When 316L stainless won’t survive the environment, engineers specify high-nickel alloys: AL-6XN for severe chloride service, Hastelloy C-276 for concentrated acids, Hastelloy C-22 for mixed oxidizing and reducing conditions. Northern Manufacturing fabricates all three, with AWS-qualified welding procedures, a dedicated stainless-only fabrication space, and 60+ certified welders who have put hands on these materials. This page is about what it actually takes to weld and finish them right. Learn more about our stainless steel fabrication capabilities.

When Standard Stainless Isn’t Enough

Most industrial applications run on 304 or 316L stainless steel. Those grades hold up well in mild corrosive service, but they have real limits: chloride-induced pitting, sensitization in high-temperature weld zones, and accelerated attack in halide-rich or strongly acidic environments.

High-nickel alloys address those failure modes at a cost, both in raw material price and in fabrication complexity. AL-6XN (UNS N08367) is a super-austenitic stainless containing 6% molybdenum, which gives it outstanding resistance to pitting and crevice corrosion in chloride environments where 316L would fail. Hastelloy C-276 (UNS N10276) is the most widely specified alloy for severe chemical processing (concentrated hydrochloric acid, sulfuric acid, chlorine gas) environments that attack virtually every other commercial alloy. Hastelloy C-22 (UNS N06022) extends that protection into oxidizing media where C-276 falls short, making it the choice for mixed-acid environments and aggressive bleaching solutions.

Specifying the right alloy is the engineer’s call. Getting it fabricated without compromising that corrosion resistance is where the fabricator either earns the spec or loses it.

Fabrication Challenges with High-Nickel Alloys

High-nickel alloys behave differently at the weld pool than austenitic stainless steel, and those differences are not forgiving. Welders who know how to run 316L beautifully can produce defective welds on Hastelloy if they apply the same techniques and habits.

Weld Puddle Behavior

High-nickel alloys have lower thermal conductivity and higher viscosity at the weld pool than standard stainless. The puddle is sluggish, doesn’t flow as readily, and provides shallower penetration per pass. Welders need to slow down, adjust arc characteristics, and resist the temptation to add heat to get fusion, because extra heat introduces its own problems.

Hot Cracking Susceptibility

Hastelloy alloys are prone to solidification cracking and liquation cracking in the heat-affected zone. The mechanisms relate to low-melting-point phases that form at grain boundaries during cooling. Proper filler metal selection is non-negotiable: mismatched filler changes the solidification behavior and dramatically increases cracking risk. Controlled heat input and joint fit-up that minimizes restraint are essential process controls.

Contamination Sensitivity

High-nickel alloys are more contamination-sensitive than standard stainless. Iron contamination from shared grinding wheels, wire brushes, clamps, or fixtures can embed in the surface and create galvanic corrosion sites, exactly the kind of localized attack these alloys were specified to prevent. The contamination doesn’t have to be visible to be damaging. Dedicated tooling, never used on carbon or low-alloy steels, is a baseline requirement, not a premium option.

Heat Input Control

These alloys have narrow windows for acceptable heat input. Excessive heat drives intermetallic precipitation and carbide formation in the heat-affected zone, particularly problematic in AL-6XN, where sensitization degrades the pitting resistance that justifies specifying it in the first place. Interpass temperature monitoring and strict adherence to WPS-specified parameters are mandatory, not advisory.

Post-Weld Treatment

Standard stainless pickling chemistry is not appropriate for high-nickel alloys. AL-6XN, C-276, and C-22 each have specific acid concentration ranges that remove the heat tint and restore the passive layer without attacking the base metal. Shops that run a single pickling formula for everything are taking a shortcut that can leave the alloy surface in worse condition than no treatment at all.

