Hydraulic and earth engineering – Subterranean or submarine pipe or cable laying – retrieving,...
Patent
1991-02-07
1992-05-26
Corbin, David H.
Hydraulic and earth engineering
Subterranean or submarine pipe or cable laying, retrieving,...
285381, 405184, F16L 1028, F16L 5818
Patent
active
051163543
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a covering for protecting a joint between pipes when the joined pipes are to be pushed or pulled through soil.
Where pipelines are to be positioned under a road or river it is not practical to dig a trench to bury the pipe. Two main techniques are generally used for positioning the pipe. In the first technique, known as directional drilling, a non-linear hole is drilled under the road or river, and the hole is filled with a special liquid to stop the soil collapsing into the hole. In the second technique there is no pre-drilling and the pipes are simply pushed into the soil, each length of pipe being joined and pushed into position on site.
The pipelines which are used in the above techniques are typically steel pipes coated with a corrosion protective layer. The corrosion protective layer may comprise a sintered polyethylene mil coating. Also increasingly popular are multi layer coatings comprising sequentially a fusion bonded epoxy layer, a hot melt adhesive layer and an outer polyethylene layer. The protective coating is typically 1.5 to 9 mm thick. The pipes are generally joined by welding, and the protective coating is removed to bare the underlying steel in the joint region to allow the weld to be made. This region is therefore open to the atmosphere and must be recovered, for corrosion protection, before the joined pipes are buried in the soil.
There are a number of existing solutions for recovering the bared joint of the steel pipes. One solution involves sintering polyethylene material in a mold positioned around the joint, thereby reformulating the mil coating around the joint. Another solution involves priming the pipe then wrapping an epoxy coated glass fibre wrap around the pipe joint and curing the epoxy. A third solution involves a triple layer recoverable sleeve positioned over the joint region again with an epoxy primer on the outside. All these solutions are operator-sensitive and time consuming. Particularly where the pipes are to be joined on site this is particularly disadvantageous, and in some instances only one pipe length per day can be added.
Also in some of the prior art, e.g. using the triple layer recoverable sleeve and epoxy outer jacket, the leading edge of the covering is prone to fraying as pipeline is pulled or pushed through the soil on the pipe covering.
Some effort has been expended to try to decrease the profile of the covering at the joint region in order to minimize the fraying at the leading edge. However we have discovered that even though it increases the profile at the leading edge, an effective corrosion protective covering can be positioned around the joint which resists leading edge fraying by using a band, made for example from a metal, from a composite, or from an engineering plastic, the band being tightened around a combination of recoverable sleeves. Therefore a first aspect of the invention provides a method of covering a joint between two coated pipes the coating of which has been bared in the joint region, and which pipes are to be pushed or pulled through soil, the method comprising:
(i) recovering a first heat recoverable sleeve around the joint region, to cover the bared joint and to overlap the coating on either side of the joint region;
(ii) recovering a second heat recoverable sleeve to overlap the first sleeve and to extend beyond the first sleeve in a direction towards the leading edge of the pipe joint; and
(iii) fastening a band around the second sleeve at the leading edge of the sleeve.
Preferably the second heat recoverable sleeve is thinner than the first heat recoverable sleeve. This means that when the band is fastened around the second sleeve there is a small step down from the sleeve to the pipe surface. Typically the first sleeve is at least 2 mm, preferably 3 mm, generally about 4 mm thick. In contrast the second sleeve is typically less than 2 mm preferably about 1 mm thick. The band is preferably 0.3 to 1.5 mm thick, typically about 0.8 mm thick.
While the double sleeve combination is preferred, it is poss
REFERENCES:
patent: 4271329 (1981-06-01), Perelmuter
patent: 4796669 (1989-01-01), St. Onge
patent: 4830539 (1989-05-01), Akesaka
Burkard Herbert G.
Corbin David H.
Gerstner Marguerite E.
N. V. Raychem S.A.
Rice Edith A.
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