Many engineers and procurement teams struggle to find welders who actually understand nickel-chromium-molybdenum metallurgy. This isn't stainless steel. It behaves differently under the torch, and it punishes shortcuts.
This guide breaks down what makes C22 unique, why it's hard to weld correctly, and what separates a code-compliant weld from a liability.
Key Takeaways
- Hastelloy C22 resists pitting, crevice corrosion, and stress cracking in both oxidizing and reducing environments
- Its weld pool is sluggish and prone to hot cracking without tight process control
- Heat input, interpass temperature, and cleanliness directly determine long-term corrosion performance
- ERNiCrMo-10 filler and high-purity argon shielding are standard for matching welds
- ASME Section IX certified welders with documented procedures reduce rework and compliance risk
What is Hastelloy C22 and Why is it Used?
Hastelloy C22 (UNS N06022) is a nickel-based superalloy built for environments that destroy ordinary stainless steel. Its composition, per manufacturer data sheets, includes:
| Element | Weight % |
|---|---|
| Nickel | Balance |
| Chromium | 20.00–22.50 |
| Molybdenum | 12.50–14.50 |
| Tungsten | 2.50–3.50 |
| Iron | 2.00–6.00 |
That chromium-molybdenum combination gives C22 excellent resistance to pitting, crevice corrosion, and stress corrosion cracking in both oxidizing and reducing media — a dual capability few alloys offer.
Fabrication-Relevant Properties
Key properties for weld planning:
- Melting range: 2,475–2,550°F (1,357–1,399°C)
- Density: 0.314 lb/in³ (8.69 g/cm³)
- Thermal conductivity: 10.1 W/m-K at 50°C, rising to 21.3 W/m-K at 600°C
These lower thermal conductivity values (compared to carbon steel) mean heat concentrates differently during welding, which feeds directly into the cracking risks discussed below.
Common Industrial Applications
C22 is specified where aggressive chemistry and high reliability requirements meet:
- Chemical reactors, heat exchangers, and process columns
- Flue gas desulfurization scrubbers at coal-fired utilities
- Spent-acid reclamation vessels and wastewater ion-exchange systems
- Hazardous waste incinerator off-gas ductwork
- Deep-well injection pumps, piping, and downhole tubular assemblies
Why Welding Hastelloy C22 is Difficult
Haynes International, the alloy's primary manufacturer, actually rates C22 as very weldable and ductile. Weldable is not the same as forgiving: poor technique can still cut corrosion resistance even when the bead looks sound.
Sluggish Weld Pool Behavior
Compared to stainless steel, C22's molten puddle moves slower and holds heat longer. Welders accustomed to carbon steel or 316 stainless often push too fast, resulting in incomplete fusion or shallow penetration.
Hot Cracking Sensitivity
Nickel alloys can develop solidification cracks in the weld metal or liquation cracks in the heat-affected zone. According to TWI's nickel alloy weldability guidance, common imperfections include porosity, oxide inclusions, lack of inter-run fusion, and microfissuring. Managing this requires:
- Low, controlled heat input
- Proper joint design (avoiding excessive restraint)
- Matching filler metal chemistry
Oxide Films and Contamination
C22 forms tenacious oxide layers during welding. TWI recommends degreasing, then removing surface oxide by grinding or machining — wire brushing alone won't cut it for high-temperature oxide. Between passes, every trace of oxide and slag needs to come off before the next bead goes down.
Contamination is just as damaging. Grease, sulfur, lead, and copper tooling can embed into the weld and create localized corrosion sites. Dedicated tooling prevents that:
- Use separate grinding discs and Scotch-Brite pads for nickel alloys
- Never share brushes between carbon steel and C22 work
- Label and store nickel-alloy consumables separately
Dissimilar Metal Welding
Those same cleanliness and heat-input rules get harder when C22 is joined to another alloy. Joining C22 to 316 stainless steel is common in mixed-material systems, but it introduces thermal expansion mismatches and dilution concerns. A buttering technique — depositing a nickel-based filler layer on the stainless side first — often manages the transition zone properly.
The Corrosion Cost of Getting It Wrong
Even correctly welded C22 shows measurable differences from wrought base metal. Haynes' own corrosion data illustrates the gap:
| Medium (150°F) | Weld Metal | Wrought Base |
|---|---|---|
| 30% sulfuric acid | 0.6 mpy | 0.4 mpy |
| 50% sulfuric acid | 9.3 mpy | 0.8 mpy |
| 90% sulfuric acid | 18.5 mpy | 13.4 mpy |
Notice the 50% sulfuric acid line: weld metal corrodes over 11 times faster than the wrought base in that specific condition. That's with a properly executed weld. Poor technique widens that gap further.
