Grantee Research Project Results
Final Report: Defect Detection in Water Pipelines Using Ultrasonic Guided Waves
EPA Contract Number: EPD12038Title: Defect Detection in Water Pipelines Using Ultrasonic Guided Waves
Investigators: Zhang, Li
Small Business: FBS Inc.
EPA Contact: Richards, April
Phase: II
Project Period: June 1, 2012 through May 31, 2014
Project Amount: $299,960
RFA: Small Business Innovation Research (SBIR) - Phase II (2012) Recipients Lists
Research Category: SBIR - Wastewater and Sustainable Infrastructure , Small Business Innovation Research (SBIR)
Description:
Phase II of this project, “Defect Detection in Water Pipelines Using Ultrasonic Guided Waves”, focused on the development of reliable and cost effective magnetostrictive sensors (MsS) for long range monitoring of steel pipes for corrosion and cracking. In order to inspect over a long distance of a pipeline, especially a coated or buried pipeline, low-frequency guided waves are required. However, current commercial low-frequency guided wave pipeline inspection systems may not have enough detection sensitivity for small defects less than 9% cross-sectional area (CSA). Higher frequency guided wave inspection provides better defect detection sensitivity, but has shorter inspection range. In this project, FBS successfully developed novel structural health monitoring (SHM) techniques and designed a long range guided wave pipeline monitoring system with MsS collars to improve defect detection sensitivity to less than 5% CSA.
Summary/Accomplishments (Outputs/Outcomes):
FBS started the project from a theoretical analysis of guided wave pipeline inspection methodologies. FBS determined now to employ MsS collars for guided wave generation in pipeline, because of low-cost, robustness, potential in SHM, and possible underground use if designed appropriately. Theoretical aspects of dispersion curves and wave structures for guided wave mode and frequency selection were first accomplished. A dispersion curve shows all of the possible guided wave modes that can be excited in a given structure. Based on the dispersion curves, wave structure profiles can be created to determine defect detection and size sensitivity. The wave structure profiles show how different types of energy, such as displacement and stress, are distributed throughout the thickness of the structure. For example, all of the energy can be concentrated at the surface or it can be evenly distributed throughout the thickness. The particle displacement can also be predominantly in or out of plane. For water loaded pipeline inspection, torsional waves with in-plane displacements should be employed to avoid guided wave energy leaking into water. The test points with little or no out-of-plane displacement were selected. Dispersion curves and wave structures were therefore calculated for bare pipes and for pipes with concrete coating.
Based on our theoretical analysis, FBS designed a suitable low-frequency, long range guided wave inspection system with MsS collars for both axisymmetric and focusing techniques. The MsS collars were mounted around the circumference of an 8” steel pipe and 4” steel pipe and were buried under ground. Guided wave inspection signals were continuously collected with the MsS collars for over one and a half years. To perform guided wave pipeline inspection, the collar is connected to a multi-channel signal generation system that is also used in an Olympus commercial guided wave piezoelectric nondestructive testing (NDT) pipeline inspection system, UltraWave LRT. Guided wave signal excitation and data acquisition were performed with the hardware and the corresponding controlling software for the UltraWave LRT. The UltraWave LRT system was developed with FBS assistance and FBS continues to cooperate with Olympus regarding this system.
In this project, FBS employed different approaches to improve defect detection sensitivity of long range guided wave inspection. The recently developed piezoelectric NDT low-frequency axisymmetric scan, synthetic focusing, and active phased array focusing inspection techniques have good sensitivity for defects with 5%~ 9% CSA. FBS has successfully combined SHM and axisymmetric scans, synthetic focusing, and active phased array focusing inspection techniques to significantly improve defect detection results for small defects 2%~5% CSA. Because temperature variation will affect guided wave signal, FBS developed temperature compensation algorithms to ensure that the signals are comparable. FBS also developed SHM based on the normalized mean square error (MSE) algorithm, which does not need temperature compensation when temperature variation is less than 200°F.
It was found that with more than one defect in a pipe, SHM synthetic focusing may not locate all of the defects accurately. SHM phased array focusing requiring a phased transducer array with variable time delays and amplitude controls for each channel can then be used to focus at one position for one particular input signal set. In order to scan the entire pipe, one needs to move the focal spot around the pipe to all the locations. Therefore, SHM phased array focusing is expensive and time consuming, even though it theoretically has the best defect detection sensitivity and accurate location analysis for multiple defects.
Conclusions:
In summary, FBS designed a low-frequency (<100kHz), 8-channel phased array torsional guided wave long range inspection system with MsS collars for small defect detection in a pipeline with or without concrete coating /water loading. The MsS would then only generate torsional waves to minimize the influences of coatings and water loading. When employing axisymmetric scans and focusing techniques, this system can reliably detect 5%~9% CSA defects in pipelines. If baseline data can be obtained, hybrid SHM axisymmetric scans and focusing techniques can be utilized to monitor for small defects (2%~5%) that could occur in pipelines.
Commercialization:
Supplemental Keywords:
Small defect detection, Guided waves, Long range pipeline inspection, Water pipe inspection, Magnetostrictive sensors.SBIR Phase I:
In-Situ Imaging of Water Pipelines Using Ultrasonic Guided WavesThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.