel alloys (primarily Monel 400, UNS N04400, and Monel K-500, UNS N05500) are nickel-copper alloys containing approximately 67% nickel and 23–30% copper. They offer excellent resistance to seawater, steam, hydrofluoric acid, and alkalis, making them widely used in marine engineering, offshore oil and gas, chemical processing, and pump and valve components.

Welding challenges

Monel alloys require careful attention to sulphur contamination — even trace levels from cutting fluids, marking pens, or surface contamination can cause hot cracking (sulphur embrittlement) in the weld. Pre-weld cleaning must be thorough. Filler metal selection must maintain the alloy's characteristic combination of strength and stress corrosion resistance.

ESAB filler metal recommendations

For welding NiCu alloy types including Monel, Exaton Ni71 covers NiCrFe alloy welding and dissimilar joints between stainless steels, NiCu alloys, carbon steels, and nickel alloys. For MIG and TIG applications, the Exaton Ni41Cu series covers the full spectrum of NiCu alloy welding requirements across MIG, TIG, SMAW, and SAW processes.

Super-Duplex Stainless Steels

Properties and applications

Super-duplex stainless steels (UNS S32750, S32760) are two-phase austenitic-ferritic alloys with very high chromium (25%), molybdenum (4%), and nitrogen content, giving them a Pitting Resistance Equivalent (PRE) above 40. They are widely used in offshore oil and gas, chemical processing, and desalination applications where high strength combined with extreme pitting and crevice corrosion resistance is required.

Welding challenges

Maintaining the correct austenite-to-ferrite balance (ideally 50/50) in the weld metal and HAZ is the central challenge. Too much ferrite reduces toughness and corrosion resistance; too much austenite reduces strength. The filler must be over-alloyed in nickel relative to the base material to compensate for the tendency of the weld metal to solidify as ferrite. Heat input and interpass temperature must be strictly controlled.

ESAB filler metal recommendations

Exaton 25.10.4.L (MIG/TIG) is designed specifically for gas-shielded arc welding of super-duplex stainless steels including UNS S32750 (SAF™ 2507) and S32760, combining high strength with excellent ductility and corrosion resistance equal to UNS S31254 (254SMO™) in most applications. It is also suitable for joining super-duplex to carbon steel or low-alloy steels.

Universal Best Practices for Exotic Alloy Welding

Contamination control

  • Dedicate separate tooling — wire brushes, grinding discs, clamps — to each alloy family. Cross-contamination from carbon steel particles is a leading cause of corrosion failure in stainless and nickel alloy welds
  • Clean joint faces and surrounding areas with an appropriate solvent (acetone for most alloys) immediately before welding
  • Wear clean gloves when handling filler metal — fingerprint contamination is sufficient to introduce defects in titanium and high-purity nickel alloy welds
  • Store filler metals in their original packaging until use and return unused material to sealed storage

Heat input control

  • Use the minimum heat input necessary to achieve fusion — multi-pass welding with controlled interpass temperatures is preferred over single-pass high-heat-input approaches
  • Follow WPS interpass temperature limits strictly — exceeding them can cause grain growth, carbide precipitation, or phase imbalance that permanently impairs joint properties
  • Allow each pass to cool to the specified interpass temperature before depositing the next

Process selection

  • TIG (GTAW) is generally preferred for exotic alloys due to precise arc control and clean, low-heat-input welds — particularly for titanium and root passes on nickel alloys
  • MIG (GMAW) may be used for nickel and super-duplex alloys in production environments where speed is required, provided shielding gas composition and heat input are correctly controlled
  • Stick (SMAW) electrodes are available for nickel alloys and are useful for site repair and maintenance where gas shielding is impractical

Procedure qualification

All exotic alloy welding in structural, pressure, or safety-critical applications should be performed to a qualified WPS in accordance with the applicable standard (EN ISO 15614-1, ASME IX, or other). For guidance on managing WPS and PQR records, see our article on WPS and PQR Management with WeldCloud Notes.

ESAB Exaton: The Specialist Range for Exotic and High-Performance Alloys

Exaton (formerly Sandvik Welding Operations) is ESAB's specialist brand for high-performance corrosion-resistant filler metals, with over 80 years of heritage in specialty alloy development. The range covers stainless steel and nickel alloy welding across MIG, TIG, SMAW, SAW, and ESW processes:

  • Exaton Ni60 (MIG/TIG) — Ni-Cr-Mo for Inconel 625 (UNS N06625); high-temperature service to 980°C; cryogenics; power generation; marine and chemical processing
  • Exaton Ni60 Overlay (MIG/TIG) — overlay welding on carbon and low-alloy steels; oil and gas valves, tubes, and flanges
  • Exaton Ni59 (SMAW) — Ni-Cr-Mo (UNS N06059); maximum corrosion resistance in oxidising and reducing media; Hastelloy C-type alloys; dissimilar joints to super-austenitic and super-duplex steels
  • Exaton Ni71 (SMAW) — NiCrFe alloys (Alloy 600, 800, 800H); 9% Ni cryogenic steels; dissimilar joints between NiCu alloys, stainless steels, and carbon steels
  • Exaton 25.10.4.L (MIG/TIG) — super-duplex stainless steels UNS S32750 and S32760; dissimilar joints to carbon and low-alloy steels