Clamp-on Flowmeters Research Articles

A virtual flow meter downstream of various elbow configurations

When flow meters are installed in disturbed flow conditions caused by pipe configurations such as junctions or elbows, significant measurement errors can occur. With existing knowledge of the flow conditions, those errors can be corrected using suitable calibration factors. This paper presents a surrogate model based on computational fluid dynamics simulation results that can predict velocity profiles downstream of single and double elbows in- and out-of-plane. The simulated flow profiles are decomposed into a fully-developed and a disturbed part, which allows changing the Reynolds number and roughness of the pipe wall without performing additional simulations. Furthermore, proper orthogonal decomposition and interpolation using piecewise linear splines enables the real-time evaluation of the model for a wide range of curvature radii and distances between the elbows. By incorporating a measurement principle, calibration factors for different flow meter designs can be predicted. The model is validated on the example of an ultrasonic flow meter by comparison with measurement data obtained from a clamp-on flow meter.

Flow disturbance compensation calculated with flow simulations for ultrasonic clamp-on flowmeters with optimized path arrangement

Ultrasonic clamp-on flowmeters (USCF) are popular among measurement technologies due to the versatility of applications, increasing accuracy, and easy, non-intrusive mounting, with the sensors being mounted directly on the external surface of the pipe. In industrial applications, installation space is usually restricted and therefore, flowmeters must be mounted often directly downstream of flow disturbances (FD). A major issue of USCF is the long inlet run needed downstream of FD to achieve a measurement within the specified accuracy. A configuration of two V-paths is proposed, axially rotated 90° relative to each other, that compensates for the flow error introduced due to disturbed flow conditions, independent of the rotational position of the flowmeter. Flow disturbance compensation (FlowDC) is achieved, i.e., accurate measurements within the specification of 2% flow rate accuracy, when the flowmeter is mounted as close as 2 pipe diameters (D) downstream of a FD. Computational fluid dynamics (CFD) are employed to generate rotationally independent correction factors that compensate for the error introduced from disturbed inlet conditions. An automated simulation method is developed to generate correction factors for 90° bend, out-of-plane bend, expansion, and contraction, at mounting distances from 2D to 100D, several flow rates, and rotational positions 0°, 90°, 180°, 270°. This study would be practically impossible with non-automated simulations or solely with measurements. In-house experiments were performed with an industrial clamp-on device at selected distances from the FD with the aim of verifying the simulation results. An independent field-test is presented that showcases the value of FlowDC in USCF applications. The automated simulations have the capability to simulate further FDs on-demand, with the aim of creating a database for the needs of the respective application in industry.

Measurement of Pipe and Fluid Properties With a Matrix Array-Based Ultrasonic Clamp-On Flow Meter.

Current ultrasonic clamp-on flow meters consist of a pair of single-element transducers that are carefully positioned before use. This positioning process consists of manually finding the distance between the transducer elements, along the pipe axis, for which maximum signal-to-noise ratio (SNR) is achieved. This distance depends on the sound speed, thickness, and diameter of the pipe and on the sound speed of the liquid. However, these parameters are either known with low accuracy or completely unknown during positioning, making it a manual and troublesome process. Furthermore, even when sensor positioning is done properly, uncertainty about the mentioned parameters, and therefore on the path of the acoustic beams, limits the final accuracy of flow measurements. In this research, we address these issues using an ultrasonic clamp-on flow meter consisting of two matrix arrays, which enables the measurement of pipe and liquid parameters by the flow meter itself. Automatic parameter extraction, combined with the beam-steering capabilities of transducer arrays, yields a sensor capable of compensating for pipe imperfections. Three parameter extraction procedures are presented. In contrast to similar literature, the procedures proposed here do not require that the medium be submerged nor do they require a priori information about it. First, axial Lamb waves are excited along the pipe wall and recorded with one of the arrays. A dispersion curve-fitting algorithm is used to extract bulk sound speeds and wall thickness of the pipe from the measured dispersion curves. Second, circumferential Lamb waves are excited, measured, and corrected for dispersion to extract the pipe diameter. Third, pulse-echo measurements provide the sound speed of the liquid. The effectiveness of the first two procedures has been evaluated using simulated and measured data of stainless steel and aluminum pipes, and the feasibility of the third procedure has been evaluated using simulated data.

