Towards the end of the 19th century, the United States depended on a rail network that linked different parts of the country together. Yet a wave of rail accidents during this period disrupted commerce and travel, threatening to curb the economic growth of the emerging industrial giant. In 1898, scientists and engineers working for the Pennsylvania Railroad responded to these mishaps by forming the American Society for Testing Materials (ASTM).
The first thing the ASTM did is develop a standard for rail fabrication, which helped make the US rail industry safer. In 1902, the ASTM changed its name to the American Society for Testing and Materials, as it symbolically moved beyond its focus on the railroad industry by adopting “and” in its name. In the early 1960s, “International” was added to the acronym as its standards were increasingly adopted globally. ASTM passivation standards are part of the organization’s range of technical recommendations and regulations, which provide guidance to many industries for numerous applications.
Purpose of ASTM Standards
Through the application of reliable engineering and science practices, along with the utilization of good judgment, members of ASTM International seek to improve a wide array of services, systems, procedures, products, manufacturing techniques and material selection for various industries. Using a collaborative approach, stakeholders from government, industry and elsewhere look at what standards produce the highest quality work while remaining relevant to commercial interests. Used worldwide, ASTM creates standards for various applications and industries, which include construction, consumer products, electronics, energy, medical devices, metals, paints, plastics, textiles and more.
ASTM International categorizes its standards into six different types:
- Classifications: Arranging materials, products, service or systems systematically into categories based on their characteristics.
- Guide: Gathered information that present options for the best course of action to take.
- Practice: Defining instructions on how to perform single or multiple operations without a test result.
- Specifications: These requirements for materials, products, service or systems help ensure customer satisfaction.
- Terminology: Text that defines terms, including for abbreviations, acronyms and symbols.
- Test methods: Define procedures to produce results from testing.
Perhaps as a relic of the organization’s historical ties to railways, most ASTM standards relate to materials containing iron and steel. Of the standards regarding metals and alloys written by ASTM, passivation standards offer companies a means to fabricate products requiring this process at the highest levels of quality and efficiency.
ASTM Passivation Standards
As a finishing method, passivation is a chemical treatment that creates a protective oxide layer, known also as a passivation film. It’s primarily used to prevent corrosion in metals, especially for steel and other iron-based alloys. ASTM passivation standards are formed by committees made up of manufacturers, academics and consumers, along with other end users. Besides the ASTM passivation standards, the organization also provides technical training and other education concerning the process to stakeholders in both government and industry to help achieve more effective regulations so that manufacturers can make more reliable products.
Diverse applications use ASTM passivation standards, including:
- Dental tools
- Domestic appliances
- Hospital equipment
- Industrial equipment
- Medical devices and implants
- Pressure vessels
- Process piping
- Stainless steel components, equipment and systems
- Storage tanks
- Surgical implements
- Titanium plating and other surfaces
Two of the ASTM passivation standards used widely by industry are B600 and A967.
ASTM Passivation Standard B600
This specification involves the descaling and cleaning of titanium and surfaces made from its alloys. These ASTM passivation standards are used commonly within the medical industry when dealing with the metal. With guidance from the ASTM, passivation processes are recommended to manufacturers on how to remove oxides, scaling, soil and other foreign substances from titanium surfaces. Using the B600 standard written by the ASTM, passivation removes these contaminants, which hinder the quality and reliability of products made from the metal. Given the importance of titanium in the medical industry,
The scope of the B600 standard outlined by ASTM on passivation involves guidance on:
- Cleaning and descaling procedures.
- Voluntary procedures for titanium and its alloys being processed into cast, fabricated or wrought form.
- Removal of foreign substances before chemical milling, fabrication, joining, plating or other processes take place.
- If and when to use acid etching after cleaning.
- Values of measurements provided regarding standard American measurements, along with conversions to metric.
- Establishment and following of practices regarding environmental, health and safety procedures that may be applicable due to regulations.
After following the procedures recommended by ASTM for passivation of titanium as described in the B600 standard, it’s unlikely a workpiece will require additional post-treatments.
