Soils aggressivity

Excavation of hellholes and visual inspection at locations deemed problematic as a result of soil aggressiveness, and the interpretation of the test results. 

Table 4.4 Soil Aggressiveness of Different Soil Resistivities Suitable Corrosion Protection...

Booth, G. H., Cooper, A. W., and Cooper, P. M., "Criteria of Soil Aggressiveness Towards Buried Metals, I. Experimental Methods, British Corrosion Journal, Vol. 2, 1967, pp. 104-108. 

Microbial leaching of metals from ores is a promising adjunct to more aggressive metal recovery technologies (77), but is generally achieved by oxidative processes that generate very acidic waters. It seems unlikely that similar approaches will be of much value in removing contaminant metals and metalloids from soils. 

The composition of the builders in an alkaline cleaner is dependent on the metal substrate from which the soil is to be removed. For steel (qv) or stainless steel aggressive, ie, high pH, alkaline salts such as sodium or potassium hydroxide can be used as the main alkaline builder. For aluminum, zinc, brass, or tin plate, less aggressive (lower pH) builders such as sodium or potassium siUcates, mono- and diphosphates, borates, and bicarbonates are used. 

The occurrence of graphitic corrosion is not location specific, other than that it may occur wherever gray or nodular cast iron is exposed to sufficiently aggressive aqueous environments. This includes, and is common to, subterranean cast iron pipe, especially in moist soil (Case History 17.1). Cast iron pump impellers and casings are also frequent targets of graphitic corrosion (Case Histories 17.2 through 17.5). 

Recommended Extended anode installation Mostly used for Aggressive soils and Soils Deep C/i... 

Tank installations below ground in the neighborhood of railway lines are often in aggressive soil that is contaminated with slag. Cathodic protection is therefore particularly important. Because of the particularities of railway operations, company standards must be followed in addition to the generally required direc-... 

Confirmation of the authority s preferred pipe material for incoming mains and any materials not recommended due to aggressive soil. 

Montmorillonite clays absorb water readily, swell greatly and confer highly plastic properties to a soil. Thus soil stress (Section 14.8) occurs most frequently in these soils and less commonly in predominantly kaolinitic types. Similarly, a soil high in bentonite will show more aggressive corrosion than a soil with a comparable percentage of kaolinite. A chalky soil usually shows low corrosion rates. Clay mineralogy and the relation of clays to corrosion deserves attention from corrosion engineers. Many important relationships are not fully understood and there is need for extensive research in this area. 

The term aggressive is often used to imply some approximately quantitative estimate of the likelihood of corrosion and depends on measuring factors such as soil water (resistivity), pH, redox potential, salt concentrations and bacterial populations in order to establish criteria for the prediction of corrosion rates . Similar measurements for predicting corrosion... 

As already stated, aggression will also depend on soil Eh according to the scale given in Table 2.21. Temperature is also a controlling factor and both psychrophylic (cold) and thermophilic (hot) forms are known, e.g. in electrical transformers, hot water systems. 

Stainless steels have not been widely used in applications where they are buried in soil, but some applications have involved underground service. Various stainless steels from the 13% Cr to the molybdenum-bearing austenitic types were included in the comprehensive series of tests in a variety of soils reported by Romanoff . High-chloride poorly-aerated soils proved most aggressive, but even here the austenitic types proved superior to the other metals commonly used unprotected. Of special interest is the fact that though corrosion was by pitting there was little or no increase in pit depth after the first few years. 

As indicated above, the bicarbonate ion inhibits the process, which does not occur, therefore, in many supply waters attack is most likely in waters which by nature or as a result of treatment have a low bicarbonate content and relatively high chloride, sulphate or nitrate content. The number of points of attack increases with the concentration of aggressive anions and ultimately slow general corrosion may occur. During exposure of 99-75% tin to sea-water for 4 years, a corrosion rate of 0-0023 mm/y was observed . Corrosion in soil usually produces slow general corrosion with the production of crusts of oxides and basic salts this has no industrial importance but is occasionally of interest in archaeological work. 

Establishing electrolyte resistivity To enable a satisfactory cathodic-protection scheme to be designed, it is necessary to determine the resistivity of the electrolyte (soil or water). This information is necessary to enable the current output of anodes to be determined together with their position and power source voltage, and it also provides an indication of the aggressiveness of the environment in general the lower the resistivity the more aggressive the environment. 

Various sequential dissolution protocols have been developed by different research groups in order to accommodate their types of soils, experimental conditions, and objectives. This makes it difficult to compare the results with different procedures. We compared two SSD procedures for humid zone and arid zone soils, developed by German and Israeli soil scientists, respectively, based on aggressiveness of extractants, their specificity and selectivity, completeness of phase-extraction by each extractant from defined phases and their effects on subsequent fractions. We also appraised the applicability as well as the limitations of each procedure under different conditions. 

Having said this, there are species that exhibit especially weedy properties in their inherent ability to occupy and thrive in areas where soil is barren, disturbed, or low in nutrients. Such species usually have at least one of the following invasive characteristics relative to competing species adaptability, aggressive reproduction, and vigorous growth. ... 

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