Four-quadrant Characterization of Hydrodynamic Phenomena in a Low Specific Speed Centrifugal Pump

Objective: Identify and characterize subsynchronous hydrodynamics phenomena in a low specific speed centrifugal pump based on its four-quadrant characteristic curve. Materials: A 1.5 HP ITT Goulds pump instrumented with pressure transductors, an accelerometer, a torque sensor and a tachometer. Flow rate measurement was done with an ultrasonic transit time clamp-on flow meter. Methods: Time and frequency domain analysis with phase analysis were used to identify spectral components linked to hydrodynamic phenomena such as rotating stall and surge. Results and discussion: This work approaches an alternative method to calculate the phase angle using pressure signals without filtering. Related with hydrodynamic phenomena, the evidence collected suggests the presence of rotating stall in some operation points of the four-quadrant characteristic curve. Furthermore, in the third quadrant, rotating stall coexist with surge. Conclusions: The instrumentation and methods regarded in this work allow to collect evidence to identify in-phase and out of phase subsynchronous hydrodynamic phenomena. The classic cross-correlation-based method was improved to ease the diagnosis of subsynchronous phenomena by visual inspection. A new quantitative approach was introduced to detect subsynchronous phenomena, based on the Fourier analysis; it was validated with a case study for which the classical method was not suitable.

Исследование применения ультразвуковых расходомеров на технологической установке по переработке нефти

It is known that changes in the flow rate of the medium can directly affect the safety of the process of refining oil and petroleum products. Therefore, the use of high-precision flow meters is one of the safety barriers to prevent possible accidents and incidents. Unfortunately, the task of parametric measurement of the consumption of oil and petroleum products before and after their processing in most cases causes certain difficulties. For this reason, each specific measurement task should be approached from a different perspective, offering different means and methods of measurement, allowing to achieve the most reliable and accurate data on the measured flow rate. Operating conditions at the oil refineries place high demands on flow meters. Conventional orifice flow meters, which are often used to measure flow in the oil refineries, have certain disadvantages: they require frequent maintenance, process interruptions during installation, cause pressure losses in the pipe. Based on the experience of foreign companies in replacing insertion flow meters with clamp-on flow meters, it was decided to use non-invasive (non-contact) flow meters for medium measurement. The advantages of these flow meters are that there is no need to cut pipes, which practically eliminates the risk of leaks occurrence during installation. Also, the ultrasonic flow meter does not have direct contact with the measured medium, which allows avoiding contamination of both the flow meter itself and the medium, as a result, increasing the accuracy and durability of flow measurement at the site. Research objectives: substantiation of the possibility of operation of an ultrasonic flow meter at the oil refining site, recommendations for the use of various sensors, as well as selection of the optimal installation site for the device. The flow rate readings matched the previously established readings taken from the orifice meters. As a result, it is concluded that the ultrasonic flow meters can be used to measure the flow rate of stripped oil.

Suppression of Lamb wave excitation via aperture control of a transducer array for ultrasonic clamp-on flow metering.

During ultrasonic clamp-on flow metering, Lamb waves propagating in the pipe wall may limit the measurement accuracy by introducing absolute errors in the flow estimates. Upon reception, these waves can interfere with the up and downstream waves refracting from the liquid, and disturb the measurement of the transit time difference that is used to obtain the flow speed. Thus, suppression of the generation of Lamb waves might directly increase the accuracy of a clamp-on flow meter. Existing techniques apply to flow meters with single element transducers. This paper considers the application of transducer arrays and presents a method to achieve a predefined amount of suppression of these spurious Lamb waves based on appropriate amplitude weightings of the transducer elements. Finite element simulations of an ultrasonic clamp-on flow measurement setting will be presented to show the effect of array aperture control on the suppression of the Lamb waves in a 1-mm-thick stainless steel pipe wall. Furthermore, a proof-of-principle experiment will be shown that demonstrates a good agreement with the simulations.

