GB2406367A

GB2406367A - Pipe with electrical connection for anode

Info

Publication number: GB2406367A
Application number: GB0421267A
Authority: GB
Inventors: Morten Bjerreegaard Jepsen
Original assignee: Subsea 7 BV
Current assignee: Subsea 7 BV
Priority date: 2003-09-25
Filing date: 2004-09-24
Publication date: 2005-03-30
Anticipated expiration: 2024-09-24
Also published as: GB0421267D0; GB2406367B; GB0322477D0; NO20044068L; NO328481B1

Abstract

The invention comprises a pipe having a tube 12, a sleeve 14 over the outer face of the tube, a coating 18 over at least a portion of the sleeve, and an electrical connector 16 extending through the coating and attached to the sleeve. Preferably the sleeve extends circumferentially around the tube. The tube may be load bearing, and the various layers of the pipe formed from steel. The pipe preferably comprises means to attach sacrificial electrodes thereto. Also claimed is a method of manufacturing a tube and a method of launching a series of the claimed pipes.

Description

1 "Pipe" 3 This invention relates to a pipe, particularly but 4 not

exclusively to pipe anode-banks used to mount sacrificial electrodes to protect the pipe and an 6 attached pipeline from degradation.

8 Stainless steel pipes are well known but will 9 undergo pitting when exposed to wet chloride containing environments and oxygen at ambient 11 temperatures, for example in sea water.

13 Traditionally, this was mitigated by using high 14 integrity coating systems but the inevitable damage and abrasion of the coating also necessitates the 16 provision of sacrificial anodes made from a metal 17 which degrades preferentially to the stainless 18 steel. The consequential flow of electrons from the 19 anodes to the stainless steel protects the latter from degradation. Pipes which include anodes or 21 means to attach anodes are known as 'anode-banks' in 22 the trade.

1 A known anode-bank for use subsea could therefore 2 comprise a stainless steel tube, a protective 3 coating, sacrificial anodes and an electrical 4 conductor to conduct the current from the sacrificial anodes to the stainless steel tube.

7 However, the coating next to the electrical 8 connector is particularly susceptible to cracking 9 when the anode-bank is subjected to bending stresses. This allows salt water to seep under or 11 past the electrical connector and contact the 12 stainless steel tube. As a result, hydrogen gas 13 builds up on the surface of the stainless steel, 14 and, being sensitive to hydrogen, the pipe can fracture or crack leading to leakage of the pipeline 16 contents. This phenomenon is known as hydrogen 17 embrittlement.

19 To tackle this problem, it is known to provide a soft steel tube which is not sensitive to hydrogen 21 nor therefore susceptible to hydrogen embrittlement.

22 A stainless steel cladding must be formed on the 23 inside of the tube in order to prevent the pipes 24 contents from rusting the pipe from inside. Such cladding is expensive and indeed does not provide 26 any further strength to the pipe. Therefore, the 27 soft steel must be of a relatively large thickness 28 in order to provide the required strength.

Although this tackles the problem of hydrogen 31 embrittlement, the cladding is very expensive and 32 further problems result when laying/launching a 1 pipeline containing such anode-banks. Pipelines are 2 typically launched by reeling them off a reel or 3 drum. However, reeling pipelines which include 4 anode-banks with such a differing wall thickness compared to the pipes in the rest of the pipeline is 6 not possible because the pipes with the smaller wall 7 thickness will tend to buckle.

9 Therefore, it is necessary to add these anode-banks to a conventional pipeline while it is being 11 launched. This is extremely time consuming because 12 the launching/laying process must be stopped, the 13 conventional pipeline cut, the anode-banks aligned 14 by a crane to the length of pipeline entering the water, welded to this pipeline, the anode-bank and 16 attached pipeline lowered, aligned with the pipeline 17 from the reel and welded thereto at its opposite 18 end. To install such an anode-bank typically takes 19 around 18 hours.

21 According to a first aspect of the present invention 22 there is provided a pipe comprising: 23 a tube; 24 a sleeve provided over a portion of an outer face of the tube; 26 a coating provided over at least a portion of 27 the sleeve; and 28 an electrical connector which extends through 29 the coating and is attached to the sleeve.

31 Preferably, the tube is a load-bearing tube.

1 Preferably, the sleeve extends circumferentially 2 around the tube.

4 Preferably, the electrical connector is connected to the sleeve away from its edge, more preferably there 6 is at least 20cm, preferably at least lOOcm, between 7 the edge of the sleeve and any edge of the 8 electrical connector. The sleeve may extend from, 9 for example, 2-lOm in a longitudinal direction. In preferred embodiments, the sleeve extends for around 11 6m in the longitudinal direction.

13 Preferably the pipe further comprises a means to 14 attach anodes thereto. Typically the means to attach anodes thereto are provided on the sleeve 16 portions such that, in use, the electrical connector 17 can connect the anodes to the sleeve portions.

