AU603176B2

AU603176B2 - Low frequency pressure oscillator

Info

Publication number: AU603176B2
Application number: AU10368/88A
Authority: AU
Inventors: John Eugene Hough
Original assignee: Saipem Australia Pty Ltd
Current assignee: Saipem Australia Pty Ltd
Priority date: 1987-01-16
Filing date: 1988-01-18
Publication date: 1990-11-08
Anticipated expiration: 2008-01-18
Also published as: AU1036888A

Description

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4, f PATENTS ACT 1952 COMPLETE SPECIFICATION

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FOR OFFICE USE 176 Form Short Title: Int. Cl: Application Number: Lodged: PH-9904 16th January 1987 .A j

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*Qomplete Specification-Lodged: Accepted: I Lapsed: Published: Ptiprity: Related Art: Name of Applicant: 'Acidress of Applicant: Actual Inventor: TO BE COMPLETED BY APPLICANT SAIPEM AUSTRALIA PTY. LIMITED 16th floor, 83 Clarence Street, SYDNEY. N.S.W. 2000.

John Eugene HOUGH HALFORD MAXWELL, Patent Trade Mark Attorneys, 49-51 York Street, SYDNEY. N.S.W. 2000.

Address for Service: Complete Specification for the invention entitled: 'LOW FREQUENCY PRESSURE OSCILLATOR'.

The following statement is a full description of this invention, including the best method of performing it known to US 3DGED Al FIC' 16 JAH l1987 Sydney P D A D AMENDMENTS 1 -2- 0 6

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"V bliq This invention relates to low frequency acoustic signal generators, suitable for the generation of acoustic waves in fluids and in particular in fluids contained under a pressure greater than atmospheric pressure.

For the sake of convenience, the invention will be described in relation to the provision of low frequency acoustic signals for determining the acoustic velocity in pressurised liquid-filled pipelines, but it is to be understood that the invention is not limited thereto.

In our co-p nding Australian patent application No. 11,870/88 entitled 'Testing of Pipelines' there is disclosed a method of detecting leaks in a pressurised fluid-filled pipeline, by examining the degree of correlation between changes in hydrostatic pressure and changes in acoustic velocity.

It is an object of the present invention to provide a low frequency acoustic signal generator that may be used in the leak detection technique disclosed in our co- pending patent application.

According to the invention there is provided apparatus for generating acoustic waves in a pressurized fluid, said apparatus being external to said fluid, said apparatus comprising piston means, conduit means for placing one end of said piston means in'communication with said fluid, pressure means communication with the other end of said piston means to apply a force which substantially balances the force applied to said one end of the piston means by said pressurised fluid, and means for oscillating said piston means.

In order that the invention may more readily be MANAGING. DiIEX1ZUUh THE COMMISSIONER OF PATENTS.

I To 4 -3understood and put in practical effect reference will now be made to the accompanying drawings which show, somewhat schematically, low frequency acoustic signal generators according to two embodiments of the invention.

The low frequency acoustic signal generator shown in Fig. 1 includes an elongated hollow body portion which has a bore 11 that carries a piston 12. The body 10 has an end cap 13 by means of which the generator is connected to a pipeline containing a pressurised fluid such as water. Passageways 14 in the end cap 13 place the end 15 of the piston 12 in communication with the fluid in the pipeline. A seal 16 is located between the end cap 13 and the body At the other end of the body 10 there is an end cap 17 adapted to be connected to a pressurised gas chamber .**eat substantially the same pressure as the fluid in the pipeline. A seal 18 is located between the end cap 17 *:ee and the body 10. Passageways 19 place the end 20 of the piston 12 in communication with the gas in the gas 4I chamber (not shown). The residual differential force, if any, is overcome by springs 21, 22.

,000 Intermediate the ends 15 and 20 of the piston 12 there i C is a flange 23 located between ports 24 and 25 formed I in the body 10. In this instance, the piston is oscillated by a hydraulic system including a valve 24 that alternately applies hydraulic fluid under pressure to either side of the flange 23 through ports 24 and 25. The piston 12 is sealed with respect to the bore 11 by seals 26 and 27.

The oscillating piston produces pressure pulses in the fluid in the pipeline in the form of pressure surges.

It should be noted that the mode of operation of the z fl AV T i -4generator is distinct from that of a double acting pump in that no liquid transfer takes place, there are no valves, and there is no change in the static pressure of the pipeline.

