The first of the two main passivation standards currently active is ASTM A967. A967 allows for passivation using nitric acid or citric acid, followed by a per-lot testing using one of several test method options, including copper sulfate. The citric acid process is subdivided into Citric 1 through Citric 5. Citric 1-3 assigns a solution of 4-10 weight percent citric acid, with treatment times that decrease with increasing temperature. Citric 4 and 5 allow for alternate parameters, including the use of other additives. CitriSurf products necessarily fall under Citric 4, but our recommended procedures also keep to the concentration and other parameters laid out in Citric 1-3.
A967 is available from the ASTM website.
The other main passivation standard currently active, used in the aerospace industry, is AMS 2700. Similarly to ASTM A967, it allows for passivation using either nitric acid or citric acid. The nitric acid treatments are labeled Method 1 and given as eight different variations called Types, in keeping with the old QQ-P-35. The citric acid process is labeled Method 2 and not subdivided further, and assigns a solution of 4-10 weight percent citric acid, with treatment times that decrease with increasing temperature, and the optional use of other additives. CitriSurf products fall under this Method 2. AMS 2700 also assigns to parts different Classes, which refers to the sampling quantity for per-lot testing using one of several test method options, including copper sulfate.
AMS 2700 is available from the SAE website.
Perhaps the most used passivation standard previously is the US military specification QQ-P-35, which described the nitric acid treatments still in use today by ASTM A967 and AMS 2700. It also assigned testing per MIL-STD-753, which described several of the test methods still in use today. The cancellation of QQ-P-35 assigns the use of ASTM A967 or AMS 2700 for all DoD related activities that list QQ-P-35 for use.
The final revision QQ-P-35C and the cancellation notices are available from the US Defense Logistics Agency ASSIST Quick Search website.
You may also see mention of AMS-QQ-P-35, which was a stopgap document used by SAE after the cancellation of the original QQ-P-35 but before the replacement AMS 2700 was ready. It is identical to the original QQ-P-35, and is also now canceled and replaced by AMS 2700.
Also well known due to having been around for a while is ASTM A380. It is primarily a document about various cleaning methods for stainless steel, but a section on nitric acid passivation was also included. Though used by many as a standard for stainless steel passivation, A380 is now outdated on that subject. A967 should be referred to where a standard for stainless steel passivation is needed.
However, as introduced in the 2013 revision of A380, it does also directly allow the use of passivation methods from A967, including citric acid (see section 6.4).
A380 is available from the ASTM website.
Citric acid passivation/iron removal for titanium and titanium alloys was introduced in the 2011 revision of ASTM B600 (see section 4.3.3).
B600 is available from the ASTM website.
ASTM F1089 assigns passivation testing of reusable surgical instruments using two test methods, including copper sulfate.
F1089 is available from the ASTM website.
ASTM F86 assigns procedures for surface cleaning of metallic surgical implants, including stainless steel and titanium. A nitric passivation treatment is described within the document, but it states that the listed treatments “should not be considered restrictive”, and it also states the following (section 6.5 in the 2013 revision):
“If acceptable alternative surface treatments for implants are used, these treatments should be specified in the production procedure documentation.”
This allows the use of citric acid passivation for implants as long as proper documentation is created.
F86 is available from the ASTM website.
Other US Military Specifications
The following specs refer to ASTM A967 and AMS 2700 for passivation of stainless steel:
- MIL-S-5002E (section 3.8.6)
- MIL-STD-171F (section 188.8.131.52, Table V. finish numbers 5.4.1 and 5.5.1)
The following specs refer to QQ-P-35 for passivation of stainless steel and thus allow the use of ASTM A967 and ASM 2700:
- MIL-STD-808A / MIL-HDBK-808 (section 184.108.40.206.1, Table II. finish code numbers F-200, F-201, F-202, F-203, F-204, Table VIII. finish code number D-200)
- MIL-S-5002D (section 220.127.116.11.1, replaced by revision E)
The following spec refers to ASTM A380 for passivation of stainless steel and thus allows the use of ASTM A967:
- MIL-DTL-14072D/E/F (Table IV. Finish E300)
The spec MIL-T-704K in section 3.2.6 directly describes a passivation process analogous to QQ-P-35’s type II followed by a chromate post-treatment. However, QQ-P-35 assigns this process as appropriate only for certain grades of stainless. MIL-T-704 does allow this process to be skipped if the stainless is “already passivated”, with no restriction on method for that.
