Tomographic methods are used with ultrasonic guided wave wall thickness monitors to provide two-dimensional maps of the wall thickness throughout a monitored area. Tomographic monitoring systems are typically configured with 16 to 32 non-intrusive ultrasound transducers positioned in predetermined patterns for optimal coverage and resolution. Other monitoring systems have much fewer transducers, positioned according to the pipe geometry and wall area of main concern. Although these systems are not optimized for wall thickness mapping, the same or similar tomographic methods can improve analysis and interpretation of the datasets they produce. Algorithms are sought for implementation in responsive, interactive software for browsing and analysis of recorded wall thickness monitoring data. Simple tomographic algorithms are also desirable for use in embedded software. A "light weight" tomographic algorithm is outlined, and a prototype implementation is tested against a proven full-scale tomography software package. The two approaches produce similar results on small datasets corresponding to wall thickness monitoring systems with few transducers installed. For the larger datasets generated for high resolution wall thickness mapping, the reference software is superior in terms of both computational load and accuracy.

Abstract Throughout the oil and gas industry corrosion and erosion damage monitoring plays a central role in managing asset integrity. This paper describes a technology for monitoring of wall-loss rates across continuous areas of pipeline wall. Permanently installed ring arrays of non-invasive ultrasonic transducers delimit a monitored section. The arrays transmit and receive guided ultrasonic waves that insonify the entire pipe section. The received signals are processed by a numerical algorithm to produce a two-dimensional map of wall thickness loss. The algorithm measures wall thickness loss differentially, detecting change between an initial and a current state of the pipe. Wall loss can be estimated with accuracy beyond the pipe manufacturing tolerances. Moreover, a strategy that combines a robust temperature compensation scheme with the intrinsic stability of electromagnetic acoustic transducers (EMATs) is used to address the intrinsic thermal dependency of all ultrasonic technologies, always experienced in field applications. Full-scale experiments are presented demonstrating maximum-depth estimation uncertainty below 0.5 % of initial wall thickness with excellent thermal stability up to 175 °C.

Detection and monitoring of corrosion and erosion damage in pipe bends are open challenges due to the curvature of the elbow, the complex morphology of these defects, and their unpredictable location. Combining model-based inversion with guided ultrasonic waves propagating along the elbow and inside its walls offers the possibility of mapping wall-thickness losses over the entire bend and from a few permanently installed transducers under the realm of guided wave tomography (GWT). This paper provides the experimental demonstration of GWT of pipe bends based on a novel curved ray tomography algorithm and an optimal transducer configuration consisting of two ring arrays mounted at the ends of the elbow and a line of transducers fixed to the outer side of the elbow (extrados). Using realistic, localized corrosion defects, it is shown that detection of both the presence and progression of damage can be achieved with 100% sensitivity regardless of damage position around the bend. Importantly, this is possible for defects as shallow as 0.50% of wall thickness (WT) and for maximum depth increments of just 0.25% WT. However, due to the highly irregular profile of corrosion defects, GWT generally underestimates maximum depth relative to the values obtained from 3-D laser scans of the same defects, leading in many cases to errors between 3% WT and 8% WT.

Ultrasonic guided wave tomography (GWT) methods for the detection of corrosion and erosion damage in straight pipe sections are now well advanced. However, successful application of GWT to pipe bends has not yet been demonstrated due to the computational burden associated with the complex forward model required to simulate guided wave propagation through the bend. In a previous paper [Brath et al., IEEE Trans. Ultrason., Ferroelectr., Freq. Control, vol. 61, pp. 815-829, 2014], we have shown that the speed of the forward model can be increased by replacing the 3-D pipe bend with a 2-D rectangular domain in which guided wave propagation is formulated based on an artificially inhomogeneous and elliptically anisotropic (INELAN) acoustic model. This paper provides further experimental validation of the INLEAN model by studying the traveltime shifts caused by the introduction of shallow defects on the elbow of a pipe bend. Comparison between experiments and simulations confirms that a defect can be modeled as a phase velocity perturbation to the INLEAN velocity field with accuracy that is within the experimental error of the measurements. In addition, it is found that the sensitivity of traveltime measurements to the presence of damage decreases as the damage position moves from the interior side of the bend (intrados) to the exterior one (extrados). This effect is due to the nonuniform ray coverage obtainable when transmitting the guided wave signals with one ring array of sources on one side of the elbow and receiving with a second array on the other side.

