Piping buried

Copper is a galvanic metal and causes corrosion, in the presence of moisture, in nearby metals, such as cable sheathes, steel structure and water, gas or drain pipes, buried in its vicinity. With all such metafs. it forms a complete electrolytic circuit and corrodes them. Tinning may give protection against its galvanic effects but this is ati expensive proposition... 

Stainless steel pipes (buried in the ground) and the interiors of stainless steel heat exchangers have been successfully cathodically protected, but CP is rarely used for materials other than steel. The protection potential usually adopted for steel is —850 mV to the saturated calomel reference electrode. This varies with temperature and the presence of other aggressive species in the environment. 

BISRA tests on galvanised steel pipe buried for five years at five different sites are described by Hudson and Acock The galvanised pipes resisted corrosion rather better than steel at all sites. Galvanised pipes of small diameter are frequently used to provide underground water services in farms and similar establishments, and little trouble is experienced. 

Technical Committee Reports of the National Association of Corrosion Engineers, USA, on pipeline corrosion control, including Statement on Minimum Requirements for Protection of Buried Pipelines , Some Observations on Cathodic Protection Criteria , Criteria for Adequate Cathodic Protection of Coated Buried Submerged Steel Pipelines and Similar Steel , Methods of Measuring Leakage Conductance of Coatings on Buried or Submerged Pipelines , Recommended Practice for Cathodic Protection of Aluminium Pipe Buried in Soil or Immersed in Water ... 

Pipes buried in the structural slab. These are connected to delivery and return headers, and glycol circulated. This is heated by waste heat from the refrigeration plant. Steel pipe should not be used under the floor unless protected against corrosion. Air vent pipes to allow a current of ambient air through the ground under the base slab. This is not very suitable in cold climates. 

Anticorrosion protection lined pipes buried gas pipelines pipes co-extruded with MDPE and HD PE to increase their performance dirty water and effluent pipes used in aggressive environments. .. 

The tracer pipeline leak testing, which is similar to the tracer tank leak testing, is effective for locating leaks in all types of pipeline installations, including pipe buried under pavement, airline runways, buildings, or underwater. Where leaks are known to exist, the tracer leak test is effective in determining their location without expensive excavation. 

Natural convective flows in porous media occur in a number of important practical situations, e.g., in air-saturated fibrous insulation material surrounding a heated body and about pipes buried in water-saturated soils. To illustrate how such flows can be analyzed, e.g., see [20] to [22], attention will be given in this section to flow over the outer surface of a body in a porous medium, the flow being caused purely by the buoyancy forces resulting from the temperature differences in the flow. The simplest such situation is two-dimensional flow over an isothermal vertical flat surface imbedded in a porous medium, this situation being shown schematically in Fig. 10.25. 

Figures 7.107 and 7.108 show the corrosive attack on samples of cast iron pipe and ductile iron pipe buried under the soil for 20 and 9 yrs, respectively. The large hole in...

In the early years of industrial development in the United States, many plants buried their outside pipelines. The initial cost for this type of installation is low because no supports are required and the earth provides insulation. However, location and repair of leaks are difficult, and other pipes buried in the same trench may make repairs impossible. Above-ground piping systems in industrial plants have proven to be more economical than buried systems, and, except for major water and gas lines, most in-plant piping systems in new plants are now located above ground or in crawl-space tunnels. 

Figure 2. Cross section of a 155 mm-inside diameter ductile cast iron pipe buried for 567 Ms.

Earth-Coupled Ground Source (Geothermal) Heat Pump - A type of heat pump that uses sealed horizontal or vertical pipes, buried in the ground, as heat exchangers through which a fluid is circulated to transfer heat. 

Fig. 3 Schematic of a corrosion cell operating on a steel pipe buried in the soil.

Figures 5.72 and 5.73 show the corrosive attack on samples of cast iron pipe and ductile iron pipe buried under the soil for 20 and 9 years, respectively. The large hole in cast iron pipe (Fig. 5.72) and the corrosion pit and perforation in ductile iron pipe (Fig. 5.73) show the severity of soil corrosion. It is suggested that cathodic protection can reduce the extent of corrosion of iron pipes.

Calculations show that the length of pipe buried at a depth of 1.5 m required to produce 1.2 kW of heat will vary between 150m in dry soil and 50m in wet soil. 

Ground source heat pumps extract heat from the ground by circulating a fluid through polythene pipes buried in the ground in trenches or in vertical boreholes. 

The potential of a cathodically protected stmcture is determined ideally by placing the reference electrode as close as possible to the structure to avoid an error caused by IR drop through the electrolyte. Any IR drop through corrosion-product films or insulating coatings will persist, of course, even where adequate precautions are exercised otherwise, tending to make the measured potential more active than the actual potential at the metal surface. In practice, for buried pipelines, a compromise position is chosen at the soil surface located directly over the buried pipe. This position is chosen because cathodic protection currents flow mostly to the lower surface and are minimal to the upper surface of a pipe buried a few feet below the soil surface. 

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