Railways – Tubular way – Internal service device
Reexamination Certificate
2000-08-28
2002-07-09
Le, Mark T. (Department: 3617)
Railways
Tubular way
Internal service device
Reexamination Certificate
active
06415722
ABSTRACT:
FIELD OF THE INVENTION
The invention lies in the field of robotic equipment used in the activities of producing and transporting petroleum and derivatives thereof.
More specifically, it relates to equipment intended to allow the introduction of tools or other equipment or materials inside pipelines for petroleum or derivatives, preferably when these pipelines are of great length and they present conditions where access is difficult, are installed at great depths, or are buried. Such tools may, for example, be used for the purposes of removing obstructions, inspection or the like.
Although designed for use in the petroleum industry, the invention may be applied in any other industrial areas which use pipelines or other confined spaces which may require a certain internal intervention such as, for example, water- and gas-distribution installations, power-generation plants of the hydraulic, thermal or nuclear type, refineries, various industrial-process facilities, etc.
BACKGROUND OF THE INVENTION
With the development of new technologies, offshore oil production has been becoming viable at increasingly greater depths. This situation gives rise to the need for the installation of diverse equipment and for an extensive network of pipelines at considerable depths. Aside from other technological challenges which are being overcome, in connection with increasingly stringent equipment specifications owing to the high pressures involved, previously unanticipated problems frequently arise as a consequence of low temperatures. Such problems are frequently associated with the characteristics of the fluid conveyed or of the oil produced.
Amongst problems arising from the low temperatures, a tendency has been observed for oils to become less fluid, for the formation of hydrates, the deposition of paraffin, and frequently the occurrence of severe flow restrictions or even stoppages in pipes. Obstructions, which may also be caused by the deposition of sand or other materials, frequently occur a long way from the nearest access point.
The equipment of the present invention is intended to be able to move inside pipelines, within specific diameter bands, using force components normal to the substantially cylindrical pipeline walls in order to obtain positive traction. It makes it possible to arrive at the desired point, or at the point of an obstruction, carrying selected equipment and having available the capacity to there carry out the operations required to induce a flow such as, for example, application of the method known as SGN (Nitrogen-Generating System), application of solvents, filming, inspections by means of non-destructive testing (NDT), scraping, etc., it being possible, therefore, for it to be equipped with interfaces suited to the aforesaid operations (not described in this specification).
In its simplest form, the equipment may be viewed as a dual-action hydraulic cylinder and through-bar, equipped with two trios of cams, or fins, connected to the through-bar and with one trio of fins connected to the casing, or body, of the hydraulic cylinder. The sets of fins, normal to the walls of the pipeline, function as independent anchoring systems for alternately the casing and the through-bar of the hydraulic cylinder. Therefore, the trios of fins are equipped with, for example, hydraulic actuators. When pressurized, this actuator applies a force to the fins, resulting in a force normal to the walls of the pipeline, which prevents movement of the casing or of the through-bar.
By pressurization of its respective trio of fins the body of the hydraulic cylinder is temporarily fastened to the wall of the pipeline. Under these conditions, by a rear chamber of the body of the said hydraulic cylinder being pressurized, the through-bar, whose fins yield, advances.
In a second stage, the fins of the casing are depressurized and the fins of the through-bar are pressurized. Then, a front chamber of the body of the hydraulic cylinder is pressurized. Since the bar is now fixed and the casing now has yielding fins, the casing advances.
At the end of this movement, the actuating system will have returned to the initial configuration, but the assembly as a whole will have advanced by one step and will be ready to initiate a further cycle.
Another aspect of importance in the design of the equipment according to the invention is that it makes use of a locking effect on the casing, by means of the contact of the fins with the inner wall of the pipeline. Even when the fins are yielding (actuator depressurized), this locking effect prevents the equipment from being moved backwards, for example owing to the efforts of the umbilical. Principally the architecture and spatial arrangement of the fins contribute to achieving this result of avoiding backwards movement of the vehicle.
STATE OF THE ART
Currently, for work involving the cleaning or unblocking of pipes, the petroleum industry generally uses equipment known as a pig. This is a round or oval object which is generally manufactured from some polymeric material, or compound of various materials, which “travels” along a section of pipe. During travel, it scrapes off the partially obstructing incrustations from the inner surface of the pipeline. The launcher is installed at the starting point and the so-called pig receiver is installed at the opposite end.
However, for the pig to move, requires a pressure differential between the two ends and the possibility of establishing a flow of fluid in the pipe. When the pipeline is completely obstructed such a differential is not achieved and the fluid does not circulate; hence a kind of hydraulic “wedge” is formed and consequently the pig cannot be used.
The starting point of the invention was an operational emergency. In 1997, an obstruction occurred in an eight-inch petroleum-export line from a Petrobrás offshore platform. The first step in solving the problem was to locate the precise point of the obstruction. A highly sensitive tool was therefore developed, based on the increase in the diameter of the pipe when the pipe is pressurized. Using this tool, the site of the obstruction was therefore located, approximately eight kilometers from the nearest end (at the offshore production platform).
Given the nature of the incident, with total interruption of the flow, it was not possible to use pigs. It was therefore decided to use another method available for interventions in pipelines. More specifically, Petrobras chose to launch “flexitube” equipment. This is a flexible tube, with a degree of resistance, which is threaded inside the pipe.
In the case in point, because the site of the obstruction was a long way from the flexitube launch point, it was not possible for the end of the flexitube to reach the obstruction. Despite having considerable resistance, the flexitube has a finite force-application capacity when pushed inside a pipeline, before it suffers excessive flexing and deformation. Principally on account of friction it is noted that, when pushed inside a pipeline, the flexitube tends to form a helicoid bearing on the inner surface of the pipeline. Under such conditions friction increases considerably and greater force is required to push the flexitube inside the pipeline. Helicoid formation is thus accentuated and there is a consequent spring effect. As of a certain point, owing to limitations either on the part of the material from which the flexitube is made or on the part of the equipment pushing it, this effect prevents progress of its front tip, limiting the extent of the intervention. In the case in point the flexitube was successfully inserted up to a distance of approximately one and a half kilometers, which was insufficient to reach the obstruction site. It was therefore not possible, as had been hoped, to take to the blockage site the heated liquid resulting from the SGN reaction or any solvent, which was the unblocking tactic selected for this case.
This was the situation which gave rise to a device to create equipment which could assist in the introduction of the flexitube or which was capable
Le Mark T.
Nixon & Vanderhye PC
Petroleo Brasileiro S.A.
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