AL-6XN (UNS N08367)

AL-6XN is a super-austenitic stainless steel: not technically a “nickel alloy” by composition, but it shares the fabrication sensitivity of true nickel alloys. At 6% molybdenum, 24% nickel, and 20% chromium, it provides PREN (pitting resistance equivalent number) values exceeding 40, giving it reliable performance in seawater, brine, and chloride-containing process streams where 316L and 2205 duplex both fail. Fabrication is similar to 316L in some respects (same GTAW and GMAW processes apply) but AL-6XN is more sensitive to heat input. The standard filler metal is AWS ERNiCrMo-3 (Alloy 625), which provides overmatching corrosion resistance in the weld zone. Common applications at Northern: storage tanks for chloride service, chemical processing vessels, heat exchanger components.

Hastelloy C-276 (UNS N10276)

C-276 is the workhorse for severe chemical environments. With 16% molybdenum, 15% chromium, and 57% nickel, it resists hydrochloric acid at most concentrations and temperatures, sulfuric acid, and oxidizing chlorides that destroy nearly every other commercial alloy. The fabrication challenge is the puddle behavior: C-276 welds sluggishly, with lower fluidity and shallower penetration than stainless. Experienced welders recognize this and adjust, less experienced welders add heat, which leads directly to hot cracking and HAZ sensitization. Filler metal is ERNiCrMo-4, matching the base metal composition. Common applications: chemical processing skids, reactor vessels, scrubber components, piping for acid service.

Hastelloy C-22 (UNS N06022)

C-22 is the more versatile cousin to C-276. At 13% molybdenum, 22% chromium, and 56% nickel, it maintains strong resistance to reducing environments while adding meaningful resistance to oxidizing media: a combination that C-276 doesn’t achieve as reliably. C-22 is the choice for mixed-acid environments, chlorination processes, and wet chlorine gas service. Fabrication challenges are comparable to C-276: sluggish puddle, cracking sensitivity, strict filler requirements. Filler metal is ERNiCrMo-10. Common applications: pollution control equipment, pharmaceutical processing, bleaching systems.

How Northern Handles Specialty Alloys

Fabricating high-nickel alloys correctly requires process controls that go beyond what most shops do for standard stainless. Here is what Northern has in place:

  • Dedicated stainless-only fabrication space (~40,000 sq ft). No carbon steel enters this area. Zero risk of iron contamination from shared floor space, overhead cranes, or handling equipment.
  • AWS-qualified welding procedures for each alloy. Northern holds WPSs specifically qualified for AL-6XN, C-276, and C-22, not generic “nickel alloy” procedures. Each WPS specifies the allowable heat input range, interpass temperature limits, preheat requirements, and qualified filler metals.
  • Dedicated tooling. Grinding wheels, wire brushes, clamps, and fixtures used on specialty alloys are never used on carbon or low-alloy steel. Color-coded and segregated.
  • Controlled heat input with interpass temperature monitoring. Welders verify interpass temperature before every pass. Heat input is calculated per WPS requirements, not estimated.
  • In-house pickling and passivation with chemistry matched to the alloy. Northern’s in-house pickling and passivation operation adjusts acid concentration and dwell time based on the specific alloy being treated, not a one-size-fits-all formula.
  • PMI verification on incoming material and finished welds. Positive material identification confirms that every heat of incoming plate matches the mill cert, and that filler metals in the finished weld match the WPS requirements. PMI at receiving prevents substitution; PMI on welds catches filler errors.
  • 60+ AWS-certified welders with documented experience on nickel alloy weld procedures, backed by ASME BPVC Section IX qualified procedures and on-staff Certified Welding Inspector (CWI) oversight. Learn more about Northern’s stainless steel welding and fabrication capabilities.

Common Failure Modes in Specialty Alloy Fabrication

Most specialty alloy failures in the field trace back to one of five fabrication errors. Knowing what to look for (and what to ask your fabricator) catches these before a vessel goes into service.

