Bitumen enamels and suited primers to be used in combination therewith are described in “Specification for Bitumen-based Hot-applied Coating Materials for Protecting Iron and Steel, Including Suitable Primers Where Required”, BS 4147: 1980 by British Standards Institution, said matter hereby being incorporated in the present specification. The same applies to examples of tar enamels and suited primers described in “Specification for Coal-Tar-Based Hot-applied Coating Materials for Protecting Iron and Steel, Including Suitable Primers Where Required”, BS 4164; 1980, also by British Standards Institution.
Tar enamels, such as for instance coal tar enamel, are old and well-known pipe coating materials possessing several excellent properties, inter alia an outstanding protecting effect against corrosion. However, the material is gradually growing outdated partly due to its environmental drawbacks and partly due to the difficulty of providing the raw materials of the correct quality. In addition, the use of tar enamel is encumbered with draw-backs relating to the production thereof because the properties of the tar enamel may change during the production which involves repeated return pumping’s, reheating and flood coatings, where it cannot be avoided that some of the ingredients of the enamel evaporate.
A typical tar enamel to be used for protection against corrosion contains tar of the quality 105/15, 105/8 or 120/5 according to BS 4164: 1980 in a quantity of 65 to 75% by weight together with filler in a quantity of 25 to 35% by weight.
Enamel pipe coat
Bitumen enamels are well-known and appreciated pipe coating materials presently used to an increasing extent instead of coal tar enamel. Most of the pipelines for oil and gas in the North Sea are coated with bitumen enamels. The material is often recommended, but has also been criticized for instance due to poor bitumen quality in connection with the oil crisis in 1972 to 1973. It is of vital importance that the correct bitumen quality is used, such as for instance oxidized bitumen 115/15, and that the supplies are reliable.
Anti-corrosion bitumen enamel
A typical conventional bitumen enamel to be used for protection against corrosion contains bitumen of the quality 115/15 according to BS 4147: 1980 in a quantity of 65 to 75% by weight together with 25 to 35% by weight of filler, most typically approximately 70% by weight of bitumen and 30% by weight of filler. The addition of filler is usually determined by the melting point of the bitumen used. A conventional bitumen enamel is heated to 220 to 230°C while being stirred and applied in a layer of a thickness of 5 to 7 mm.
GB-PS No. 1538267 discloses a process for coating a pipe comprising applying to the pipe a bituminous composition comprising from 80 to 99% by weight of bitumen and from 1 to 20% by weight of a block polymer having the general configuration: A-B-(-B-A) n
Wherein each A is a thermoplastic polymer block of a monovinyl aromatic hydrocarbon or a 1-alkene, B is an elastomeric polymer block of a conjugated diene or more than one 1-alkene, and n is an integer or a hydrogenated derivative of the block copolymer.
However the above coating process has not yet been accepted for industrial use due to insufficient bonding of the bituminous composition to the pipe.