ASTM Passivation Standard A967
This ASTM passivation standard is used generally by numerous industries. Standards A967 and A967M offer guidance from the ASTM on passivation of stainless steel alloys in order to improve their existing qualities. Based upon chemical methods for passivation using either citric or nitric acid, this ASTM passivation standard advises on the elimination of free iron particles from the alloy’s surface. This takes place under precisely controlled conditions to provide a passive metal oxide layer that makes it more corrosion-resistant.
Used in various chemical treatments besides passivation, nitric acid is a commonly used mineral acid. In contrast, citric acid is an organic acid that’s used within the food and beverage industry. While nitric acid has a longer history of use in passivation processes for treatment of metal surfaces, citric acid poses less of a safety concern and requires less strict handling procedures.
The scope of the A967 standard outlined by ASTM on passivation involves guidance on:
- Cleaning, descaling and passivating stainless steel parts; it covers several methods for passivation via chemical treatments.
- Procedures for chemical and mechanical treatments as discussed in ASTM A380.
- A number of alternative chemical passivation treatments for stainless steel components, with regard to specific grades of stainless steel.
- Testing to confirm passivation effectiveness, which include the following testing techniques that use:
- Water immersion
- High humidity
- Salt spray
- Copper sulfate
- Potassium ferricyanide and nitric acid Test
- Damp cloth
- Boiling water immersion
- Values of measurements provided in either metric or standard American measurements, using each measuring system independently of the other to prevent non-conformance within the standard.
These ASTM passivation standards also advise as to the methods used for verifying whether the process is successful. However, passivation occurring spontaneously due to air and moisture are not covered within either A967 standards by the ASTM. Passivation as per these standards also don’t look at more aggressive surface treatments like pickling.
Differences Between Versions of A967 ASTM Passivation Standard
The ASTM passivation standard A967 was updated in 2017, with the current version replacing the previous one from 2013. The newer 2017 version adds new tests and removes a test for the food processing sector, while also clarifying restrictions that can result in hydrogen embrittlement, information in newly written appendixes and other specifications.
The main differences between the older and updated ASTM passivation standards are:
- Addition of boiling water immersion test, with minor changes to other existing tests.
- Copper sulfate test now applicable to components used in food processing industry.
- Appendix X1 that restricts higher strength grades of acid due to hydrogen embrittlement don’t apply to citric acid passivation, though still apply to passivation via nitric acid.
- Appendix X2 that provides generalized guidance for choosing types of passivation treatments for various stainless steel grades.
Both of the current and previous A967 ASTM passivation standards describe the process, along with recommendations on whether to use citric or nitric acid for specific applications. It continues to offer guidance on concentrations, timetables, temperatures and other requirements concerning each acid, while also retaining tests to establish efficacy after passivation.
Other ASTM Passivation Standards
Various other standards for passivation are also used by ASTM to advise businesses, regulators and other stakeholders. Many of these are subject to change whenever new research shows more efficient methods, materials or other factors that make the passivation process more efficient.
Other ASTM passivation standards include:
- ASTM F1089-18: Provides a means to evaluate corrosion test methodologies to help better serve material choice and appropriate treating procedures.
- ASTM A380: Covers recommendations and precautions regarding passivating new stainless steel assemblies, components, equipment and whole systems, while also acting as a preliminary ASTM passivation practice to support the A967 standard.
- ASTM B912-02: Comprises guidance for passivating stainless steel alloys in the 400, 300 and 200 series, along with alloys hardened by precipitation, via electropolishing.
- ASTM D6492-99: Used to detect hexavalent chromium on steel surfaces that are coated with galvanized aluminum and zinc alloys.
- ASTM F1026-86: Deals with aspects of workmanship generally for reusable hemostatic forceps made from stainless steel.
RP Abrasives & ASTM Passivation Standards for Manufacturers
With ISO 9001:2015 certification for quality management, RP Abrasives offers passivation and other finishing services for metals and alloys, including stainless steel and titanium. We follow ASTM passivation standards B600 and A967, utilizing citric acid passivation methods where possible to support our objectives in minimizing our environmental impact. To learn more about ASTM passivation standards and how we can help you achieve a better finish to your project, we invite you to contact our team at RP Abrasives today.