How to Passivate Stainless Steel with Citric Acid. ASTM-Compliant & Safe.
Non-toxic passivation you can do in-house.Stainless steel passivation has traditionally relied on nitric acid baths — hazardous and environmentally unfriendly. Today, CitriSurf® citric acid technology offers an ASTM-compliant, non-toxic alternative. Safer, greener, and proven more effective, it makes stainless steel passivation practical even for in-house use.
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Why Engineers are Moving Away from Nitric Acid
Meeting ASTM Standards with Safer, Smarter Chemistry
| Property | Nitric Acid | Citrisurf |
|---|---|---|
| Safety | Very hazardous | Very safe to use as directed |
| Air Breathing | Emits toxic gases | No toxic gases emitted |
| Ease of use | Bulky safety equipment and extreme care required | Minimum of safety equipment and caution in use |
| Passivation | Excellent passivation of most grades of stainless | Excellent passivation of nearly all grades of stainless |
| Cost | Low cost raw material; high cost maintenance and waste disposal. High cost of safety and ventilation system | Lower overall cost to use due to lower maintenance and waste disposal costs; longer lasting solutions and lower concentration necessary |
| Environment | Environmentally hazardous | Environmentally friendly |
| Speed | 20 minutes to several hours required | 4-20 minutes typical, depends on process and grade |
| Temperature | Elevated temperature required for many grades | Room temperature satisfactory for many grades. Elevated temperature improves speed and performance |
| Maintenance | Regular solution replacement required with removal of hazardous waste. | Solutions lasts much longer and most operations have no hazardous waste to remove at all |
| Iron Oxide removal | Removes iron oxide slowly | Readily removes iron oxide |
| Equipment | Long-term degradation of tanks and area equipment is expected | No deleterious effects on recommended tanks and equipment, or corrosion of equipment in area |
| Flexibility in use | Must control time/temperature carefully and danger of NO x emissions is always present | No hazard of leaving product in the tank too long for most products, no hazardous emissions even with poor grades of stainless steel parts. |
| ASTM A-967 / A380 | Meets requirements | Meets requirements |
| AMS 2700 | Meets requirements | Meets requirements |
CitriSurf® is a registered trademark of Stellar Solutions, Inc., McHenry, IL USA.
Proven Performance Advantages of Citric Acid
✔ Thicker protective layer – Citric acid passivation selectively removes iron over nickel and chromium, producing a thicker and more corrosion-resistant oxide layer than nitric acid passivation.
✔ No heavy metal waste – Unlike nitric acid, citric acid passivation does not introduce heavy metals into the bath, avoiding hazardous waste.
✔ Improved 302 & 316 performance – Stainless steels 302 and 316 show greater corrosion resistance after citric acid passivation compared to nitric acid passivation.
✔ Solves 420 stainless issues – Nitric passivation often causes rust and corrosion problems in 420 stainless steel (common in surgical applications), but organic acid passivation eliminates these failures.
✔ Proven in testing – Citric acid passivation passes rigorous salt spray, immersion, and high humidity tests.
✔ Safe, compliant storage – Raw citric acid materials can be stored as non-hazardous chemicals, reducing storage and compliance costs.
Independent Validation: NASA Study
A 2011 study sponsored by NASA and the United Space Alliance concluded that “citric acid most likely performs as well or better than nitric acid” in stainless steel passivation.
In-House Passivation Made Possible
Now you can schedule your own in-house passivation, and meet the requirements of the ASTM A967, ASTM A380, ASTM B600, and AMS 2700 standards.
Stainless Steel Passivation & Galvanising Stop Off Services in Melbourne
Our Products
CitriSurf® | Citric Acid Based Rust Removal and Passivation Products |
|---|---|
| CitriSurf 77 Plus | For applications where it is desired to spray the product on a local area. (May not be appropriate for sensitive grades) |
| CitriSurf 2310 | Gelled version for use on weld joints, vertical surfaces, and large items or areas. (May not be appropriate for sensitive grades) |
| CitriSurf 2325 | For tanks, pipe systems, and bulk quantities of parts. (May not be appropriate for sensitive grades) |
Product | Copper Sulfate Passivation Test Kit |
|---|---|
| Copper Sulfate Passivation Test Kit | To verify the effectiveness of the stainless steel passivation treatment. |
CitriSurf® | Citric Acid Based Passivation Products |
|---|---|
| CitriSurf 2250 | For most grades of stainless steel, including austenitic, ferritic, martensitic, precipitation hardening, and duplex. |
| CitriSurf 2450 | Designed for improved performance with very sensitive grades (e.g. 420) of stainless steel. |
| CitriSurf 3050 | For austenitic grades of stainless steel where very low foaming is required, i.e. baths with air agitators and spraying/CIP applications |
| CitriSurf 3250 | For most grades of stainless steel where very low foaming is required, i.e. baths with air agitators. |
| CitriSurf 77 | For applications where it is desired to spray the product on a local area. (May not be appropriate for sensitive grades) |
| CitriSurf 2210 | Gelled version for use on weld joints, vertical surfaces, and large items or areas. |
By Category
Galvanizing Stop-off
Are you battling zinc residue after galvanising?Traditional methods like tape, silicone, and lime are still used in galvanising shops, but they’re messy, time-consuming, and inconsistent.
