Girth weld cracking is one of the main failure modes in oil and gas pipelines; girth weld cracking inspection has great economic and social significance for the intrinsic safety of pipelines. This paper introduces the typical girth weld defects of oil and gas pipelines and the common nondestructive testing methods, and systematically generalizes the progress in the studies on technical principles, signal analysis, defect sizing method and inspection reliability, etc., of magnetic flux leakage (MFL) inspection, liquid ultrasonic inspection, electromagnetic acoustic transducer (EMAT) inspection and remote field eddy current (RFDC) inspection for oil and gas pipeline girth weld defects. Additionally, it introduces the new technologies for composite ultrasonic, laser ultrasonic, and magnetostriction inspection, and provides reference for development and application of oil and gas pipeline girth weld defect in-line inspection technology.

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Literature Review: Theory and Application of In-Line Inspection Technologies for Oil and Gas Pipeline Girth Weld Defection

A broad overview of the field of laser‐ultrasonics is presented. This overview draws from developments at the Industrial Materials Institute of the National Research Council of Canada as well as elsewhere. The principles of generation and detection are presented, stressing a few key characteristics of laser‐ultrasonics: the material is actually the emitting transducer and transduction is made by light, thus eliminating any contact. These features carry both advantages and limitations that are explained. Another feature, which has been an impediment, is actually the complexity of the “laser‐ultrasonic transducer”, but in spite of this complexity, it can be made very reliable for use in severe industrial environments. It also can be very cost effective for a number of applications. Three applications that are now used in industry are presented: the inspection of polymer matrix composites used in aerospace, the measurement of thin layers in microelectronics and the thickness gauging of hot steel tubing in production. Technological aspects, such as interferometer design, detection lasers and others are also discussed. As an overall conclusion, laser‐ultrasonics that was for a long time a laboratory curiosity has definitely now made its transition to industry. Nevertheless, developments should continue to improve performance, to make it well adapted to specific inspection or characterization tasks and more affordable.

Laser‐Ultrasonics: From the Laboratory to Industry

This paper studies the ultrasonic detection and evaluation of internal volume defects in metals using laser generation and electromagnetic acoustic transducer (EMAT) detection. A finite element model is developed to simulate the interaction of laser-generated ultrasonic waves with the defect in the material. Not only have the directly scattered shear waves been observed, but also the mode-converted creeping waves on the defect surface. A noncontact laser-EMAT ultrasonic testing experimental system was successfully applied to validate the observed phenomena in the simulation results. The defect can not only be detected and located by the directly scattered shear waves, but can also be quickly evaluated with a new method based on quantitative time-of-flight analysis of the directly scattered waves and the mode-converted waves on the defect surface.

A study of internal defect testing with the laser-EMAT ultrasonic method

This paper studies the optimal inspection of autonomous robots in a complex pipeline system. We solve a 3-D region-guarding problem to suggest the necessary inspection spots. The proposed hierarchical integer linear programming optimization algorithm seeks the fewest spots necessary to cover the entire given 3-D region. Unlike most existing pipeline inspection systems that focus on designing mobility and control of the explore robots, this paper focuses on global planning of the thorough and automatic inspection of a complex environment. We demonstrate the efficacy of the computation framework using a simulated environment, where scanned pipelines and existing leaks, clogs, and deformation can be thoroughly detected by an autonomous prototype robot.

On Optimizing Autonomous Pipeline Inspection

The prototype implementation of a permanently installable high temperature crack monitoring system is described. The system uses an array of waveguides to excite shear horizontal (SH) waves on the surface of the component that is to be inspected. The waveguide is made of poorly heat conducting stainless steel so that it can sustain a large temperature gradient. This ensures that conventional piezoelectric transducers can be used at one end of the waveguide to excite ultrasonic waves while the other end is in contact with the component to be monitored which is situated in a harsh environment at elevated temperature (up to 600 °C). Different crack monitoring strategies using SH waves are discussed. Simulation and experimental results for the array prototype on notched plates are presented. Furthermore, experimental results on samples containing fatigue cracks are shown and measurement results that were collected from a notched plate in a furnace at 550 °C are also presented.

High temperature ultrasonic crack monitoring using SH waves

A method is presented for imaging the detailed structure of surface-breaking tight cracks from the surface opposite to the cracks The technique combines laser-ultrasonics and data processing with an improved version of the Fourier-domain Synthetic Aperture Focusing Technique (F-SAFT) The key point of this study is to use laser-generated shear waves, which interact very effectively with the crack roots Ultrasonic images of the stress corrosion cracks, having depths of typically 05 mm and widths of less than 005 mm, are successfully reconstructed and compared with results from liquid penetrant testing

Laser-ultrasonic inspection of surface-breaking tight cracks in metals using SAFT processing

A new method to obtain a detailed image of surface‐breaking tight cracks by using laser‐ultrasonics is proposed. The surface opposite the cracking is scanned by the generation and detection lasers. Detected signals are processed by the Fourier‐domain Synthetic Aperture Focusing Technique (F‐SAFT). The point of this study is to use the laser‐generated shear waves, which interacts very effectively with the crack roots. A detailed image of the stress corrosion cracks, having depths of typically 0.5 mm and widths of less than 0.05 mm, is successfully reconstructed.

Visualization of Surface‐Breaking Tight Cracks by Laser‐Ultrasonic F‐SAFT

Ultrasonic diffraction pattern at a crack tip and crack depth sizing based on the diffraction are studied by using laser‐generated bulk waves Directivity patterns oriented essentially along the normal for the diffracted longitudinal wave and essentially at 45 (deg) for the diffracted shear wave for any incident angles is obtained A laser‐ultrasonic system combined with time‐of‐flight (TOFD) analysis is produced and demonstrates accurate crack sizing on an artificial slot having a variable depth from 0 mm to 10 mm An improvement of signal‐to‐noise ratio by split spectrum processing (SSP) is also suggested

Laser Ultrasonic Study of Crack Tip Diffraction

A laser‐ultrasonic method based on the shadowing effect is used for sizing and locating surface‐breaking tight cracks in metals The two laser spots are separated by a fixed distance to detect ultrasound propagating at oblique incidence with respect to the sample surface The laser spots are scanned along the same line across the path of cracks on the cracking surface or opposite surface The amplitude of the longitudinal or shear waves specularly reflected from the backwall is extracted from each signal to construct an amplitude profile In the presence of a crack, the profile shows regions of reduced amplitude due to shadowing of the direct or reflected beam from the backwall The sharp amplitude drop and the gentle signal recovery observed are well predicted by a model of crack tip diffraction The crack depth can be simply determined by considering the immediate vicinity of the amplitude drop Results are shown on a stainless steel sample having a variable depth slot as well as on a sample containing actual surface‐breaking tight cracks having widths of less than 30 μm

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A. Fukumoto

Papers

Laser-ultrasonic inspection of surface-breaking tight cracks in metals using SAFT processing

Visualization of Surface‐Breaking Tight Cracks by Laser‐Ultrasonic F‐SAFT

Laser Ultrasonic Study of Crack Tip Diffraction

Characterization of Surface‐Breaking Tight Cracks Using Laser‐Ultrasonic Shadowing