Introduction
The corrosion of stainless steel by sulfates and copper sulfates is a well known phenomenon, which can lead to potentially catastrophic failures of metal components. To avoid such failures, it is important to be able to measure the corrosion rate of stainless steel when exposed to these types of environments. The GB/T 4334.5-90 standard outlines the method to be used to assess the corrosion rate of stainless steel in sulfates and copper sulfates.
The standard method involves two distinct tests, both of which use stainless steel coupons as specimen holders, with samples of the alloy to be tested placed in them. The first test is to measure the corrosion rate of the stainless steel when in a solution of sulfates, ranging from 5 g/L to 200 g/L. The coupons are exposed to this solution, and the corrosion rate is measured by weighing the specimens and comparing them over time.
The second test involves exposure of the specimens to copper sulfate solutions. These solutions range from 0.1 g/L to 0.5 g/L. Again, the corrosion rate is measured by weighing the specimens over time and comparing the weights, to determine how much corrosion has taken place.
The purpose of this paper is to discuss the procedure outlined in the GB/T 4334.5-90 standard for measuring the corrosion rate of stainless steel in sulfates and copper sulfates. It will discuss the types of specimen holders used for the tests, the range of concentrations of the solutions that can be used, the duration of exposure to the solutions, and how to measure the corrosion rate.
Specimen Holders
The type of specimen holders used to hold the samples of stainless steel alloy to be tested is specified in the GB/T 4334.5-90 standard. It outlines that the specimens must be placed in holders made of stainless steel, with dimensions of at least 12mm in both length and width. The specimens must be securely fastened within the holders, so that no contact with the test medium occurs during the test.
Test Solutions
The two tests involve different solutions, with different concentrations. For the sulfate test, the concentrations range from 5 g/L to 200 g/L, and for the copper sulfate test, the concentrations range from 0.1 g/L to 0.5 g/L. The concentration of each solution is dependent on the alloy being tested, and the range of concentrations should be determined based on the results of previous tests.
Duration of Test
The duration of the tests specified in the GB/T 4334.5-90 standard is 24 hours for both tests. This length of time has been determined to allow for sufficient time for corrosion to take place.
Measuring Corrosion Rate
The corrosion rate is measured by weighing the specimens at the start and end of the test period. The weight loss is then divided by the test period to give the corrosion rate in grams per hour.
Conclusion
The GB/T 4334.5-90 standard outlines the method to be used to assess the corrosion rate of stainless steel in sulfates and copper sulfates. Specimen holders made of stainless steel are used to hold the test samples, with solutions of varying concentrations used to assess the corrosion. The tests should be run for 24 hours, with the weight of the specimens taken at the start and end of the period used to measure the corrosion rate. Using this method, it is possible to accurately measure the corrosion rate of stainless steel in sulfate and copper sulfate solutions.
