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

Abstract

Clamp-on transit-time ultrasonic flowmeters (UFMs) suffer from poor accuracy compared with spoolpiece 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. Index Terms-Clamp-on flowmeter, roughness, transit time, ultrasound, uncertainties. I. INTRODUCTION T RANSIT-time ultrasonic flowmeters (UFMs) are widely used in many industrial sectors, such as oil and gas, power, nuclear, process, water distribution, and chemical plants. These flowmeters measure flow velocity by calculating the difference in arrival time between the ultrasonic signals that are traveling with the flow (downstream signal) and against the flow (upstream signal). There are two common ways to install the ultrasonic transducers, "inline" and "clampon" (Fig. 1). The installation of the inline UFM requires cutting the pipe and subsequent insertion of a premanufactured and calibrated spool piece that contains integrated ultrasonic transducers. The clamp-on flowmeter only requires transducers to be mounted on the outside of the pipe wall to take a measurement. This clamp-on flowmeter has a number of Manuscript

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

“…Calculating the difference between the upstream and downstream arrival time. 6 The flow velocity is calculated using the transit time equation…”

“…Simulation and experiments have been carried out on the effect of roughness on the conventional clamp-on UFM [6]. In order to make an unbiased comparison with this previous study, the same roughness profiles with the same combination of roughness parameters were used in this paper.…”

“…The wave scattering due to the rough surface causes phase modulation and reduction in the amplitude of the signal and therefore reduces the accuracy of the measurements [4] [5]. [6] has discussed and quantified the effect of roughness due to wave scattering (non-flow profile related effect). It shows that there could be as much as 2% accuracy error induced for a moderately corroded pipe (a typical moderately corroded pipe has RMS height 0.2 mm [7]).…”

Design of Miniature Clamp-On Ultrasonic Flow Measurement Transducers

“…where kh is the flow profile correction factor which depends on the Reynolds number [2,7]; cw is the ultrasonic velocity in the liquid; D is the inner diameter of pipe and w  is the refraction angle in the liquid. Further correction factors can also be introduced for internal pipe roughness [8].…”

New semi three-dimensional approach for simulation of Lamb wave clamp-on ultrasonic gas flowmeter

“…Gas flow measurement has always been a key requirement in all industrial operations such as natural gas distribution, compressed air systems, air conditioning and process control. Ultrasonic flowmeters are one of the fast-growing technologies in these fields (Gu and Cegla, 2018;Sun et al, 2018a;Mousavi, 2019). Ultrasonic flow measurement with the transit time method includes invasive and non-invasive techniques (Fan et al, 2018;Peter Baldwin, 2012).…”