Soils corrosion

Copper and its alloys can be safely buried in most soils, although high corrosion rates have been observed when cinders and acidic peat are present in the soils. When high corrosion rates are expected it is preferable to protect the samples with bituminous, plastic or paint coatings. When brasses are used dezincification problems may be encountered and hence their use should be avoided, unless high sulfide concentration is present in the soils. 

---

Cathodic Protection This electrochemical method of corrosion control has found wide application in the protection of carbon steel underground structures such as pipe lines and tanks from external soil corrosion. It is also widely used in water systems to protect ship hulls, offshore structures, and water-storage tanks. 

The development of soil corrosivity assessment techniques has largely been due to the pipeline industry s requirements for better corrosion risk assessment and the reduction of pipeline failures. Corrosion in soil is a complex process and over the years several parameters have been identified as having a significant effect on the corrosion rate in a given soil. 

Table 2.20 Soil Corrosivity Assessment Technique from the German Gas and Water Works Engineers Association Standard (DVGW GW9)...

Although certain conditions very often lead to a particular type of attack, attempts to categorise soil corrosion in this way cannot be made on a general basis and most corrosivity assessment techniques categorise the soil as reacting to bare steel or iron in one of four ways ... 

Perhaps the most widely known measurement technique is that adopted by the West German Gas Industry and developed by Steinrath for buried pipework. This assigns a value (See Table 2.20) to each parameter measured the summation of these values determines the corrosivity of the soil. The parameters measured are shown in Table 2.20. Although this technique was developed for the pipeline industry it can be used with some success for general soil corrosivity assessment. 

Although the high-silicon irons are often used in circumstances which expose them to atmospheric, water or soil corrosion, they are rarely installed specifically to resist these agencies. Their corrosion resistance is such, however, that in fact no normally occurring environment ever causes serious attack. This is not to say that these irons can be regarded as stainless, and in fact alloys containing less than 14-7% silicon have been reported as becoming rusty in a moist atmosphere ... 

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...

Soil corrosion does not lend itself readily to direct study in the laboratory. However, indirect methods involving the action of differential aeration cells have yielded valuable information in comparing the probable corrosivities of different soils towards steel. The details of this technique were described by Denison , Ewing , Schwerdtfeger, and by Logan, Ewing and Denison ... 

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... 

Such intensive use of land will make very large demands on available water supplies and soil corrosion is also an important issue. There is even a debate over the overall reduction in fossil energy use and actual contribution to C02 abatement for the case of ethanol production from com [9]. Since waste arises from biomass or fossil fuel, to introduce waste products in the conversion scheme, which of course should be done, does not help in the overall scheme we discuss here. This is bom out by economic predictions (Table 1.2). 

Figure 28 illustrates a soil hydrogen permeation cell mounted in a general-purpose probe used for screening soil corrosivity. Other examples of specific hydrogen probes are illustrated in Fig. 29. 

V. Nielsen, Evaluation of Soil Corrosivity Design of an Electrochemical Soil Probe, technical report, Department of Manufacturing Engineering, Corrosion and Surface Technology, The Technical University ofDenmark, 1996. 

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. 

Table 4,4b Soil corrosivity Based on Oxidation-Reduction Potential...

Soil Corrosion. The extent of corrosion of the alloy buried underground depends on the soil composition and climatic conditions. Some typical data29 are given in Table 4.24. The corrosive attack of samples exposed to marshy soils was more severe than the samples exposed to well-drained soils. 

---