1 This practice is under the jurisdiction of ASTM Committee A01 on Steel, Last previous edition approved in as A – 99 (). Standard. Standard number, ASTM-A ; ASTM-A Title, Standard Practice for Cleaning, Descaling, and Passivation of Stainless. May 2nd, – Below is a technical summary of specification ASTM A 99 Advanced Plating Technologies is not. Gold plating is an exceptional finish for.
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Evidence of in-service pitting in the heat tint in the HAZ may be seen in Figure 2.
Once the surface is cleaned and the bulk composition of the stainless steel is asrm to air or an oxygen-containing chemical environment, the passive film forms immediately. Naturally occurring conditions such air or aerated water will do this and satm under many exposure conditions stainless steels will naturally self-passivate.
Passivation results in the formation of an oxide film having a higher chromium-to-iron ratio than the underlying stainless steel because of the preferential oxidation of chromium and the preferential dissolution of iron.
Many combinations of these variables can be used, but two of the most common are:. An example of reduced corrosion resistance is shown in Figure 1. Bright annealing entails heating the stainless steel to a suitably high temperature usually more than 1, degrees F, or 1, degrees C in a reducing atmosphere such as dry hydrogen gas. Such chemical treatment is generally not necessary for the formation of the passive film. Parts treated however must pass specific tests to confirm the effectiveness of the passivation, although in practice the tests are for the detection of the effects of residual aatm contamination on the surface of the parts.
The standard notes that the high carbon martensitic stainless steels, such as C, are not suitable for acid passivation as wstm can be attacked or be subject to hydrogen embrittlement. You May Also Like. Die fully sensored and still getting miss-hits?
This condition can be measured using electrochemical techniques as a potential of 0. Link to Active This link will always route to the current Active version of the standard.
The term “iron,” when hereinafter referred to as a surface contaminant, shall denote free iron. Pickling, passivation and removing iron contamination with nitric acid Passivation treatments are sometimes specified, but it is important to consider whether this is strictly necessary or a80-99.
Article: Passivation of stainless steels
It should be stressed that the protective oxide film formed during effective passivation of the stainless steel is transparent and not observable to the naked eye. 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.
It is likely that the darker, thicker oxide tints are the result of the formation of an oxide with higher iron and magnesium content; that is, reduced chromium content.
Some of the various meanings associated with the term passivation that are in common usage include the following: Citric acid treatments can also be considered as an alternative to nitric acid as both provide the oxidising conditions necessary for passivation. On the other hand, some of the practices may be applicable for these purposes.
Keeping stainless steels stainless
It therefore in no way precludes the necessity for careful planning and judgment in the selection and implementation of such procedures. Stainless steels cannot be passivated unless the steel surface is clean and ashm from contamination and scale from welding operations.
Stainless steel owes its corrosion resistance to its ready oxidation to form this protective film; however, stainless steel’s exposure to an oxidizing environment at higher temperatures or to a more highly oxidizing environment at a aetm temperature will result in the formation of an oxide heat tint of increasing thickness, ranging in color from a light straw to a3380-99 dark black. 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.
However, some confusion still exists about the definition a3809-9 passivation and what really causes a passive film to form on the surface of stainless steel. Organic contaminants are volatilized and most metal oxides including those of iron, nickel, and chromium will be reduced, resulting in a clean, oxide-free surface.
ASTM A sets forth several techniques to determine the presence awtm free iron a measure of adequate passivation on the surface of stainless steel.
Fabricators, designers, and users of stainless steel components must understand the factors involved in successful passivation, identify the conditions under which that protective oxide film may be compromised, and use techniques that expose inadequate passivation.
This test may be readily conducted on stainless steel sheet, tube, pipe, and fittings, as well as on welds and heat-affected zones HAZ. Thus, passivation may refer to the chemical removal of free iron or iron compounds from the surface, or it may refer to the spontaneous development of a chemically inactive surface protective oxide film on the stainless steel.
This protective film develops when more than In some cases, no more than degreasing or removal of gross contamination is necessary. The standard also allows any combination of citric acid concentration, temperature and time, provided awtm the passivation test criteria can be met. The most commonly used of these is the copper sulfate test, in which a sulfuric acid-copper sulfate solution is swabbed on the surface for six minutes.
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. Acid concentrations up to 50 percent can be used, and the solution and residual effluent must be monitored closely.
The thicker this heat tint oxide ashm, the asm the probability that corrosion will occur beneath aetm oxide film. He can be reached atfaxloper engr. Specific treatments are however also specified. This process is described in a general way in 6. In asrm, visual inspection of internal surfaces is often impossible because of the configuration of the item.
Stainless steel’s corrosion resistance 3a80-99 due to a thin, chromium-rich, transparent oxide film on the surface 1. Passivation typically is accomplished either through an appropriate bright annealing of the stainless steel or by subjecting the surface to an appropriate chemical treatment. The degree of cleanness required on a wstm depends on the application. Best performance is achieved with a Cr-Fe ratio of the surface oxide of more than 1.
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. Light oxides can be removed with bright annealing when possible; light tints and iron contamination may be cleaned with citric acid solutions; darker tints may require cleaning with various pickling pastes; while heavier, darker oxide films will require pickling solutions.
This condition will accelerate the rate of metal dissolution into the surrounding electrolyte. The treatments are then defined by the process classes. Unlike ASTM A, the standard does not require specific solutions for particular stainless steel grades or types, although 3 specific treatments are identified. Most Popular Content This Week Fabrication, additive manufacturing companies produce part for airliner Solving the skills gap one class at a time Top 5 in —Articles 3a80-99 waterjet cutting 3D scanning—The first step in making a dream come to fruition SLM Solutions white paper: When the section was placed in service, a corrosive environment preferentially attacked the stainless steel surface under the heat tint.
In the case of classes C3 and C4, a a380-999 step process is defined, with a clean water rinse between aztm two steps, shown in a3800-99 table below.
It is essential that the entire surface be in a passive condition.