Pipeline scanning: Novel technology for detection of voids and internal defects in non-conductive buried pipes
May 18, 2007
Non-conductive buried pipe systems deteriorate over time under the action of various applied and environmental loads, chemical and microbiological induced corrosions, and differential settlements. A key for effective infrastructure management practices is the availability of reliable and timely inspection data that serve as the basis for the selection of proper rehabilitation/replacement methods. CCTV inspection is limited to detection of visible defects on the inner wall of the pipe. Defects hidden beneath encrustation, cement mortar lining or a thermoplastic liner, as well as voids immediately outside of the pipe, are currently difficult if not impossible to detect. It is proposed to develop a novel inspection technology, employing ultra-wideband (UWB) pulsed radar system, for detecting “below surface” defects, corrosion, and out-of-pipe voids in non-metallic buried pipes. This paper presents the theoretical foundation for the proposed method, followed by the results of a detailed numerical simulation. The numerical simulation employed custom-developed finite difference time domain (FDTD) code using a cylindrical coordinate system. Results from simulating the scanning of selected soil-pipe interface scenarios are presented. Experimental validation efforts of the proposed pipe scanning approach are also described.
The finite difference time domain (FDTD) method is widely used to simulate the transient electromagnetic phenomena in many areas of engineering including the study of antenna radiation patterns in communications, tumor detection in biomedical engineering and detection of buried objects in geotechnical engineering. The relative simplicity in implementing variety of material types, such as soils and biological materials (e.g., tissues) over a wide frequency bandwidth coupled with the ability to model structures with arbitrary geometry have gained the FDTD method increasing popularity.
A schematic diagram for the simulation model in shown in Figure 3. The simulation domain consist of a radial cross-section with a pipe layer (vitrified clay) surrounded by a layer of soil (sandy loam with approximately 10 % moisture content). The outer diametrical boundary is terminated by a 20 cell-thick PML layer. The antenna is represented by two perfect electric conductors (PEC), each 50 cells in length, separated by 60 degrees. The same antenna functions both, as transmitter and receiver, and hence termed ‘trans-receiver’. A circular source between the two PEC boundaries is excited with a differentiated Gaussian pulse of 80 picoseconds (ps) wide. The inner and outer radii of the pipe are 0.48 m and 0.56 m, respectively. The surrounding soil layer is about 0.1 m thick. Strictly speaking, electrical properties (e.g., dielectric permittivity) of geotechnical materials are frequency dependant (Francisca et. al, 2003). However, for simplicity the dielectric permittivity of the verified clay and soil were considered to be constants in this work and their values were set to be 3 and 10, respectively (Hippel et. al,1954).
Three different cases are studied during the numerical experiment. The first case represents an ideal pipe-soil section, while the remaining two cases represent non-ideal pipe-soil sections (i.e., presence of voids). In Case II, void approximately 4 cm thick is present within the soil surrounding the outside wall of the pipe, but the pipe wall was intact. In Case III, the pipe has wall thickness loss as well as a void running across both the soil and the pipe. Figure 4 shows snapshots of the pulse traveling inside an ideal pipe-soil cross-section. In Figure 4(a) the pulse is within the antenna, while in Figure 4(b) the pulse has traveled outside the antenna. In Figure 4(c) shows two individual reflected signals, one from the air-pipe inner wall interface and other from the pipe outer wall-soil interface.
- The numerical simulation presented in this paper demonstrated the advantages of using a directional antenna inside the pipeline in comparison with more conventional GPR systems. The increased directivity of the antenna and the use of ultra-short pulses enable a more detailed investigation (i.e., higher resolution) of the pipe wall while maintaining adequate penetration depths.
- The pipe wall along with the soil acts as a dielectric concave lens system to help focusing the reflected signal back into the antenna. Consequently, the signal to noise ratio is maximized, thus increases the reliability of the data collected.
- Since the same antenna functions both as a transmitter and receiver, the placement of antenna inside the pipe is straightforward. Rotation of antenna in the circumference direction coupled with longitudinal advancement along the pipe can be processed to produce a three dimensional contour map of the pipeline. These features are more difficult to incorporate with traditional GPR units, where the transmitter and receiver shape and size affect the operational frequency, so antenna configuration is not easily altered to suit survey configurations.
- The thickness of the pipe wall and other distinct layers (i.e., thermoplastic liner, cement mortar lining) can be measured with relatively high precision in a continuous manner. Forward processing algorithms are available to back calculate the dielectric constant of the various materials intercepted by the pulse, eliminating the need for special technical training and/or experience for interpreting the collected data.
- The transmitted signal has a broad bandwidth and thus the analysis could be carried within wide frequency range in a single run.
The authors are currently undertaking an experimental program to validate the results of the numerical model presented herein. An experimental setup placed at the TTC/CAPS nano-pulse laboratory is shown in Figure 6. Following the completion of the model validation, a prototype system will be constructed and tested in the TTC full-scale soil-structure interaction chamber. Results of these tests are expected to be available in the summer of 2007.
