If the piping system is already assembled, there passsivation service companies which specialize in on-site projects of this sort, like Astropak. Stainless steels cannot be passivated unless the steel surface is clean and free from contamination and scale from welding operations.
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Privacy Overview. Frequently, post-erection flushing is accomplished by circulating the process fluid through the system until contamination is reduced to tolerable levels. Inspection After Cleaning 7. There is no substitute for good, uniform, cleaning practices which yield a metallurgically sound and smooth surface, followed by adequate protection to preserve that condition. Establishment of the most reliable tests and test standards for cleanness are helpful in attaining the desired performance of parts, equipment, and systems.
Testing should be sufficiently extensive to ensure the cleanness of all surfaces exposed to process fluids when in service. The following represent some tests that have been successfully applied to stainless steels. The purchaser shall have the option of specifying in his purchase documents that any of these quality assurance tests be used as the basis for acceptability of the cleanness or state of passivity of the stainless steel item.
Some deposited atmospheric dust will normally be present on exterior surfaces but should not be present on interior surfaces. Visual inspection should be carried out under a lighting level, including both general and supplementary lighting, of at least lx [ footcandles], and preferably lx [ footcandles] on the surfaces being inspected. Visual inspection should be supplemented with borescopes, mirrors, and other aids, as necessary, to properly examine inaccessible or difficult-to-see surfaces.
Lights should be positioned to prevent glare on the surfaces being inspected. Wipe tests of small diameter tubing are made by blowing a clean white felt plug, slightly larger in diameter than the inside diameter of the tube, through the tube with clean, dry, filtered compressed air. Cleanness in wipe tests is evaluated by the type of contamination rubbed off on the swab or plug.
The presence of a smudge on the cloth is evidence of contamination. In cases of dispute concerning the harmful nature of the contamination, a sample of the smudge may be transferred to a clean quartz microscope slide for infrared analysis. The wipe test is sometimes supplemented by repeating the test with a black cloth to disclose contaminants that would be invisible on a white cloth.
The presence of stains or water spots on the dried surfaces indicates the presence of residual soil and incomplete cleaning. The test is rapid but not very sensitive. It is applicable only for items that can be dipped in water and should be made with high-purity water.
The test procedure and interpretation of results are described in Test Method F The test is moderately sensitive. The wet-dry cycles should be such that the sample remains dry for a total of 8 h in a h test period. After completion of this test, the surface should show no evidence of rust stains or other corrosion products. It is not recommended for the martensitic and lower chromium ferritic stainless steels of the Series since the test will show a positive reaction on these materials.
Warning—This test must not be applied to surfaces of items to be used in food processing. The test solution is prepared by first adding sulfuric acid to distilled water and then dissolving copper sulfate in the following proportions Warning—Always add acid to cold water.
The specimen shall be rinsed and dried in a manner not to remove any deposited copper. Copper deposit will indicate the presence of free iron. Instead, a specialized copper sulfate test is extensively used for the purpose of detecting free iron and determining overall good manufacturing practice.
Copper deposits at the surface of such instruments are wiped with moderate vigor to determine if the copper is adherent or nonadherent.
Instruments with nonadherent copper are considered acceptable. The specialized test solution is prepared by first adding 5. A comparison standard is prepared by placing on a clean quartz microscope slide a single drop of high-purity solvent and allowing it to evaporate.
Next place another drop on the surface to be evaluated, stir briefly, and transfer, using a clean capillary or glass rod, to a clean quartz microscope slide and allow the drop to evaporate.
Make as many test slides as necessary to give a reasonable sample of the surface being examined. If foreign material has been dissolved by the solvent, a distinct ring will be formed on the outer edge of the drop as it evaporates.
The nature of the contaminant can be determined by infrared analysis, comparing the infrared analysis with that of the standard. In an area that is blacked out to white light, inspect all visible accessible surfaces with the aid of a new, flood-type, ultraviolet lamp. For inaccessible areas, use a wipe test as described in 7.
Fluorescence of the surface, cloth, or plug indicates the presence of contaminants. The nature of the contamination can be determined by subjecting a sample of the contaminant, that has been transferred to a clean quartz microscope slide, to infrared analysis. The test will not detect straight-chain hydrocarbons such as mineral oils.
High-purity water should be used for the test. The test can be used on stainless steel to detect iron contamination from sources including, but not limited to, iron-tool marks, residual-iron salts from pickling solutions, iron dust, atmospheric exposure, iron deposits in welds, embedded iron and iron oxide. Apply solution with an aluminum, plastic, glass, or rubber atomizer having no iron or steel parts, or a swab atomizer spray is preferred.
