BS EN ISO 8407:2021 download.Corrosion of metals and alloys – Removal of corrosion
products from corrosion test specimens.
WARNING — Safety rules for personnel: handling of the solutions used for the removal of corrosion products shall be left to skilled personnel or conducted under their control. The equipment shall be used and maintained by skilled personnel, not only so that the procedures can be performed correctly, but also because of the hazards to health and safety that are involved.
1 Scope
BS EN ISO 8407 specifies procedures for the removal of corrosion products formed on metal and alloy corrosion test specimens during their exposure in corrosive environments. For the purpose of BS EN ISO 8407, the term metals refers to pure metals and alloys.
The specified procedures are designed to remove all corrosion products without significant removal of base metal. This allows an accurate determination of the mass loss of the metal, which occurred during exposure to the corrosive environment.
In some cases, these procedures are also applicable to metal coatings, providing the possible effects from the substrate are considered.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
No terms and definitions are listed In this document.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
Whichever method is used, it might be necessary to repeat the cleaning treatment to ensure complete removal of the corrosion products, Removal shall be confirmed by visual examination. The use of a low- power microscope (i.e. x 7 to x 30)is particularly helpful with a pitted surface since corrosion products can accumulate in pits.
4.1.3 An ideal procedure should remove corrosion products and not result in the removal of any
base metal. Two procedures can be used to confirm this point One procedure uses a control specimen
(see 4L4) and the other requires a certain number of cleaning cycles on the corroded specimen (see
4J). The procedures shall be maintained while the rust removal performance of the solutions listed in
Table.sAI and &2 is not impaired.
NOTE 1 Indications that the solution needs to be discarded can be discoloration or the presence ol a significant amount ot corrosion products in the solution.
NOTE 2 Some solutions might need some aging before working without etching the substrate
4.1.4 Uncorroded control specimens, which should be similar chemicali3 metallurgically and geometrically to the test specimens, should be cleaned by the same procedure as used for the test specimen. By weighing the control specimen before and after cleaning (weighing to the fifth significant figure Is suggested, e.g. a 70 g specimen should be weighed to three decimal places), the metal loss resulting from cleaning may be determined. The mass loss of the control specimen will reflect the mass loss of test specimens resulting from the cleaning procedure.
4.1.5 The cleaning of each corroded test specimen should be repeated several times after the removal of the corrosion products Is completed. The mass shall be plotted as a function of the periods of cleaning cycles with the same interval time or time units (see Figure fl. Point A represents the mass of corroded specimens before the start of the cleaning. In many cases. two straight lines. All and BC. will be obtained. Line All characterizes the removal of corrosion products and may not always be visible. Line BC characterizes the removal of the substrate after the corrosion products are completely removed. Point I), which characterizes the mass of the pure metal at zero number of cleaning cycles. is obtained by extrapolation of line BC to the ordinate axis. in some cases, the relationship may not be linear, and the most appropriate extrapolation shall then be made. if the relationship of B and C is not linear, a linear regression method, e.g. by applying the least squares from later points of cleaning cycles, can be used for estimation of the point for the D value.
l the durations of each cleaning step are not equal, the x-axis should be expressed in units ot cumulative exposure time in the cleaning solution, rather than the number of cleaning steps used up to that point.
NOTE The number of points needed to establish the line BC is sometimes less than Indicated in the figure for the specific case, especially if there is significant experience for the pickled material and solution,
4.1.6 The true mass of the specimen, after removal of the corrosion products, will be a value between the masses represented by the points B and D. depending on the degree of protection provided by the corrosion products during the cleaning procedure.
4.1.7 The preferred cleaning method will be one that:
a) provides efficient removal of corrosion products
b) provides low or zero mass loss when applied to new uncorroded specimens (see 4.14);
c) provides a curve of mass as a function of the number of cleaning cydes or time of pickling, which is close to horizontal when the latter is plotted as the abscissa (see £L5).
4.1.8 When chemical or electrolytic procedures are used, solutions rreshly prepared with distilled or deionized water and reagent grade chemicals shall be used.
4.1.9 After cleaning, the specimen should be thoroughly rinsed with Lap water. A light brushing during this procedure will help to remove any remaining surface products resulting from the cleaning proce. Finally, the specimens shall be rinsed with distilled or deionized water. The specimen shalt then be rinsed thoroughly in ethanol and dried in air. Drying in an air stream is strongly recommended, or optionally a hot air blower or an oven may be used. After drying, the specimens shall be allowed to coot in a dessicator to the balance room temperature before weighing.
4.2 Chemical procedures
4.2.1 Chemical procedures involve the immersion of the corroded test .specimen in a chemical solution that is specifically designed to remove the corrosion products with minimal dissolution of any base metal. Several procedures are listed in AnnezA (see Tahle.&1). To facilitate the cleaning, an ultrasonic bath treatment should be used.
4.2.2 Chemical cleaning is often preceded by a light brushing of the test specimen to remove lightly adherent, bulky corrosion products.
4.2.3 Before the chemical treatment, clean the specimens as described in 4.1.1. In connection with the Intermittent removal of specimens for weighing, brush the specimens, If necessar to facilitate the removal of tightly adherent corrosion products.
4.3 ElectrolytIc procedures
Electrolytic cleaning can also be used to remove corrosion products. Several methods of electrolytic cleaning of corrosion test specimens are given in Annex A (see Table k2). To facilitate the cleaning, an ultrasonic bath treatment should he used.
Brushing should follow electrolytic cleaning to remove any loose deposits. This will help to minimize any redeposition of metal from reducible corrosion products in solution that would reduce the measured mass loss,
4.4 Mechanical procedures
Mechanical procedures can include scraping, scrubbing, brushing, ultrasonic methods, mechanical shock and impact blasting, e.g. grit blasting, water-let blasting. These methods are often used to remove heavily encrusted corrosion products. Scrubbing with a bristle brush and a mild abrasive/distilled water slurry can also be used to remove corrosion products.