GB2082324A

GB2082324A - Flow monitoring apparatus

Info

Publication number: GB2082324A
Application number: GB8124396A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1980-08-20
Filing date: 1981-08-10
Publication date: 1982-03-03

Abstract

Apparatus for monitoring the operation of a fluid flow system comprises a microphone (4) for attachment to a conduit (5) of the system to sense the spectrum of noise produced by operation of the system e.g. by the flowing of the fluid and by operation of a pump (1) and associated motor (2). Noise signals from the microphone are fed to a micro-processor unit (7) which controls a visual display unit (9) so that the VDU displays the received spectrum. The MPU also cooperates with a store (8) which stores reference data relating to normal and abnormal noise spectra which may occur in the system. The store may also store previously occurring spectra from the system. Comparison of the currently-sensed spectrum with the stored data can initiate shutting-down of the motor (2) and/or sounding of an alarm in the event of a dangerous situation arising. <IMAGE>

Description

SPECIFICATION Monitoring apparatus This invention relates to the monitoring of conditions occurring in a fluid flow system and particularly to the detection of unusual conditions occurring in the fluid flow or in machinery associated with the fluid flow.

It is current practice to fit instruments to pipelines and other conduits for measuring various quantities such as the rate of fluid flow or the amount of vibration produced in the plant.

Furthermore, sensors are used to detect malfunction or danger, for example overloading, overheating or loss of pressure. Although these devices may be used to control the system or to switch it off to prevent danger, it is often desirable to include personal judgment, if only to avoid false action being taken due to instrument malfunction.

Automatic control systems suffer from the limitation that the devices which are used for monitoring can indicate only what has already happened, and it may then be too late to prevent damage to the apparatus.

An object of the present invention is to provide monitoring apparatus for a fluid flow system, such that the operation of the system is continually surveyed so that any change may be assessed and its likely cause deduced and its growth watched with a view to corrective action, preferably before damage occurs.

According to the invention, monitoring apparatus for monitoring the operation of a fluid flow system comprises means to sense continually the spectrum of noise produced by operation of the fluid flow system; means to store data relating to previous sensing of the spectrum and/or data relating to a reference spectrum; and means to compare the sensed spectrum with the stored date.

Preferably, a wide-band sensor is used which responds to vibration and sound waves from below audio frequencies up to the ultrasonic range. The sound energy in this spectrum will vary with the system conditions. For example, an increase in flow rate will increase the frequency of maximum noise. Pulsations will occur due to the rotation of pump blades, and the resulting sounds will have a repetition frequency which is related to the pump speed. Stones in the pumped fluid would result in erratic noises at this frequency.

Worn bearings and cavitation have characteristic sounds, and a loss of pumping power would result in a corresponding reduction in volume and frequency throughout the spectrum relative to the normal sound pattern. The frequencies produced by a blown or burning oil well will be quite different from the frequencies produced by normal oil flow.

In one application of the present invention the frequencies generated by each well of a multi-well oil platform are monitored and an alarm indication is given if abnormal frequencies are produced. The frequencies can be transmitted to a safe remote location, such as an emergency supply vessel or an adjacent platform, so that the status of each well can be continuously and reliably assessed. It is possible to obtain an early warning of possible trouble, which can be watched and, if confirmed, can be acted upon, preferably before danger arises.

Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 of the drawings illustrates the use of the in use with a domestic pumped water supply, Fig. 2 is a schematic diagram of an offshore oil production platform and associated risers, and Fig. 3 is a schematic section through a riser and detection apparatus attached thereto.

Fig. 1 of the drawings illustrates the use of the present invention to detect the operation of a submerged pump 1 and motor 2 in the depths of a borehole 3 from which a domestic water supply is obtained. It is necessary to protect the motor against supply faults, overload and/or running dry and to guard against failure of the pump due, for example, to overheating or bearing failure.

Instead of using many sensors for sensing the various parameters, only one wide-band sensor is used. This comprises a microphone 4, preferably of the "electret" type, which is attached to a pipe 5 at a convenient location and is connected via an amplifier 6 to a micro-processor 7 which together with a program store 8 may be constituted by what is known as a "home computer". The store 8 contains data relating to normal noise frequency patterns which are to be expected, and also abnormal noise frequency patterns which may occur. The processed output of the MPU 7 is fed to a visual display unit 9 and/or controls a motor power supply switch 10 which switches off the supply in the event of an abnormal spectrum being sensed. The MPU output may also control an alarm (not shown).The display unit 9 may comprise a cathode ray tube on which is displayed a histogram showing the amplitude of the noise at various frequencies.

Referring to Figs. 2 and 3, the invention may be used to monitor conditions on an oil production platform 28, which may have twenty or more risers 11, each bringing oil from a particular area underground. A "blowout" preventer (not shown) is fitted to control the production rate and to enable shut-down to be effected if danger occurs.

It is not unknown for the blowout preventer to fail, in which case it is necessary to drill the appropriate area separately in order to relieve the pressure and to allow the defective riser to be capped. It is therefore essential to have a measure of the flow in each individual riser and this measurement must be very reliable and readily available, after a catastrophe, to assist rescue or recovery personnel.

Conventional flowmeters are not reliable and would not withstand a fire. However, use can be made of the present invention by providing a microphone on each riser and by comparing their outputs in order to detect any changes in the flow or in the condition of the riser, for example the build-up of wax.

