Corrosion of metals and alloys—Corrosivity of atmospheres—Part 4:Determination of corrosion rate of standard specimens for the evaluation of corrosivity
GB/T 19292.4-2018 Corrosion of metals and alloys - Corrosivity of atmospheres - Part 4: Determination of corrosion rate of standard specimens for the evaluation of corrosivity
1 Scope
This part specifies methods which can be used for the determination of corrosion rate with standard specimens.
The values obtained from the measurements (corrosion rates for the first year of exposure) are intended to be used as classification criteria for the evaluation of atmospheric corrosivity according to GB/T 19292.1. They can also be used for informative evaluation of atmospheric corrosivity beyond the scope of GB/T 19292.1.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition (including any amendments) applies.
Corrosion of metals and alloys - Removal of corrosion products from corrosion test specimens
Metals and alloys - Atmospheric corrosion testing - General requirements
Corrosion of metals and alloys - Corrosivity of atmospheres - Classification, determination and estimation
Corrosion of metals and alloys - Corrosivity of atmospheres - Guiding values for the corrosivity categories
3 Principle
The corrosivity of the exposure locations or of industrial installation sites is deduced from the corrosion rate, calculated from the loss of mass per unit area of standard specimens following the removal of corrosion products from the specimens after exposure periods of one year.
In the case of alloys of iron, zinc and copper, mass loss is a proven measure of corrosion damage. In the case of aluminium alloys, mass loss is a valid measure of corrosion. This International Standard describes only evaluation by mass loss and not corrosion penetration.
Corrosion rates for the first year of exposure may be used for the calculation of corrosion rates for long-term exposures in accordance with ISO 9224.
4 Standard specimens
The specimens are rectangular plates with dimensions of preferably 100 mm×150 mm, but at least 50 mm×100 mm, and a thickness of approximately 1 mm.
The materials used to prepare the standard specimens are of current fabrication, i.e.
——Steel: carbon structural steel (Cu 0.03% to 0.10%, P<0.07%);
——Zinc: 98.5% min.;
——Copper: 99.5% min.;
——Aluminium: 99.5% min.
Prior to exposure, all specimens shall be solvent degreased. The sample shall be free from oil and grease; in order to achieve this, it may be necessary to use different solvents in successive steps. Steel specimens with visible rust stains or corrosion products on their surfaces shall be polished with 120 grit abrasive paper prior to degreasing to remove these visible corrosion products. The cleaning of metal specimens by sand blasting can result in a surface that is more prone to corrosion and is therefore not recommended for the cleaning of the standard specimens for corrosivity classification in accordance with ISO 9223. Copper, zinc and aluminium specimens shall not be used if visible corrosion products are present before exposure.
5 Exposure of standard specimens
Prior to exposure, the specimens shall be weighed and marked, and the exposure of these specimens shall be carried out in accordance with the specifications of ISO 8565.
Three specimens of each metal shall be exposed for one year, starting at the beginning of the worst corrosive period of the year.
After exposure, the corrosion products formed on specimens shall be removed in accordance with the specifications of ISO 8407 and reweighed to the nearest 0.1 mg. For procedures suitable for chemical cleaning, see Annex A. The cleaning procedure shall be repeated several times in equal cleaning cycles.
Foreword i
Introduction i
1 Scope
2 Normative references
3 Principle
4 Standard specimens
5 Exposure of standard specimens
6 Expression of results
Annex A (Informative) Chemical cleaning procedures for removal of corrosion products
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