Modeling Surface Roughness-Related Uncertainties of Leaky Lamb Wave Clamp-on Ultrasonic Flowmeters

Transit time clamp-on ultrasonic flowmeters (UFMs) are widely used in industry due to their ease of installation. However, these ultrasonic clamp-on flowmeters are also known to be less accurate than ultrasonic inline flowmeters because of the uncertainties induced by the installation process. Amongst the installation-related parameters that influence the measurement uncertainties, internal pipe wall roughness is one of the most significant but uncontrollable parameters. The effect of roughness on accuracy can be reduced by operating the flowmeter at a longer wavelength. This article investigates the effect of roughness on a clamp-on UFM using low-frequency (200 kHz) leaky Lamb waves. This results in operation at roughly five times lower frequency compared with conventional clamp-on UFMs. The ultrasonic signals of this leaky Lamb wave UFM were simulated using the 2-D finite-element (FE) analysis. Using the simulated signals, the roughness effects on the uncertainties were quantified. The simulation results show that the uncertainty related to pipe wall roughness of leaky Lamb wave UFMs is approximately half that of conventional UFMs for corroded pipe walls with rms value larger than 0.1 mm (0.2, 0.35, and 0.5 mm). Demonstration experiments were also carried out to detect leaky Lamb wave using an electromagnetic acoustic transducer (EMAT). The experiment shows that the simulation correctly captures all the physics of the wave propagation and that we, therefore, can trust the simulation results with incorporated roughness.

Accuracy improvement of a clamp-on type flowmeter utilizing a circumferential heater

Accuracy improvement of a clamp-on type flowmeter utilizing a circumferential heater

Ultrasonic Time Delay Difference Estimation With Analytic Signals and a Model System

In this brief, we present an approach for the subsample time delay difference estimation (TDDE) of two narrowband ultrasonic signals. TDDE with an accuracy in the low picosecond range and a low computational cost is essential to extend the application of compact ultrasonic clamp-on flow meters to flow velocities below 50 mm/s. A digitized sinusoidal measurement signal of an ultrasonic flow meter is transformed into an analytic signal by using a time-discrete Hilbert transform. The phase shift between two analytic signals is proportional to the time delay difference of the two ultrasonic waves. In our approach, the response of the measurement system is compared with that of a model system. The standard error for the TDDE is 5 ps for a sampling time of 100 ns without interpolation under typical operating conditions. The time delay difference is calculated with tight tolerances, paving the way to the measurement of the smallest volume flows with high accuracy.

Pipe geometry calibration measurements for the improvement of ultrasonic clamp-on flow meters

Clamp-on flow meters need a-priori knowledge of pipe geometry and material properties for their operation. Estimation of these properties may limit the accuracy of flow measurements. We are currently investigating the use of clamp-on flow meters based on matrix transducer arrays. Besides the benefits for flow measurement, these can be used for a-priori measurement of the required pipe properties. In the axial direction, average longitudinal wave speed and thickness of the pipe can be obtained from the dispersion curves of the Lamb waves in the pipe wall. In the circumferential direction, the arrival time of the fastest Lamb wave mode can be used to measure the pipe diameter. In our presentation, this method is discussed and proof of principle is provided through FEM simulations and measurements. The setup consisted of two pipes (outer diameters 64.5 mm and 93 mm), with two transducers (1 MHz) on top. The arrival time of the fastest Lamb wave mode was measured. For the outer diameter, the error between simulation and measurement was below 1% (small diameter) and below 3% (large diameter). The results suggest that further exploration of the unique possibilities of matrix transducers to accurately measure pipe parameters is opportune.