The piston can be oscillated by any convenient means and the gas balancing of the piston could be replaced by a spring, or by means such as the hydraulic accumulator described below in relation to the second embodiment.

Fig. 2 shows an alternative embodiment of the invention, in which the piston 12 is operated electromagnetically.

In this case, the piston 12 is actuated by means of a e osolenoid winding 28 surrounding the body 10 and functioning when energized, to draw the piston 12 downwardly as viewed in Fig. 2, to the limit of its :S.20 travel towards the end cap region 13 by which the 5065 generator is connected to the pressurised pipeline.

In the absence of energization of the solenoid, the piston 12 rests in the position illustrated in Fig.

2, and this is assisted by the presence of a small bore 29 which when the piston is stationary, allows O*O fluid to bleed past the piston 12 and into the upper region of the generator, thereby equalizing the pressure on each side of the piston. Equalization of the hydrostatic pressure on each end of the piston 12 in this way, considerably simplifies the operation of 41:. the generator.

As the end of the piston must during operation be maintained under a hydrostatic pressure substantially equivalent to that existing in the pipeline, in this embodiment the end cap 17 is connected with an hydraulic accumulator (not shown) pressurised to the required hydrostatic pressure. This accumulator may be of conventional construction, comprising a liquid chamber containing a gas-pressurised bladder. The accumulator will therefore tolerate the existence of liquid in the region of the assembly on that side of the piston 12, allowing the use of the bleeding referred to above, but will also allow the piston freely to move in either direction.

Devices of the kind described allow frequencies from approximately 10 to 200 Hz to be generated at levels higher in comparison with conventional underwater transmitters, which are totally immersed in the fluid, and can produce frequencies below the range of capability of such underwater transmitters. These frequencies can be generated at a differential pressure in the region of 10,000 to 20,000 kPa which goes is typical of pressures employed during leak testing Se of pipelines. By comparison underwater transmitters 20 have negligible differential pressure between the .0BO.* outside and inside of the transmitter housing with alll parts of the housing being subject to substantially the same pressures.

25 Many modifications may be made in details of design *SO and construction of the device without departing from the scope of the invention.

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Claims

1. Apparatus for generating acoustic waves in a pressurized fluid, said apparatus in use being external to said fluid, said apparatus comprising piston means, conduit means for placing one end of said piston means in communication with said fluid, pressure means in communication with the other end of said piston means to apply a force which substantially balances the force applied to said one end of the piston means by said pressurised fluid, and means not connected with I said piston means for oscillating said piston means.

2. Apparatus according to claim 1 wherein said pressure means comprises a source of gas pressure connected with said apparatus and communicating with said other end.

3. Apparatus according to claim 1 wherein said pressure means comprises an hydraulic accumulator connected with said lo other end

4. Apparatus according to claim 1 wherein said pressure means comprises primary resilient means biased against said other end.

Apparatus according to any preceding claim further comprising secondary resilient means biasing said piston means towards an intermediate rest position.

6. Apparatus according to any preceding claim wherein said means for oscillating said piston means comprises an electric solenoid.

7. Apparatus according to any one of claims 1-5 wherein said means for oscillating said piston means comprises hydraulic drive means. m i% a s

8. Apparatus according to any preceding claim wherein said fluid communicates with said one end and said other. end of said piston means.

9. Apparatus according to claim 8 wherein said piston means includes a passage therethrough whereby said fluid communicates said one end with said other end of said piston means.

Apparatus according to claim 8 wherein said piston means has clearance from the walls with respect to which it moves whereby said fluid communicates between said one end and said other end of said piston means.

11. Apparatus according to claim 8 further including additional conduit means whereby said fluid communicates with said other end of said piston means.

12. Apparatus according to any combination of claims 9, 10 and 11.

13. Apparatus for generating acoustic waves, substantially as described herein with reference to Fig. 1 of the accompanying drawings.

14. Apparatus for generating acoustic waves, substantially as described herein with reference to Fig. 2 of the accompanying drawings. DATED this 9th day of May 1990 SAIPEM AUSTRALIA PTY. LIMITED Patent Attorneys for the Applicant: HALFORD CO. i ;ic;c lrl~i~~ !Rr~''~--ii"(iriOtl! ,1:I L,