What is passivation of stainless steel?

A chemical treatment with nitric or citric acid that removes free iron and other surface contaminants so stainless steel's natural chromium-oxide passive film can re-form. It restores corrosion resistance without adding a coating or changing dimensions.

What is the difference between ASTM A967 and AMS 2700?

Both cover chemical passivation with nitric or citric acid. ASTM A967 is the general industrial specification; AMS 2700 is the SAE aerospace specification. Drawings that reference the cancelled federal spec QQ-P-35 are normally met with either.

Should I use nitric or citric passivation?

Follow the specification first. Where either is allowed, citric is preferred for medical, food and pharmaceutical work and is safer to handle; nitric remains the choice for heavier contamination and for grades that need a stronger oxidant. Harrison runs both.

How do you verify passivation?

With the test the specification calls for — most often the copper sulfate test or the ferroxyl test for free iron — recorded on the certificate of conformance. Chromium-to-iron ratio results are available on request.

Does passivation remove weld discoloration or rust?

No. Passivation removes free iron and contaminants but not oxides, heat tint or scale. Those are removed by pickling to ASTM A380 first; welded fabrications normally get both.

Can you passivate equipment on-site?

Yes. Harrison field crews passivate installed piping, vessels, skids and systems across the Houston area and the Gulf Coast.

Stainless Steel Passivation Services in Houston, Texas

Welded stainless steel bracket assembly after pickling and passivation at Harrison Electropolishing in Houston

Reviewed by Tom Harrison, member of the ASME BPE Surface Finish Subcommittee · Updated October 2026

The short answer: Passivation is a chemical treatment that removes free iron and other contaminants from the surface of stainless steel and corrosion-resistant alloys so the metal's own chromium-oxide film can re-form and protect it. It does not add a coating and does not change dimensions or finish. Harrison has passivated stainless, duplex and nickel-alloy components since 1980 in Houston — with both nitric and citric acid lines under one roof — to ASTM A967, ASTM A380, AMS 2700 or your specification, verified by copper sulfate or ferroxyl test and shipped with a certificate of conformance. Parts that cannot ship are passivated on-site across the Houston area and the Gulf Coast.

When to passivate

Every corrosion-resistant alloy benefits from passivation before it goes into service, because every fabrication step — machining, welding, grinding, forming, even handling with steel tools — leaves free iron and contaminants on the surface. Those are the sites where rust, pitting and crevice corrosion start, even on the correct alloy. Passivate after fabrication or repair, before parts go into cleanroom, food, medical, pharmaceutical, marine or chloride service, whenever the customer or industry specification requires it, and on a maintenance schedule where chlorides are high; some plants passivate annually, others more often.

What passivation does and does not do

Passivation removes free iron and surface contamination and restores the chromium-rich passive layer, which improves long-term corrosion resistance. It does not remove weld scale, heat tint or existing rust — those need pickling first — and it does not smooth or brighten the surface; for that, see electropolishing. The electropolishing vs passivation page covers the choice in detail.

Fabricated stainless steel vessel with nozzles pickled and passivated at Harrison Electropolishing

Specifications we work to

Specification	Scope
ASTM A967	Chemical passivation treatments for stainless steel parts — nitric and citric methods and verification tests
ASTM A380	Cleaning, descaling and passivation of stainless steel parts, equipment and systems
SAE AMS 2700	Passivation of corrosion-resistant steels (aerospace) — Method 1 nitric, Method 2 citric
QQ-P-35	Federal passivation specification, cancelled and superseded by AMS 2700 / ASTM A967, still referenced on older drawings
ASTM B912	Passivation of stainless steels using electropolishing
ASTM B600	Descaling and cleaning of titanium and titanium alloy surfaces
Customer specifications	Medical, semiconductor, defense and company-specific procedures

Our passivation process

Pre-cleaning. Alkaline or ultrasonic cleaning to remove oils, grease and particulate so the acid reaches the metal.