19 Preferably, the tube is made from a robust material.

21 Preferably, the tube is a material resistant to 22 degradation by a mixture of water and hydrocarbons 23 flowing therethrough.

Typically the tube is sensitive to hydrogen 26 formation on its surface, and is typically made from 27 stainless steel. The tube may be made from, for 28 example 13Cr, 22Cr and 25Cr steel.

Preferably, the sleeve is manufactured from a 31 material which is not sensitive to hydrogen 32 formation on its surface. More preferably, the 1 sleeve is made from a soft steel. Examples of 2 suitable materials include St255 or St355.

4 Preferably, the electrical conductor is manufactured from a similar soft material, such as St255.

7 Optionally, additional sleeve portions may be 8 provided on the tube.

According to a second aspect of the present 11 invention, there is provided a method of 12 manufacturing a pipe according to the first aspect 13 of the invention, the method comprising: 14 providing the tubed securing the sleeve over the tube; 16 attaching the electrical connector to the 17 sleeve; and 18 coating a portion of the pipe.

Preferably, the sleeve is provided as two shells 21 with semi-circular cross sections. Typically the 22 shells are welded together over and around the tube.

23 Preferably, the each end of the sleeve is secured to 24 the tube by a circumferentially extending weld.

26 When the optional additional sleeve portions are 27 provided, these are typically welded to each end of 28 the sleeve and welded to the tube.

According to a further aspect of the present 31 invention there is provided a method of launching a 32 series of pipes, the method comprising: 1 connecting a pipe according to the first aspect 2 of the invention to a plurality of pipes; 3 mounting the said connected pipes on a reel; 4 launching the said connected pipes from the reel.

6 Typically the launching of the said connected pipes 7 is paused as the pipe according to the first aspect 8 of the invention comes off the reel, and anodes are 9 connected to the said pipe in accordance with the first aspect of the invention.

12 An embodiment of the present invention will now be 13 described, by way of example only, with reference to 14 the accompanying drawings in which: 16 Fig. 1 is a perspective view of a pipe in 17 accordance with the present invention, but not 18 showing the coating; 19 Fig. 2 is a perspective view of the Fig. 1 pipe but including the coating and having attached 21 anodes; 22 Fig. 3 is a side view of the Fig. 2 pipe and 23 attached anodes; 24 Fig. 4 is a sectional view through line D-D of Fig. 3; 26 Fig. 5a is an enlarged view of the portion of 27 the Fig. 1 pipe labelled A; 28 Fig. 5b-5c are views showing a weld between 29 various components of the pipe; Fig. 6 is an enlarged view of the portion of 31 the Fig. 1 pipe labelled B; 1 Fig. 7 is an enlarged of the portion of the 2 Fig. 3 pipe labelled C; 3 Fig. 8 is a side view of the Fig. 1 pipe with 4 the coating omitted for clarity) Fig. 9 is a top view of the Fig. 1 pipe, also 6 with the coating omitted for clarity; 7 Fig. 10 is a detailed view of the portion of 8 the Fig. 8 pipe labelled A; 9 Fig. 11 is an end view of the Fig. 8 pipe along the line B-B; and 11 Fig. 12 is a detailed view of a portion of the 12 Fig. 11 pipe labelled C. 14 A pipe 10 comprises an inner stainless steel load bearing tube 12, a steel sleeve 14, electrical 16 connectors 16 and a protective coating 18 (the 17 coating 18 is not shown on Figs. 1, 5a, 6 & 8-12).

19 The steel sleeve 14 is provided over the tube 12 and the electrical connectors 16 extend from the steel 21 sleeve 14 through the coating 18 for further 22 electrical connection with anodes 20. The 23 electrical connector 16 includes a mounting member 24 22 for mounting to the steel sleeve 14. Thus, attached anodes 20 can provide an electrical current 26 to the stainless steel tube 12 via the electrical 27 connectors 16 and the steel sleeve 14.

29 The sleeve is typically around 6-15mm preferably 8 12mm thick. It will be noted that ingress of any 31 water through cracks in the coating 18 near the 1 electrical connectors 16 will not contact the 2 stainless steel tube 12.

4 To provide a stronger connection between the sleeve 14 and the pipe 12, additional sleeve portions 17 6 may be provided on the ends 30 of the sleeve 14 7 (shown only in Figs. 8-10).

9 The pipe 10 is adapted for receiving anodes 20 and will therefore be referred to as an anode-bank 10.

11 The anodes 20 are typically provided as two semi 12 circular portions which can be bolted together over 13 the electrical connector 16 of the anode-bank 10.

14 They are held onto the anode-bank 10 by the friction provided when the two halves of the anodes 20 are 16 secured together and compressed around the 17 anode-bank 10.

19 The anode-bank 10 is assembled during manufacture by the provision of two shells 14a, 14b (shown in Fig. 21 8) of a semi-circular profile which are placed over 22 the stainless steel tube 12 and secured together by 23 a longitudinal weld 15. The sleeve 14 is also 24 welded to the tube 12 at its ends 24, 26.

