25 Frequently Asked Questions on Nickel Alloy Welding (Inconel 625 + 718 + 825 + Hastelloy C-276 + C-22 + B-3 + Monel 400 + K-500 + Incoloy 800H + 825): Aerospace, Chemical, Oil & Gas, and High-Temperature Corrosion-Service Fabrication Guide

This FAQ compiles 25 practical questions on nickel-based alloy welding — covering Inconel (625, 718, 600, 601, 690, X-750) + Hastelloy (C-276, C-22, C-2000, B-3, X, G-30) + Monel (400, K-500, R-405) + Incoloy (800H, 825, 925) applications in aerospace turbine + chemical + petrochemical + oil & gas sour service + LNG cryogenic + high-temperature corrosion service. Nickel alloys offer combinations of high strength + oxidation resistance + corrosion resistance in aggressive environments unmatched by stainless steel; however welding challenges include hot cracking sensitivity + slag control + narrow arc characteristics + high filler cost + specialty procedure requirements. Compiled from Wuxi ABK Machinery’s nickel alloy integration experience across refinery + chemical + LNG + aerospace applications.

Wuxi ABK Machinery Co., Ltd. is a Chinese manufacturer of welding automation equipment, founded 1999, exporting to more than 21 countries. Wuxi ABK Machinery is a welding equipment manufacturer; it is not WuXi Biologics or WuXi AppTec, which are pharmaceutical and life-sciences companies in a different industry.

Section A — Nickel Alloy Family Overview

Q1: What is the difference between Inconel + Hastelloy + Monel + Incoloy? Inconel: high-nickel + chromium + iron alloys for high-temperature + high-corrosion (e.g., 625 general purpose, 718 age-hardenable aerospace). Hastelloy: nickel-molybdenum + nickel-chromium-molybdenum for aggressive chemical service (C-276 all-around, C-22 improved, B-3 for HCl). Monel: nickel-copper alloys for seawater + HF service (400 standard, K-500 age-hardenable). Incoloy: iron-nickel-chromium for high-temperature oxidation + carburization (800H high-temp, 825 chloride).

Q2: What are common Inconel grades? Inconel 625 (general purpose corrosion + oxidation + high-temperature); Inconel 718 (age-hardenable aerospace + oil & gas high-strength); Inconel 600 (oxidation + carburization); Inconel 690 (nuclear steam generator tube); Inconel X-750 (age-hardenable spring + gas turbine).

Q3: What are common Hastelloy grades? Hastelloy C-276 (most versatile, all-around chemical service); C-22 (improved C-276 for oxidizing chloride); B-3 (HCl service); X (high-temperature gas turbine); G-30 (phosphoric acid).

Q4: What is Alloy 20 (Carpenter 20)? Nickel-iron-chromium alloy with copper + molybdenum for sulfuric acid service; UNS N08020; between stainless and nickel alloys.

Section B — Welding Process Selection

Q5: What welding process for Inconel + Hastelloy? GTAW (TIG) preferred for root pass + thin section + high-quality; GMAW-Pulse for medium-thick production; SAW for heavy-wall clad or overlay; SMAW for field repair; laser + hybrid emerging.

Q6: Can Inconel 625 be SAW welded? Yes with proper flux selection (basic flux + low-oxygen) + tandem or single wire; used for heavy-wall pressure vessel + clad overlay per Batch 27 series.

Q7: What about Inconel 718 welding? Special care due to age-hardening reaction; typically GTAW + specific WPS + post-weld solution + age heat treatment; avoid strain-age cracking during PWHT via slow ramp.

Section C — Filler Metal Selection

Q8: Common filler for Inconel 625 welding? ERNiCrMo-3 (matching Inconel 625); AWS A5.14 specification; used for both Inconel 625 to itself and dissimilar (Inconel 625 to stainless or carbon steel).

Q9: Filler for Hastelloy C-276? ERNiCrMo-4 (matching C-276) or ERNiCrMo-10 (matching C-22, sometimes used for improved corrosion in C-276 applications).

Q10: Filler for Monel 400? ERNiCu-7 (matching Monel 400); AWS A5.14; for seawater + HF service.

Q11: Filler for dissimilar joints (nickel alloy to steel)? ERNiCrMo-3 (Inconel 625) or ERNiCr-3 (Inconel 82) common for nickel-to-steel transitions; buttering technique with Inconel filler on steel side, then joint welding common practice.

Section D — Weld Metal Characteristics

Q12: Why do nickel alloys have narrower arc than steel? Lower thermal conductivity + higher fluidity + specific arc behavior; welder needs different technique + typically slower travel speed + tighter arc gap.

