GB2230060A

GB2230060A - Pressure balanced retriever

Info

Publication number: GB2230060A
Application number: GB8900129A
Authority: GB
Inventors: Frederick Thomas Trowsdale
Original assignee: STORTFORD ENGINEERING DESIGNS
Current assignee: STORTFORD ENGINEERING DESIGNS
Priority date: 1989-01-05
Filing date: 1989-01-05
Publication date: 1990-10-10
Anticipated expiration: 2009-01-05
Also published as: GB8900129D0; GB2230060B

Abstract

A tool for inserting or retrieving plugs, probes, samples or other devices in pipes and vessels which contain gas or liquid at or above atmospheric pressure is provided with a means of balancing the pressure derived forces such that the force required to operate it is substantially the same regardless of the pressure. The centre rod 24, to which the various devices 17 are releasably attached, may be freely moved both rotationally and axially thus allowing the pressure balanced retriever to be used in conjunction with different types of device and for different purposes. Pressure from the pipe or vessel passes through rod 24 to chamber 23. The chamber between the rod and cylinder 25 opposed to sealed chamber 23 is vented to atmosphere. <IMAGE>

Description

PRESSURE BALANCED RETRIEVE This invention relates to a pressure balanced retriever, and particularly to the type of retriever which is used to install or remove plugs, probes, monitoring, testing or dosing devices in pipes and vessels which contain gas or liquid under pressure. such retrievers are frequently used in the oil and gas industry.

Pipelines, production facilities and process plants are frequently required to operate on a continuous basis. It is therefore necessary to be able to install or remove the various testing and monitoring devices without shutting down. The tool used to do this is generally referred to as a retriever.

The pipe or vessel is equipped with a special fitting in which the testing or monitoring device is installed. The device is exposed to the contents of the pipe or vessel and leakage is prevented by means of a seal between the fitting and the device.

To remove the device, a full bore valve is attached to the fitting and the retriever is attached to the other side of this valve. The retriever is operated, first by extending its centre rod through the open valve then by attaching the end of the rod to the device installed in the fitting. The retriever is then used to disconnect the device from the fitting, usually, but not necessarily, by unscrewing it. This breaks the seal between the device and the fitting and the whole assembly is exposed to the contents of the pipe or vessel. Leakage to atmosphere is prevented by seals in the valve and the retriever. The centre rod is then fully retracted with the device still attached and the valve is closed. The contents which are still trapped in the retriever above the valve are then bled off so the retriever can be safely removed.

To install a device into the fitting, the device is attached to the centre rod of the retriever, which is then installed on the valve. The valve is opened, again exposing the retriever to the contents of the pipe or vessel. The retriever is then used to install the device in the fitting. The e seal created between the device and the fitting allows the contents in the valve and the retriever to be bled off, thus normally allowing the retriever and the valve to be removed and used to repeat the operation elsewhere.

During these operations, the pressure of the contents within the pipe or vessel acts upon the retriever such that, when the pressure is above atmospheric, it creates a force that must be overcome when the centre rod is being inserted, or that must be restrained when it is being retracted. When below atmospheric pressure, the reverse occurs. These forces can be controlled by mechanical means, but a common and widely used method, is to design the retriever in such a way that the forces created by the pressure acting in one direction are balanced by the forces created by the same pressure acting in the opposite direction.

The examples of existing pressure balanced retrievers will now be described with reference to the accompanying drawings in which: Figure 1 shows the basic concept of the most widely used pressure balanced retriever.

Figure 2 shows the basic concept of a more recent design.

Fig. 1 and Fig.2 show the retriever lowering a device through the valve prior to installation in the fitting.

Referring first to Fig.1, the inner tube 1 is fixed to the valve at one end. The centre rod 2 passes through a seal 3 at the other end of the inner tube and is fixed to the outer tube 4. The outer tube is equipped with handles and is free to slide longitudinally and rotate about the inner tube via a seal 5 mounted on the inner tube and another seal 6 mounted inside the outer tube. Peripheral holes 7 in the inner tube allow the pressure within the annulus between the inner and outer tubes to be equal to that within the inner tube. Holes 8 in the end of the outer tube maintain atmospheric pressure between the inner and the outer tubes above the seals 3 and 5.The e axial outward force caused by the pressure acting on the cross-sectional area of the centre rod (which passes through to atmosphere) is balanced by the axial inward force created by the pressure acting on the same cross-sectional area within the annulus 9. This means that the force required to operate the tool is, with the exception of the friction effect on the seals, essentially the same regardless of the pressure at which it must operate. This design, however, results in a very heavy tool which when manufactured in special materials also becomes very expensive.

In the more recent design concept shown in Fig.2, the body tube 10 is fixed to the valve at one end and is blanked off at the other end. The centre rod 11 passes through a seal 12 within the body tube at the valve end and another seal 13 as it enters the blanked off chamber at the other end. The body tube has longitudinal slots 14 cut in it between the two seals so as to expose the centre rod.

Handles 15 are inserted through these slots and atttached to the centre rod, thus allowing the centre rod to be moved longitudinally within the limits imposed by the slots but not radially. The centre rod is in fact a heavy wall tube, thus allowing pressure to enter the blanked off chamber at the end of the body tube.As the cross-sectional area of the centre rod is constant and the pressure at either end of it is the same then the force required to operate it is, with the exception of the friction effect on the seals, essentially the same regardless of the pressure at which it must operate. This design, although far less expensive than that previously described; has a major disadvantage in that, because it cannot be rotated, it cannot be used to insert devices which must be screwed into place , neither can it be released from the majority of the devices which it is designed to install and therefore must be permanently fitted at a single location.