The Effect of Internal Pipe Wall Roughness on the Accuracy of Clamp-On Ultrasonic Flowmeters

Clamp-on transit-time ultrasonic flowmeters (UFMs) suffer from poor accuracy compared with spool-piece UFMs due to uncertainties that result from the in-field installation process. One of the important sources of uncertainties is internal pipe wall roughness which affects the flow profile and also causes significant scattering of ultrasound. This paper purely focuses on the parametric study to quantify the uncertainties (related to internal pipe wall roughness) induced by scattering of ultrasound and it shows that these effects are large even without taking into account the associated flow disturbances. The flowmeter signals for a reference clamp-on flowmeter setup were simulated using 2-D finite element analysis including simplifying assumptions (to simulate the effect of flow) that were deemed appropriate. The validity of the simulations was indirectly verified by carrying out experiments with different separation distances between ultrasonic probes. The error predicted by the simulations and the experimentally observed errors were in good agreement. Then, this simulation method was applied on pipe walls with rough internal surfaces. For ultrasonic waves at 1 MHz, it was found that compared with smooth pipes, pipes with only a moderately rough internal surface (with 0.2-mm rms and 5-mm correlation length) can exhibit systematic errors of 2% in the flow velocity measurement. This demonstrates that pipe internal surface roughness is a very important factor that limits the accuracy of clamp on UFMs.

Zero-Flow Offset Variation in Ultrasonic Clamp-On Flowmeters Due to Inhomogeneity and Nonlinearity of Pipe Materials

The objective of this paper is to measure the zero-flow offset variation in ultrasonic Clamp-on flowmeters produced by using pipes made of materials with a nonhomogeneous and nonlinear behavior. The evaluation of this phenomenon has been tested by the experimental measurement, the experiments consist of measuring the variation in the flow measurement when in “no-flow condition,” the transducers are moved along the pipe. Experimental results reveal that the reciprocity criterion is not fulfilled when nonhomogeneous and nonlinear pipe materials are used. Consequently, in these types of pipes materials, it is necessary to calibrate the offset when transducers are installed, and probably will need recalibration if the transducers are displaced to another position on the pipe. However, in installations, where it is not possible to stop flow in order to calibrate, the flowmeter will have an error in the measured value and this error will depend on the acoustic characteristics of the pipe material.

クランプオン式流量計の蒸気への応用

クランプオン式流量計の蒸気への応用

Sonar Metering Optimizes Production in Liquid-Loading-Prone Gas Wells

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 166652, ’Use of Sonar Metering To Optimize Production in Liquid-Loading-Prone Gas Wells,’ by C.A. Shields and M. Dollard, Marathon Oil UK, and S. Sridhar, G. Dragnea, and M. Illingsworth, Expro Meters, prepared for the 2013 SPE Offshore Europe Oil and Gas Conference and Exhibition, Aberdeen, 3-6 September. The paper has not been peer reviewed. This paper discusses the use of clamp-on sonar flowmeters to minimize losses associated with well testing and to gain the subsequent benefits seen with respect to production optimization and well deliquefication. Clamp-on sonar flowmetering is a nonintrusive technology that measures the flow velocity of the fluid stream. This intensive well-management strategy has assisted in reducing the production decline of the East Brae field in the North Sea. Introduction The East Brae platform (Fig. 1) is located 275 km northeast of Aberdeen in Block 16/3a in a water depth of 110 m. The reservoir comprises high- permeability sands deposited by turbidity currents. The reservoir has an average porosity of 17% and an average permeability of 558. md. The platform initially started producing condensate, while reinjecting the gas, in December 1993. Exporting of the gas began in 1994, and reinjection was phased out. The current topside holds a low- pressure (LP) separator (test separator) operated at 217 psig, a high-pressure (HP) separator (first-stage separator) currently operated at 406 psig, and second- and third-stage separators. It also includes a gas-processing and - dehydration plant, three gas-compression trains, and produced-water-processing facilities for discharge into the sea. There are currently 12 producing monobore wells on the East Brae platform. Former gas-injection wells have now been converted to producing wells. The wells are inclined up to a maximum deviation of 45°. The reservoir fluid is a retrograde gas condensate that exhibits compositional variation with depth. The reservoir has an active aquifer that has encroached into the producing layers as reservoir pressure has depleted through production. Background: Allocation and Well Testing On the East Brae platform, production allocation for the wells has typically been carried out by individual well tests of each well in the test separator on a monthly basis. The well test records the amount of oil and gas produced from a well during the first stage of separation. The oil and gas are then processed further in the plant. Some of the oil is vaporized into the gas phase as it is stabilized in lower-pressure separators, and some of the gas is liquefied as it is cooled and compressed. As a result of these equilibrium changes, the oil and gas rates exported from the platform (known as its “potentials”) that are attributable to a single well are not directly comparable with the oil and gas rates measured at the test separator for that well.

