Underground structures

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. 

NFPA 328 Recommended Practice for the Control of Flammable and Combustible Liquids and Gases in Manholes, Sewers, and Similar Underground Structures, 1992 edition. National Fire Protection Association, Quincy, MA. 

The modern procedure to minimise corrosion losses on underground structures is to use protective coatings between the metal and soil and to apply cathodic protection to the metal structure (see Chapter 11). In this situation, soils influence the operation in a somewhat different manner than is the case with unprotected bare metal. A soil with moderately high salts content (low resistivity) is desirable for the location of the anodes. If the impressed potential is from a sacrificial metal, the effective potential and current available will depend upon soil properties such as pH, soluble salts and moisture present. When rectifiers are used as the source of the cathodic potential, soils of low electrical resistance are desirable for the location of the anode beds. A protective coating free from holidays and of uniformly high insulation value causes the electrical conducting properties of the soil to become of less significance in relation to corrosion rates (Section 15.8). 

Spencer, K. A, in Anti-Corrosion Manual, Scientific Surveys Ltd., London, 359 (1962) Vrable, J. B., Protecting Underground Steel Tanks , Mat. Prot., 6 No. 8, 31, August (1967) West, L. H., Cathodic Protection —The Answer to Corrosion Prevention of Underground Structures , Mat. Prot., 7 No. 7, 33, July (1968)... 

Groundbed in cathodic protection of underground structures, a buried mass of inert material (e.g. carbon), or scrap metal connected to the positive terminal of a source of e.m.f. to a structure. 

The odor of motor fuel present in underground structures such as basements and sewers is also a sign of leakage. 

The fate of gasoline in the subsurface is dependent on its interaction with soil and groundwater, volatilization, chemical reaction, biodegradability, and its movement, which in turn depends on the properties of both gasoline and the underground structure. 

In humid or wet climates, ED breaks down rapidly. It is more persistent in shaded desert areas and creates the greatest hazard in buildings and underground structures such as tunnels, caves, utility conduits, and stagnant sewer lines.1 As a form of calibration, a downwind evacuation from a 55-gallon spill should be a minimum of 1.0 mile.2 See Table 3.3 for a summary of the symptoms of exposure and potential medical treatment options. 

EN 13256, Geotextiles and geotextile-related products. Characteristics required for use in the construction of tunnels and underground structures, 2001. 

Today, trends in waste disposal have changed markedly, as shown in the table on page 165. The single most common method of disposal is deepwell or underground injection, in which wastes are buried in abandoned mines, caves, or other underground structures, where, the assumption is, they will remain for very long periods. 

GROUNDWATER. At varying depths below the surface of the earth, depending upon wet or dry seasons, underground structures, and other natural and unnatural factors, is a zone which is saturated with water most of which comes from rain which has penetrated the ground. The upper surface of this saturated zone is called the water table, and the water itself, the groundwater or the subsurface water. The region above the upper surface of the water table is called the zone of aeration or vadose /.one. 

Other made electrodes, such as underground structures, rod and pipe electrodes, and plate electrodes, when none of the above-listed items is available. 

Common uses of the impressed current method of protection include long transmission pipelines, complex underground structures, marine structures, ship hulls, and replacement for dissipated galvanic systems, large condenser water boxes, reinforcing steel in concrete, bare or poorly coated structures, unisolated structures and water storage tank interiors. 

Underground structures and pitting. The bottom of a metallic pipe or hose buried in the earth, with a relatively limited surface of metal poorly aerated, has the tendency to... 

It is recommended to examine the strained portions of metal including the welded areas that tend to be anodic with respect to unstrained portions (cathodic areas) and the bottom of underground structures such as steel tanks in aggressive environments, etc. 

The liverworts are one of three classes in the plant phylum Bryophyta. The other two classes are mosses and hornworts. Liverworts are small, green, terrestrial plants. They do not have true roots, stems, or leaves. Instead, they have an above ground leaf-like structure, known as a thallus, and an underground structure, known as a rhizoid. Most liverworts are found in moist environments and they tend to be less resistant to desiccation than their relatives, the mosses. Many liverwort species are found in temperate North America, but most species grow in the tropics. 

The evaluation of field of current density is essential in problems of galvanic corrosion. In many cases the direct measurement of current density is not feasible, while the electric potential can be obtained from experimental measurements. This is particularly true in case of cathodic protection systems in general, where many surveying techniques (for example DCVG and CIS for underground structures) rely in potential measurements at different points at the electrolyte in order to identify the current distribution along the metallic structures. 

Preconstruction exploration found no natural groundwater within 200 ft of the surface, in deposits consisting of 3 to 5 ft of silty sand, 15 ft of silty sand with white caliche beds, and 20 ft of shattered basalt underlain by competent, dense columnar basalt. During this study it became known that the site was within a planned federal irrigation project. Rather than move the site to nonirrigable land, it was decided to provide waterproofing to the underground structures. 

Grouting was also done in several locations beneath existing underground structures prior to excavating below them, as shown in Fig. 18.12. 

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