According to the present invention there is provided a pressure balanced retriever comprising a rod which passes through seals at each end of a cylinder, a collar fixed to the rod which has seals on the inside diameter of the cylinder, a cylinder with seals at each end to carry the rod and which has a means of allowing atmospheric pressure to be maintained internally at one end and whose inside diameter is directly related to the outside diameters of the rod where it passes through the seals at each end, a means of allowing the pressure applied to the rod when in use to be transmitted to the annual chamber formed between the closed end of the cylinder and the collar, a means of moving the rod both axially and radially, a means of releasibly securing various devices to the rod and a means of releasably securing the cylinder to a valve either directly or via another component.

Specific embodiment of the invention will now be described by way of examples with reference to the accompanying drawings in which: Figure 3 shows a cross-section of the retriever with single seals and with pressure transmitted to the annular chamber via a hollow centre rod.

Figure 4 shows a similar retriever fitted with double seals and lubricator.

Figure 5 shows a similar retriever fitted with double seals and vent.

Figure 6 shows a means of transmitting the pressure via external piping.

Figure 7 shows a means of transmitting the pressure via an annular sleeve.

Figure 8 shows a means of moving the position of the operating handles.

Referring to Fig. 3, a fitting 16 designed to accept a device 17 has been incorporated in a pressurized vessel 18. In order to retrieve the device a temporary valve 19 is mounted on the fitting. A housing 20 of length and diameter sufficient to contain the device is attached to the retriever (or may be an integral part of the retriever) and mounted on the other side of the valve. After ensuring that all joints are tight, the centre rod 21 passing through the seal 22, and equipped with a suitable means of attaching to the particular device, is pushed through the open valve using the handles 33 and connected to the device. The seal between the device and the fitting is then disengaged allowing the contents of the vessel to enter into and pressurize the whole assembly.

In this embodiment of the design, the pressure enters the annular chamber 23 via the hole 24 in the centre rod. The effective diametrical cross-sectional area of this chamber is determined by the inside diameter of the cylinder 25 and the diameter of the centre rod where it passes through this seal 26. By making this cross-sectional area equal to the diametrical cross-sectional area of the centre rod where it passes through the seal 22 in the cylinder, ignoring the hole 24, the pressure derived forces acting in one direction, will be opposed by similar forces acting in the opposite direction. e.g. If the inside diameter of the cylinder in the pressurized annulus is 'D', the diameter of the centre rod where it passes through the seal 26 is dt and the diameter of the rod where it passes through the seal 22 is d2 then D2 - d2 = d2 When d, = d2= d, then D2= 2d2 .This pressure balance is achieved rapidly and the device can then be completely removed from the fitting and pulled back through the valve into the housing.

The e valve is then closed and the contents of the vessel remaining in the assembly above the valve are bled off via a suitably positioned vent valve(s). The vent valve(s) may also be used during installation or retrieval operations if it is necessary to purge air out of the system.

The assembly can then be removed from the valve to gain access to the device.

To reinstall a device in the fitting the procedure is essentially reversed. The valve, housing and retriever can then be removed fron the fitting for use in other locations.

Referring to Fig.4, retrievers may come into contact with liquids or gases which cause excessive seal wear or friction. In this event double seals may be used at any or all of these seal locations, with a simple lubricated pad 27 installed between them.

Referring to Fig.5, retrievers may come into contact with liquids or gases which are potentially hazardous. In this event, double seals may again be used but with a vent incorporated between them.

The vent nay be used to bleed off any fluid which may leak past the first seal or to inject an inert fluid between the seals at a higher pressure so that any leakage is into and not out of the vessel. The vent between the seals 28 on the centre rod can be via a hole 29 in the outer end of the centre rod.

Referring to Fig. 6, the pressure may also enter the annular chamber 23 via other means, such as external piping 30 or, referring to Fig.7, an outer sleeve 31, in which case, atmospheric pressure would be maintained in one end of the cylinder via a tube(s) 32.

Referring to Fig.8, the operating handles 33 may be moved to a more convenient position by mounting them on a sleeve 34.

Claims

1. A pressure balanced retriever comprising a rod which passes

through a seal or seals at each end of a cylinder, a collar fixed to the rod which has as seal or seals on the inside diameter of the cylinder, a cylinder with a seal or seals at each end to carry the rod and which has a means oi allowing atmospheric pressure to he maintained internally at one end and whose inside diameter is detennined by the outside diameters of the tod where it passes through the seal or seals at each end, a means Of allowing the pressure applied to the rod when in use to be trensmitted to the annular chamber formed between the closed end of the cylinder and the collar thus allowing the pressure derived forces acting on the rod in one direction to be opposed by substantlally equal pressure derived forces acting on the collar in the opposite direction, a means of moving the rod both axially and radially, a means of releasably swing various devices to the rod and a means of releasably securing the cylinder to a valve either directly or via another o#oent.

2. A pressure balanced retriever as claimed in Claim 1, wherein any or all of the seal or seals are fitted with a moans of lubrication.

3. A pressure balanced retriever as claimed in any preceding claim, wherein any, or all of the seals are installed as multiple units allowing the space space between them to be vented.

4. A pressure balanced retriever as claimed in any preceding claim wherein the operating handle or handles are punted either at the top of the centre rod, or at any other convenient position within the length of the retriever by attaching then to a sleeve.

5. A pressure balanced retriever subetantially as described herein with reference to Figures 3 - 8 of theaccompanying drawing,