Patent Description:
Typically, pipe sections which are factory-coated with an elastomer and/or insulation coating are not fully coated along their entire lengths, but rather are left with uncoated ends to facilitate joining of the pipe section ends (e.g., using a welding process) in the field. Each uncoated end on a pipe section may be about <NUM> in length. The pipe sections are typically welded together as part of the pipe laying process. This welding may take place at the location where the pipe sections are to be reeled, or, such as in the case of sub-sea or offshore pipes, on a lay barge or a reel ship.

After welding, the field joint should be coated. The field joint coating is typically an insulation material that is typically different than, but having similar properties as, the parent coating provided on the pipe section at the factory. For the purpose of speed and ease, the field joint coating is typically applied using an injection moulding process in which the field joint coating is injected into a mould placed about the field joint and overlapping with the parent coating.

The result is typically a coated field joint as shown in the longitudinal cross-sectional view of <FIG>. For simplicity, only the upper half of the cross-sectional view is shown, however it should be understood that the bottom half of the cross-sectional view is a mirror of the shown half. This example illustrates a field joint between two pipe sections A and B, each having factory-applied parent coatings CA and CB, respectively. The field joint coating D typically fills in the gap between the parent coatings CA and CB, and also overlaps the parent coatings CA and CB. This overlap means that the field joint coating D has a greater radius than the parent coatings CA and CB, and this difference is referred to as the upstand E. In a typical coated field joint, the upstand may be <NUM> or greater. The presence of a large upstand (e.g., an upstand that is <NUM> or greater) may cause damage to pipe handling equipment and/or the field joint, such as when the field joint is reeled out over rollers during laying of the pipeline.

<CIT> discloses a process for coating a field joint. Two pipes, which are coated with an epoxy layer, an adhesive layer and polypropylene layers are provided. Cut backs are provided on the epoxy layer, the adhesive layer and the polypropylene layers. The ends of pipes are welded together, forming a field joint. The field joint is coated with an epoxy layer and an adhesive layer and a field joint coating is then applied to the coated field joint and the cut back.

<CIT> discloses a method for coating a field joint. The pipes are coated with a layer of anti-corrosion agent and a layer of coating. Cut backs are provided on each layer. The cut back in the anti-corrosion agent layer is perpendicular to the surface of the pipe, while the cut back in the coating layer is angular. After the pipes are joined, a coating layer is applied at the pipe joint, covering the field joint and the cut backs.

The present invention is defined in independent claim <NUM>. Preferred or advantageous features of the present invention are defined in the dependent claims.

In some examples, the present disclosure provides a method of coating a field joint joining uncoated ends of two pipe sections, each pipe section being coated with a parent coating and having at least one uncoated end, the method including: providing a first angular cut back in the parent coating of each pipe section, the first angular cut back being at an angle of about <NUM>° ± <NUM>° relative to a longitudinal axis of the field joint; providing a second angular cut back in the parent coating of each pipe section, the second angular cut back being positioned further from the field joint than the first angular cut back; the first and second angular cut backs resulting in the parent coating having a stepped profile, a step in the stepped profile being defined between the first and second angular cut backs, the step being substantially parallel to the longitudinal axis of the field joint and being free of indentations; and injection moulding a field joint coating over the uncoated ends and the first and second angular cut backs, the field joint coating being moulded to have an upstand that is less than or equal to about <NUM>.

In some examples, the present disclosure provides a pipe section for forming a field joint, the pipe section including: a pipe section end to be joined with another pipe section end for forming the field joint; and a parent coating over an outer surface of the pipe section, the outer surface in the vicinity of the pipe section end being free of the parent coating; the parent coating in the vicinity of the pipe section end having provided therein first and second angular cut backs, the first angular cut back being at an angle of between <NUM>° and <NUM>° with a manufacturing tolerance of +/- <NUM>°, for example, about <NUM>° ± <NUM>°, relative to a longitudinal axis of the pipe section and the second angular cut back being positioned further from the pipe section end than the first angular cut back; the first and second angular cut backs resulting in the parent coating having a stepped profile, a step in the stepped profile being defined between the first and second angular cut backs, the step being substantially parallel to the longitudinal axis of the pipe section and being free of indentations.