The UWB technology is introduced and the theoretical aspects involved in simulation of an UWB antenna, including the performance of a perfectly matched absorbing boundary condition, discussed. The results of a numerical simulation study conducted on a vitrified clay pipe-soil interface for condition assessment purposes are presented. It was demonstrated the UWB technology is capable of identifying voids in the pipe cross section and in the soil envelope surrounding it. In addition, the technology is capable of precise measurements of the pipe wall thickness in an automatic and continuous manner. The advantages of using UWB technology for buried non-ferrous pipes compared with existing methods (i.e., CCTV and GPR) are discussed. Other potential applications of UWB technology are also listed.
Andrews, J R, 2003, UWB Signals, Sources, Antennas and Propagation, Picosecond Pulse Labs Appl.Note, AN-14a, pp.3.
Francisca, F M & Rinaldi, V A, 2003, Complex Dielectric Permittivity of Soil–Organic Mixtures (20 MHz– 1.3 GHz), J. Envir. Engrg., Volume 129, Issue 4, pp. 347-357.
Hippel V & Arthur R, 1954, Dielectric Materials and Applications, M.I.T. Press, Cambridge, MA.
Loulizi, A., Al-Qadi, I.I. and Lahouar, S. 2003. Optimization of Ground-Penetrating Radar Data to Predict Layer Thicknessess in Flexible Pavements. ASCE, Journal of Transportation Engineering, Vol 129(1), pp. 93-99.
Robert W. Brocato, R W, 2004, FDTD Simulation Tools for UWB Antenna Analysis, Sandia Report, SAND2004-6577, Sandia National Laboratories.
Taflove, A & Hagness, S C, 2000, Computational Electrodynamics: The Finite-Difference Time- Domain Method 2nd edn, Artech House, Narwood. Taylor, J D, 1995, Introduction to Ultra-Wideband Radar System, RC Press LLC,Boca Raton.
Yee, K S, 1966, Numerical solution of initial boundary value problems involving Maxwell's equations in isotropic media,” IEEE Trans. Antennas Propagat., vol. AP-17, pp. 585-589.
More News and Articles
Mar 24, 2023
Innovative technologies remove pharmaceutical residues from wastewater
Every year on 22 March, World Water Day reminds us of the importance of one of the most important resources of life. Almost two-thirds of our planet is covered with water, but not even three percent is drinkable freshwater. Every …
Mar 22, 2023
Delivering sustainable solutions to solve water challenges
With British Water’s conference on creating a more sustainable water sector approaching, Stephen Kennedy, head of digital and innovation at MWH Treatment shares his views on celebrating recent successes in creating a more sustainable sector while also discussing the challenge …
Mar 20, 2023
Supporting the National Water Strategy through scientific research
This month, the federal government of Germany introduced the first National Water Strategy. “With this strategy, the federal government is shining a spotlight on the necessity of integrated water resource management, serving as a leading example of resource use in …
Mar 17, 2023
Trenchless manufacturer celebrates installation of 100,000th liner
SAERTEX multiCom®’s trenchless pipe relining product, SAERTEX-LINER, has been installed for the 100,000th time.
Mar 13, 2023
Spring collaborates with Microsoft and Impact X on water innovation
The water sector’s innovation centre of excellence – Spring - is collaborating with Microsoft and Impact X on a new initiative to make tools and funding available for start-ups to accelerate their companies.
Mar 10, 2023
State of Global Water Resources report informs on rivers, land water storage and glaciers
WMO reports on freshwater availability in a changing climate
Mar 08, 2023
Australia: Centenarian sewer gets after-dark upgrade
Over 100 years since its inception, Brisbane’s S1 Main Sewer has undergone a seven-year upgrade.
Mar 06, 2023
UKWIR gives access to hundreds of water sector research reports
UK Water Industry Research (UKWIR) is providing free access to over 1,000 of its water sector research reports aimed at helping to improve water and wastewater services for customers, and protecting the environment.
Mar 03, 2023
Sector must challenge public misconceptions through engagement
The water sector must tackle “unfair criticisms” by sharing more about the great work it delivers, Yorkshire Water’s chief executive, Nicola Shaw, told attendees at British Water’s Better Together reception in Hull.
Mar 01, 2023
World-first project to ‘self heal’ cracked concrete using sludge could save $1.4 billion repair bill to Australia’s sewer pipes
Water treatment sludge could be used to prevent 117,000 kilometres of sewer pipes in Australia from cracking in future, without any intervention by humans, helping to save $1.4 billion in annual maintenance costs.
Feb 27, 2023
Delaware Water Treatment Plant Opts for Penetron to Protect New Concrete Structures
The final 2022 commissioning of the Doe Run Road Water Treatment Plant enables the city of Newark, Delaware (USA), to increase the quantity and quality of the city's drinking water to better meet growing demand – and EPA guidelines. PENETRON …
Feb 24, 2023
Aussie Trenchless: the future of pipe rehabilitation solutions
Aussie Trenchless has been passionate about progressing future infrastructure opportunities and accomplishing superior outcomes since it was founded in 2014.
Erez Allouche (Trenchless Technology Center)
LA 71272 Ruston, Louisiana, USA
+1 318 257-4072
+1 318 257-2777