Joint industry project to investigate the potential benefits of clamp-on flowmeters in the oil and gas industry

Joint industry project to investigate the potential benefits of clamp-on flowmeters in the oil and gas industry

Vortex Shedder Fluid Flow Sensor

This paper was motivated by the possibility of extracting from a vortex-shedding strut, in addition to flow velocity V, information on fluid density rho or temperature T, and combining them to obtain mass flowrate. Shedder shapes were diamond and bluff polygon. These shapes are compared as vortex shedders in flowing air or water. V is obtained from the shedding frequency f. In water, V ranged from 0.5 to 4 m/s and, in air, from 0.3 to 15 m/s. Clamp-on ultrasonic transducers generated and, on the diagonally opposite side of the pipe, received the beam that obliquely traversed the wake of the shedder. A continuous-wave transmission across the fluid was modulated by vortices passing through the beam. The modulation frequency yielded f. In air, the bluff polygon yielded f over a 50 : 1 flow range, which was better than the diamond's flow range of 20 : 1. Whether the shedder was a diamond or a bluff polygon, and the fluid air or water, f correlated approximately linearly with the flow velocity V. Using one path of an ultrasonic tag clamp-on flowmeter system, the measured vortex-shedding frequencies were found to be in reasonable agreement with computational-fluid-dynamic predictions for diamond and for bluff-polygon struts. Collectively, the pipe Reynolds number (Re) range was 1000-200 000. With both shedders, operation was demonstrated in laminar- and turbulent-flow regimes. In water flow tests, rotating the diamond (aspect ratio=3) through 90deg about its axis, from broadside to airfoil, diminished the Strouhal number by 17%. When the diamond shedder was tested as a torsional density sensor in flowing air or water, no torsional transit time effect of V was observed, confirming for the first time a 1989 prediction. The negative result in flowing water implies that there were no attached bubbles or microbubbles

Application of ultrasonic clamp-on flow meters for in situ tests of billing meters in district heating systems

Three methods of using ultrasonic flow meters for the purpose of testing small- and medium-sized billing flow meters in district heating subscriber stations in situ were investigated. Four subscriber stations, six billing flow meters, and three ultrasonic clamp-on meters were part of the investigation. The obtained results show that clamp-on meters have measurement accuracy problems on the ordinary steel piping in the subscriber stations. When using well defined pipes mounted in series with the billing flow meters the results are clearly better; provided that the flow rates exceed a Reynolds number of approximately 10 000. In this flow region, billing flow meter deviations >±5% can be detected. A flow rate below this Reynolds number renders the method less reliable. The useful flow range is extended when using calibration data from the clamp-on meter to correct the measured data, making it possible to determine deviations >±10% in flow rates below a Reynolds number of 10 000. The investigation also showed that not all clamp-on meters are suited for this type of in situ test.

Acoustic transfer function of the clamp-on flowmeter

An angular spectrum approach is used to derive the acoustic transfer function of the clamp-on flowmeter. The flowmeter factor is calculated as a function of the position of the transducers by numerical evaluation of the transmission function. This method enables high measurement accuracy even in the case of the practically unavoidable mispositioning of the transducers. Simulations and measurement results show the influence of the transducer aperture and the pipe wall on the flowmeter factor.

A novel ultrasonic/thermal clamp-on flowmeter for low liquid flowrates in small diameter pipes

This paper reports on experimental work into the development of a clamp-on flowmeter for the measurement of low liquid flowrates in small diameter pipes. The meter is based on the interaction of ultrasound with changes in temperature generated by electrical heaters. Results are presented showing the performance of the meter in both laminar and turbulent flow regimes. The variation in response of the meter when mounted on vertical and horizontal pipes is demonstrated and discussed. The need for different heater powers, and the options for scaling results based on heater power are investigated. Repeatability measurements (including the effects of unclamping and reclamping the meter) are presented and compared with currently available devices.