GB2572628A

GB2572628A - Method of strain relief of a bonded coating or cladding at a junction on a prismatic or tapered section

Info

Publication number: GB2572628A
Application number: GB1805709.1A
Authority: GB
Inventors: Frederick Stokes Kevan; Conrad Stokes Andrew
Original assignee: Individual
Current assignee: Individual
Priority date: 2018-04-05
Filing date: 2018-04-05
Publication date: 2019-10-09
Also published as: GB201805709D0

Abstract

A method of alleviating tensile strain at junction of changes in cross section of pipe cladding or coating comprises introducing at the junction an extensible component made from a material with a lower tensile modulus than the cladding. The extensible component may be bonded to the pipe prior to application of the cladding. A cavity or recess may be provided in the cladding prior to bonding to the pipe or structural member, or may be cut or machined in the cladding after it has been cast to the pipe. The junction may be a tee joint or branch in a pipe section.

Description

Method for Strain Relief of a Bonded Coating or Cladding at a Junction on a Prismatic or Tapered Section.

Background

Cladding and coating materials often have a mismatch in their thermal and or mechanical properties relative to the structure and or pipework that they are bonded to, which can result in the occurrence of tensile strains in the cladding or coating where junctions or attachments occur on the conic or prismatic pipework or structural sections, that are high enough to cause failure and cracking of the coating or cladding.

It is known that bonded coatings applied to steel pipelines, for example, are prone to cracking at step changes in their cross section such as occurs at tee junctions. See for example US 2018/0043584.

Such cracks are also known to occur; after the coating or cladding has been applied and moulding or casting shrinkage of it occurs; after the coating or cladding has set, and is cooled; when the coated or clad pipe or structure is subjected to hydrostatic pressure; and when the pipe or structure is subsequently heated or cooled.

Such cracks can result in a portion of the underlying pipe or structure being exposed to corrosion or, in the case of insulation, unacceptable cooling local to the crack. This becomes an issue of major importance for pipelines that are deployed to the seabed with a planned operational life of decades.

The materials used for coating and cladding such, usually metallic, pipelines are often polymers or polymer composites that are prone to creep and other viscoelastic behaviour.

Their behaviour is often not well understood and, whilst there is a lot of reliable design guidance regarding details such as tees in the metallic pipelines, there is little, if any, in the public domain regarding the design of such details in the coating or cladding.

(2)

Cracks that occur after deployment to the seabed are very expensive to repair and there exists a need for an improved, reliable and cost effective method that negates this issue.

Statement of invention

To overcome these problems the present invention introduces a compatible and extensible third component in place of a small section of the coating of cladding at discontinuities and junctions for strain relief of the bonded coatings and cladding at such locations.

This invention relates to the field of coatings and claddings used for protection from corrosion and or insulation and or the provision of positive or negative buoyancy.

Advantages

This component may be applied before or after the cladding or coating in applied to the pipeline or structure.

Preferably, this component will have a lower tensile modulus that the cladding or coating, a high and sustainable strain to break, adequate bond strength and compatibility with the intended operating environment.

Preferably, the dimensions of this third component are such that the impact upon heat transfer or buoyancy or corrosion due to any disparity in their properties from that of the coating or cladding is minimal.

Introduction to drawings

Figure 1 shows a junction [1] in the insulation or such like |2| bonded to a pipe or such like [5] where an insulated branch or attachment @ in situated.

Figure 2 is a side elevation of the junction or Tee shown in figure 1 and shows the exterior of a typical crack [s| at such a location.

Figure 3 is a vertical section through axes of pipes shown in the preceding figures shows typical cracks in cross section |β|.

(3)

Figure 4 is of the same elevation as figure 2 and indicates where the coating or cladding would be omitted or removed |?] to accommodate the extensible third component.

Figure 5 indicates a typical section through the extensible third component |δ| in its unstrained condition.

Figure 6 indicates the outline of the bonded coating in the unstressed condition at |§] and in the compressed condition at [Ϊ0| when, for example the coating is subject to hydrostatic pressure.

Figure 7 is a close up of the section of interest in figure 6 and indicates a section cross section through the extensible third component in the unstressed condition HI and after hydrostatic pressure has been applied [Ϊ2.

Figure 8 shows how a point at a crack initiation location |13|, that would have displaced to |14| if there was no extensible third component, will displace to |15| if a third component made from a suitable , extensible material is introduced thereby lessening the tension in the coating in a direction aligned with the branch pipe axis.

Figure 9 shows an example of a structure that includes a branch @ that is remotely attached [ϊβ| to the principal member |3| before the application of any cladding or coating has been applied.