That’s why chemical engineers developed Galvastop®, a paint-on stop-off product for hot dip galvanising. Unlike tape or silicone, Galvastop® passes through all pre-treatments and comes out of the kettle as a light ash that brushes away easily. Unwanted zinc bonds to the Galvastop®, not the steel — so you can remove it cleanly without grinding or retapping.
Why engineers choose Galvastop® for hot dip galvanising:
✔ Faster curing than silicone
✔ Quicker application than high-temperature aluminium tape (HTAP)
✔ Easy to apply — no sticky adhesives like HTAP
✔ Cleaner finish on threads after galvanising compared to HTAP and silicone
✔ Safe removal — no scraping or thread damage like with HTAP
Galvastop® is also suitable as a corrosion-preventative coating in extreme environments, making it a versatile solution for galvanising operations.
BlowOut®
The safe alternative to acid descalers for industrial cleaningTraditional descalers rely on acids, caustics, and dangerous solvents to break down calcium, lime, scale, milk stone, beer stone, and other deposits. These chemicals are hazardous, increase insurance premiums, raise OHS costs, add storage and discharge fees, and reduce staff morale.
That’s why engineers and global organizations trust BlowOut® — the non-toxic, non-corrosive descaler designed for safe, effective industrial use.
Why BlowOut® is the smarter choice:
✔ Aggressive cleaning power without acids or caustics
✔ Non-fuming, non-toxic, biodegradable formula
✔ No trace metal removal — safe for effluent disposal
✔ Approved by the U.S. Navy and U.S. Coast Guard
✔ Only non-acid descaler cleared for Navy ship heat exchangers
✔ Protects staff and the environment while lowering compliance costs
BlowOut® is more than just a non-toxic descaler — it’s the proven, environmentally safe solution for industries needing reliable descaling without the risks of nitric or hydrochloric acids.
Solvent-free degreaser
Solvent-Free, Non-Toxic, BiodegradableUnlike others, Synclean HD is a Solvent-free, heavy-duty, non-toxic, and eco-friendly, patented water-based formula that removes grease, oils, and fats without harsh chemicals.
Heat Treatment
Non-Toxic, Biodegradable, and Free From Mineral Oils and Nitrites.Induction hardening has never been easier or safer than with Aquatensid BW, the advanced water-based quench. This thick green liquid is completely non-toxic, biodegradable, and free from mineral oils, nitrites, and other harmful substances traditionally found in quenching chemicals.
Why engineers choose Aquatensid BW:
✔ Provides consistent, fast, and uniform quenching for carbon and alloy steels.
✔ Short vapor phase minimizes distortion and cracking in hardened steels.
✔ High concentration reduces water quenching speed, delivering safer and more precise results.
✔ Eco-friendly alternative that supports safer working environments and compliance with modern standards.
Aquatensid BW is designed to give engineers reliable, repeatable results while eliminating the hazards and waste issues of traditional quenchants.
Lubricants
High lubricating properties and film strengthIsoform TD 50
Isoform TD 50 is a water-immiscible coolant that contains chlorine and is designed for metal forming operations on both ferrous and non-ferrous metals. It is distinguished by its high lubricating properties and strong film strength, making it ideal for applications such as bolt head moulding, thread rolling, wire drawing, tube forming and bench drawing operations. Isoform TD 50 also performs well in heavy-duty fine blanking and deep drawing applications across a wide range of alloys.
📄 Download Isoform Technical Data
Isolube 3411
Isolube 3411 is a low-viscosity metalworking fluid formulated primarily for aluminium. Its fluidity makes it effective in punching operations, while the residual liquid has low odour and is barely noticeable after use. For best performance, Isolube 3411 should be applied at room temperature and not exposed to extreme heat. It is not classified as hazardous under GGVS and GGVE regulations, making it a safer and compliant choice for precision aluminium processing.
“Highly effective in cleaning four years’ accumulation of deposits from the interior of the sewage system piping.”