GB2462149A

GB2462149A - Pipeline field joint having an epoxy layer extending between the existing coatings

Info

Publication number: GB2462149A
Application number: GB0814137A
Authority: GB
Inventors: David Jackson; Damian Daykin
Original assignee: Pipeline Induction Heat Ltd
Current assignee: Pipeline Induction Heat Ltd
Priority date: 2008-08-02
Filing date: 2008-08-02
Publication date: 2010-02-03
Anticipated expiration: 2028-08-02
Also published as: GB2462149B; GB0814137D0

Abstract

A pipeline field joint is bordered at opposite ends by existing coating, the field joint comprising a continuous epoxy or epoxy phenolic layer 5 which contacts and extends from the existing coating (4 in figure 1) at one end to the existing coating at the opposite end of the pipe joint. The epoxy (or epoxy phenolic) layer 5 may be a primer layer, and the epoxy primer layer is ideally applied as a liquid resin to the field joint. Preferably, the epoxy primer layer extends over the existing / original coating. The existing coating may be a plastics material, preferably polyolefin, more preferably polypropene. Once the epoxy primer has cured, a mould 6 may be located over the dried joint, and subsequently filled with a curable coating 7, preferably a polyurethane coating. The mould may be subsequently removed.

Description

PIPE COATING

The present invention relates to pipe coating, and in particular to a method for coating pipeline field joints, and a pipeline field joint.

Pipelines, such as those used to carry oil or gas, are typically formed from many lengths of steel pipe welded together end to end as they are laid. To prevent corrosion and provide other protection to the pipes they are coated with one or more protective andlor insulative layers. Individual lengths of pipe are usually coated at a factory remote from the location at which they are to be laid. At the factory, the coating is applied to the outside of the pipes leaving a short uncoated length of pipe at each end of the pipe andlor the factory applied coating is cut back to reveal an uncoated length of pipe. The uncoated ends enable the lengths of pipe to be welded together to form a pipeline.

Before the pipeline can be laid, the welded ends of the individual lengths of pipe, known as field joints, must be coated to provide protection to the exposed pipe which is, ideally, equivalent to that of the factory applied coating which extends over the remainder of the pipe. In addition, it is desirable that the field joints can be coated as quickly as possible since this affects the rate at which the pipeline can be laid.

A variety of different materials are employed to coat pipes. Polyolefins, especially polypropylene, are widely used to fonn the factory applied coating of a pipe. Actual coatings may comprise layers of different materials. Similarly, a variety of different materials are used to coat pipeline field joints.

EP 0654632 discloses two approaches to coating pipeline field joints when the individual pipe lengths are coated with a factory applied polypropylene coating, and the field joint is coated with a curable polyurethane composition.

* In the first approach, after physical preparation of the field joint a polyurethane primer is brushed onto the bare steel of the pipeline field joint and the solvent allowed to evaporate. A sheet steel mould is then wrapped around the field joint and a dual component polyurethane composition is injected into the mould to fill the field joint and then allowed to cure before the mould is removed.

In the second approach a layer of fusion bonded epoxy (FBE) is applied to the bare steel of the field joint and cured in place of the polyurethane primer.

There are, however, disadvantages with both of these approaches.

With the first approach corrosion protection is only afforded to the pipe by the polyurethane primer and joint coating. This is not considered adequate in all circumstances. In practice additional corrosion protection is routinely specified.

The FBE coating of the second approach affords additional corrosion protection, but it brings with it a series of other drawbacks. In particular FBE is messy and time consuming to use. First, the pipe must be heated to about 240°C in the region of the field joint. This is time consuming and involves the risks associated with the use of high temperatures discussed in EP 0654632, as well as possible damage to, and disbondment from the pipe of, the factory applied coating. Then, the FBE is applied to the heated pipe as a powder. This is messy as it can be difficult to contain the powder, yet care must be taken to ensure that the powder does not come into contact with the polypropylene factory applied coating as this will impair adhesion between the polypropylene coating and the polyurethane field joint coating.

In practice the ends of the polypropylene factory applied coating are often protected with masking tapes during application of the FBE powder. Whilst protecting the S factory coating, this can lead to a discontinuity between the factory applied coating and the FBE coating to the pipe.

After the FBE has been applied it is, in practice, necessary to quench the pipe to reduce its temperature to a level compatible with the polyurethane coating to be applied. The quenching step is time consuming and brings the risk that the quenching medium, usually water, contaminates the applied coating.

Embodiments of the present invention have been made in consideration of the abovementioned problems.