USDA Approval (discontinued)
The USDA Food Safety and Inspection Service previously had a program for prior approval of nonfood compounds for use in food processing plants, but has eliminated the requirement. They now only require the product to be safe and effective under the conditions of use. This allows our CitriSurf products to be used in food processing plants. A program similar to the cancelled USDA program was subsequently created by the NSF.
The USDA documentation on the requirement change can be found at their website.
NSF International launched its voluntary Nonfood Compounds Registration Program in 1999 to re-introduce the previous authorization program administered by the U.S. Department of Agriculture (USDA). NSF Registration assures inspection officials and end users that formulations and labels meet appropriate food safety regulations including FDA 21 CFR.
The following CitriSurf products are registered in NSF’s Nonfood Compounds Registration Program White Book as acceptable for use in and around food and pharmaceutical processing areas, tanks, and piping, where its use is not intended for inclusion into food ingredients. This means that NSF certifies the products, when sufficiently rinsed, will not leave a residue. (However, this is also true of the CitriSurf products that Stellar Solutions has chosen not to register.) Please contact Stellar Solutions if you have further questions about this registration program.
- CitriSurf 2250 (category A3, Reg # 148469)
- CitriSurf 3050 (category A3, Reg # 137373)
- CitriSurf 2210 (category A3, Reg # 137374)
- CitriSurf 2310 (category A3, Reg # 148468)
- CitriSurf 77 (category A3, Reg # 137375)
- CitriSurf 77 Plus (category A3, Reg # 148467)
- CitriSurf 2325 (category A3, Reg # 148470)
- CitriSurf 8050 (category A3, Reg # 139951)
NSF also has regulations for drinking water chemical additives (NSF 60) and materials that drinking water comes into contact with (NSF 61). CitriSurf does not fall under the purview of either of these. For the same reason that CitriSurf may be used on food contact surfaces, it may be used on drinking water contact surfaces.
To our knowledge, the US Food and Drug Administration neither approves nor disapproves passivation products for use on food contact surfaces, medical instruments, and pharmaceutical manufacturing equipment. When passivating these items, complete rinsing must be achieved to ensure no product residue remains. NSF Nonfood Compounds Registration may be used to provide assurances that this is the case.
The European Restriction of Hazardous Substances Directive (RoHS) forbids the presence of a short list of hazardous materials within electronic equipment in an effort to reduce toxic waste in discarded devices. Similar regulations have been created by some other countries as well. Passivation does not add or introduce new material to the surface of stainless steel and therefore does not fall under the purview of RoHS. Additionally, CitriSurf does not contain any of the substances banned by RoHS.
The European Registration, Evaluation, Authorization and restriction of Chemicals (REACH) regulation governs the import and manufacture of chemical substances within the European Union. For the use of our products within Europe, please refer to our distributors there for REACH information. For exporting passivated stainless steel parts to Europe, the REACH status of the passivation chemicals is not relevant because passivation does not add or introduce new material to the surface of the stainless steel.
5.11 D, Section 3 of the NIOP Trading Rules states:
“Ship tanks, which have been newly coated, or fully recoated, or passivated stainless steel tanks shall be considered as new buildings. Cargoes carried prior to the date of such coatings or passivation shall not be considered as relevant. Owners are required to provide independent verification when requested. Owners will not withhold prior cargo information if requested. Ship owners should employ a passivation process such as that recommended under the current version of ASTM A967. NIOP accepts the media for passivation listed under the ASTM guidelines including, but not limited to, Nitric Acid and Citric Acid solutions.”