Plastic and nonmetallic article shaping or treating: processes – Mechanical shaping or molding to form or reform shaped article – To produce composite – plural part or multilayered article
Reexamination Certificate
1999-01-14
2001-07-24
Vargot, Mathieu D. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Mechanical shaping or molding to form or reform shaped article
To produce composite, plural part or multilayered article
C156S304200, C156S304500, C264S265000, C285S047000, C285S053000
Reexamination Certificate
active
06264871
ABSTRACT:
This invention relates to a method of forming a field joint for insulated pipelines for use especially, but not exclusively, sub-sea and, more specifically, to a method of forming a field joint for insulated pipelines which facilitates smooth reeling and laying of the pipelines.
Pipes which are factory-coated with an elastomer or insulation coating can only be coated to within approximately 200 mm of the pipe ends as a section of the pipe end must be left bare to allow pipes to be joined together, normally by a welding process.
The pipes are normally welded together as an integral part of the pipe laying process. Where this is carried out off shore the pipe welding would generally take place on a lay barge or a reel ship on a continuous basis.
In order to minimise the rate of installation, it is necessary to be able to complete the coating of a welded field joint within the ten to fifteen minutes in which another field joint is being welded. In theory, the insulation at the field joint should meet a similar specification as that of the parent coating but using the process used for applying the parent coating to the body of the pipe would increase the production time by an unacceptable amount. The presently used solution to the problem of filling the field joint within the time taken for the welding process is to apply a sheet metal mould around the parent coating of the pipe, inject a quick setting insulation material such as polyurethane or polyolefin, allow it to set and remove the mould.
FIG. 1
of the drawings illustrates a typical field joint produced in accordance with this known method between two coated pipe sections A and B. Although the above method produces a satisfactory field joint C between the ends of two pipe sections, as the polyurethane filler overlaps the polypropylene coating D at the ends of the pipe, this reduces the reliability of the resulting pipeline. The coated pipe has to pass over a roller as it heads out-board of the lay barge or reeling ship and this often results in snagging of the field joint during both reeling and subsequent laying of the pipeline. This can damage both the field joint and also lead to damage to the rollers over a period of time due to the large number of field joints passing over the rollers during a pipe-line laying operation.
The present invention aims to provide an improved field joint which overcomes or at least mitigates the disadvantages suffered by the known field joints. The present invention also aims to provide a method for forming an improved field joint.
According to one aspect of the present invention there is provided a method of forming a field joint around the bare joint of two joined insulation covered pipes comprising the steps of providing a first angular cut back in the parent coating to expose the end of a pipe, providing a second cut back in the parent coating to provide an annular band of the parent coating of a lesser diameter than the parent coating on the pipe, securing a mould around the lesser diameter band, pumping polyurethane into the mould in a sufficient amount to form a field joint which extends into the second cut back and lies flush with the parent coating of the pipes to allow for reeling and laying of the pipe without snagging.
Whilst this method for forming a field joint has advantages in the reliability of the finished pipeline, a further advantage of this method of producing a field joint lies in the mechanical connection formed between the polyurethane infill and the parent coating of the pipes. As the polyurethane is pumped into the mould it pours into the recess in the lesser diameter band and when set forms an interference fit with the parent coating. This establishes a more secure field joint on the pipes and prevents shifting of the field joint once the pipe has been laid.
Preferably, the second cut back may also be angular.
Advantageously, the first and second cut backs are provided in the parent coating by either a grinding process or a lathing method.
Conveniently, the surface of the pipes is blasted in order to clean the surface, the surface of the pipes are then heated to a temperature between 70 and 90° C. and a primer is applied before the mould is secured around the field joint.
Advantageously, a thin coating of polyurethane may be applied over the first and second cut backs.
According to a further aspect of the present invention there is provided a field joint and located around the bare joint of two joined insulated pipes, the field joint comprising a polyurethane infill recessed into the insulated parent coating of the pipes such that the infill lies flush with the surface of the parent coating on the pipes.
Preferably, the field joint further comprises means for effecting a mechanical connection between the polyurethane infill and the parent coating.
Preferably, the mechanical connection is formed by a groove in the parent coating into which the polyurethane infill extends.
Advantageously, a plurality of grooves are provided in the parent coating to provide a series of mechanical connections between the parent coating and the polyurethane infill.
Alternatively, the mechanical connection is formed by a plurality of indentations in the parent coating into which the polyurethane infill extends.
REFERENCES:
patent: 3711124 (1973-01-01), Gerholt et al.
patent: 3731710 (1973-05-01), Bauer et al.
patent: 4019761 (1977-04-01), Heidemann
patent: 1767264 (1958-05-01), None
patent: 3822090 (1989-07-01), None
patent: 0030776 (1981-06-01), None
patent: 0038051 (1981-10-01), None
patent: 0360028 (1990-03-01), None
patent: 310515 (1973-10-01), None
patent: WO89/11618 (1989-11-01), None
patent: WO 94/29635 (1994-12-01), None
Mullen Douglas Thomas
Smith Iain
Bredero Price Coaters Ltd.
Lalos & Keegan
Vargot Mathieu D.
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