The Effect of Bends on the Long-Range Microwave Inspection of Thermally Insulated Pipelines for the Detection of Water

Abstract

The detection of corrosion under insulation is an ongoing challenge in the oil and gas industry. An early warning of areas of pipe at risk of corrosion can be obtained by screening along the length of the pipeline to inspect the insulation layer for the presence of water, as water is a necessary precursor to corrosion. In a recent paper [Jones et al. in J. Nondestruct. Eval. 2011] we have shown that long-range detection of water volumes can be achieved with microwave signals, using the structure of the clad and insulated pipeline as a coaxial waveguide, with water volumes presenting an impedance contrast and producing reflections of the incident microwave signal. To achieve long-range inspection of complex pipe networks it is essential that the selected guided wave signal can transmit through structural features such as bends and supports whilst retaining a sufficient signal-tonoise ratio. This paper therefore presents a study on the effects of bends on the propagation of the fundamental Transverse Electromagnetic (TEM) mode. First, numerical simulations are used to study the amplitude of the TEM mode transmitted through a bend, as a function of bend radius and angle. It is found that for typical industrial bends with a bend angle of 90 • and bend radii between three and five times the pipe diameter, the transmission coefficient varies between 96% and 93%, respectively. As the bend angle varies from 0 to 180 • the transmission coefficient oscillates with maxima around 0, 90 and 180 • and minima at around 45 and 130 • . Moreover, the amplitude of the oscillation decreases as the bend radius increases. Then, experimental results on a 12 diameter waveguide with a length of 7 m are used to validate the simulated results and are found to be in excellent agreement.

Propagation Characteristics and Defect Sensitivity Analysis of Guided Wave From Single Excitation Source in Elbows

“…Demma et al [18] used finite element (FE) analysis to study the transmission and reflection coefficient of guided wave in a bend and indicated that the amplitude of reflected signal increases with the cross sectional area loss of the pipe caused by the defect [19]. A comprehensive study of the effects of bending angles on the transmission coefficient of T mode was reported in [20] by R. E. Jones using simulation and experimental methods. Nishino et al [21] detected defects in circumferential welds before and after pipe bend using the T(0,1) mode ultrasonic guided wave and a wideband laser ultrasonic system was used to describe the propagation phenomena of wideband guided wave in bended pipes with time-frequency analysis [22].…”

An Experimental Model for Guided Microwave Backscattering from Wet Insulation in Pipelines

“…This thesis instead focuses on a recent guided microwave method that has been introduced to screen an extended length of pipeline for the presence of wet insulation from a single sensor position [11,12]. Here, the pipe and metallic cladding naturally form a large coaxial transmission line in which the insulation acts as a dielectric and supports the propagation of microwave signals.…”

“…Laboratory experiments conducted on a 6" diameter pipe with 3" thickness insulation have shown that water volumes equivalent to 5% of the insulation annulus cross-sectional area are readily detectable [11]. Importantly, the microwave signal can travel through bends and supports with limited attenuation [12] thus opening the possibility for monitoring complex pipeworks such as those present in refineries and other petrochemical plants.…”

Identification of defects in HDPE piping thermal fusion welds based on microwave inspection and true density measurement

“…Microwaves are part of the electromagnetic spectrum with wave lengths in the centimeter range and frequencies from 0.3 to 300 GHz [1]. Microwave technique is well suited to characterize the properties of nonconductive or weakly conductive materials in noncontact way.…”