Passivation bath. Immersion in nitric or citric acid at the concentration, temperature and time the specification and alloy call for.

Rinse. Deionized-water rinse to remove residual acid.

Drying. Filtered air, nitrogen or cleanroom drying depending on criticality.

Verification and inspection. Visual inspection plus the test the specification requires — copper sulfate (a copper-colored deposit indicates free iron) or ferroxyl (a blue coloration indicates free iron) — with results recorded against the part.

Nitric vs. citric acid

Both are recognized by ASTM A967 and AMS 2700. Nitric acid is the traditional method, effective on heavier contamination and on grades that respond better to a stronger oxidant; it is regulated for environmental and handling reasons. Citric acid is biodegradable and safer to handle, preferred for medical, food and pharmaceutical work, and increasingly the default where the specification allows it. The alloy matters too: some grades — 400-series and precipitation-hardening stainless among them — need a specific method. Harrison runs both and will recommend the method that meets your specification; see citric vs nitric passivation.

Materials we passivate

200-, 300- and 400-series stainless steels; duplex and super duplex; 6Mo alloys such as AL-6XN; and nickel alloys including Hastelloy, Inconel and Monel — see nickel alloy passivation. Titanium is cleaned to ASTM B600; see titanium.

Documentation and packaging

Every job ships with a certificate of conformance naming the specification and method; inspection records and traceability reports are available. Passivated parts are packaged to prevent recontamination — clean double-bagging for medical and food-grade parts, vacuum sealing, cleanroom packaging for critical components, and labeling for full traceability, or your packaging instructions.

Industries

Semiconductor · Data Center Liquid Cooling · Aerospace & Space · Pharmaceutical · Biotech · Oil & Gas · Industrial Gas · Petrochemical · LNG & Cryogenic · Hydrogen · Nuclear · Polymer · Marine · Paper & Pulp · Solar

Capacity, turnaround and certifications

Facility: 25,000 sq ft in northwest Houston, expanded and updated in 2021, with four overhead cranes and 15,000 lb material-handling capacity. Nitric and citric passivation lines under one roof. On-site service: across the Houston area and Gulf Coast, parts too large or too fixed to transport are passivated at your facility. Turnaround: expedited service is available and lead times vary with shop load; tell us your deadline and we will confirm it. Quotes go out within one business day. Hours: Monday–Friday, 7:00 AM – 5:00 PM. Quality system: ISO 9001:2015 and ISO 14001:2015 registered, with a certificate of conformance on every job and full traceability from receipt to release. Local to Houston? See electropolishing and passivation in Houston.

Request a Quote · Call 800-245-5707

More to Know

Frequently Asked Questions

What is passivation of stainless steel?

A chemical treatment with nitric or citric acid that removes free iron and other surface contaminants so stainless steel's natural chromium-oxide passive film can re-form. It restores corrosion resistance without adding a coating or changing dimensions.

What is the difference between ASTM A967 and AMS 2700?

Both cover chemical passivation with nitric or citric acid. ASTM A967 is the general industrial specification; AMS 2700 is the SAE aerospace specification. Drawings that reference the cancelled federal spec QQ-P-35 are normally met with either.

Should I use nitric or citric passivation?

Follow the specification first. Where either is allowed, citric is preferred for medical, food and pharmaceutical work and is safer to handle; nitric remains the choice for heavier contamination and for grades that need a stronger oxidant. Harrison runs both.

How do you verify passivation?

With the test the specification calls for — most often the copper sulfate test or the ferroxyl test for free iron — recorded on the certificate of conformance. Chromium-to-iron ratio results are available on request.

Does passivation remove weld discoloration or rust?

No. Passivation removes free iron and contaminants but not oxides, heat tint or scale. Those are removed by pickling to ASTM A380 first; welded fabrications normally get both.

Can you passivate equipment on-site?

Yes. Harrison field crews passivate installed piping, vessels, skids and systems across the Houston area and the Gulf Coast.

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.