Welding Nickel Alloys

Nickel-base alloys (Inconel, Monel, Hastelloy, Incoloy) handle extreme temperatures and corrosive environments that destroy other metals. They also punish welding mistakes with hot cracking. The trace elements sulfur, phosphorus, lead, and boron form low-melting films at grain boundaries during solidification, and even small amounts cause centerline cracking.

Cleanliness is everything on nickel alloys. Scrub the joint with acetone or solvent. Use carbide burrs or stainless-only grinding wheels to prep the bevel. Mark parts with a vibrating engraver, not soapstone or paint markers, which can leave sulfur or silicon residue. Wear clean gloves, and keep the shop air free from grinding dust and coolant mist.

TIG (GTAW) is the preferred process for most nickel alloy work. Run DCEN with 100% argon or argon/helium blend. Keep beads narrow: 2.5 times the filler rod width is the maximum recommended weave. Stringer beads prevent the centerline sulfur segregation that causes cracking. Control interpass temperature (keep it under 250F for most alloys) and avoid remelting previous beads.

Filler selection follows the base metal. ERNiCr-3 handles Inconel 600 and 601. ERNiCrMo-3 (Inconel 625) is the workhorse for high-strength and corrosion-resistant joints, and it also works for dissimilar welds between nickel alloys and stainless steel. ERNiCrMo-4 matches Hastelloy C-276 chemistry. ERNiCu-7 welds Monel 400.

Back purging with argon is standard on pipe and enclosed joints to prevent root-side oxidation. Nickel alloys oxidize differently than stainless, forming heavy, tenacious oxides that weaken the root if left unprotected. Purge until oxygen levels drop below 50 PPM for critical applications.