The effective life management of pipelines in the Oil and Gas industry requires monitoring techniques that can probe an extended section of a pipe and can sample its state with relatively high frequency so as to implement corrosion mitigation in a timely fashion. Due to the typically low corrosion rates, 1 mm/yr or less, the monitoring technique must be sensitive to wall-thickness changes that are in the order of a few tens of micrometers. Ultrasonic guided wave tomography (GWT) with permanently installed sensors offers an attractive compromise between sensitivity and area coverage by combining the long range propagation characteristics of guided ultrasonic waves with the principles of model-based inversion. Here, the pipe section to be monitored is delimited by two ring arrays of ultrasonic transducers that encircle the pipe and measure guided wave signals after traveling inside the pipe wall from one array to the other. The signals are interpreted by advanced GWT algorithms to form a wall thickness map of the entire pipe section. In this paper we review the principle of operation of GWT, discuss its performance, and present the first long term field results obtained for a pipe in a deepwater rig in the Gulf of Mexico. The field results show that GWT based on EMAT transduction provides highly stable wall thickness estimations even in the presence of multiphase flow inside the pipe undergoing a wide range of pressure and temperature fluctuations.

Throughout the oil and gas industry corrosion and erosion damage monitoring plays a central role in managing asset integrity. This paper introduces a novel technology for continuous monitoring of wall-loss rates in pipelines. A pair of permanently installed ring arrays of ultrasonic transducers encircles the pipe and delimits the section to be monitored. The arrays excite and receive guided ultrasonic waves that travel inside the pipe wall and insonify the entire pipe section. The received signals are then processed by advanced tomographic algorithms to produce a point-by-point map of wall thickness loss between the arrays. The algorithms are designed to detect changes between two material states of the pipe and use differential measurements to eliminate time-independent experimental uncertainties. As a result, wall loss can be estimated with accuracy beyond the pipe manufacturing tolerances. Moreover, a strategy that combines a robust temperature compensation scheme with the intrinsic thermal stability of electromagnetic acoustic transducers (EMATs) is used to address signal instabilities caused by typical thermal fluctuations experienced in field applications. Full-scale experiments are presented demonstrating maximum-depth estimation accuracy better that 0.5% of wall thickness with excellent thermal stability up to 175 °C.

Abstract This paper discusses the latest developments in non-invasive corrosion/erosion monitoring with guided wave tomography for subsea and topside asset management. There are many technologies available for corrosion/erosion monitoring topside, but much fewer subsea. The subsea environment is difficult to access for instrument maintenance and verification of monitoring data, and many pre-installed systems have proven to be of little use. A technology for non-intrusive wall thickness monitoring based on ultrasonic guided waves has been available for permanent installation topside and subsea for some years. A subsea retrofit solution has also been delivered. The system utilizes ultrasonic guided Lamb waves to monitor wall thickness over extended areas; much larger than any spot measurement system with a comparable number of transducers. The ClampOn CEM® received a Spotlight on Technology award at the 2012 OTC. Monitoring data from this instrumentation platform are well suited as basis for tomographic processing to produce two-dimensional wall thickness maps of pipe sections. A technique has been established that holds promise of unprecedented capability for wall thickness monitoring, offering previously unavailable real-time imaging of eroding wall surfaces. Points of minimum wall thickness can be located, their depths can be measured, and their developments over time can be tracked.

Corrosion under insulation (CUI) is a common cause of pipeline failure in the oil and gas industry. Its detection with conventional inspection techniques is challenging due to the presence of the insulation layer and a protective metallic cladding that prevent direct access to the pipe surface. Currently, several techniques are being developed to detect sections of wet insulation since water is a necessary precursor to corrosion. Among these, guided microwave testing has been proposed as a cost-effective approach to screen an extended length of pipeline. 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. The inspection is performed by launching a microwave signal from an array of antennas permanently installed at one location along the pipeline. Wet insulation is then detected according to the radar principle; water results in the partial reflection of the incident microwave signal owing to the permittivity contrast between dry and wet insulation. This paper reviews the underpinning principles of long-range guided microwave testing and presents a new study aimed at demonstrating the sensitivity of the technique in the presence of complex water saturation gradients inside the insulation.

