Does AL-6XN need to be passivated?

After fabrication, yes. Welding, machining and handling leave free iron and oxides that corrode before the base alloy does. Passivation removes them and restores the alloy's designed chloride resistance.

What specification covers AL-6XN passivation?

ASTM A967 for the chemical passivation treatment and its verification, and ASTM A380 for cleaning and descaling of fabricated equipment. Harrison also works to customer specifications.

Nitric or citric for AL-6XN?

Either is effective on the super-austenitic chemistry; Harrison follows the specification and recommends citric where the drawing allows it and the application is food, pharmaceutical or medical.

Can you passivate installed AL-6XN piping?

Yes. Harrison field crews passivate installed piping and vessels by circulation or spray across the Houston area and the Gulf Coast.

Should AL-6XN be electropolished instead?

Only if the surface must also be smoother, brighter or more cleanable. For corrosion resistance alone, passivation is sufficient and does not change the part.

AL-6XN Passivation

Passivated AL-6XN stainless steel fittings at Harrison Electropolishing

The short answer: AL-6XN is a 6Mo super-austenitic stainless steel (a registered trademark of ATI) chosen for seawater, brine, bleach and hot-chloride service where 316L pits. Its corrosion resistance depends on a clean surface, and welding, machining and handling leave free iron and oxides that break the passive film. Passivation removes those contaminants with a mild oxidant so the chromium-rich film re-forms, without changing the finish or dimensions. Harrison passivates AL-6XN components of all sizes to ASTM A967 or your specification, with verification and a certificate of conformance, in Houston and on-site.

Why AL-6XN needs passivation after fabrication

The alloy's resistance to pitting, crevice corrosion and chloride stress-corrosion cracking comes from its chromium, molybdenum and nitrogen content and the passive film they form. Free iron embedded by steel tooling and grinding, and oxides left by welding, sit on top of that film and corrode first — a 6Mo alloy with a contaminated surface will tea-stain and pit like a lesser grade. Passivation restores the surface the alloy was specified for. Welded fabrications with heat tint are pickled first.

Process and verification

Pre-cleaning to remove oils and particulate; immersion or circulation in a nitric or citric passivation bath at parameters set for the alloy; deionized-water rinse; filtered-air or nitrogen drying; verification by the test the specification requires, recorded on the certificate of conformance. Harrison works to ASTM A967, ASTM A380 or your industry or company passivation standard.

Typical AL-6XN components

Seawater and brine piping, heat-exchanger tubes and tubesheets, pulp-and-paper bleach-plant equipment, flue-gas desulfurization components, offshore and marine hardware, pharmaceutical and food process equipment, and chemical-process vessels. Large fabrications are handled in Houston with four overhead cranes and 15,000 lb material-handling capacity; installed systems are passivated on-site across the Houston area and the Gulf Coast.

For electropolishing and mechanical polishing of AL-6XN — finishes certified as low as 4 µin Ra — see AL-6XN under materials.

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More to Know

Frequently Asked Questions

Does AL-6XN need to be passivated?

After fabrication, yes. Welding, machining and handling leave free iron and oxides that corrode before the base alloy does. Passivation removes them and restores the alloy's designed chloride resistance.

What specification covers AL-6XN passivation?

ASTM A967 for the chemical passivation treatment and its verification, and ASTM A380 for cleaning and descaling of fabricated equipment. Harrison also works to customer specifications.

Nitric or citric for AL-6XN?

Either is effective on the super-austenitic chemistry; Harrison follows the specification and recommends citric where the drawing allows it and the application is food, pharmaceutical or medical.

Can you passivate installed AL-6XN piping?

Yes. Harrison field crews passivate installed piping and vessels by circulation or spray across the Houston area and the Gulf Coast.

Should AL-6XN be electropolished instead?

Only if the surface must also be smoother, brighter or more cleanable. For corrosion resistance alone, passivation is sufficient and does not change the part.

Request a Quote

800-245-5707

Passivation

Harrison Electropolishing, the Leading Electropolishing, Passivation, Oxygen Cleaning & Mechanical Polishing Company World Wide.

Electropolishing is an electrochemical process by which surface material is removed by anodic dissolution. Electropolishing removes surface material, beginning with the high points within the microscopic surface texture. By removing these points, the electropolishing process will improve the surface finish of a metal such as stainless steel, nickel, and Hastelloy, leaving a smoother and more reflective surface. Common parts and components electropolished include tanks, piping, fittings, rods, discs, large parts & surfaces, and more.