In some examples, the present disclosure provides a coated field joint joining ends of two pipe sections, the coated field joint including: a field joint joining the ends of the two pipe sections, each of the two pipe sections being as described above; and a field joint coating over the field joint and the first and second angular cut backs, the field joint coating forming an upstand that is less than or equal to about <NUM>.

The present disclosure provides methods for coating a field joint, coated field joints formed thereby and pipe sections for forming such coated field joints. The coated field joint in accordance with the present disclosure may achieve an upstand that is substantially flush with the parent coating on the pipe section, or that is minimal (e.g., <NUM> or less). The present disclosure may enable a coated field joint that uses a smaller volume of field joint coating material. A field joint that is flush with the parent coating or that has a reduced upstand may enable easier handling in the yard and/or on the vessel prior to laying of the pipe, may help to reduce the risk of damage to laying equipment (e.g., tensioners on reel-lay vessels), and/or may enable more pipe to be reeled (due to the smaller diameter of the disclosure coated field joint, compared to conventional coated field joint).

<FIG> shows a cross-sectional view of a coated field joint in accordance with an example of the present disclosure. In this example, two pipe sections <NUM>, <NUM> are joined together at their respective ends <NUM>, <NUM>. For simplicity, details will be described only for one side of the field joint corresponding to pipe section <NUM>, however it should be understood that the configuration is the same for the other side of the field joint corresponding to pipe section <NUM>.

The pipe section <NUM> is provided with a parent coating <NUM>, which may have been applied at a manufacturing site, such as a factory. The parent coating <NUM> may be any thermoplastic or thermosetting material. The parent coating <NUM> may be a multi-layered coating. For example, the parent coating <NUM> may include an inner anti-corrosion layer (e.g., a polyurethane or epoxy layer), a middle insulation layer (e.g., a foamed or unfoamed polypropylene layer) and an outer protective layer (e.g., an unfoamed polypropylene, polyurethane, epoxy resin or rubber layer). Different single-layered or multi-layered coatings may be used for the parent coating <NUM>. For simplicity, the parent coating <NUM> is illustrated without showing different layers. The parent coating <NUM>, as initially applied at the factory, may leave the end <NUM> of the pipe section <NUM> uncoated, for example about <NUM> from each end of the pipe section <NUM> may be free of the parent coating <NUM>. The parent coating <NUM> may end abruptly or gradually (e.g., taper off) near the ends of the pipe section <NUM>.

Initially, the field joint is formed by joining (e.g., by welding) the uncoated ends <NUM>, <NUM> of the pipe sections <NUM>, <NUM>. Initially, the pipe sections <NUM>, <NUM> in the vicinity of the joint are uncoated. The joint may be coated by a field joint coating, as described below. Prior to application of the field joint coating, cut backs may be made in the parent coating <NUM>, as described below.

As shown in <FIG>, a first angular cut back <NUM> is provided in the parent coating <NUM>. The first cut back <NUM> may be made using any suitable technique, such as by a grinding process or a lathing method. The first cut back <NUM> is provided at an angle x relative to the longitudinal axis L of the field joint (which may also be the longitudinal axis of the pipe sections <NUM>, <NUM>). The first cut back <NUM> is provided about the entire circumference of the pipe section <NUM>, resulting in a frustoconical shape (see <FIG>).

A second angular cut back <NUM> is provided in the parent coating <NUM>. The second cut back may be made using any suitable technique (which may be the same or different from that used for the first cut back <NUM>), such as by a grinding process or a bevelling method. The second cut back <NUM> is provided further away from the end <NUM> than the first cut back <NUM>, resulting in a stepped profile, as shown in the cross-sectional view of <FIG>. The second cut back <NUM> is provided at an angle y relative to the longitudinal axis L of the field joint. The angle y may be the same as or different from the angle x of the first cut back <NUM>. The second cut back <NUM> is provided about the entire circumference of the pipe section <NUM> (see <FIG>).

While the first cut back <NUM> is made through the entire thickness of the parent coating <NUM>, the second cut back <NUM> is made to a depth h<NUM> that is less than the entire thickness of the parent coating <NUM>. In a longitudinal cross-section, as shown in <FIG>, the first and second cut backs <NUM>, <NUM> form a stepped profile, with the first cut back <NUM> forming an incline at an angle x to a height of h<NUM>, the second cut back <NUM> forming an incline at an angle y to a height of h<NUM>, and a step <NUM> of length l<NUM>, substantially parallel to the longitudinal axis L, being defined between the first and second cut backs <NUM>, <NUM>. The surface of the step <NUM> is substantially free of indentations or grooves. Further details about the dimensions of the cut backs <NUM>, <NUM> are described below.