Additional sleeve portions 17 may be provided on the 26 stainless steel tube 12. These are welded around 27 their circumferential perimeter to the ends 24, 26 28 of the sleeve 14 and at their opposite end to the 29 stainless steel tube 12. This provides additional strength to the connection between the sleeve 14 and 31 stainless steel tube 12, which may be stressed 32 during use.

1 Thus, in use, anode-banks 10 would be installed in a 2 standard pipeline at regular intervals, such as 3 every 2-3km. The whole pipeline (not shown) 4 including the anode banks 10 and standard pipes (not shown) can be mounted on a reel or drum (not shown) 6 and reeled out when being launched because the 7 thickness of the sleeve 14 does not make an 8 appreciable difference to the overall thickness of 9 the anode-banks 10 compared to the standard pipes in the pipeline. During launching of the pipeline, the 11 drum is paused each time an anode-bank 10 comes off 12 the drum, and anodes 20 are secured to the anode 13 bank 10 over the electrical connector 16. The drum 14 is then started and the anode-bank 10 with attached anodes 20 is launched as part of the overall 16 pipeline.

18 In contrast, known anode banks based utilising a 19 soft steel tube which is resistant to hydrogen embrittlement, are greater in thickness because the 21 stainless steel inner cladding provided is not load 22 bearing. Therefore the soft steel tube must be 23 greater in thickness in order to provide the 24 required strength. Thus such known anode banks cannot be launched using a reel because the 26 differing thickness of the known anode banks and the 27 standard pipes would cause the pipes to buckle if 28 they were mounted and launched on a reel.

Thus, should sea water seep into a crack near the 31 electrical connector 16, it will come into contact 32 with the sleeve 14 and not the stainless steel tube 1 12. Hydrogen could also be produced on the surface 2 of the sleeve 14 by the current moving from the 3 anodes 20 to the sleeve 14. However, the sleeve 14 4 is not sensitive to hydrogen on its surface and therefore the formation of hydrogen at this point is 6 not problematic and does not result in hydrogen 7 embrittlement or fracture/cracking of the sleeve 14.

8 Since the hydrogen does not come into contact the 9 stainless steel tube 12, this does not suffer hydrogen embrittlement either.

12 Thus, an advantage of certain embodiments of the 13 invention is that the pipes, such as the anode-bank 14 10, are less susceptible to problems associated with hydrogen formation.

17 A further advantage of certain embodiments of the 18 present invention is that the anode-bank 10 may be 19 reeled onto a drum which allows for convenient launching of the pipeline in use.

22 A further advantage of certain embodiments of the 23 present invention is that the process of 24 launching/laying the pipeline is far quicker it takes around 8 minutes to add the anodes onto the 26 each anode-bank 10 compared with around 18 hours for

27 some known prior art systems.

29 A further advantage of certain embodiments of the present invention is that cladding is not required 31 and so their manufacture is considerably cheaper

32 than certain known prior art systems.

1 Modifications and improvements may be made without 2 departing from the scope of the invention. For 3 example, any number of anodes 20 can be attached to 4 the anode-bank 10 and the length of the sleeve 14 can be varied depending on the number of anodes 20 6 being attached.

Claims

1 Claims 3 1. A pipe comprising: 4 a tube; a sleeve provided over a

portion of an outer 6 face of the tube; 7 a coating provided over at least a portion of 8 the sleeve; and 9 an electrical connector which extends through the coating and is attached to the sleeve.

12

2. A pipe as claimed in claim 1, wherein the tube 13 is a load-bearing tube.

3. A pipe as claimed in any preceding claim, 16 wherein the pipe further comprises a means to attach 17 sacrificial electrodes thereto.

19

4. A pipe as claimed in any preceding claim, wherein the sleeve extends circumferentially around 21 the tube.

23

5. A pipe as claimed in any preceding claim, 24 wherein the tube is made from a robust material which is resistant to degradation by a mixture of 26 water and hydrocarbons flowing therethrough.

28

6. A pipe as claimed in claim 5, wherein the tube 29 is substantially made from stainless steel.

31

7. A pipe as claimed in any preceding claim, 32 wherein the sleeve is manufactured from a material 1 which is resistant to degradation caused by hydrogen 2 formation on its surface.

4

8. A pipe as claimed in claim 7, wherein the sleeve is substantially made from steel.

7

9. A method of manufacturing a pipe, the method 8 comprising: 9 providing a tube; securing a sleeve over an outer face of the 11 tubed 12 attaching the electrical connector to the 13 sleeve; and 14 coating a portion of the pipe.

16

10. A method of launching a series of pipes, the 17 method comprising: 18 connecting a pipe as claimed in any one of 19 claims 1 to 8 to a plurality of pipes) mounting the said connected pipes on a reel; 21 launching the said connected pipes from the 22 reel.