Stainless Steel Passivation Procedure: ASTM A967 Guide

Passivation is often specified with a short drawing note: “Passivate per ASTM A967.” That note is useful, but it is not a complete manufacturing instruction. The actual stainless steel passivation procedure depends on alloy, surface condition, weld condition, contamination risk, part geometry, inspection method and the evidence the buyer needs with shipment.

For OEM buyers, the goal is not to become a chemical processing expert. The goal is to know what must be defined so the supplier does not treat passivation as a cosmetic add-on. A part can be made from the correct stainless grade and still fail in service if cutting, bending, grinding or welding leaves free iron, abrasive residue or heat tint on the surface.

For sourcing rather than process guidance, review our passivated stainless steel parts scope and surface finishing service. The drawing and RFQ still need to define the governing treatment, verification and documentation requirements.

What ASTM A967/A967M covers

ASTM A967/A967M is the common specification for chemical passivation treatments for stainless steel parts. The current ASTM page identifies the 2025 edition, so buyers should avoid using an old drawing note that simply says “ASTM A967” without revision control when the program is compliance-sensitive.

In practical sourcing terms, ASTM A967/A967M helps define:

• Acceptable chemical treatment families, including nitric and citric methods.
• Process controls such as solution, time and temperature.
• Cleaning and post-treatment requirements.
• Verification options used to confirm free iron removal.
• Rejection conditions when rust, staining or visible contamination remains.

It does not automatically define the best process for every part. The buyer still needs to define the alloy, surface finish, weld condition, inspection method and documentation requirement.

The procedure below connects the standard to the buyer-side decisions that affect fabricated parts: surface condition, weld cleanup, verification evidence and protected packaging.

A practical stainless steel passivation procedure

A controlled passivation workflow normally follows eight steps.

Step	Purpose	Buyer risk if skipped
1. Material and drawing review	Confirm grade, surface finish, welds and required standard	Wrong chemistry or missing test requirement
2. Pre-cleaning	Remove oil, coolant, dust and shop residue	Acid bath cannot reach contaminated areas
3. Scale and heat-tint removal if needed	Remove welding oxides or heavy discoloration	Passivation cannot remove thick oxide scale
4. Passivation treatment	Remove free iron and activate the stainless surface	Embedded iron can rust after shipment
5. Rinse	Remove residual chemistry	Staining, residue or downstream contamination
6. Drying and handling	Prevent water marks and recontamination	Fingerprints, carbon steel transfer or stains
7. Verification testing	Confirm the surface is acceptable	No evidence that treatment worked
8. Documentation and packaging	Preserve traceability and surface condition	Accepted parts can be damaged before arrival

The exact parameters are process-specific. A supplier should not quote passivation as a single uncontrolled line item if the parts are for medical equipment, food equipment, semiconductor equipment, marine hardware, liquid cooling components or other corrosion-sensitive applications.

Step 1: review the material and part condition

Start by confirming the stainless grade and the condition of the surface before chemical treatment.

Common passivation candidates include:

• 304 and 304L stainless steel.
• 316 and 316L stainless steel.
• 17-4 PH stainless steel after suitable heat treatment and cleaning.
• Welded stainless frames, brackets, trays, worktables and enclosures.
• Machined stainless manifolds, fittings and fluid components.

The grade matters because chemistry and process windows differ. The surface condition matters because passivation is not a magic repair process. A bright, clean, mechanically finished 316L panel is very different from a welded stainless assembly with heat tint, grinding debris and handling marks.

For material selection, read our 304 vs 316 stainless steel guide and stainless surface finishes guide.

Step 2: clean before acid treatment

Pre-cleaning is not optional. Oil, cutting fluid, polishing compound, adhesive residue and shop dust can block the acid from reaching the stainless surface. They can also react with the treatment chemistry and create stains.

A typical cleaning plan may include:

• Alkaline cleaning or detergent cleaning for oils and coolants.
• Solvent wipe where compatible with the material and process.
• Ultrasonic cleaning for small precision parts or complex features.
• DI water rinse for high-cleanliness applications.
• Visual inspection before chemical treatment.

For sheet metal fabrication, the most common contamination sources are laser cutting residue, press brake tooling transfer, grinding dust, carbon steel contact, shared worktables and dirty gloves. Good passivation starts on the shop floor, not in the acid tank.

Step 3: remove weld heat tint before passivation

This is where many passivation problems start. Weld heat tint is not just a color change. It indicates an oxide layer formed by heat exposure. Under and near that oxide, chromium depletion can reduce corrosion resistance.

Passivation can remove free iron, but it is not intended to remove heavy weld scale or heat tint. If the part has visible weld discoloration, the supplier may need a separate operation before passivation, such as:

• Mechanical finishing.
• Pickling or localized weld cleaning.
• Electropolishing for high-cleanliness stainless surfaces.
• Controlled brushing with stainless-only abrasives.

The buyer should state the required weld condition. For example:

Weld discoloration shall be removed before passivation. Final surface shall show no loose scale, carbon steel contamination or visible rust after verification.

For welded assemblies, see our weld inspection guide and welding distortion control guide.

Step 4: choose citric or nitric passivation

ASTM A967/A967M includes different passivation treatment options. In buyer conversations, the two common families are citric acid and nitric acid.