After the first and second cut backs <NUM>, <NUM> are provided in the parent coating <NUM>, a field joint coating <NUM> may be injection moulded over the uncoated ends <NUM>, <NUM> and the first and second cut backs <NUM>, <NUM>. The field joint coating <NUM> may be any suitable material, including any thermoplastic or thermosetting material typically known and used for such applications, for example including an insulation material similar to or same as the insulation layer of the parent coating <NUM> (e.g., a foamed or unfoamed polypropylene material). Other materials may be suitable for the field joint coating <NUM>, including materials suitable for high temperature applications. The field joint coating <NUM> may extend past the second cut back <NUM> and cover the parent coating <NUM> to a distance l<NUM>, and may have an upstand <NUM> of less than or equal to about <NUM>. In some examples, the upstand <NUM> may be substantially <NUM> (in which case the distance l<NUM> may be substantially <NUM>).

In order to injection mould the field joint coating <NUM>, a mould (not shown) may be positioned about the first and second cut backs <NUM>, <NUM> on both pipe sections <NUM>, <NUM> and including the welded field joint. The field joint coating <NUM> may be injected into the mould. The injection moulding process may be carried out at a sufficient temperature and/or pressure to ensure that the field joint coating <NUM> fully fills in the mould and fully covers the exposed surfaces of the pipe sections <NUM>, <NUM>, the cut backs <NUM>, <NUM>, and the step <NUM> (and optionally a portion of the parent coating <NUM> to a distance l<NUM>). The mould may be preheated, for example to about <NUM>, which may help with setting and/or curing of the field joint coating <NUM>. The mould may be removed after the field joint coating <NUM> has set and/or cured. In some examples, the mould may be removed when the field joint coating <NUM> is partly or mostly set and/or cured, and full setting and/or curing of the field joint coating <NUM> may occur without the mould.

In some examples, the exposed surfaces of the first and second cut backs <NUM>, <NUM> and the step <NUM> (and optionally uncut portions of the parent coating <NUM> near the second cut back <NUM> that may be coated by the field joint coating <NUM>) may be pre-treated prior to injection moulding the field joint coating <NUM>. For example, one or more such surfaces may be cleaned (e.g., using a solvent, such as xylene). In some examples, exposed metal surfaces of the pipe sections <NUM>, <NUM> in the vicinity of the welded field joint may be heated (e.g., using an induction heating coil), such as to a temperature in the range of about <NUM> to about <NUM>. A primer, which may improve binding of the field joint coating <NUM>, may be applied to the heated or unheated metal surfaces. In some examples, exposed surfaces of the first and second cut backs <NUM>, <NUM> and the step <NUM> (and optionally uncut portions of the parent coating <NUM> near the second cut back <NUM> that may be coated by the field joint coating <NUM>) may be abraded (e.g., using a grinder). The surfaces of the first and second cut backs <NUM>, <NUM> and the step <NUM> (and optionally uncut portions of the parent coating <NUM> near the second cut back <NUM> that may be coated by the field joint coating <NUM>) may be flame treated and may be coated with a primer. The entire area to be coated by the field joint coating <NUM> may be flame treated and/or primed with a primer. One or more of these pre-treatments may be used in combination. The pre-treatments may help the field joint coating <NUM> to better bond to the exposed surfaces of the pipe sections <NUM>, <NUM>, the cut backs <NUM>, <NUM>, and the step <NUM>.

In some examples, after the field joint coating <NUM> has been applied, a quality check may be performed to ensure that the upstand <NUM> is within acceptable values (e.g., less than or equal to <NUM>).

Further details of the cut backs <NUM>, <NUM> are now described with reference to <FIG>. For simplicity, these figures illustrate the cut backs <NUM>, <NUM> for one pipe section <NUM>, prior to injection of the field joint coating <NUM>. For simplicity, the parent coating <NUM> is shown as a uniform single layer, however it should be understood that the parent coating <NUM> may be multi-layered.