Each microphone 13 is fixed to a concrete casing of the respective steel riser 11 and can be located ten or more metres under the water level so that it would still be intact even if the production rig were destroyed. Several microphones can be employed on each riser in case one fails, and a pre-amplifier 14, a microprocessor 1 5 and a program store 1 6 can all be self-contained in a housing 20, clamped or otherwise fixed to the riser. The housing can also contain a modulator 21 and a transmitter 22 for transmitting the micro-processor output up to the surface. A power supply 23 is provided for energising the modulator and the transmitter.

Preferably the housing 20 is filled with a resin to withstand corrosion and pressure. Each housing 20 may be made of gunmetal for long life.

The power supply 23 can be primary cells or storage batteries which are trickle-charged. The power required by each sensor and associated circuitry may be only 0.01 watt and a battery life of five years could be expected. For use in sea water, the power supply could conveniently comprise sacrificial electrodes 25 of suitable metals arranged to form a primary battery.

The transmission is preferably by ultrasound, via a transducer 24, using known techniques.

The broad band of frequencies (typically 100--100,000 Hz) converted by the microphone can be processed by known technology, the technique which is preferred being dependent upon the specific application. Thus, for flow information the energy contained in various bands in the spectrum, such as 100--500 Hz, 600-2KHz, 2.1 K-50KHz, 5.1 KHz-20KHz, 21KHz--SOKHz and above 51 KHz, is noted periodically. A change in the flow rate or the ratio of gas to liquid will result in a shift in the frequency spectrum.

In addition, any specific frequency caused by cavitation or pump vibration can be followed accurately by a frequency-agile filter. Thus the speed of an induction motor driving a pump can be accurately assessed and compared with the mains frequency feeding the motor to monitor the slip of the motor, which is a measure of the mechanical loading. This can be related to the power supplied to the motor and, if necessary, safety action can be instituted. The noise from a worn bearing can be detected, and subsequent wear monitored in order to obtain the maximum safe life from the bearing.

Each housing 20 may be tightly strapped to the wall of the respective riser so that it can be readily removed for replacement. No modification of the plant is necessary in order to instal the apparatus.

The date from each sensor may be transmitted through the sea from the respective transducer 20 to a receiver 30 on a ship 26 or on another platform. A further receiver 27 can be provided on the platform 28 itself, and connected to a display 29 in the control room to provide information indicating that the system is operative. For this purpose, signals received due to normal oil flow in a riser can be employed.

An array of indicator lamps may be provided in each display, each lamp representing a condition associated with a riser. If the amplitude of response in a selected frequency range from any sensor exceeds a preset value, the appropriate indicator can be illuminated. An audible alarm may also be sounded. A tape recording may be made as a permanent record of the status of the wells.

The units can be self-checking.

It has been thought that the noise developed -' by one well blowing might travel along the pipes and other structure so that all of the sensors would detect that noise, thereby making it impossible to determine which well has blown.

However, the natural frequency of a platform structure is typically 3-4Hz, so that the transmission of noise in the frequency range which is being monitored, for example 10-20KHz, would be severely attenuated and would not, therefore, be detected after spurious transmission through the structure to other microphones.

It will be appreciated that the amount of information that can be extracted from the broad band measurements is limited only by Ine operator's ability to carry out meaningful tests and to observe the results obtained, for example, in the clearing of blockages, etc. The recording of the sound spectrum in known conditions and the comparison with the present state not only provides a method which shows that satisfactory conditions still pertain, but also enables comparison with incipient fault conditions and so gives early warning of a failure. The continuous monitoring allows the operator to log frequency data received in the period leading up to a failure, and hence to recognise the approach of such failure at an earlier stage next time. It also enables the pin-pointing of the cause after a catastrophe has occurred.

Claims

1. Monitoring apparatus for monitoring the operation of a fluid flow system, comprising i means to sense continually the spectrum of noise produced by operation of the fluid flow system; means to store data relating to previous sensing of the spectrum and/or data relating to a reference spectrum; and means to compare the sensed spectrum with the stored data.

2. Apparatus as claimed in Claim 1, wherein the sensing means includes a microphone for attachment to a conduit of the fluid flow system.

3. Apparatus as claimed in Claim 2, wherein the comparison means comprises a microprocessor unit.

4. Apparatus as claimed in Claim 3, including a transmitter; and a modulator coupled to the output of the microprocessor unit to modulate the transmitter in accordance with the microprocessor output.

5. Apparatus as claimed in Claim 4, wherein the transmitter includes a transducer for transmitting ultrasonic signals representing the microprocessor output.

6. Apparatus as claimed in Claim 4 or Claim 5, wherein the transmitter, the modulator, the microprocessor, the microphone and the storage means are encapsulated in synthetic resin material.

7. Apparatus as claimed in any preceding claim, including a visual display unit for displaying the sensed spectrum.

8. Apparatus as claimed in any preceding claim, including switching means operable in response to the output of the comparison means to terminate a supply of power to a motor of the fluid flow system in the event of an abnormal condition arising in the system.

9. An oil production platform including apparatus according to any one of Claims 1 to 7.

10. Apparatus as claimed in Claim 1 and substantially as hereinbefore described with reference to Fig. 1 or Figs. 2 and 3 of the accompanying drawings.