Protective coatings fusion-bonded epoxies

Recent trends in protective coatings used on buried pipelines have been away from reinforced hot applied coal tar and asphalt enamels and butyl rubber laminate tapes, particularly where applied over-the-ditch . The more recently developed coatings based on fusion bonded epoxies, extruded poly-ethylenes, liquid-applied epoxies and polyurethanes, require factory application where superior levels of pipe preparation and quality control of the application process can be achieved. 

Omori, K., Watanabe, U. and Takeda, T., Improvement of Fusion Bonded Epoxy Coating, 5lh International Conference on the Internal and External Protection of Pipes, Innsbruck Austria, pp. 67-79, BHRA, London (1983)... 

At present, epoxy-coated rebar is the most common corrosion protection system and is used in 48 states. At present, there are nearly 20,000 bridge decks using fusion-bonded epoxy-coated rebar as the preferred protection system. This amounts to nearly 95% of new deck construction since the early 1980s. 

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. 

Since the maximum voltage that can be generated with zinc anodes is extremely unlikely to generate hydrogen embritdement, galvanic systems have been used to protect prestressed concrete members. They are also used on fusion bonded epoxy coated steel reinforced piles as the effects of electrical discontinuity between bars is unlikely to lead to significant stray current induced corrosion as the currents and potentials are low. 

The protection system of choice on highway bridges in North America for a ressive chloride conditions continues to be fusion bonded epoxy coated reinforcement (FBECR). It was first installed in a bridge deck in Philadelphia in 1973 (Manning, 1996). It was estimated by the EHWA that 100 million sqnare feet (10 million m ) of bridge deck on the US federal-aid highway system contains epoxy coated rebar up to 1889 (Virmani and Clemena, 1998). 

A specific example for epoxy is fusion bonded epoxy (FEE) coating [8]. It is widely used to protect steel pipes. In this case, the resin and hardener components of a dry powder stock of FEE do not react until the coating application temperature is reached. Then the powder contents melt and form a liquid which flows onto a steel surface where it becomes a solid coating by chemical crosslinking and the use of heat. This is known as fusion bonding and the chemical crosslinking reaction is not reversible. 

Paints, in general, are not useful for protecting buried structures, one reason being that mechanical damage to thin coatings by contact with the soil is difficult to avoid. Tests have shown that, for this purpose, their fife is relatively short. Coatings based on coal tar or on fusion-bonded epoxy have been found to be far more practical. Similarly, the usual linseed-tung oil paints are not durable for metal structures totally immersed in water, except possibly for short periods of time on the order of one year or less. In hot water, life is stiU shorter. More ade-... 

The problems of pitting and under-coating corrosion are more difficult and are well known in pipeline corrosion where fusion bonded epoxy coatings are frequently applied to the outside of pipelines and then cathodic protection applied to protect the pinholes that inevitably occur. However, these cathodic protection systems are applied from new so no corrosion is established. The FBECR structures are already corroding when cathodic protection is applied. It is therefore possible for corrosion to be established under the coating where the cathodic protection current cannot reach, The small driving voltage of a sacrificial anode system means even less protection or penetration of current than for an impressed current system. 

The demonstrated reliability of these pipelines has required the use of several different corrosion protection schemes. To reduce attacks on the outer surfaces of pipelines, improved cathodic protection systems and coating materials (fusion-bonded epoxy, which replaced coal tar systems) have been used along with better inspection programs. 

C116/A21.16 ANSI Standard for Protective Fusion-Bonded Epoxy Coating for the Interior and Exterior Sinfeces of... 

Corrosion Protection. Although steel underground transmission lines are often protected by coal tar or fusion bonded epoxy coatings, a large volume of polyethylene tapes as well as some vinyl-backed tapes are used for corrosion protection. Pipes of large diameter, such as oil line pipes, are usually machine-wrapped in the field just prior to placement in the ground. The tapes are unusual in that the backing is from 12 to 15 mils thick and the butyl-based adhesive is approximately of the same thickness. For the pipeline industry the rolls are 18 in. wide and contain up to 800 feet of tape. There is a reduction currently in domestic pipeline construction but appreciable amounts of pipewrap are exported. 

D. G. Enos, J. A. Kehr and C. R. Guilbert, A high-performance, damage-tolerant, fusion-bonded epoxy coating , in Pipeline Protection Conference n 13 (1999) (Edinburgh, Scotland, 29 September-1 October 1999). 

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