Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C63/00—Lining or sheathing, i.e. applying preformed layers or sheathings of plastics; Apparatus therefor
  • B29C63/38—Lining or sheathing, i.e. applying preformed layers or sheathings of plastics; Apparatus therefor by liberation of internal stresses
  • B29C63/42—Lining or sheathing, i.e. applying preformed layers or sheathings of plastics; Apparatus therefor by liberation of internal stresses using tubular layers or sheathings
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
  • F16L—PIPES; JOINTS OR FITTINGS FOR PIPES; SUPPORTS FOR PIPES, CABLES OR PROTECTIVE TUBING; MEANS FOR THERMAL INSULATION IN GENERAL
  • F16L58/00—Protection of pipes or pipe fittings against corrosion or incrustation
  • F16L58/18—Protection of pipes or pipe fittings against corrosion or incrustation specially adapted for pipe fittings
  • F16L58/181—Protection of pipes or pipe fittings against corrosion or incrustation specially adapted for pipe fittings for non-disconnectable pipe joints

Definitions

• This invention relates to the protection of joints in elongate substrates and more particularly to the protection of welded joints in submerged, weight-coated pipelines.
• Submerged weight-coated pipelines are usually installed by a purpose- built offshore vessel known as a laybarge.
• an anti-corrosion coating for example, coal tar enamel, asphalt, or a fusion-bonded epoxy coating, leaving a bare section at each end of the pipe to allow subsequent welding of adjacent lengths to take place without contamination or coating damage.
• This bare area normally extends up to 250 mm from each end of the pipe.
• the weight coating which is usually a mixture of concrete and iron oxide, is applied over the anti-corrosion coating to a thickness of from about 25 mm to about 150 mm, depending upon the degree of negative buoyancy required.
• the weight coating is also cut-back from the pipe ends to expose the bare section of pipe and about 200 mm of the anti-corrosion coating, in order to allow subsequent overlap and completion of weld area corrosion protection.
• the coated pipes are strung together, aligned, welded, and the welds x-ray inspected.
• An anti-corrosion layer is then applied over the welded region which may, for example be a sealant-coated tape, or a heat- shrinkable wraparound sleeve.
• the joint area is mechanically protected, to restore the weight coating at the joint, and to protect the joint from mechanical damage during subsequent operations.
• the laybarge is divided into a number of work stations each carrying-out a specific function at a pipe joint area.
• the completed pipeline leaves the rear of the laybarge and encounters a series of rollers and guides which assist, correct and control entry of the pipeline into the sea, river or lake.
• This collection of rollers and guides known as the stinger, is towed along by the laybarge and is subjected to any sea movements or wave impacts, hence the pipeline supported by the stinger is itself buffeted about and impacts with the rollers and guides, particularly in rough weather.
• Such impacts can be severe and could result in damage to the joint area weight coating and exposed anti-corrosion coating if no mechanical protection system were to be employed.
• a single, flat metal sheet is wrapped around the joint area, overlapping the adjacent weight coating, and onto itself to form a mould.
• Steel straps are wrapped around the mould and tightened to hold the mould in place.
• the hot marine mastic from the hopper is introduced through a hole cut in the top of the sheet mould and fills up the annulus formed by the mould. The hole is then sealed by means of a metal sheet that is held in place by means of straps.
• EP-A-0079610 One example of a hot mastic approach is described in EP-A-0079610 where a covering is formed on a joint between covered steel pipes each having a protecting concrete layer by first wrapping a heat-shrinkable sheet of low shrinkage temperature around the joint, then installing a metal tube around the joint to form a closed space around the joint, and finally pouring fused mastic into an opening in the metal tube, the mastic shrinking the shrinkable sheet and solidifying to form a covering protecting layer.
• Another mechanical protection system for joints which is available involves the use of polymer cement in-fill systems instead of hot marine mastic. Yet another system uses special liquids that foam-up to fill in the annular space between pipe and mould. Again special chemicals must be correctly stored and then mixed using sophisticated application equipment requiring skilled operators.
• the metal mould is no longer required. It is merely a delivery container to hold the mastic while is sets. However typically cooling takes several hours, while the offshore laybarges can complete a joint in less then 15 minutes. Therefore the metal moulds are usually left in place on the pipe. This, however, can lead to problems in the lifetime of the pipeline.
• the metal mould and /or the straps holding it around the pipeline may corrode after exposure to the sea water. This may cause the mould to lose contact with the pipeline, or even spring away from the pipeline. If this occurs jagged edges of the metal mould project from the pipeline. These may, for example, cause damage to fishing nets, or interfere with shipping anchors.