Recent improvements in tomographic reconstruction techniques generated a renewed interest in short-range ultrasonic guided wave inspection for real-time monitoring of internal corrosion and erosion in pipes and other plate-like structures. Emerging evidence suggests that in most cases the fundamental asymmetric A0 mode holds a distinct advantage over the earlier market leader fundamental symmetric S0 mode. Most existing A0 mode inspections operate at relatively low inspection frequencies where the mode is highly dispersive therefore very sensitive to variations in wall thickness. This paper examines the potential advantages of increasing the inspection frequency to the so-called constant group velocity (CGV) point where the group velocity remains essentially constant over a wide range of wall thickness variation, but the phase velocity is still dispersive enough to allow accurate wall thickness assessment from phase angle measurements. This paper shows that in the CGV region the crucial issue of temperature correction becomes especially simple, which is particularly beneficial when higher-order helical modes are also exploited for tomography. One disadvantage of working at such relatively high inspection frequency is that, as the slower A0 mode becomes faster and less dispersive, the competing faster S0 mode becomes slower and more dispersive. At higher inspection frequencies these modes cannot be separated any longer based on their vibration polarization only, which is mostly tangential for the S0 mode while mostly normal for the A0 at low frequencies, as the two modes become more similar as the frequency increases. Therefore, we propose a novel method for suppressing the unwanted S0 mode based on the Poisson effect of the material by optimizing the angle of inclination of the equivalent transduction force of the Electromagnetic Acoustic Transducers (EMATs) used for generation and detection purposes.

Guided wave tomography is being developed as an effective tool for continuous monitoring of corrosion and erosion depth in pipelines. A pair of transmit- and receive-ring arrays of ultrasonic transducers encircles the pipe and delimits the section to be monitored. In curved ray tomography (CRT), the depth profile is estimated from the time delay matrix, Delta tau, whose i j-th entry is the phase traveltime difference between the current and baseline signals measured between transducers i and j of the transmit and receive-ring arrays, respectively. Under perfectly stable experimental conditions, the non-zero entries of Delta tau are only due to the occurrence of damage and provide a reliable input to CRT. However, during field operation, Delta tau can develop non-zero entries due to a number of environmental changes ranging from temperature variations to degradation of transducer-pipe coupling and transducer intrinsic performance. Here, we demonstrate that these sources of instability can be eliminated by exploiting the spatial diversity of array measurements in conjunction with EMAT transducer technology which is intrinsically stable owing to its non-contact nature. The study is based on a full-scale experiment performed on a schedule 40, 8" diameter, 3 m length steel pipe, monitored with two EMAT ring arrays. It is shown that for an irregularly shaped defect the proposed method yields maximum depth estimations that are as accurate as single point ultrasonic thickness gaging measurements and over a wide temperature range up to 175 degrees C. The results indicate that advanced inversion schemes in combination with EMAT transduction offer great potential for continuously monitoring the progression of corrosion or erosion damage in the oil and gas industry.

Recently, the use of guided wave technology in conjunction with tomographic techniques has provided the possibility of obtaining point-by-point maps of corrosion or erosion depth over the entire volume of a pipeline section between two ring arrays of ultrasonic transducers. However, current research has focused on straight pipes and little work has been done on pipe bends and other curved tubular structures which are also the most susceptible to developing damage. Tomography of curved tubes is challenging because of the complexity and computational cost of the 3-D elastic model required to accurately describe guided wave propagation. Based on the definition of travel-time-preserving orthogonal parametric representations of curved tubes, this paper demonstrates that guided wave propagation and scattering can be approximated by an equivalent 2-D acoustic model which is inhomogeneous and elliptically anisotropic. Numerical methods to solve the full wave equation and predict ray paths and travel times are introduced and applied to the case of a bend. Particular emphasis is given to the shortest-path ray tracing method, which is applied to the 2-D model to compute ray paths and predict travel times of the fundamental flexural mode, A0, propagating across a curved pipe. Good agreement is found between predictions and experiments performed on a 220-mm-diameter (8-in-diameter) (D) pipe with 1.5D bend radius. The 2-D model also reveals the existence of an acoustic lensing effect which leads to a focusing phenomenon also confirmed by the experiments. The computational efficiency of the 2-D model makes it ideally suited for tomographic algorithms.

Throughout the oil and gas industry corrosion and erosion damage monitoring play a central role in managing asset integrity. Recently, the use of guided wave technology in conjunction with tomography techniques has provided the possibility of obtaining point-by-point maps of wall thickness loss over the entire volume of a pipeline section between two ring arrays of ultrasonic transducers. However, current research has focused on straight pipes while little work has been done on pipe bends which are also the most susceptible to developing damage. Tomography of the bend is challenging due to the complexity and computational cost of the 3-D elastic model required to accurately describe guided wave propagation. To overcome this limitation, we introduce a 2-D anisotropic inhomogeneous acoustic model which represents a generalization of the conventional unwrapping used for straight pipes. The shortest-path ray-tracing method is then applied to the 2-D model to compute ray paths and predict the arrival times of the fundamental flexural mode, A0, excited by a point source on the straight section of pipe entering the bend and detected on the opposite side. Good agreement is found between predictions and experiments performed on an 8" diameter (D) pipe with 1.5 D bend radius. The 2-D model also reveals the existence of an acoustic lensing effect which leads to a focusing phenomenon also confirmed by the experiments. The computational efficiency of the 2-D model makes it ideally suited for tomography algorithms.

