Hydraulic and earth engineering – Subterranean or submarine pipe or cable laying – retrieving,... – Submerging – raising – or manipulating line of pipe or cable...
Patent
1994-10-20
1996-12-03
Neuder, William P.
Hydraulic and earth engineering
Subterranean or submarine pipe or cable laying, retrieving,...
Submerging, raising, or manipulating line of pipe or cable...
4051683, 405173, F16L 114, B63B 3503
Patent
active
055801870
DESCRIPTION:
BRIEF SUMMARY
This invention relates to apparatus for laying and/or retrieving elongate flexible elements and particularly, but not exclusively, to apparatus for laying and/or retrieving elongate flexible pipes or cables which have an accessory spaced at intervals along their length.
One form of apparatus for laying and/or retrieving elongate flexible pipes or cables is an arrangement mounted on and supported by a floating vessel such as a barge. Such an apparatus is adapted for laying pipes or cables in a deep sea environment and in one embodiment has a guide means positioned in order to permit a pipe or cable to pass over an edge of the vessel and means arranged to support the pipe or cable during this operation.
A problem encountered with the above mentioned apparatus was that the pipe or cable could not be bent into an arc, beyond a particular limiting radius of curvature, without damaging the pipe or cable. This was partly due to the presence of linkages or accessories which connected lengths of pipe or cable together. It was also partly due to the fact that the pipe or cable when laid or retrieved was placed under considerable tensile loads and when subject to bending this gave rise to stress concentrations, particularly at or close to accessory pipe/cable junctions. The problem of maintaining the cable in a relatively shallow arc with respect to accessories has been made more difficult by the fact that the accessories have a greater diameter than the pipe or cable. In addition to the aforementioned accessories which are integral with the pipe, secondary accessories, such as anodes for cathodic protection or bend restrictors are often fitted in the form of strings of "bracelets" around the pipe or cable adjacent to the accessory. An additional problem arises as these secondary accessories cannot be passed over the relatively small radius of the guidance means without serious risk of damage to the secondary accessories and/or the pipe/cable.
Equipment and techniques were developed to limit the stresses which occurred in an attempt to mitigate this effect of stress concentration occurring at pipe/cable accessory junctions. One such piece of equipment is described in U.K. Patent GB 2,173,760B
GB 2,173,760B describes and claims a device for laying or naturally raising a pipe which comprises in one embodiment a grooved wheel of relatively large diameter. The grooved wheel is positioned at the rear of a pipe/cable laying vessel and is able to rotate about a supporting axis. A pipe/cable is curved to pass over the wheel, in the groove, and is either laid or retrieved depending upon the sense of rotation of the wheel. The radius of curvature of the grooved wheel is such that the pipe/cable is never bent beyond the limiting minimum radius of curvature.
During the laying process, pipe/cable is unwound from a storage drum or reel and passed through one or more sets of linear traction devices. These devices are similar to caterpillar type tensioners. They are sometimes known as trichenilles. They ensure that the pipe/cable is held in sufficient tension during the laying process. The pulling force by the or each set of tensioners depends on the amount of pipe which has already been paid out the water depth, and the horizontal distance between the barge and the touch down point of the pipe/cable on the sea bed. During the pipe/cable retrieving stage the process is effectively reversed.
So as to enable the accessories to be passed without damage over the edge of the barge or vessel during the laying (or retrieving) process the system described in GB 2,173,760B incorporates a handling device, known as a gantry arrangement, which is pivotally linked to the supporting axis and is able to rotate thereon and independent of the grooved wheel. The purpose of the gantry is to engage the accessory which is fitted with trunnions.
Engagement of the trunnions occurred at an instant just as an accessory "approached" the supporting wheel. The gantry was then urged against the accessory by the pipe tension and a portion of the pipe/cable proxi
REFERENCES:
patent: 4917540 (1990-04-01), Recalde
patent: 5000619 (1991-03-01), Kordahi
patent: 5011333 (1991-04-01), Lanan
Edwards Robert J.
McDermott Subsea Constructors Limited
Neuder William P.
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