Pitting soils

The test pit method consists of excavating a pit using a backhoe to a depth where hydrocarbon pools in the bottom of the pit. Soil samples are subsequently obtained above and below the hydrocarbon-affected zone using hand-driven tubes (acrylic small-diameter shelby tubes). Problems associated with this method include ... 

Gather these materials Three funnels an upright stand and 3 ring supports pieces of gauze 3 pint jars sand from a nearby beach or sand pit soil from the backyard or garden gravel from the driveway of your home, from some nearby area, or from a pet shop. 

April, T. M., Foght, J. M. Currah, R. S. (2000). Hydrocarbon-degrading filamentous fungi isolated from flare pit soils in northern and western Canada. Canadian Journal of Microbiology, 46, 38 9. 

Leachates associated with incineration wastes, bum pit soils, and filtration ponds have been identified. The solids composition in these wastes would likely depend on the nature and completeness of the burning process. The bum wastes are generally poorly characterized very little data are available. 

S) The facility features highly contaminated gravel-covered areas and debris pits. Soil profiles In discolored areas indicated Aroclor 1260 levels of... 

High-alloy steels with >16% Cr" (e.g. 1.4301, AISI 304) Neutral waters and soils (25°C) <0.2 <-0.1 Protection against pitting and crevice corrosion... 

Stainless steels in soil can only be attacked by pitting corrosion if the pitting potential is exceeded (see Fig. 2-16). Contact with nonalloyed steel affords considerable cathodic protection at f/jj < 0.2 V. Copper materials are also very resistant and only suffer corrosion in very acid or polluted soils. Details of the behavior of these materials can be found in Refs. 3 and 14. 

For corrosion protection in soils, the anodes can be brought close to the object to be protected in the same construction pit so that practically no further excavations are needed. By connecting anodes to locally endangered objects (e.g., in the case of interference by foreign cathodic voltage cones) the interference can be overcome (see Section 9.2.3). 

Fig. 12-7 Voltage cone and pipe/soil potential near a concrete pit.

If insulated sleeves and spark gap isolators lie directly in soil, they eonstitute danger spots. Currents ean exit and then reenter. This danger is redueed if they are installed in a dry pit and the first meter of the eable on either side is insulated. 

Nonuniform corrosion or pitting corrosion frequently occurs on steel structures in seawater and in soil. Nonuniform and pitting corrosion easily lead to damage in tanks, pipelines, water heaters, ships, buoys and pontoons, because these structures lose their functional efficiency when their walls are perforated (see Chapter 4). 

Material Acid droplet pitting, nylon hose destruction Rubber cracking, silver tarnishing, paint blackening Corrosion, soiling, materials deterioration... 

The aluminum smelter solid wastes, in the form of spent pot lining, are disposed of in engineered landfills that feature clay or synthetic lining of disposal pits, provision of soil layers for covering and sealing, and control and treatment of any leachate. Treatment processes are available to reduce hazards associated with spent pot lining prior to disposal of the lining in a landfill. Other solid wastes... 

Absorption Field A system of properly sized and constructed narrow trenches partially filled with a bed of washed gravel or crushed stone into which perforated or open joint pipe is placed. The discharge from the septic tank is distributed through these pipes into trenches and surrounding soil. While seepage pits normally require less land area to install, they should be used only where absorption fields are not suitable and well-water supplies are not endangered. 

The Brio refining site is approximately 58 acres in size and is the location of a former chemical production, recovery, refinery, and regeneration facility. The site includes closed impoundments into which hazardous substances were disposed in bulk, storage tanks, and approximately 1,750 drums of hazardous substances. Remediation activities included the excavation and incineration of contaminated soil, installation of protective liners around selected pits, and the installation of a groundwater extraction system adjacent to a gully. 

In 1955 it was discovered that mixtures of ammonium nitrate and fine coal dust have satisfactory blasting capabilities in large (9 inch) holes used in open-pit coal mines to remove the rock and soil covering the coal. Polyethylene bags containing this material deform to fit the hole and provide moderate water resistance. ANFO is used in open-pit iron and copper mines and for construction such as road building. The mixture is air blown into 2-inch holes or less m maiiv underground mines. 

Sumpf, m. Swamp, marsh, bog (Tech.) pit, sump basin pool (of mercury) wave absorbent, -boden, m. marshy or swampy ground or soil, -eisenstein, m. bog iron ore. 

Test pits permit visual examination of the soil in place. Such pits also allow manual sampling of undisturbed soil samples. These samples can be taken from the side walls of the pit. 

Upon elimination of the fluids, the liner to the pit is folded over the residual solids in a way to prevent fluid migration. The liner is then buried inplace. The operator may choose to remove the liner contents completely to preclude any future contamination. In the case of a producing well, the location is reclaimed up to the deadmen. The adjacent areas are contoured to provide for drainage away from the production facilities. In the case of a dryhole, the entire location is reclaimed to the initial condition. All of the reclaimed area should be ripped to enhance soil conductivity. The top soil is then spread over the reclaimed area followed by seeding. Local seed mixtures are broadcast to quicken reintroduction of native plants. 

Rossum, J. R., Prediction of Pitting Rates in Ferrous Metals from Soil Parameters , J. Amer. 

Local corrosion or pitting is more important for practical purposes than the rate of general corrosion, and may proceed 10 times or so more rapidly than this. Inasmuch as certain types of cast iron are liable to suffer graphitic corrosion, whereas steel does not, steel might theoretically be expected to show to some advantage when used for buried pipelines. In practice, however, a cast-iron pipe has to be of stouter wall than a steel pipe for equal strength, and it is doubtful whether any distinction between the rust resistance of the two materials in the soil is justified. 

Finally, it should be added that the extensive field tests made in the United States indicate that buried steel rusts less and less rapidly as time goes on, both as regards general attack and pitting. This can be illustrated by the typical results shown in Fig. 3.5. Field tests made in British soils by BISRA have not, however, exhibited the same tendency in these rusting has been roughly proportional to the duration of burial. 

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. 

It should be noted that it is extremely difficult to predict service lives of buried pipelines from the results of controlled trials with small specimens, whether in the laboratory or in the field. For example a study on the comparative corrosion resistances of ductile and grey iron pipes carried out jointly by European pipemakers in 1964-1973 indicated a mean pitting rate of 0 -35 mm/y for uncoated ductile iron pipe exposed in a typical heavy Essex clay of 500-900 ohm cm resistivity for 9 years. This is clearly at odds with the rate of 1 mm/y normally found on a corroded service pipe from such a soil. The discrepancy appears to be due to the use of specimens that were only a third of a pipe length each and were buried separately. It may reflect the contribution of the total surface area of the pipe as a cathode to the corrosion current at the anodic area at the pitting site. 

Patches of conductive lead sulphide can be formed on lead in the presence of sewage. This can result in the flow of a large corrosion current . Sulphate-reducing bacteria in soils can produce metal sulphides and H2S, which results in the formation of deep pits containing a black mass of lead sulphide . Other micro-organisms may also be involved in the corrosion of lead in soil . 

In tests carried out by the National Bureau of Standards in the USA specimens of copper alloys, lead, zinc and zinc alloys were buried at a number of different sites for periods varying from 11 to 14 years. The soils tested covered a pH range from 2-6 to 9-4 and resistivities ranged from 62 to 17 800 fi cm. The weight losses and maximum depths of pitting were recorded, and the results indicated that the most severe corrosion occurred in soils of poor aeration having high acid and soluble-salt contents. 

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