The transmission of guided ultrasonic waves across corrosion or erosion damage encodes information about the defect depth. Tomography maps the depth profile from multiple transmission experiments performed under different insonification angles by solving the so-called inverse problem; the accuracy of the depth estimation being dependent on the range of angles available for the inversion. Practical application of tomography to tubular structures, such as pipes and bends, requires the use of two ring arrays of ultrasonic transducers at the two ends of the pipe section to be inspected. However, such a configuration leads to an insufficient angular coverage when considering the signals that travel along the shortest temporal path between a pair of transducers. This paper introduces a general inversion method that extends the range of insonification angles by exploiting the information carried by the signals that wrap around the pipe multiple times before reaching the receive array, thus resulting in superior image resolution and increased depth estimation accuracy. In addition, to address typical thermal fluctuations encountered during continuous monitoring, a strategy that combines a temperature compensation scheme with the intrinsic thermal stability of electromagnetic acoustic transducers (EMATs) is developed and tested with full-scale experiments performed on a schedule of 40, 8″ diameter steel pipe instrumented with two ring arrays of EMAT transducers. It is shown that for an irregularly shaped defect the proposed inversion method yields maximum depth estimations that are as accurate as single point ultrasonic thickness gaging measurements and over a wide temperature range up to 175°C. The results indicate that advanced inversion schemes in combination with EMAT transduction offer great potential for continuously monitoring the progression of corrosion or erosion damage in the oil and gas industry.

Abstract The ClampOn DSP Well Collision Detector is a real time ultrasonic monitoring system for detection of a drill bit in the proximity of existing wells. The system provides real time data during drilling and thus supplements collision risk analyses and positioning data. The monitoring system lends from ClampOn's well-proven series of ultrasound sensors for sand monitoring, PIG detection, and leak detection. The working principle of the Well Collision Detector is discussed briefly. An application example from a drilling operation is shown to illustrate the utility of the system.

Detection and monitoring of corrosion and erosion are essential prognostic means in preserving material integrity and reducing the life-cycle cost of industrial infrastructure, ships, aircrafts, ground vehicles, pipelines, oil installations, etc. Even topside, the operating conditions can be extremely difficult, facing problems like pipe surface roughness, fluid loading, temperature variations, and a host of other factors that make development of a robust wall thickness assessment tool a challenging task. Deploying a monitoring system subsea makes the application even more demanding when factors such as high pressure and limited access must be taken into account. The ClampOn Corrosion-Erosion Monitor has already been successfully installed at several locations topside and is now in its final stages of the subsea development. Non-invasiveness, high repeatability and high coverage are among its advantages, making it an excellent candidate for subsea use. The technology is based on the dispersion of ultrasonic guided wave modes. By using electromagnetism these waves can be transmitted through the pipe wall without the sensor being in direct contact with the metallic surface. It is installed on the outer pipe wall to produce real-time wall thickness information, not as a spot measurement, but as a unique average path wall thickness.

Abstract Corrosion and erosion detection and monitoring are essential prognostic means of preserving material integrity and reducing the life-cycle cost of industrial infrastructure, ships, aircraft, ground vehicles, pipelines, oil installations, etc. Spatially dynamic pipeline monitoring systems have to necessarily face extremely hostile conditions of operation including surface roughness, fluid loading issues, temperature variations, and a host of other factors that make development of a robust wall thickness assessment tool a challenging task. This paper describes the working of Corrosion-Erosion Monitor (CEM) - an online, real-time path based thickness assessment tool that deploys a set of transducers over a given pipe area, and utilizes a dispersion based principle to assess wall thickness loss. This instrument was developed keeping the needs of the oil, gas and petrochemical industry in mind, both upstream and downstream, but because it essentially monitors reductions in wall loss, it can find applications in many other industries. Experimental work and field trials provide very promising results pertaining to the functionality of the CEM system, and some of these results have been discussed in this paper. The CEM can be used as a permanent installation or as a relocatable instrument, a result of the development of so called "dry contact" transducers. It is installed on the outer pipe wall to produce real- time pipe wall thickness information, not as a spot measurement, but as a unique average path wall thickness.