Underground structures applications

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. 

Polyethylene (PE), polypropylene (PP), polystyrene (PS), polycarbonate (PC), and PUR are the most common foams however, PP foams can provide favorable properties at a lower material cost. PP is stiffer than PE and can perform better in load bearing or structural applications. The low glass transition temperature of PP compared to PS provides increased flexibility and impact strength. Use of PP foams include packaging, automotive, insulation, and protection of underground pipe. 

Many other issues are involved in the application of cathodic protection. For example, consider the case of cathodic protection of underground structures in which the corrosivity of soil is likely to play a major role, as does the degree of aeration and the resistivity. Bacterial effects also can change the corrosion potential. AU these factors influence the corrosion process so that along a pipeline there can be varying cathodic control requirements that have to be estimated from potential measurements, experience, and so forth. 

Steels are the most common materials used for oil and gas applications. The most common use of steel is for structural applications, such as support structures, piles, superstructures, underground pipelines, storage tanks, pipings, and so forth. The main requirements of structural steel are as follows ... 

For the application of cathodic protection to structures to be protected, the initial considerations are best made at the early design and preconstruction phase of the structure. For underground structures, it may be necessary to visit the proposed site, or for pipelines the proposed route, to obtain additional information on low-resistivity areas, availability of electric power, and the existence of stray dc current or other possible interactions. Other considerations will include fundamental design decisions to select the type of system and the most suitable type of anode appropriate to that system. In addition, it will be a requirement to determine the size and number of the power sources or sacrificial anodes and their distribution on the structure. Other factors that must be considered to ensure that cathodic protection is applied in the most economic and reliable manner are given as follows. 

Cathodic protection was incidental to the mechanism of protecting steel sheet coated by dipping into molten zinc (galvanizing)(see Section 14.3.3), a method first patented in France in 1836 and in England in 1837 [3]. However, the practice of zinc coating of steel was apparently described in France as early as 1742 [4]. The first application of impressed electric current for protection of underground structures took place in England and in the United States, about... 

In the past, the Mononobe-Okabe method was used to calculate the seismic-induced dynamic earth pressures on underground structures. The method assumes the earthquake load is caused by inertial forces of the surrounding soil and calculates the load using soil properties and a determined seismic coefficient. This method is not applicable in the case of underground structures. 

The Institute has many-year experience of investigations and developments in the field of NDT. These are, mainly, developments which allowed creation of a series of eddy current flaw detectors for various applications. The Institute has traditionally studied the physico-mechanical properties of materials, their stressed-strained state, fracture mechanics and developed on this basis the procedures and instruments which measure the properties and predict the behaviour of materials. Quite important are also developments of technologies and equipment for control of thickness and adhesion of thin protective coatings on various bases, corrosion control of underground pipelines by indirect method, acoustic emission control of hydrogen and corrosion cracking in structural materials, etc. 

Coal tar enamel This is derived from the coking of coal and is further distilled to produce coal tar pitches. It is used for hot application on-site. It will crack and craze if exposed to sunlight but has been employed successfully for over 50 years for the protection of underground or immersed structures. The main use is now for the exteriors of buried or immersed pipelines. Different types of enamel are available to give various degrees of heat resistance. It is now generally used for pipelines below 155 mm diameter. 

Limitations on the use of sulphur concrete are imposed by its high temperature and fire susceptibility. Although it will not sustain combustion, under applied flame the sulphur will burn to produce SO2. At temperatures above the melting point of sulphur, the product loses structural integrity. Thus sulphur concrete is best suited for outdoor and underground use as well as indoor construction applications where fire hazard is not a concern and building codes are not applied. 

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