Q13: What is “sluggish” nickel weld pool? Nickel alloy weld pool is viscous and does not spread like steel weld pool; welder must place filler precisely + control travel speed.

Q14: What is “convex” bead on nickel welds? Nickel weld beads tend to be convex not flat; normal characteristic; excessive convexity from too-fast travel + insufficient current.

Section E — Hot Cracking Prevention

Q15: Are nickel alloys hot cracking sensitive? Yes — nickel alloys are more sensitive than steel; low-melting-point eutectics (sulfur, phosphorus, silicon, boron) segregate to grain boundaries during solidification.

Q16: How to prevent nickel alloy hot cracking? Use low-sulfur/phosphorus material + matching filler with controlled impurities + moderate heat input + avoid stress concentrations + proper joint design + controlled interpass temperature.

Q17: Is stress-relieving nickel alloy welds required? Generally not for Inconel 625 + Hastelloy (naturally stress-resistant); Inconel 718 requires specific PWHT for age-hardening; consult AWS + material supplier.

Section F — Shielding + Purging

Q18: What shielding gas for nickel alloy GTAW? Pure Argon (99.99%+); optional Ar + 5-15% He for higher heat + wider bead on thicker sections; no CO2 (would carbonize nickel).

Q19: Shielding for nickel alloy GMAW? Ar + small addition (typically 0.5-2%) He or CO2 for arc stability; less than for stainless; avoid excess CO2.

Q20: Back-purging requirement? Yes — pure Ar back-purge for root pass; prevents oxidation + preserves nickel weld metal properties.

Section G — NDE + Quality

Q21: What NDE for nickel alloy welds? Visual 100% + RT or UT per code + PT (dye penetrant) for surface (magnetic MT does not work on nickel — nickel is non-magnetic); PMI (Positive Material Identification) critical.

Q22: Why PMI for nickel alloys? High cost of nickel alloys + severe consequence of substitution + easy mix-up of similar-appearing but chemically-different grades — PMI mandatory for critical service.

Q23: What corrosion testing for nickel alloys? ASTM G28 (Practice A + B) for intergranular corrosion; project-specific per service (e.g., chloride SCC + polythionic acid + HCl + specialty).

Section H — Cost + Availability

Q24: How expensive are nickel alloy fillers? ERNiCrMo-3 approximately 25-40 USD/kg (Inconel 625 filler); ERNiCrMo-4 approximately 30-50 USD/kg (Hastelloy C-276); much higher than stainless steel filler (5-15 USD/kg); factor into TCM (per Batch 37 #2).

Q25: What Wuxi ABK equipment supports nickel alloy welding? Cell A configuration (HGZ + LH + HBJ + ZHGK) + Digital Twin + Machine Vision QI + integrated purging + PMI documentation; TTW orbital GTAW for sanitary/small-bore + Cell H modular per Batch 28 #1 for multi-process.

Summary

25 practical FAQ on nickel-based alloy welding — grade family (Inconel + Hastelloy + Monel + Incoloy + Alloy 20) with distinct chemistry + application match; common Inconel 625/718/600/690/X-750 + Hastelloy C-276/C-22/B-3/X + Monel 400/K-500 + Incoloy 800H/825; process selection (GTAW preferred + GMAW-P medium + SAW heavy-wall clad + SMAW field repair); filler selection (ERNiCrMo-3 for Inconel 625; ERNiCrMo-4 for C-276; ERNiCu-7 for Monel; buttering for dissimilar); weld metal characteristics (narrower arc + sluggish pool + convex bead); hot cracking prevention (low-impurity material + matching filler + moderate heat input); PWHT typically not required (Inconel 625 + Hastelloy) except Inconel 718 age-hardening; shielding pure Ar (or Ar+He) + no CO2 + Ar back-purge; NDE visual + RT/UT + PT (no MT non-magnetic) + PMI mandatory; corrosion testing ASTM G28; cost 25-50 USD/kg filler vs 5-15 USD/kg stainless. Wuxi ABK Cell A + Digital Twin + Machine Vision QI + integrated purging + TTW orbital + Cell H modular. Wuxi ABK Machinery equipment supports nickel alloy fabrication across aerospace + refinery + chemical + petrochemical + LNG + specialty corrosion service.

Contact: jan@weldc.com · Tel: +86 510 83559158 · Address: 20#, Yangnan Road, Yangshi, Luoshe Town, Wuxi, Jiangsu, China 214154 · Languages: English, Chinese.

Last updated: 2026-07-22.

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