According to a first aspect of the present invention there is provided a method of coating a pipeline field joint bordered at opposite ends by an existing coating, the method comprising the steps of applying a liquid epoxy or epoxy phenolic coating to the field joint, the coating forming a substantially continuous layer which contacts and extends from the existing coating at one end of the field joint to contact the existing

coating at the opposite end of the field joint.

According to a second aspect of the present invention there is provided a pipeline field joint bordered at opposite ends by an existing coating, the field joint comprising a substantially continuous epoxy or epoxy phenolic layer which contacts and extends from the existing coating at one end of the field joint to contact the existing coating at the opposite end of the field joint.

The existing coating may be a factory applied coating. It may comprise or consist of a plastics material, particularly a polyolefin, such as polypropylene. The existing coating may be cut back. Edges of the existing coating may be chamfered or stepped.

* Prior to application of the epoxy or epoxy phenolic coating the field joint may be prepared. This may involve cleaning and/or abrading the surface of the pipe to be coated andlor the edges of the existing coating bordering the field joint. The existing coating bordering the field joint may be activated by plasma, generated by an oxidising flame, electrical arc or other suitable means, to promote adhesion of the liquid coating to the existing coating. The pipe may also be heated.

The epoxy or epoxy phenolic coating may be a primer.

The layer of epoxy or epoxy phenolic coating preferably extends over the surface of the existing coating bordering the field joint.

After the epoxy or epoxy phenolic coating is allowed to dry a layer of a curable coating, for example a polyurethane coating, may be applied over the epoxy or epoxy phenolic coating. Preferably the curable coating is applied by placing a mould around the field joint, such as by wrapping a sheet of flexible material, for example sheet metal or plastics material, around the field joint overlapping the existing coating at either side of the field joint, to define a cavity, and injecting curable material into the cavity. After the curable material has cured the mould may be removed, or left in place to provide additional protection to the joint. The curable material may comprise a polyurethane material.

In order that the invention may be more clearly understood an embodiment thereof will now be described, by way of example, with reference to the accompanying drawings of which: Figures 1 to 4 show a longitudinal cross-sectional view of a pipeline field joint at various sequential stages of a coating process.

* Referring to Figure 1 a pipeline field joint is formed between two lengths of steel pipe 1 welded together at weld 2. Each length of pipe I is coated with a factory applied coating comprising a primer layer 3 and a polyolefin, e.g. polypropylene, layer 4. The factory applied coating 3,4 on each length has been cut back to form a chamfer and leave the steel pipe exposed in the region of the weld.

It is to be understood that the factory applied coating can take any suitable form and may comprise a single layer or more than two layers. Also, the factory applied coating may be cut back in any suitable way.

After the two lengths of pipe have been welded together the exposed steel pipe and adjacent factory coating is cleaned. Several different cleaning processes may be employed to make the joint, for example the exposed steel surface may be blast cleaned using abrasive particles and the polypropylene coated surfaces may be cleaned and abraded using a powered abrasive disc. The entire joint area may then be blown clean with compressed air in order to remove any dust particles. After cleaning, the polyolefin surfaces of the factory coating are treated using plasma generated by a controlled flame or electrical arc leaving the exposed field joint in an activated state and as state shown in Figure 1.

Next, referring to Figure 2, a liquid epoxy or epoxy phenolic primer layer 5 is applied to the field joint. The liquid primer is applied to completely cover the exposed bare steel pipe and at least the adjacent cut back factory applied coating. It is important that the liquid primer layer covers the interface between the factory applied coating and exposed pipe to provide a continuous layer of coating extending from the cut back factory coating of one pipe length, over the exposed pipe, to the cut back factory coating of the other pipe. It is desirable, although not essential, that the liquid primer covers all or most of the exposed chamfer of the cut back factory coating as shown in Figure 2.

A suitable liquid primer is that sold under the name Sigmaline 2500 by Sigma Coatings. It is a two component solvent free amine cured phenolic epoxy coating.

The epoxy or epoxy phenolic liquid primer layer provides a corrosion resistant coating to the steel pipe, with better corrosion resistant properties than those (if any) of a polyurethane primer. As the liquid primer layer overlaps the cut back factory applied coating it provides a coating with better integrity than existing polyurethane primer or FBE layers, for both of which there is a risk that a region of the pipe adjacent the cut back factory coating will be left uncoated.

The liquid primer layer is allowed to partially cure, and a sheet of metal or plastics material 6 is wrapped around the field joint, overlapping the adjacent factory applied coating to form a mould defining a cavity 7.

