RU2470274C1 - Method and device to measure pressure inside pipelines - Google Patents

Abstract

FIELD: measurement equipment.

SUBSTANCE: invention relates to acoustic diagnostics and can be used in manifold oil and gas pipelines. The pressure of the product pumped along the pipeline is measured by the method of spectral analysis of process vibrations of the pipe with the help of an information-measurement system comprising sensors of vibrations joined by cable lines with a system computer of a dispatcher's station. The method to measure pressure inside the pipeline consists in detection of frequency of internal pipe resonances with subsequent calculation of pressure using the formula that sets the functional connection between frequency and pressure. To implement the method specified above a device is also proposed, which comprises sensors of vibrations with buffer amplifiers, installed on the surface of the pipeline, a multiplexor, a filter and an analogue-to-digital converter. At the outlet of the analogue-to-digital converter there is a multichannel analyser installed with a logic of quick Fourier transform.

EFFECT: expansion of device functional capabilities.

2 cl

Description

The invention relates to acoustic diagnostics for use in stationary monitoring systems of oil and gas pipelines.

Known devices for controlling the density or pressure of a liquid, comprising an acoustic oscillation generator, a plane acoustic wave generator and a sound pressure meter, which are supplemented by a pneumatic container and a device for moving a sensitive element. The density or pressure of the controlled medium is judged by the distance from the acoustic oscillation generator to the surface of the sensitive element, on which a stepwise change in the phase of the standing wave occurs [1].

The disadvantage of this method and device is the use of a standing sound wave, which excludes the possibility of its use inside a pipeline with a rapidly moving flow of oil.

There are also known methods and devices for measuring the density or pressure of petroleum products, based on measuring the frequency of resonant vibrations of sensitive elements such as a tuning fork immersed in the medium [2]. These methods require the presence of a resonator, oscillation sensors of the resonator, and an oscillating excitation generator. The resonant sensitive element interacts with the medium in which the density or pressure is measured; as a result of interaction with the medium, its resonant frequency changes. The functional relationship between the resonance frequency and pressure is assumed to be known, which makes it possible to calculate pressure from the measured frequency. The disadvantage of this method and device is the possibility of sticking to the walls of the resonator of the solid phase of the oil product, which violates its performance.

The closest in technical essence and combination of features to the claimed is a method and device for non-contact pressure measurement in a vessel [3]. The method consists in the fact that a resonant sensitive element of magnetically conductive material is placed inside the container, made in the form of a plate rigidly connected to a rod vibrating along the length, and acoustic longitudinal vibrations are excited in it using an electromagnetic excitation source in the form of a solenoid. The pressure inside the vessel is measured by the resonant frequency of oscillations of the sensing element. To connect the terminals of the solenoid winding to an electronic measuring circuit, a sealed current lead with a bushing is installed in the vessel wall. The disadvantage of this method and technical implementation, from the point of view of the task, is the placement of the sensing element inside the pipeline in a rapidly moving oil product stream. In main pipelines, the placement of any devices inside the pipe is not allowed, since these devices interfere with the flow of the product and contribute to the deposition of a solid phase on the pipe walls. Another disadvantage of the prototype design is the presence of through holes in the pipe for the conclusions of the solenoid, which significantly complicates the production technology and reduces the operational reliability of the pipeline.

The objective of the present invention is to provide a method and device that allows you to measure the pressure of the medium inside the pipeline, free from these disadvantages of analogues and prototype.

This goal is achieved by the proposed method for measuring pressure inside the pipeline and a device that implements this method.

1. A method of measuring pressure in main oil and gas pipelines using the natural noise of the pumped product is that vibration sensors are installed on the outer surface of the pipeline and with their help a noise signal spectrum containing the spectral vibration components of the natural resonant frequencies of the pipeline is recorded in a computer, the pressure calculated by the formula establishing the functional relationship between pressure and the frequency of resonant harmonics.

2. The device for measuring pressure in the main oil and gas pipelines according to claim 1, containing vibration sensors with buffer amplifiers installed on the surface of the pipeline at fixed distances of the order of several kilometers and connected to the system computer via communication lines through a multiplexer, band-pass filter and an analog-to-digital converter (ADC) ), is characterized by the fact that a high-resolution microprocessor-based spectrum analyzer with a fast Fourier transform algorithm emitting proper s resonant frequency of the pipeline on which the computer system is calculated pressure in each section of the pipeline.

The advantage of the proposed method of measuring pressure, which eliminates the disadvantages of analogues and prototype, is the absence of through holes in the pipe wall and any devices inside the pipe, which increases operational reliability and increases the service life of the measuring device.