• the problems of the prior art can be overcome by providing a sleeve positioned around the mould, and engaged tightly around the mould substantially to prevent it leaving the pipeline, or projecting therefrom.
• the present invention provides a method of protecting a joint between two corrodible, weight coated elongate substrates which have been bared of weight coating in the joint region, comprising (a) positioning a wraparound mould around the joint region, and (b) filling the mould with a corrosion resistant material, characterised in that a wraparound sleeve is positioned around the mould, and engaged around the mould, substantially to retain the mould within the sleeve.
• the mould if metal as is usual, can corrode away completely within the confines of the sleeve.
• the sleeve is preferable a recoverable sleeve, preferably a radially heat shrinkable sleeve.
• Heat recoverable articles are those that recover on heating toward an original shape from which they have previously been deformed, but the term "heat-recoverable” also include those articles which adopt a reconfiguration even if not previously deformed.
• Traditional recoverable sleeves comprise a polymeric material such as polyethylene. Examples are described in US 2027962, 3086242 and 3597372. More recently heat recoverable fabrics have been found to be useful.
• Heat recoverable fabrics are described in US 3669157, EP-A-115905, EP-A-116390, EP-A-116391, EP-A-116392, EP-A-116393, EP-A-117025, EP-A-117026, EP-A- 118260, EP-A-137648, EP-A-153823, EP-A-175554 and EP-A-0202898
• the covering sleeve comprises a recoverable fabric. Any of those described above are suitable.
• the split resistance is preferably exhibited at operation temperatures, and also at elevated temperature e.g.. up to 180°C, 200 or even 250°C. Temperatures of this order will be encountered if the corrosion resistant in-fill material within the mould is a marine mastic or the like, having a melting point of 180°C or higher, e.g.. 200°C or 250°C.
• the wraparound sleeve has a tear strength at 25°C, 180°C or 200°C or even 250°C of at least 20N preferably at least 30N especially at least 50N, more especially at least 100N when tested in on Instron tensometer employing a draw rate of 100mm /mm.
• the tear strength is greater than 300N/25mm, preferably greater than 400N/25mm or even as high as 500N/25mm.
• the material of the sleeve also preferably consists of components that can all resist temperatures encountered in use e.g.. 180°C, 200°C or even 250°C.
• the fabric is typically used in conjunction with a polymeric matrix laminated on one or both sides of the fabric preferably have melting points above, preferably 10, 20 or 50°C above the temperatures encountered in use that are described above.
• Figure 1 is a longitudinal sectional view of a joint region prior to attachment of a metal mould and in-fill mastic
• Figure 2 shows the joint region of Figure 1 similarly inside sectional view, after the mould in-fill mastic and covering sleeve according to the invention has been installed.
• Figure 1 shows two steel pipes 1 and 2, having anti corrosion coatings 3 and 4, and weight coatings 5 and 6.
• the anti corrosion coatings and the weight coatings are cut back to expose lengths of bare pipe which are welded at 7.
• the lengths of the bared region is typically of the order of 700 mm.
• Figure 2 shows the arrangement of Figure 1 after a sheet steel mould 8 has been wrapped around the bared region. The mould 8 is wrapped so that it overlaps the weight coatings 5 and 6 on either side of the bared joint region. Hot marine mastic 10 has been poured into the mould 8, and the entry hole sealed.
• a heat recoverable fabric sleeve 9 Over the mould 8 a heat recoverable fabric sleeve 9, has been installed into close conformity with the mould 8 and also to project beyond the edges of the mould 8 on to the weight coatings 5 and 6.
• the sleeve 9 may have any composition as described hereinbefore, and is radially heat recoverable.
• the sleeve 9 completely encloses the sheet steel metal mould 8.
• sleeve 9 does not have to be sealed or bonded in any way to the mould 8 or weight coatings 4 and 5. It merely needs to retain within its confines the mould 8, to prevent the mould loosening and springing or pulling away from the pipes in use, which could cause anchor foulage or interfere with fishing nets.
• the fabric also needs to be resistant to tearing so that it is not damaged when the finished joint is pulled over rollers on the laybarge when the finished joint is entered into the sea.

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• Engineering & Computer Science (AREA)
• General Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Manufacturing & Machinery (AREA)
• Protection Of Pipes Against Damage, Friction, And Corrosion (AREA)

Applications Claiming Priority (3)

Publications (1)

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ID=10715929

Family Applications (1)

Country Status (4)

Cited By (1)

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• 1992
  • 1992-05-22 GB GB929210984A patent/GB9210984D0/en active Pending
• 1993
  • 1993-05-21 WO PCT/GB1993/001047 patent/WO1993024782A1/en not_active Application Discontinuation
  • 1993-05-21 EP EP93910252A patent/EP0641424A1/de not_active Ceased
  • 1993-05-21 JP JP6500298A patent/JPH07507377A/ja active Pending

Non-Patent Citations (1)

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