The first cut back <NUM> may be provided at an angle x, which is between <NUM>° and <NUM>° with a manufacturing tolerance of +<NUM>°/-<NUM>° and in certain embodiments may be about <NUM>° ± <NUM>° relative to the longitudinal axis L. The second cut back <NUM> may be provided at an angle y, which may, in certain embodiments, also be between <NUM>° and <NUM>° with a manufacturing tolerance of +<NUM>°/-<NUM>° and in certain embodiments about <NUM>° ± <NUM>° relative to the longitudinal axis L, or may be different.

The second cut back <NUM> may be set back from the first cut back <NUM>, such that the step <NUM>, in profile, has a length l<NUM> of up to <NUM>.

In profile, the second cut back <NUM> can have any height h<NUM> that is greater than or equal to <NUM>. Of course, one can appreciate that the height h<NUM> of the first cut back is equal to the thickness of the parent coating <NUM>, minus h<NUM>.

The outer diameter of the pipe is typically between <NUM> and <NUM>.

Referring back to <FIG>, the field joint coating <NUM> may extend over the uncut parent coating for a length l<NUM> , typically less than <NUM> but desirably about <NUM> or less. As explained above, where the upstand is <NUM>, by definition, I<NUM> would be <NUM>.

In some cases, although reducing the upstand <NUM> may help to reduce risk of damage to the coated field joint and/or pipe-laying equipment, it may be necessary to have a small amount of upstand <NUM> (i.e., less than or equal to <NUM>). The presence of a small upstand <NUM> may be required depending on mould tolerances, application conditions, etc. This small amount of upstand <NUM> may still be sufficient to avoid or reduce the disadvantages of a large upstand E, as discussed with respect to <FIG> above.

Although the cut backs have been described as being provided in the parent coating after the field joint is welded, in some examples the cut backs may be provided in the parent coating before welding the field joint. For example, the cut backs may be provided at a manufacturing site, rather than on site or on the reel-lay vessel. This may be useful to help reduce the time needed for handling and laying the pipeline at the site. Where the cut backs are provided offsite, one or more pre-treating steps, such as those described above, may also be performed offsite (e.g., at the same or a different manufacturing site). In examples where the ends of the pipe sections have been pre-treated offsite, the pre-treated ends may be protected (e.g., wrapped with sheet plastic) to help retain the integrity of the treated field joint area. The protective sheet plastic may expose the pipe section ends, to allow the field joint to be welded, while protecting the pre-treated cut back surfaces. When the welding is complete and the field joint coating is to be moulded, the protective sheet plastic may then be removed, any additional pre-treatment steps may be carried out, and the field joint coating may be injection moulded over the field joint. By providing the cut backs offsite (and optionally one or more pre-treatment steps offsite), the time for processing and laying of the pipeline onsite may be reduced. Further, the amount of equipment needed onsite may be reduced. Performing these steps offsite may also enable more rigorous quality checking and testing.

The present disclosure includes methods for forming the coated field joint, as well as the coated field joint formed thereby. The present disclosure may also include pipe sections in which the first and second cut backs have been made in the parent coating, prior to or after welding of the field joint.

Claim 1:
A method of coating a field joint joining uncoated ends (<NUM>,<NUM>) of two pipe sections (<NUM>, <NUM>), each pipe section being coated with a parent coating (<NUM>) and having at least one uncoated end (<NUM>, <NUM>), the method comprising:
providing a first angular cut back (<NUM>) in the parent coating (<NUM>) of each pipe section (<NUM>, <NUM>), the first angular cut back (<NUM>) being at an angle of between <NUM>° and <NUM>°, preferably about <NUM>°, with a manufacturing tolerance of +<NUM>°/-<NUM>°, relative to a longitudinal axis of the field joint;
providing a second angular cut back (<NUM>) in the parent coating (<NUM>) of each pipe section (<NUM>, <NUM>), the second angular cut back (<NUM>) being positioned further from the field joint than the first angular cut back (<NUM>);
the first and second angular cut backs (<NUM>, <NUM>) resulting in the parent coating having a stepped profile, a step (<NUM>) in the stepped profile being defined between the first and second angular cut backs (<NUM>, <NUM>), the step (<NUM>) being substantially parallel to the longitudinal axis of the field joint and being free of indentations; and
injection moulding a field joint coating (<NUM>) over the uncoated ends (<NUM>, <NUM>) and the first and second angular cut backs (<NUM>, <NUM>), the field joint coating being moulded to have an upstand (<NUM>) that is less than or equal to about <NUM>, preferably about <NUM>.