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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Typical chemical treatment involves exposing the stainless steel surface to an oxidizing acid solution in which the significant variables are time, temperature, and concentration.
Link to Active This link will always route to the current Active version of the standard. 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.
This test may be readily conducted on stainless steel sheet, tube, pipe, and fittings, as well as on welds and heat-affected zones HAZ. 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 about waterjet cutting 3D scanning—The first step in making a dream come to fruition SLM Solutions white paper: However, some confusion still exists about the definition of passivation and what really causes a passive film to form on the surface of stainless steel.
The color of this film is a function of the film thickness that developed at various distances from the weld. 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. In some cases, no more than degreasing or removal of gross contamination is necessary.
Unless otherwise specified, it is this definition of passivation that is taken as the meaning of a specified requirement for passivation. Process Class Stainless Steel Types C1 or C2 Austenitics, austenitic precipitation hardening and duplex C3 High chromium martensitics C4 Ferritics, martensitics and martensitic precipitation hardening. In the interior of an orbitally welded section of L, the inner surface of the weld bead, and the adjacent HAZ, are covered with a varicolored oxide film, or heat tint.
Figure 1 This interior view of a weld made on L exhibits the formation of heat tint on the weld and HAZ caused by the presence of oxygen during orbital welding. In the case of classes C3 and C4, a two step process is defined, with a clean water rinse between the two steps, shown in the table below. 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.
Keeping stainless steels stainless
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. In addition, this standard also includes citric acid treatments.
It therefore in no way precludes the necessity for careful planning and judgment in the selection and implementation of such procedures. Evidence of in-service pitting in the heat tint in the HAZ may be seen in Figure 2. EDTA is a chelating agent that keeps iron in solution over a wide pH range.
The thicker this heat tint oxide is, the greater the probability that corrosion will occur beneath the oxide 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 iron contamination on the surface of the parts.
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. In both procedures the surface is cleaned of contaminants and the metal surface is subsequently oxidized. This process is described in a general way in 6.
More Content by Carl R. Unless otherwise specified, it is this definition of passivation that is taken as the meaning of a specified requirement for passivation. For more specific safety precautions see 7. For certain exceptional applications, additional requirements which are not covered by this practice may be specified upon agreement between the manufacturer and the purchaser.
Keeping stainless steels stainless – The Fabricator
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.
The standard notes that the high carbon martensitic stainless steels, such as C, are not suitable for acid passivation as they can be attacked or be subject to hydrogen embrittlement.
Citric acid treatments can also be considered as an alternative to nitric acid as both provide the oxidising conditions necessary for passivation. Acid concentrations up to 50 percent can be used, and the solution and residual effluent must be monitored closely. Naturally occurring conditions such air or aerated water will do this and so under many exposure conditions stainless steels will naturally self-passivate.
Preservation of the passive film requires the presence of oxygen in the environment to which the stainless steel is exposed. It was at one time considered that an oxidizing treatment was necessary to establish this passive film, but it is now accepted aatm this film will form spontaneously in an oxygen-containing environment providing that the surface has been thoroughly cleaned or descaled.
The author would like to thank Monty B.
Related Links Suppliers of Passivating Products. Some of the various meanings associated with the term passivation that are in common usage include the following: Methods are described for a38-099 detection of free iron and transparent chemical and oily deposits. Asttm May Also Like. 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.
ASTM A Passivation Standard | Able Electropolishing
Extreme chloride concentrations may develop because of evaporation in systems that are not properly drained, which negates the corrosion protection expected of stainless steels. Office and Postal Address: This 3a80-99 will accelerate the rate of metal dissolution into the surrounding electrolyte. It is essential that the entire surface be in a passive condition.
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. Under these conditions, the surface is passive, or resistant to corrosion. 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. 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 x380-99 metals if due consideration is given to corrosion and possible metallurgical effects.
Stainless steels are designed to naturally self-passivate whenever a clean surface is exposed to an environment that can provide enough oxygen to form the chromium rich oxide surface layer, on which the corrosion resistance of these alloys depends.