Soils corrosion testing

Several extensive series of soil-corrosion tests have been carried out by the National Bureau of Standards in the United States, and the results have been summarised by Romanoflf. In one series two types of copper and ten copper alloys were exposed in fourteen different soils for periods up to 14 years. The results for the copper specimens are summarised in Table 4.12. 

Table 4.12 Soil-corrosion tests on copper by National Bureau of Standards and British Non-ferrous Metals Research Association...

Two civil engineering operations require particular attention when soil corrosion tests in the field are required. These are (1) the use of reinforced earth structures in which the corrosion conditions will differ from those at... 

Galvanized pipe and flat specimens were included in the soil corrosion tests (Table 4.3) conducted by the Subcommittee on Buried Metals of the Corrosion Committee of the British Iron and Steel Research Association (Hudson and Acock, 1952). The galvanized test pieces averaged 670 g/m coating (about 95 p,m). The specimens were buried for 5 years at a depth of 0.6 m in five British soils. With the exception of the specimens buried in cinders at Corby, all the test pieces were rated excellent (no sign of breakdown) on visual examination. However, the weight loss data show that... 

Escalante, E Measuring the Corrosion of Metals in Soil, Corrosion Testing and Evaluation, R. Baboian and S. W. Dean, Ed., ASTM International, West Conshohocken, PA, 1990. 

A number of standards exist for the determination of some of these parameters. BS 1377 Part 3 1990 refers to methods of tests for soils for civil engineering purposes, and Part 9 refers to these and corrosivity tests in situ. It is significant that the standard draws attention to the fact that the results of the tests that are described should be interpreted by a specialist. ASTM tests for pH and resistivity of soil used for corrosion testing are covered by G51 1977(R1984) and G57 1978 (R1984), respectively. 

Recommended practice for conducting atmospheric stress corrosion tests on metals Test method for pH of soil for use in corrosion testing... 

Two weeks to a month is recommended for plant tests. Atmospheric corrosion and soil corrosion involving low-corrosion rates require periods of the order of several years of exposure. 

Due to the wide range of condition for corrosion occurring, there are many tests to evaluate corrosion. These tests include the study of atmospheric corrosion, corrosion during episodic wet/dry conditions, corrosion under fully immersed conditions, corrosion in soil, corrosion in aqueous solutions and corrosion in non-aqueous solutions and in molten salts. Moreover, it is important to consider the in-service environment and the objectives of the tests being performed. 

In some of the more corrosive soils, corrosion of the steel (after the zinc has been completely destroyed) is considerably less than that observed on uncoated steel control specimens. Also, it appeared in some soils that the protection afforded to the steel was not due solely to sacrificial corrosion of the zinc but was supplemented by some other mechanism. A few tests indicated that a film, consisting primarily of zinc silicate formed by galvanic action between the zinc and the underlying zinc-iron alloy or bare steel, was responsible for the additional protection. 

In the laboratory, the technique of ac impedance is superseding polarization resistance, because it provides additional information on mechanisms of the processes involved. Guidance on performing corrosion tests in the laboratory in liquids or in soils is provided in ASTM G 31 smd ASTM G 162 [iS,79]. Ac impedance S3 tems are now commercially available, but these units are limited to low polarization currents of 1 A or less, making them unsuitable for most field applications where larger current capabilities (>1 A) are needed. 

ASTM G 51 Standard Test Method for pH of Soil For Use In Corrosion Testing, Annual Book of Standards, Vol. 03.02, ASTM International, West Conshohocken, PA, 1993. 

Escalante, E., Corrosion Testing In Soil, Corrosion, J. R. Davis, Ed., ASM International Materials Park, OH, 1987,... 

Several field and laboratory tests are used to correlate soil corrosion aggressivity to its physical and chemical properties. Sampling errors are the most common errors encountered... 

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