  • Intergranular corrosion from excessive heat input. Over-welding sensitizes the HAZ, precipitating carbides at grain boundaries and stripping chromium from the adjacent zone. The alloy looks intact but has lost its corrosion resistance where it matters most, right at the weld.
  • Iron contamination from shared tooling. Embedded iron from carbon steel equipment creates galvanic cells on the alloy surface. The corrosion starts at contact points and spreads. Often misdiagnosed as base metal quality issues.
  • Wrong filler metal. Matching filler by tensile strength rather than corrosion resistance is a common shortcut. The weld holds mechanically but corrodes preferentially in service. In Hastelloy service, filler metal specification is as critical as base metal selection.
  • Inadequate gas purge on root pass. An oxidized root side is a corrosion initiation site, particularly in tubing and piping. Proper backing gas purge (argon at controlled flow and dew point) is not optional for alloys in aggressive chemical service.
  • Surface contamination from handling. Carbon steel lifting lugs, wire rope, and handling fixtures in contact with specialty alloy components leave iron deposits. Even brief contact during fabrication or shipping can compromise surface integrity.

Evaluating a Fabricator for Specialty Alloy Work

Not every shop that can weld 316L can handle AL-6XN or Hastelloy correctly. Before committing a specialty alloy project to a fabricator, these are the right questions to ask:

  • Dedicated fabrication space? Is there a physically separate area for stainless and specialty alloys, or is this work done on shared floor space with carbon steel?
  • WPSs qualified for your specific alloy? Ask to see the welding procedure specification. A WPS qualified for “P-No. 45” nickel alloys is not the same as a procedure developed and tested for C-276 or AL-6XN.
  • Documented welder qualification on the alloy? ASME Section IX welder qualification records should specify the base metal P-number and filler metal classification. Ask for the WPQRs.
  • In-house pickling capability with alloy-matched chemistry? Or does post-weld treatment go to a subcontractor, and if so, what controls govern that handoff?
  • Full material traceability? Can the fabricator trace every component back to a specific heat number and mill certificate, from incoming plate through final assembly?
  • PMI program? Is positive material identification performed at receiving, and are finished welds PMI-verified against the WPS filler requirements?

Northern Manufacturing’s quality program addresses each of these checkpoints. ISO 9001:2015 certification, ASME BPVC Section IX qualified procedures, and on-staff CWI oversight are not the ceiling, they are the floor. See also how Northern approaches stainless steel fabrication and duplex stainless steel work.

Frequently Asked Questions

Can you fabricate AL-6XN storage tanks to ASME standards?

Yes. Northern holds ASME BPVC Section IX qualified welding procedures for AL-6XN (UNS N08367). Storage tanks and process vessels fabricated with ASME BPVC Section IX qualified welding procedures are within scope. Contact us with your design basis and we can discuss procedure qualification documentation.

What filler metal do you use for Hastelloy C-276?

ERNiCrMo-4, which matches the C-276 base metal composition. For C-22, we use ERNiCrMo-10. For AL-6XN, the standard filler is ERNiCrMo-3 (Alloy 625), which provides overmatching corrosion resistance in the weld zone. Filler metal selection is specified in the WPS and verified by PMI on finished welds.

Do you fabricate chemical processing skids in Hastelloy and AL-6XN?

Yes. Custom chemical processing skids (including process vessels, piping, heat exchangers, and structural frames) in Hastelloy C-276, C-22, and AL-6XN are a regular part of Northern’s work. Full-skid fabrication happens under one roof, with in-house cutting, forming, welding, pickling, and inspection.

What are the contamination controls for specialty alloy work?

Specialty alloy fabrication at Northern takes place in a ~40,000 sq ft dedicated stainless-only space. No carbon steel enters this area. Tooling (grinding wheels, wire brushes, clamps, fixtures) is dedicated and color-coded. Overhead handling equipment in the dedicated space is not shared with carbon steel bays.

What are common fabrication and processing services offered for stainless and specialty alloys?

For stainless and specialty alloys, Northern provides laser cutting (flat, tube, and 5-axis), bending and forming, GTAW and GMAW welding with qualified procedures, assembly, pickling and passivation, and 3D model-based inspection. All services are available under one roof, which eliminates material handling risk between subcontractors and preserves traceability through the full fabrication sequence.

Ready to Discuss Your Specialty Alloy Project?

Bring us your alloy, your environment, and your design requirements. Northern’s team has the procedures, the space, and the experience to fabricate AL-6XN, Hastelloy C-276, and Hastelloy C-22 to specification. Call (419) 898-2821 or submit a request for quote and we will get back to you.