Coal-tar enamel

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. 

Asphalt Asphalt is a natural occurring mineral or as the residue from the distillation of asphaltic petroleum. It is less brittle and has better resistance to sunlight and temperature changes than coal tar enamel. Its water resistance is good but less than for coal tar enamel. It is not resistant to solvents or oils. It may crack at low temperatures and age at elevated ones. Like coal tar enamels, it is primarily black in color and difficult to overcoat with other materials. Its main use is for the in-situ coating of roofs or aboveground steel structures. 

Hz for thick coatings such as reinforced coal tar enamel, being selected to minimise interference from commonly occurring frequencies while maximising the distance the signal will travel, some 5-10 km on a reasonably well-coated pipeline. For thin film, coatings, such as a fusion-bonded epoxy, a frequency of 200 Hz has been found more appropriate. 

In the special case of pipelines operating at relatively high temperatures such as for the transmission of heavy fuel oil at up to 85°C, heat insulation and electrical insulation are provided by up to 50 mm of foam-expanded polyurethane. As a further insurance against penetration of water, and to prevent mechanical damage, outer coatings of polyethylene (5 mm), butyl laminate tape (0-8 mm) or coal-tar enamel reinforced with glass fibre (2-5 mm) have been used. 

It is often claimed that a coal-tar-base coating absorbs less water than an asphalt coating and there is evidence in practice to support this claim, but some asphalt enamels in practice have been as good as the best coal-tar enamels. 

Coal-tar enamels are claimed to have better adherence than the asphaltic enamels to clean metal, probably because of the presence of polar compounds, but little difference can be noted in practice under proper pipelining conditions. 

Asphalt mastic is a heavy duty system that is shop-applied in thicknesses up to 1 in. (25.4 mm). Although asphalt mastics perform well, they are very costly. Their use is usually limited to river crossing and swamp areas. Coal-tar enamel has more than 50 y of successful performance underground, but it is subject to cracking when the temperature is below 20° F (-7°C), and there are environmental constraints. The EPA has shut down applicators in the middle of production because of air pollution. These problems rule out asphalt mastic and coal-tar enamel as feasible materials for most pipelines. In addition, coal-tar enamels are often ruled out because of long-term deterioration. Asphalt enamel is generally considered inferior to coal-tar enamel therefore, its use is limited. Polyvinyl chloride tape is becoming obsolete because of the superior performance of polyethylene tape. 

The use of coatings in conjunction with CP is the most popular form of corrosion protection of pipelines. Some of the coatings used are fusion-bonded epoxy, extruded polyethylene, coal tar enamel, liquid epoxy, tape, polyurethane, mastic, and wax. Pipelines with each of these coatings remain in service at the present. The most widely used coating on pipelines is fusion-bonded epoxy. New multilayered coatings are now on the market. 

W.R. Roder. Coal tar enamel the protective pipeline coating of the past, present and what s new. Proceedings of the PIC on Conference, May 20, 2000, Canada. 

When a coal tar enamel is applied to steel pipes, corrosion can be inhibited. For this reason, almost 75%... 

Recommendations for Training and Qualifying Personnel as Railcar Coating and Lining Inspectors Plant Applied, External Coal Tar Enamel Pipe Coating System Application, Performance and Quality Control... 

Pipeline Coatings Thermoplastic coatings based on bituminous coal tar enamels or asphalt mastics. 

Fusion Bonded Epoxy (F.B.E.). The steel is decontaminated, abrasive blast cleaned and heated by electrical induction heaters to the prescribed temperatures, before uniformly applying epoxy powder. Another example is the use of hot applied coal tar enamels used mainly as pipeline coatings. 

Painting System Specification No. 10.01 Hot-Apphed Coal Tar Enamel Painting System... 

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