Figure 10 is a cross section of figure 9 on a plane that contains the pipe axes after that the addition of coating or cladding, and this shows a typical crack |β| in the coating or cladding |g| when the connection between the branch @ and the main member |2| is remote from the intersection at [Ϊ6·

Detailed description

A change in section or a junction [1] that occurs in a cladding or coating |g| bonded to a conical or prismatic pipe or structural member [5| where there is a branch or attachment @ to or on the pipe or structural section often causes a stress concentration that results in the occurrence of fractures |s| and |β| of the coating or cladding at the change in section or junction [1] when the cladding or coating is (4) subjected to, moulding or casting shrinkage that occurs after the coating or cladding has been applied, cooling after the coating or cladding has set, hydrostatic pressure when immersed in a fluid; and or thermal or mechanical strains when put into service.

A portion of the coating or cladding |2| is omitted or removed [7| to allow for the introduction of a portion of extensible material |s| with a lower tensile modulus that the cladding or coating |g|, a higher and sustainable strain to break, adequate bond strength and compatibility with the intended operating environment is introduced at junctions [Ϊ] to relieve the strain in the coating or cladding to a level below that which may result in the incidence of fracture.

When, for example, a subsea pipeline insulation coating is immersed in deep water, the out skin of the coating will be compressed, typically, from |9| to [Ϊ0 and a cross section through the extensible material will deform, typically, from the shape indicated by the dashed outline [ϊϊ| to that indicated by the solid outline and hatching |12| thus reducing the displacement of, for example, a point in the coating at |13| from |14| to |15| thus alleviating the strain in the coating at that point.

The location of the connection |13| of the conical or prismatic pipe or structural member [5| with the branch or attachment @ can be remote from the change in section or junction [1] in a cladding or coating |g| and the fracture sites change in section or a junction [Ϊ] that occurs in a cladding or coating |β|.

Claims

1. A method of alleviating tensile strain at junctions or changes in the cross section of cladding or coating materials that are bonded to pipes or structural members of substantially prismatic or conical section by introducing an extensible component, made from a material with a lower tensile modulus that the cladding or coating and a high elongation to break, at the junction or change in cross section.

2. A method of alleviating tensile strain according to claim 1, whereby the extensible component is bonded to the pipes or structural members prior to the application of the cladding or coating.

3. A method of alleviating tensile strain according to claim 1, whereby a cavity or recess is provided in the coating or cladding, when it is cast on or bonded to the pipes or structural members, to accommodate the extensible component.

4. A method of alleviating tensile strain according to claim 1, whereby a cavity or recess is cut or machined in the coating or cladding, after it has been cast on or bonded to the pipes or structural members, to accommodate the extensible component.

5. A method of alleviating tensile strain according to claim 2, whereby the junction is a Tee or branch on a pipe section.

6. A method of alleviating tensile strain according to claim 2, whereby the junction is a Tee or branch or tapping on a subsea wellhead Xmas tree.

7. A method of alleviating tensile strain according to claim 2, when the junction or change in cross section of the cladding or coating is largely coincident with the location of a connection between the principal pipe or structural member and the branch or attachment that causes the change in cross section of the cladding or coating.

8. A method of alleviating tensile strain according to claim 2, when the junction or change in cross section of the cladding or coating is not coincident with the location of a connection between the principal pipe or structural member and the branch or attachment that causes the change in cross section of the cladding or coating.

(6)

9. A method of alleviating tensile strain according to claim 3, whereby the junction is a Tee or branch on a pipe section.

10. A method of alleviating tensile strain according to claim 3, whereby the junction is a Tee or branch or tapping on a subsea wellhead Xmas tree.

11. A method of alleviating tensile strain according to claim 3, when the junction or change in cross section of the cladding or coating is largely coincident with the location of a connection between the principal pipe or structural member and the branch or attachment that causes the change in cross section of the cladding or coating.

12. A method of alleviating tensile strain according to claim 3, when the junction or change in cross section of the cladding or coating is not coincident with the location of a connection between the principal pipe or structural member and the branch or attachment that causes the change in cross section of the cladding or coating.

13. A method of alleviating tensile strain according to claim 4, whereby the junction is a Tee or branch on a pipe section.

14. A method of alleviating tensile strain according to claim 4, whereby the junction is a Tee or branch or tapping on a subsea wellhead Xmas tree.

15. A method of alleviating tensile strain according to claim 4, when the junction or change in cross section of the cladding or coating is largely coincident with the location of a connection between the principal pipe or structural member and the branch or attachment that causes the change in cross section of the cladding or coating.

16. A method of alleviating tensile strain according to claim 4, when the junction or change in cross section of the cladding or coating is not coincident with the location of a connection between the principal pipe or structural member and the branch or attachment that causes the change in cross section of the cladding or coating.