Pitch epoxy coatings

Like pitch-epoxy coatings, pitch-polyurethane coatings are excellent materials for use under very corrosive conditions such as for sewage work, marine and port installations, chemical works and power stations. Particular applications are for ... 

A tank with a fixed cover of plain carbon steel for storing 60°C warm, softened boiler feed water that had a tar-pitch epoxy resin coating showed pits up to 2.5 mm deep after 10 years of service without cathodic protection. Two separate protection systems were built into the tank because the water level varied as a result of service conditions. A ring anode attached to plastic supports was installed near the bottom of the tank and was connected to a potential-controlled protection rectifier. The side walls were protected by three vertical anodes with fixed adjustable protection current equipment. 

Figure 20-14 shows the protection of a gravel filter in the treatment of raw water. The 200-m internal surface was coated with 300 jlm of tar-pitch epoxy resin. Long-term experiments indicated that at = -0.83 V, no cathodic blisters were formed, but were formed at more negative potentials (see Section 5.2.1.4). TiPt anodes 400 and 1100 mm in length, 12 mm in diameter, and with an active surface of 0.11 m were installed [29]. 

The thickness and water resistance of the normal air-cured film can now be much improved by the incorporation of suitable coal-tar pitch material. A typical coal tar/epoxy coating material would be constituted as follows ... 

Hoiberg, A. J., (ed.). Asphalts, Tars and Pitches, Interscience Publishers (John Wiley) (1965) ANSI/AWWA C213-79, Standard for Fusion Bonded Epoxy Coatings for the Interior and Exterior of Steel Water Pipelines... 

Table IX gives a typical formulation for coal tar epoxy. It contains approximately 30% epoxy and 25% coal tar. This type of coating will perform better than either the pure coal tar or the pure epoxy coatings in several applications. Because of the relatively low cost of coal tar pitch, the raw material cost is significantly less than for a pure epoxy.

Epoxy coatings, crosslinked with amines or polyamines, are widely used in atmospheric fume environments. Because of the sensitivity of coal tar pitch to UV light, coal tar epoxies are not normally used in atmospheric exposures. 

A modified form of epoxy is known as coal-tar epoxy coating. This consists of a two package epoxy-amide combination with the addition of coal-tar pitch to either the amide or epoxy portion. It is possible to spray this material up to a thickness of 20 (xm. Its chief use is on underground pipes or aboveground structures where high chemical resistance is needed and appearance is not important. 

Coal tar pitch is the most widely used resinous extender for epoxy resins. It is primarily used in surface coating formulations, but can also be used as a cost reducer and flexibi-lizer in epoxy adhesives and sealants. In addition to the increase in flexibility (and reduction in thermal and chemical resistance), coal tar pitch extenders provide excellent water resistance. Their primary applications, therefore, are often in the marine, pipe, tank, and general industrial maintenance areas. 

Bubject to wear on pumps, agitators, etc. In dilute solutions, wood is aatisfactory where conditions allow it to swell and seal pores, cracks, etc. Care must be taken that hoops, tie rods, etc., are coated with an inert material such as tar, pitch, silicates, epoxy and polyester resins, polyvinyl chloride, etc. For hydrochloric acid, rubber-lined steel is excellent at low... 

Coal tar pitches are less readily available than they used to be their content of polynuclear aromatic hydrocarbons makes their safe use suspect. They have been replaced to some extent by the less effective petroleum bitumens whose mechanical properties are improved by combination with poly(vinyl chloride) and other chlorinated polymers as one-pack, nonconvertible coatings, or by combination with epoxy or polyurethanes in high-performance two-pack convertible coatings. Similar materials are preferred for coating ballast spaces and double bottoms in vessels, where economical systems are required that do not have to be attended throughout the lifetime of the vessel (15-25 years). Multiple coats with a total thickness of 250-400 pm are usually employed. 

Epoxy cresol novolac epoxy-pitch coatings, marine paints Cresylic acid Epsom salt mfg. 

Coal tar, or pitch, is the black organic resin left over from the distillation of coal. It is nearly waterproof and has been added to epoxy amine and polymide paints to obtain coatings with very low water permeability. It should be noted that coal tar products contain polynuclear aromatic compounds, which are suspected to be carcinogenic. The use of coal tar coatings is therefore restricted or banned in some countries. 

Figure 2.4 Photographs (a) of hollow pol5mier tubes with helical interconnect used for actuation testing. The pitch of the helix can be altered with examples shown in (a) of 20, 15 and 10 turns/cm. A hoUow tube with no helix (0 tums/cm in (A)) is also shown. Schematic diagram (b) showing method of construction for these helix tubes, (a) 25-pm platinum wire is wrapped around the 125 mm wire as a spiral, (b) Polymer synthesis — the assembly is placed in polymer electrolyte solution (0.5 M Py, 0.25 M TEA PF in PC) and electroplated for 24 hours at -28°C. (B) Polymer coating forms around wire and spiral, (C) 125-micron center wire is withdrawn from the polymer tube/helix, (D) two short connectors of 125 mm wire are inserted into each end, (E) 25 mm wire is pulled tight around these ends for a good electrical connection and epoxy glued to hold in place.

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