Storage tanks buried

The validity of Eq. (3-15) further follows from the results given in Fig. 3-4. It represents the current-potential curve for a buried storage tank. The difference f/ n - I/off is proportional to the current /. The quotient R is equal to the grounding resistance of the tank. The (/) curve corresponds to the true polarization curve. 

Fig. 3-4 Current-potential measurements on a buried steel storage tank with bitumen coating (surface area 4 m with four defects 5 cm x 20 cm soil resistivity p 30Q. m).

In the cathodic protection of storage tanks, potentials should be measured in at least three places, i.e., at each end and at the top of the cover [16]. Widely different polarized areas arise due to the small distance which is normally the case between the impressed current anodes and the tank. Since such tanks are often buried under asphalt, it is recommended that permanent reference electrodes or fixed measuring points (plastic tubes under valve boxes) be installed. These should be located in areas not easily accessible to the cathodic protection current, for example between two tanks or between the tank wall and foundations. Since storage tanks usually have several anodes located near the tank, equalizing currents can flow between the differently loaded anodes on switching off the protection system and thus falsify the potential measurement. In such cases the anodes should be separated. 

For economical and complete cathodic protection against external corrosion without harmful effects on nearby installations, the storage tank to be protected must have good coating and therefore require a low protection current density. In addition, it must have no electrical contacts with other buried installations, such as... 

Based on past experience, it has been found that the protection current density for buried storage tanks coated with bitumen is over 100 /xA m. With coatings in very good condition, it can amount to a few tens of jiA but for coatings in a very poor state, it can rise to a level of mA The protection current demand can... 

Tank installations with underground storage tanks and station piping should, if possible, be provided with conventional cathodic protection [3]. This is sometimes not possible because electrical separation cannot be achieved between the protected installation and other parts of the plant (see Section 11.4). The necessity for cathodic protection can be tested as in Ref. 13. In tank farms, a distinction should be made between coated, buried storage tanks and aboveground, flat-bottomed tanks in which the base contacts the soil. 

Further chapters cover in detail the characteristics and applications of galvanic anodes and of cathodic protection rectifiers, including specialized instruments for stray current protection and impressed current anodes. The fields of application discussed are buried pipelines storage tanks tank farms telephone, power and gas-pressurized cables ships harbor installations and the internal protection of water tanks and industrial plants. A separate chapter deals with the problems of high-tension effects on pipelines and cables. A study of costs and economic factors concludes the discussion. The appendix contains those tables and mathematical derivations which appeared appropriate for practical purposes and for rounding off the subject. 

It is recommended that storage tanks should not be buried directly in contact with soil, since it is almost impossible to avoid corrosive attack. Where, for some reason, it is not possible to provide a tank chamber as already... 

Subsurface drains include any type of buried conduits that convey and collect aqueous discharges by gravity flow (Figure 16.11). Water collected in a storage tank or a collection sump is then pumped for further treatment. Filters are usually needed in drain systems to prevent fine particles from causing clogging. 

Special features such as jackets on heat exchangers or special conditions such as the burying of a storage tank... 

Sources include oil and gas wells buried pipelines and storage tanks transport vehicles... 

For means of protection, the use of water based suppression systems may be a hazard due to the disposal of firewater water, which will freeze quite readily in exposed locations. This may also be the case with exposed hydrocarbon fluid lines that, if isolated, say for an ESD activation, may freeze up due to lack of circulation. This will hamper restart operations for the facility. Typical use in the past has been the reliance on gases fire suppression agents for enclosed area, particularly Halon. Other methods include fire water storage tanks that are kept warm, together with fire mains deeply buried and continually circulated. 

Coimecting iron objects to a more active metal is called cathodic protection. Cathodic protection is widely used to protect underground storage tanks, ship hulls, bridges, and buried pipes. One of the most common forms of cathodic protection is to connect the object to magnesium. When magnesium is coimected to an iron object, magnesium rather than iron becomes the anode in the oxidation process. In cathodic... 

Whiting, Indiana, USA 1955 2 died, 30 injured following a detonation in a hydroformer. Storage tanks punctured by shrapnel buried for 8 days ( 8M) DET... 

In order to minimize hazards, storage tanks for inflammable or toxic materials may be buried. Then they are provided with an overburden of 1.3 times the weight of water that the tank could hold in order to prevent floating after heavy rainfalls. 

A large spherical storage tank, 2 m in diameter, is buried in the earth at a location where the thermal conductivity is 1.5 W/m °C. The tank is used for the storage of an ice mixture at 0°C, and the ambient temperature of the earth is 20°C. Calculate the heat loss from the tank. 

Cathodic protection has many applications, e.g. in refineries, power stations, gas, water, and oil utilities on marine structures, e.g. jetties, piers, locks, offshore platforms, pipelines, ships hulls, etc. and on land structures, e.g. buried pipeline, storage tanks, cables, etc. For each use, the cathodic protection system requires careful design, either impressed current, sacrificial anodes, or a combination of both may be chosen. There may also be other protection systems, e.g. paint, the nature of which will affect the design parameters and must be taken into consideration. 

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