More A Consideration shall be given in the design of parts, equipment, and systems that will require cleaning to minimize the presence of areas in which dirt, or cleaning solutions might become trapped, and to provide for effective circulation and removal of cleaning solutions. Materials shall be precleaned. Scales shall be removed through chemical descaling, acid pickling, and mechanical descaling. Degreasing and general cleaning shall be accomplished by immersion in, swabbing with, or spraying with alkaline, emulsion, chelate, acid, solvent, or detergent cleaners or a combination of these; by vapor degreasing; by ultrasonics using various cleaners; by steam, with or without a cleaner; or by high-pressure water-jetting.
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ASTM A 1. Scope 1. These recommendations are presented as procedures for guidance when it is recognized that for a particular service it is desired to remove surface contaminants that may impair the normal corrosion resistance, or result in the later contamination of the particular stainless steel grade, or cause product contamination.
For certain exceptional applications, additional requirements which are not covered by this practice may be specified upon agreement between the manufacturer and the purchaser. Although they apply primarily to materials in the composition ranges of the austenitic, ferritic, and martensitic stainless steels, the practices described may also be useful for cleaning other metals if due consideration is given to corrosion and possible metallurgical effects.
In order to avoid ambiguity in the setting of requirements, it may be necessary for the purchaser to define precisely the intended meaning of passivation. Some of the various meanings associated with the term passivation that are in common usage include the following: Passivation is the process by which a stainless steel will spontaneously form a chemically inactive surface when exposed to air or other oxygen-containing environments.
It was at one time considered that an oxidizing treatment was necessary to establish this passive film, but it is now accepted that this film will form spontaneously in an oxygen-containing environment providing that the surface has been thoroughly cleaned or descaled.
Passivation is removal of exogenous iron or iron compounds from the surface of a stainless steel by means of a chemical dissolution, most typically by a treatment with an acid solution that will remove the surface contamination but will not significantly affect the stainlees steel itself. This process is described in a general way in and defined precisely in with further reference to the requirements of and Part II of the table on acid cleaning of steel.
Unless otherwise specified, it is this definition of passivation that is taken as the meaning of a specified requirement for passivation. Passivation is the chemical treatment of a stainless steel with a mild oxidant, such as a nitric acid solution, for the purpose of enhancing the spontaneous formation of the protective passive film. Such chemical treatment is generally not necessary for the formation of the passive film.
Passivation does not indicate the separate process of descaling as described in Section , although descaling may be necessary before passivation can be effective. On the other hand, some of the practices may be applicable for these purposes. While the practice provides recommendations and information concerning the use of acids and other cleaning and descaling agents, it cannot encompass detailed cleaning procedures for specific types of equipment or installations.
It therefore in no way precludes the necessity for careful planning and judgment in the selection and implementation of such procedures. The degree of cleanness required on a surface depends on the application. In some cases, no more than degreasing or removal of gross contamination is necessary. Others, such as food-handling, pharmaceutical, aerospace, and certain nuclear applications, may require extremely high levels of cleanness, including removal of all detectable residual chemical films and contaminants that are invisible to ordinary inspection methods.
The term "iron," when hereinafter referred to as a surface contaminant, shall denote free iron. Meaningful tests to establish the degree of cleanness of a surface are few, and those are often difficult to administer and to evaluate objectively. Visual inspection is suitable for the detection of gross contamination, scale, rust, and particulates, but may not reveal the presence of thin films of oil or residual chemical films.
In addition, visual inspection of internal surfaces is often impossible because of the configuration of the item. Methods are described for the detection of free iron and transparent chemical and oily deposits.
For such tests, it is appropriate to specify one of the practices listed in Specification A This standard does not purport to address all of the safety concerns, if any, associated with its use.
It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. For more specific safety precautions see , , Section , , and.
ASTM A380-17: Cleaning and Passivation of Stainless Steel
Stainless passivation is the process by which stainless steel will spontaneously form a chemically inactive surface when exposed to air or other oxygen-containing environments. It is this passive layer that gives stainless steels their corrosion resistance. If a stainless steel surface is scratched, then more Chromium is exposed which reacts with oxygen allowing the passive layer to reform. However, if a particle of carbon steel is embedded in the scratch then the passive layer cannot reform and corrosion will occur when the metal is wetted or exposed to a corrosive environment. Stainless passivation is the chemical treatment of a stainless steel surface with a mild oxidant such as citric acid passivation solution.
Stainless Steel Passivation
Want this as a site license? Changes from the previous issue A redline edition is available for this document, with all changes visible. Ask Document Center Inc. Scope 1. These recommendations are presented as procedures for guidance when it is recognized that for a particular service it is desired to remove surface contaminants that may impair the normal corrosion resistance, or result in the later contamination of the particular stainless steel grade, or cause product contamination. The selection of procedures from this practice to be applied to the parts may be specified upon agreement between the supplier and the purchaser.