Several minutes may be required for detection of oxide scale. Flush the surface with water several times after use of vinegar or acetic acid. NOTE 3—Potassium ferricyanide is not a dangerous poison as are the simple cyanides.
However, when heated to decomposition or in contact with concentrated acid, it emits highly toxic cyanide fumes. NOTE 4—Rubber gloves, clothing, and face shields should be worn when applying the test solution, and inhalation of the atomized spray should be avoided.
NOTE 5—The test is not recommended for process-surfaces of equipment that will be used for processing food, beverages, pharmaceuticals, or other products for human consumption unless all traces of the test solution can be thoroughly removed.
NOTE 6—The test solution will change color on standing and must be mixed fresh prior to each use. Precautions 8. If reasonable care is taken in fabrication, simple inexpensive cleaning procedures may suffice for its removal, and very little special cleaning should be required. Fabrication should be confined to an area where only the one grade of material is being worked. Powder cutting should be minimized or prohibited.
Handling equipment such as slings, hooks, and lift-truck forks should be protected with clean wood, cloth, or plastic buffers to reduce contact with the iron surfaces. Walking on corrosion-resistant alloy surfaces should be avoided; where unavoidable, personnel should wear clean shoe covers each time they enter. Kraft paper, blotting paper, paperboard, flannel, vinyl-backed adhesive tape or paper, or other protective material should be laid over areas where personnel are required to walk.
Shearing tables, press breaks, layout stands, and other carbon-steel work surfaces should be covered with clean kraft paper, cardboard, or blotting paper to reduce the amount of contact with the carbon steel.
Hand tools, brushes, molding tools, and other tools and supplies required for fabrication should be segregated from similar items used in the fabrication of carbon steel equipment, and should be restricted to use on the one material; tools and supplies used with other materials should not be brought into the fabrication area. Wire brushes should be stainless steel, or of an alloy composition similar to the steel being cleaned, and should not have been previously used on other materials.
Only new, washed sand, free of iron particles, and stainless steel chills and chaplets should be used for casting.
Solutions may become spent or depleted in concentration after extended use, and it is necessary to check concentrations and to replace or replenish solutions when cleaning or pickling action slows.
It may be impractical or uneconomical to discard solutions after a single use, even in precision cleaning operations that is, finish-cleaning using very high-purity solvents and carried out under clean-room and rigidly controlled environmental conditions. When solutions are re-used, care must be taken to prevent the accumulation of sludge in the bottom of cleaning tanks; the formation of oil, scums, and undissolved matter on liquid surfaces; and high concentrations of emulsified oil, metal or chemical ions, and suspended solids in the liquids.
Periodic cleaning of vats and degreasing tanks, decanting, periodic bottom-drain, agitation of solutions, and similar provisions are essential to maintain the effectiveness of solutions. Care must be taken to prevent water contamination of trichloroethylene and other halogenated solvents, both while in storage and in use. Redistillation and filtering of solvents and vapor-degreasing agents are necessary before reuse. Makeup is often required to maintain concentrations and pH of cleaning solutions at effective levels.
Do not overuse chemical cleaners, particularly acids and vapor-degreasing solvents; if light films or oily residues remain on the metal surfaces after use of such agents, additional scrubbing with hot water and detergent, followed by repeated rinsing with large quantities of hot water, may be necessary.
Biologically tested potable water should be used for final rinsing of food-handling, pharmaceutical, dairy, potable-water, and other sanitary equipment and systems. Rinsing and flushing of critical components and systems after finish-cleaning often requires high-purity deionized water, having strict controls on halide content, pH, resistivity, turbidity, and nonvolatile residues. Analytical methods that may be used for establishing the purity of rinse water should be demonstrated to have the sensitivity necessary to detect specified impurity levels; the analytical methods given in the Annual Book of ASTM Standards, Vol To minimize the use of costly high-purity water, preliminary rinses can often be made with somewhat lesser quality water, followed by final rinsing with the highpurity water.
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. Inspection After Cleaning 7. There is no substitute for good. Acid pickling may also provide sufficient passivation, depending on its specific application.
ASTM A details these three services in detail, thoroughly addressing their acceptable methods for new stainless steel parts, equipment, and systems. The standard does not cover decontamination or cleaning of equipment or systems that have been in service or descaling and cleaning of materials at the mill.
This document revises and replaces the edition of the same international standard, and it has undergone several changes. Does A allow for the continual reuse of cleaning and passivation chemicals or are chemicals to be used only once and discarded? Your email address will not be published. This site uses Akismet to reduce spam. Learn how your comment data is processed.
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