Referring to Figure 3 a curable coating 8, such as a polyurethane coating, for example that sold as Hyperlast 2851239 by Hyperlast Limited, United Kingdom, is then injected into the cavity 7 and allowed to cure. The mould 6 can then, optionally, be removed as shown in Figure 4. The coating of field joints by injection of a curable coating into a cavity in this way is known, at least from EP 0654632, and therefore need not be described in further detail.

This coating process confers considerable advantages over prior art processes as exemplified by EP 0654632.

The liquid primer layer provides improved corrosion protection as compared to a polyurethane primer layer. It is, however, significantly more convenient to apply than an FBE coating. No, or only moderate, heating of the pipe is required and there is no problem with containing powder. As the liquid is applied over both the steel pipe and adjacent factory applied coating the difficulty of keeping FBE powder off the factory applied coating is avoided. The continuous layer of liquid primer extending from the factory coating of one pipe to the other provides for a coating with an overall improved integrity, especially since the risk of there being an uncoated region of pipe adjacent the factory applied coating is significantly reduced. The liquid epoxy or epoxy phenolic primer also improves adhesion between the subsequently applied polyurethane composition and both the pipe surface and factory applied coating. Overall the coating process is less troublesome and can be carried out more quickly than prior processes, and leads to a better quality field joint coating being produced.

The above embodiment is described by way of example only. Many variations are possible without departing from the invention.

Claims

CLAIMS1. A pipeline field joint bordered at opposite ends by an existing coating, the field joint comprising a substantially continuous epoxy or epoxy phenolic layer which contacts and extends from the existing coating at one end of the field joint to contact the existing coating at the opposite end of the field joint.
2. A pipeline field joint as claimed in claim 1, wherein the existing coating is a factory applied coating.
3. A pipeline field joint as claimed in either claim I or claim 2, wherein the existing coating comprises or consists of a plastics material
4. A pipeline field joint as claimed in claim 3, wherein the plastics material is a polyolefin.
5. A pipeline field joint as claimed in claim 4, wherein the polyolefin is polypropylene.
6. A pipeline field joint as claimed in any preceding claim, wherein the existing coating is cut back.
7. A pipeline field joint as claimed in any preceding claim, wherein the existing coating is chamfered or stepped.:.
8. A pipeline field joint as claimed in any preceding claim, wherein the epoxy or ::. *: epoxy phenolic coating is a primer. I...
9. A pipeline field joint as claimed in any preceding claim, wherein the epoxy or epoxy phenolic extends over the surface of the existing coating bordering thefield joint.
10. A pipeline field joint as claimed in any preceding claim, further comprising a layer of a curable coating.
11. A pipeline field joint as claimed in claim 10, wherein the curable coating is layered on top of the epoxy or epoxy phenolic coating.
12. A pipeline field joint as claimed in either claim 10 or claim 11, wherein the curable coating comprises a polyurethane material.
13. A method of coating a pipeline field joint bordered at opposite ends by an existing coating, the method comprising the steps of applying a liquid epoxy or epoxy phenolic coating to the field joint, the coating forming a substantially continuous layer which contacts and extends from the existing coating at one end of the field joint to contact the existing coating at the opposite end of thefield joint.
14. A method of coating a pipeline field joint as claimed in claim 13, comprising the additional step of cleaning and/or abrading the surface of the pipe to be coated and/or the edges of the existing coating bordering the field joint prior to application of the epoxy or epoxy phenolic coating.
15. A method of coating a pipeline field joint as claimed in either claim 13 or claim 14, comprising the additional step of activating the existing coating bordering the field joint by plasma to thereby promote adhesion of the epoxy * or epoxy phenolic coating to the existing coating.*:::::
16. A method of coating a pipeline field joint as claimed in any of claims 13 to 15, *::: : wherein the epoxy or epoxy phenolic coating is applied such that it extends over the surface of the existing coating bordering the field joint.*::::
17. A method of coating a pipeline field joint as claimed in any of claims 13 to 16, wherein the epoxy or epoxy phenolic coating is allowed to dry and a coating of a curable material is applied over the epoxy or epoxy phenolic coating.
18. A method of coating a pipeline field joint as claimed in claim 17, wherein the curable material is applied by placing a mould around the field joint such that it overlaps the existing coating at either side of the field joint to define a cavity, and injecting the curable material into the cavity.
19. A method of coating a pipeline field joint as claimed in claim 18, wherein the mould is removed after the curable material has cured.
20. A method of coating a pipeline field joint as claimed in claim 18, wherein the mould is left in place after the curable material has cured.
21. A pipeline field joint substantially as herein described with reference to the corresponding drawings.
22. A method of coating a pipeline field joint substantially as herein described with reference to the corresponding drawings. **$ * * * ** I * S.. * SS S. a * * S. * ) S..-IS