This is the standard used by general industry to describe and control the passivation of stainless steel. Passivation is a process of making stainless steel more stainless than it would be if left alone. It is based on using an acid (nitric or citric) under highly controlled conditions to remove free iron particles from the surface and to help form a metal oxide layer that increases its ability to resist rusting. It is important to understand that passivation is not a coating applied to the surface; it is a process that makes the surface itself more resistant to staining or rusting.
The ASTM A967 standard is produced and controlled by ASTM International, an international standards-setting organization based in West Conshohocken Pennsylvania. The current version of the standard, ASTM A967/A967M – 17 was approved on July 1, 2017, and published later that month. It supersedes the previous standard, ASTM A967/A967M – 13 which was approved February 15, 2013.
The current and previous standards describe the process and the specific parameters when using nitric acid or citric acid. Each acid has several specific combinations of concentration, temperature, and required time as well as other specific requirements. Both standards also describe a number of different tests which can be used to determine the effectiveness of the process.
AMS refers to Aerospace Material Specification which is developed and published by SAE International. The Society of Automotive Engineers started in 1905 and quickly began working with other engineering societies. In 2006, at the age of 101, its name changed to SAE International.
AMS 2700 is the standard most frequently used by the aerospace industry for describing and controlling the process of passivation.
Differences Between ASTM A967 and AMS 2700
There are several important differences between the two standards. The first difference is the addition of a new test which can be used instead of any of the current tests which are continued. The new test is a boiling water immersion test. In addition to this new test, there are slight modifications to several of the existing tests.
The second difference is that the copper sulfate test can now be applied to parts used in food processing. The third important difference is in appendix X1 which states that restrictions on certain high-strength grades such as 440 C that is subject to hydrogen embrittlement are limited to nitric acid and these restrictions do not apply to citric acid passivation.
The fourth significant difference is the addition of appendix X2 which serves as a general guide for the selection of a passivation treatment for different grades of stainless steel.
In summary, the new version clarifies a number of specific details, adds an additional new test, removes restrictions on testing parts used in food processing, clarifies restrictions applying to high-strength steels subject to hydrogen embrittlement and adds clarifying information in the new addendum X2. For more information about how RP abrasives innovative passivation services may help you, please contact us today.
In summary, both standards describe and control how stainless steel (corrosion-resistant steel) can be made more stainless or corrosion resistant, thereby allowing products to work in harsh conditions, to work longer and to be more reliable than they otherwise would be. To learn more about the innovative passivation services RP Abrasives provides, including citric acid passivation contact us today.