Factor	Citric passivation	Nitric passivation
Typical buyer reason	Lower environmental and handling burden	Legacy specification or established qualification
Mechanism	Chelates and removes free iron	Strong oxidizing acid removes surface iron contamination
Common use	Many modern stainless parts and assemblies	Aerospace, legacy drawings, specific customer requirements
Key control	Cleanliness, concentration, temperature, time, rinse quality	Concentration, temperature, time, safety and waste handling
Buyer advice	Accept if the specification permits and testing passes	Use when the drawing or customer standard requires it

Do not select the process only by habit. Select it by contract requirement, alloy, surface condition, supplier capability and verification method. If the drawing names a specific ASTM method or internal customer procedure, the supplier should follow that requirement unless an approved deviation is issued.

Step 5: rinse and dry correctly

Poor rinsing can ruin a good passivation process. Residual chemistry trapped in corners, seams, blind holes, hems, threads or gasket channels can cause staining and corrosion complaints later.

Complex sheet metal parts need special attention at:

• Hemmed edges and folded seams.
• Welded corners and lap joints.
• PEM hardware, threaded inserts and blind standoffs.
• Drain holes and enclosed cavities.
• Brushed or bead-blasted surfaces that hold residue.

Drying is also part of the procedure. Water left in pockets can create stains, especially if the final packaging traps humidity. For high-cleanliness stainless parts, final handling should prevent fingerprints and carbon steel transfer.

Step 6: verify the passivated surface

Passivation verification should be chosen before production, not argued about after parts are finished. ASTM A967/A967M includes several verification approaches; the correct one depends on the product requirement and practical risk.

Common verification methods include:

• Water immersion or high-humidity exposure.
• Salt spray exposure where required by specification.
• Copper sulfate testing for certain stainless grades and surfaces.
• Visual inspection for rust, staining, residues and discoloration.
• Documentation review for solution, time, temperature and lot control.

The important buyer question is simple: what proves acceptance?

For a commodity indoor bracket, visual inspection plus process certification may be sufficient. For a medical, food, marine, semiconductor or fluid-system component, you may need a stricter verification method and lot-level records.

304 vs 316 passivation considerations

304 and 316 stainless steels are both passivated in OEM fabrication, but the application risk is different.

304 stainless is common, cost-effective and suitable for many indoor and mildly corrosive environments. Passivation removes fabrication contamination and improves the chance that the surface performs as intended.

316 and 316L stainless add molybdenum for improved chloride resistance. That does not eliminate the need for passivation. A contaminated 316 surface can still show rust staining if free iron is embedded during fabrication.

For buyers, the rule is:

• Choose 316/316L when the environment needs it.
• Specify passivation when the surface condition and application require it.
• Do not assume that 316 automatically compensates for poor fabrication hygiene.

Documentation to request from the supplier

For normal industrial parts, a certificate of conformance may be enough. For regulated or high-risk work, ask for more detail.

Useful documentation can include:

• Material grade and heat-number traceability where required.
• Passivation standard and method used.
• Process lot or batch identification.
• Verification test method and result.
• Visual inspection record.
• Nonconformance and rework records, if applicable.
• Packaging method used to protect the surface.

If material traceability matters, pair the passivation requirement with an MTR requirement. See our material test report and traceability guide.

RFQ wording buyers can use

Clear RFQ wording prevents weak quotes. Here is a practical starting point:

Stainless steel parts shall be cleaned and passivated per ASTM A967/A967M after fabrication. Remove visible weld scale, heat tint, free iron contamination and shop residue before passivation. Supplier shall confirm citric or nitric method, verification test, lot traceability and packaging method. No visible rust, staining, acid residue or carbon steel contamination is acceptable at shipment.

For more critical parts, add:

• Required ASTM method or customer specification.
• Required verification test and sample size.
• Surface finish requirement before and after passivation.
• Whether weld heat tint must be fully removed.
• Whether DI rinse, clean packaging or cleanroom handling is required.
• Required certificates and inspection records with delivery.

Standards and verification sources

Use the current purchased standard and the contract revision as the controlling requirement. The public standard pages are useful for confirming scope, but they do not replace the full text:

• ASTM A967/A967M-25 covers chemical passivation treatment options and alternative verification tests for stainless steel parts.
• ASTM A380/A380M-25 addresses cleaning, descaling, pickling and passivation practices in greater detail.

The drawing, purchase order or customer specification should state which revision and acceptance method govern. Do not infer a test method from the word “passivate” alone.

Where passivation fits in DRAmetal projects

DRAmetal uses passivation as part of a broader stainless fabrication plan when the application requires corrosion resistance, cleanliness or surface integrity. It is relevant to:

• Passivated stainless steel parts with drawing-defined cleaning, treatment, verification and documentation requirements.
• Medical device housings and cleanable equipment panels.
• Stainless worktables and food-processing structures.
• Cooling manifolds and fluid-system components.
• Semiconductor equipment enclosures where contamination control matters.
• Welded stainless brackets, trays, covers and frames.

The best result comes from deciding the surface requirement before fabrication starts. Material selection, welding method, abrasive choice, cleaning, passivation, inspection and packaging all affect the final corrosion performance.

If you need stainless parts with controlled passivation, send us your drawings and surface requirements. Include the grade, finish, weld condition, standard, test requirement and documentation level, and our engineering team will review the correct process boundary before quoting.