Recommended Welding Methods, Filler Metals, and Gas Selection
Three processes handle C22 well: GTAW (TIG), GMAW (MIG), and SMAW (Stick). Oxy-acetylene welding and cutting should be avoided entirely: the heat profile is too uncontrolled for this alloy.
| Process | Control Level | Best Application |
|---|---|---|
| GTAW (TIG) | Highest | Thin sections, precision fittings, root passes |
| GMAW (MIG) | Moderate-high | Thicker sections, higher deposition rates |
| SMAW (Stick) | Moderate | Field repairs, limited access joints |
Filler Metal Selection
Haynes' matching filler for C22 is ERNiCrMo-10, classified under AWS A5.14 and ASME IX F-43. It is formulated to match C22's corrosion resistance profile, including low iron content to limit dilution effects.
Shielding Gas Requirements
- GTAW: 100% argon at roughly 25 ft³/h, with 100% argon backing gas on root passes
- GMAW: 100% argon or specified argon-helium-CO2 blends at roughly 35 ft³/h
- Trailing shields: Protect multi-pass welds from atmospheric contamination as the bead cools
At Alloy Metalworks, this is where engineering-aware fabrication pays off. Selecting the wrong shielding blend or skipping a trailing shield on a multi-pass vessel weld is exactly the kind of mistake that shows up months later as a pinhole leak.
Heat Input and Temperature Control Best Practices
C22 generally doesn't need aggressive preheating. Manufacturer guidance indicates ambient temperature is typically sufficient. Warming is only needed to prevent moisture condensation or freezing, which could cause porosity.
Interpass Temperature Limits
Keep interpass temperatures at or below 200°F (93°C). This is the single most important limit to hold during a multi-pass weld. Exceeding it risks harmful phase precipitation that weakens corrosion resistance at the grain boundaries.
Cooling methods:
- Water quenching or rapid-air cooling between passes is acceptable
- Avoid contamination during any forced cooling step
Post-Weld Heat Treatment
For solid-solution-strengthened alloys like C22, standard carbon-steel stress relief (1,000–1,500°F) is ineffective and can actively harm performance. When PWHT is genuinely required, a full solution anneal at 2,050°F (1,121°C) followed by water quench or rapid-air cooling is the accepted approach. Most C22 work is used as-welded.
Post-Weld Cleaning, Inspection, and Quality Assurance
A technically sound weld still needs the right finishing steps to deliver on C22's corrosion promise.
Cleaning and Passivation
- Remove all oxide and scale with dedicated stainless steel brushes (never carbon-steel brushes)
- Degrease thoroughly on both sides of the joint before and after grinding
- Passivation with nitric acid solutions restores the protective chromium oxide layer that welding heat disrupts
Inspection Methods
Standard NDE practices for C22 weldments, per ASME guidelines, include:
- Visual inspection — the fastest, lowest-cost screen for surface defects
- Liquid penetrant testing — reveals surface-breaking cracks invisible to the eye
- Radiographic testing — checks internal fusion and porosity
- Ultrasonic testing — finds subsurface defects when joint geometry and code requirements call for it
At Alloy Metalworks, this inspection sequence is built into the job, not bolted on at the end. Weld procedures are qualified under ASME Section IX, and every job runs through ISO 9001-controlled documentation: material certs, filler metal lot traceability, and inspection records all tie back to the finished part.
For clients in aerospace, energy, and regulated chemical processing, that paper trail is often just as important as the weld itself when an auditor reviews the work.
Frequently Asked Questions
Can you weld Hastelloy to 316 stainless steel?
Yes. Use a nickel-based ERNiCrMo filler and butter the stainless side to manage thermal expansion differences and limit dilution.
Why is welding Hastelloy so hard?
The weld pool is sluggish, hot cracking risk is elevated, and oxide films form readily during heating. Combine that with strict cleanliness and interpass temperature requirements, and there's little room for error.
What is Hastelloy C22 made of?
C22 is primarily nickel (balance), with chromium (20–22.5%), molybdenum (12.5–14.5%), tungsten (2.5–3.5%), and iron (2–6%). This blend gives it resistance across both oxidizing and reducing chemical environments.
What welding process works best for Hastelloy C22?
GTAW (TIG) is preferred for thin sections and precision joints. GMAW suits thicker sections needing faster deposition. Avoid oxy-acetylene due to poor heat control.
How do you prevent cracking when welding Hastelloy C22?
Keep heat input low, hold interpass temperature at or below 200°F, use proper joint design to reduce restraint, and match filler metal chemistry to the base alloy. Cleanliness between passes matters just as much.
Does welding affect the corrosion resistance of Hastelloy C22?
Yes. Excess heat or contamination can form grain boundary precipitates that cut corrosion resistance. Correct procedure and post-weld treatment keep weld performance closer to wrought base metal.