A device for implementing this method of measuring pressure in certain sections of the pipeline has an advantage over analogues and prototype in the simplicity of design, efficiency of power supply and a minimum set of technical means to solve the problem.

The simplicity of the design is achieved by the fact that in each section of the pipeline in which it is necessary to measure the pressure of the product, a minimum set of technical means is installed, including only a vibration sensor with a buffer amplifier. Piezoceramic type sensors are used mainly, which do not require power supply. The microcircuit buffer amplifier, which is necessary for matching the sensor with the communication line, has very low power consumption. The remaining devices that are part of the measuring circuit: a bandpass filter, an ADC, a microprocessor analyzer of the noise signal spectrum, are connected by communication lines through the multiplexer to the system computer and are on the side of the system computer in one copy, since they are common to the entire chain of primary sensors installed along the route gas pipeline.

The necessary accuracy of pressure measurement, of the order of 1% of the measuring range of 25 MPa, is provided by a strict and unambiguous dependence of the frequency of the own resonant harmonics of the pipe on pressure. The temperature dependence of the resonance harmonics is taken into account by introducing corrections to the pressure measurement result. Pipe temperature is measured by separate sensors.

The operation of the device for measuring pressure inside the pipeline is as follows. The noise of the flow of the pumped product creates vibration of the pipe wall in the frequency band from 0.05 to 10 kHz with a relatively uniform spectrum. In this spectrum, individual components are distinguished in amplitude, due to the intrinsic resonance harmonics of the pipe. The harmonic frequency depends on the stress state of the pipe wall due to internal pressure. The effect of the dependence of the resonant frequency on mechanical stress is equivalent to the excitation of a stretched string, in which the frequency of natural vibrations increases with increasing tension. Vibration sensors sense pipe vibrations and transmit them to the communication line through a matching buffer amplifier. From the full spectrum of noise, the filter distinguishes the band in which the tube's own resonant frequencies are located. The pressure dependence of the resonance harmonics of a pipeline can be described by an empirical formula, for example, in the form of a power polynomial of the second degree.

The resonant frequencies of the pipeline with a steel pipe diameter of about 1 m are in the range from 0.3 to 2 kHz. After filtering, the noise signal together with resonant harmonics is converted to digital form using the ADC. From the ADC output, the signal is fed to the input of a microprocessor spectrum analyzer with a high resolution of 0.1 Hz. Using the fast Fourier transform algorithm, the spectrum analyzer extracts the resonant harmonics of the pipeline oscillations with the largest amplitude and measures the exact value of their frequency. The data from the spectrum analyzer is transferred to a system computer in which the internal pressure is calculated, for example, according to the formula of the power polynomial of the second degree:

P = α · Δf + bΔf ² + cf ₀ (20-T),

where P is the measured pressure;

a, b, c - calibration coefficients;

Δf is the increment of the frequency of the resonant harmonic;

f ₀ is the nominal value of the frequency;

T is the temperature of the pipe wall.

In this formula, the coefficients a and b characterize the steepness of the dependence of the resonance frequency on pressure, and the coefficient c the frequency dependence of temperature. The requirements for high resolution spectral analysis in frequency are due to the relatively small increment of the resonance frequency in the full pressure range of about 30–70 Hz at a nominal value of 1600 Hz.

Laboratory bench tests of the prototype device confirmed its operability, reliability in the full range of influencing environmental conditions and the expected accuracy of pressure measurements at the level of 1% of the range.

Information sources

1. RU 2045029, 09/27/1995 "Device for measuring the density of a liquid."

2. RU 2124714, 01/10/1999 "Device for measuring the density of a liquid."

3. RU 2273007, 03/27/2010 "Device for non-contact pressure measurement in a vessel" (prototype).

Claims (2)

1. A method of measuring pressure in main oil and gas pipelines using the natural noise of the pumped product is that vibration sensors are installed on the outer surface of the pipeline and with their help a noise signal spectrum containing the spectral vibration components of the natural resonant frequencies of the pipeline is recorded in a computer, the pressure calculated by the formula establishing the functional relationship between pressure and the frequency of resonant harmonics. 2. The device for measuring pressure in the main oil and gas pipelines according to claim 1, containing vibration sensors with buffer amplifiers installed on the surface of the pipeline at fixed distances of the order of several kilometers and connected to the system computer via communication lines through a multiplexer, band-pass filter and an analog-to-digital converter (ADC) ), is characterized by the fact that a high-resolution microprocessor-based spectrum analyzer with a fast Fourier transform algorithm emitting proper s resonant frequency of the pipeline on which the computer system is calculated pressure in each section of the pipeline.