Inspection Robots in Oil and Gas Industry: a Review of Current Solutions and Future Trends <s> II. INSPECTION METHODS AND SENSORS <s> Introduction to NDE, P.J. Shull Liquid Penetrant, F.A. Iddings and P.J. Shull Ultrasound, P.J. Shull and B.R. Tittmann Magnetic Particle, A. Lindgren, P.J. Shull, K. Joseph, and D. Hagemaier Eddy Current, P.J. Shull Acoustic Emission, W.H. Prosser Radiology, H.E. Martz, Jr., C.M. Logan, and P. J. Shull Active Thermography, J.W. M. Spicer and R. Osiander Microwave, A.J. Bahr, R. Zoughi, and N. Qaddoumi Optical Methods, D.D. Duncan, J.L. Champion, K.C. Baldwin, and D.W. Blodgett Index <s> BIB001 </s> Inspection Robots in Oil and Gas Industry: a Review of Current Solutions and Future Trends <s> II. INSPECTION METHODS AND SENSORS <s> Oil and gas transmission pipelines are critical items of infrastructure in providing energy sources to regions and countries. Steel pipes are commonly used which can be subject to both internal and external corrosion. This paper presents an advanced nondestructive inspection technique for detection of oil-gas pipeline corrosion defect. The Pulsed Eddy Current (PEC) method has been successfully applied in corrosion detection of unburied gas pipeline without removing the insulation. First, the principles of pulse eddy current method is pointed out then, the pulsed eddy current test on a pipe is simulated by Maxwell software to obtain optimum test parameters. To test the new technique, some artificial defects are fabricated on the inner surface of a gas pipe to simulate different corrosions phenomena in practice. Three isolation layers are applied to the pipe in order to show the efficiency of PEC in the detection of wall thinning areas without removing the insulation. <s> BIB002 </s> Inspection Robots in Oil and Gas Industry: a Review of Current Solutions and Future Trends <s> II. INSPECTION METHODS AND SENSORS <s> Magnetic flux leakage (MFL) detection is one of the most popular methods of pipeline inspection. It is a nondestructive testing technique which uses magnetic sensitive sensors to detect the magnetic leakage field of defects on both the internal and external surfaces of pipelines. This paper introduces the main principles, measurement and processing of MFL data. As the key point of a quantitative analysis of MFL detection, the identification of the leakage magnetic signal is also discussed. In addition, the advantages and disadvantages of different identification methods are analyzed. Then the paper briefly introduces the expert systems used. At the end of this paper, future developments in pipeline MFL detection are predicted. <s> BIB003
For the inspection purposes in oil and gas industry, a number of onboard NDT sensors are used to detect corrosions and cracks. According to different types of sensors, the most commonly applied inspection technologies can be roughly divided into four classes, i.e., visual inspection, ultrasonic inspection, magnetic inspection and eddy current inspection. Visual inspection is one of the oldest and popular inspection means. At the very beginning, experienced engineers used their naked eye to check the condition of assets. But now, cameras have allowed the inspection robots have the ability to pursue a view of the structure. When in visual degradation environment, LEDs can be used to deal with the absence of proper illumination. Visual inspection is simple and it is one of the easiest inspection techniques to perform. However, it is only suitable for detecting damages on the surface and the inspection quality is sensitive to illumination  . Besides the visual inspection mentioned previously, the ultrasonic sensor is another primary sensor found on many inspection robots. Ultrasonic sensors can emit and receive the ultrasound, which is propagated into the material. Cracks can be detected by measuring the time difference between the generated and reflected ultrasound. The comparison of these two signals tells the location and size of the crack. There are many advantages in using ultrasonic sensors, such as high accuracy, high sensitivity and suitability for monitoring all kinds of materials. However, it will not work when the defect lays along the line of wave travelling BIB001 . Magnetic sensitive sensors work with ferrous material assets. After applying a magnetic field on these facilities, most of the magnetic flux lines will go through these metal materials. If there is a defect, magnetic flux lines will be bent. Some of the magnetic flux lines will leak out. The magnet sensitive sensors can detect the magnetic leakage field. The detected signal can be analysed to reveal the changes in structure. This method can realise relatively high-speed inspection and very good sensitivity to pitting. However, it can only work for ferromagnetic materials and the sizes of defects detected are very limited BIB003 . Eddy current inspection is similar to magnet sensitive inspection in some ways. It uses eddy currents generated by coils. When there is a crack in the structure, the eddy current will be altered. At the same time, the impedance of the coil will also be affected. Monitoring the change in impedance in the coils can tell the condition of the facility. This method is sensitive to surface detects and can be used to inspect multilayer structures. Nonetheless, it is very susceptible to magnetic permeability changes and cannot detect the defects parallel to the surface BIB002 . Through the sensor technologies discussed above, we can see that each sensor has its own advantages and disadvantages. When choosing the proper sensor for inspection robots, the application scenario and constraints need be taken into consideration.