ASTM B912, “Standard Specification for Passivation of Stainless Steels Using Electropolishing,” establishes requirements for producing and verifying a passive stainless steel surface through electropolishing. The specification covers stainless steels in the 200, 300, and 400 series, as well as precipitation-hardened alloys, and addresses the surface preparation, electropolishing, post-treatment, verification testing, and documentation necessary to ensure an effective, repeatable electropolishing process. ASTM B912-26 is the current active edition, published in 2026. The standard provides a qualification and verification framework rather than one universal electropolishing procedure.
Why Passivate Post Electropolishing
Two major points must be made about ASTM B912 before a detailed explanation of the standard begins. First, it is true that a sound electropolishing operation results in a passive stainless steel surface. However, Astro Pak researchhas found that a passivation treatment following electropolishing can provide additional corrosion-resistance benefit by further improving the passive layer composition, depending on alloy, surface condition, and service environment. The graph below details the increased benefit in the form of the passive layer’s chromium-to-iron ratio.
Second, ASTM B912 is not a procedure. The standard is not meant to provide process parameters such as: electrolyte solution chemistry, electrical contact time, or the required current density to adequately polish a stainless steel surface. The goal of the standard is to provide a framework for an electropolishing provider to qualify a self-developed electrochemical process via cleaning recommendations, acceptance criteria, and verification tests.
ASTM B912 Specifics
ASTM B912, like other ASTM standards, begins with sections on the specific scope, referenced documents, and terminology relevant to the standard. Ordering information is the first section of non-standard ASTM Standards content. In this section, the standard specifies it is the responsibility of the purchaser to determine the acceptable electropolishing process for the following:
- finish (bright vs. dull)
- level of contact marks
- minimum and maximum amount of metal removal
Due to the language in this section, there is no universal requirement per ASTM B912 for a minimum amount of metal removed nor a minimum surface finish in terms of reflectivity or roughness for the electropolishing operation to be considered complete. The only requirement set in the standard for the electropolishing procedure is that the chosen parameters result in a component that passes one of the verification tests mentioned later in this post. The Surface Finish chapter of the ASME BPE Standard has seven defined Surface Designations with various roughness requirements, and a minimum amount of material removal if these are desired requirements for the purchaser.
Section 5 of ASTM B912
Section 5 of ASTM B912 introduces the actual electropolishing operation. Before any electrochemical work, the standard specifies to preclean the components per ASTM A380 or ASTM B322, “Guide for Cleaning Metals Prior to Electroplating.” No process parameters are mentioned in Section 5.5.2, “Electropolishing,” the section explains that parts should be electropolished at the current, temperature, and time necessary to provide both a passive surface and previously agreed upon surface finish. Although ASTM B912 is not meant to be a procedure, it does contain a basic set of process parameters suitable for multiple stainless steel alloys in its Appendix.
The electrolyte solution used in electropolishing often leaves a residual phosphate film on the workpiece that must be removed. ASTM B912 recommends rinsing the piece in a nitric acid solution to remove this film as a “Post Dip” operation. Nitric acid is not mandated, other acids or chemical solutions that maintain a passivated surface are allowed according to Section 5.2.3.1 of the standard. The final operation mentioned in Section 5 is to rinse the polished workpiece. ASTM B912 does not provide a rinse procedure but recommends that deionized or distilled water is used to remove all acidified water left on the surface during the electropolishing and post dip operations.
Verification Testing
Following the rinse procedure are passivation verification tests. All five of these tests are the same as the first five introduced in our previous blog post on ASTM A967. As noted in the previous post, the verification tests are qualitative; they do not show how corrosion resistant the passive layer is. Instead, they determine whether a passive surface is present.
Five more sections of content round out ASTM B912. They are:
- Part Sampling
- Part Rejection
- Certification
- Packaging
- Process Test Report
The first three are intended for electropolishing operations in which components are batch processed, addressing how quality can be maintained at scale when inspecting every processed component is not feasible. The test report is documentation certifying that components have been tested in accordance with one of the verification tests mentioned above. It is not a comprehensive report on the full electropolishing procedure performed.
How ASTM B912 Relates to ASTM A967 and ASTM A380
ASTM B912, ASTM A967, and ASTM A380 address related but different aspects of stainless steel surface treatment. ASTM B912 is specific to passivation by electropolishing. ASTM A967 addresses chemical passivation treatments for stainless steel parts, while ASTM A380 is the most comprehensive chemical processing document, addressing cleaning, descaling, and passivation practices for stainless steel parts, equipment, and systems.
These standards are not interchangeable. A project may reference more than one of them depending on the required cleaning, surface preparation, electropolishing, passivation, and verification sequence.
ASTM B912 and Astro Pak
Proper following of ASTM B912 results in a repeatable and verifiable electropolishing process for stainless steel. Astro Pak utilizes its processes developed from this standard in all of its shop facilities across the nation, or via its electropolishing crews that mobilize to customer locations when systems are too large to transport or cannot be easily disassembled.
Astro Pak also provides a robust documentation package upon completion of all jobs to serve as detailed evidence of the work performed on the processed system. Additional technical information is available through Astro Pak’s Electropolishing & Mechanical Polishing and passivation resources.
Frequently Asked Questions
ASTM B912 is the standard specification for passivation of stainless steels using electropolishing. It covers stainless steels in the 200, 300, and 400 series as well as precipitation-hardened alloys.
ASTM B912-26 is the current active edition as of 2026. Project and purchasing documents should identify the required edition when revision control is important.
No. ASTM B912 establishes process and verification requirements but does not prescribe one universal electrolyte chemistry, current density, temperature, or processing time for every stainless steel component.
No universal Roughness Average (Ra) value is required by ASTM B912. Surface finish and material-removal requirements are established for the specific component or project.
No. ASTM B912 addresses passivation through electropolishing, while ASTM A967 addresses chemical passivation treatments for stainless steel parts. Depending on project requirements, both standards may be relevant.
Electropolishing can be performed on installed systems when access, geometry, electrical control, containment, and other process conditions allow the work to be executed in a controlled manner.
