Coated pipes and methods of making them

Details Coated pipes and methods of making them Coated pipes and methods of making them

1996-04-25

1999-08-17

Beck, Shrive

Coating processes

Applying superposed diverse coating or coating a coated base

Synthetic resin coating

427409, 427410, 427413, 427231, B05D 126, B05D 140

Patent

active

059391456

DESCRIPTION:

BRIEF SUMMARY
This invention relates to methods of pipe coating, pipes made by the methods, and apparatus for making the pipes.
The invention provides for providing insulating or protective coatings on pipes by pouring or otherwise applying material onto a rotating pipe.
According to the invention there is provided a method of coating a pipe comprising the steps of: to the pipe parallel to its axis of rotation.
In some embodiments of the invention the heads are fixed and the bed traverses.
An embodiment of the invention will be illustrated by reference to FIG. 1.
The apparatus comprises a bed 1 provided with chucks 2. The pipe 3 to be coated is mounted in the chucks 2 and caused to rotate. To obtain very high quality product the rate of rotation should be carefully controlled by first controller 3a.
Coating is dispensed from head 4. Head 4 is typically air or electrically driven and may traverse along guides. Where the coating is the reaction product of two components they may be supplied by separate feeds 5,6 to the head where they mix and react. Alternatively or additionally they may be mixed prior to supply to the head or they may react on the pipe.
Head 4 is arranged to move parallel to the axis of the pipe 3. The rate of traverse and rate of dispersing are controlled by second controller 7 which may be microprocessor based.
Typically layers up to about 20-25 mm can be routinely dispensed. Further layers can be applied from further heads 4a,4b traversing behind head 4. Multiple layers can readily be applied in this manner with extremely good inter-layer adhesion being achieved. The further heads may apply the same or different material to the pipe. Four layers can be routinely applied in a single pass. The further heads need not wait for the first head to complete its traverse before applying their coating. Where the heads are fixed and the bed traverses it then the heads generally make a single pass. One or more heads in some embodiments make multiple traverses.
The coating is allowed to cure to a handleable condition and then removed from the apparatus. The coated pipe may have a central coated portion and bare ends. The ends are thus free of the poured coating ready for joining, for example using currently available field joint systems or as described in copending UK application number 93 24 147.9.
A wide range of coatings can be applied.
For example a conventional steel pipe may be coated with an anticorrosion coating of fusion bonded epoxy (FBE) or rubber. These layers may be applied in conventional manner for example spraying or extrusion. Application of epoxy primer in liquid form is a preferred pretreatment. Syntactic polyurethane (PU) can then be applied. Multiple layers of total thickness up to 60 mm giving a U-value of less than 2.5 Wm.sup.-2 K.sup.-1 can readily be applied. This system has been tested on pipes up to (16 inch) 0.4 m diameter to give a very satisfactory product substantially free of voids and consistent throughout the thickness.
Table 1 compares the properties of a syntactic PU applied in accordance with the invention with product moulded in a traditional way.


TABLE 1 ______________________________________ Invention Control ______________________________________ Density 700-760 kgm.sup.-3 700-760 kgm.sup.-3 Hardness 80 Shore A 90 Shore A Tensile Strength 5.5 MPa 6.5 MPa Compressive Modulus 1.5 MPa 2.0 MPa Elongation at Break 100% 60% Abrasion Resistance 1300 mm.sup.3 1300 mm.sup.3 ______________________________________ are very satisfactory with notably good elongation at breaking. Additionally traditional coating of thick layer syntactic foam on large diameter pipe can lead to a poor quality, low density product due to thermal expansion of the polymer spheres in what is known as a "free rise situation". The process of the invention has a marked decrease in the probability of this problem.
The process of the invention is also cost effective. Typically the process of the invention is 5-15% cheaper than traditional methods. Savings occur in a number of areas. Losses i

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patent: 5439711 (1995-08-01), Vu et al.
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Oil & Gas Journal; Polypropylene System Scores High as Pipeline Anti-Corrosion Coating; pp. 42-45; Dec. 14, 1992.
Kunststoffe; Walzen mit Pur-Elastomeren Beschichten; pp. 958-960; 1992.

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