Applications of Ultrasonic Techniques in Oil and Gas

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W M Alobaidi et al, Ultrasonic Testing Guided Waves Nondestructive Testing NDT Pipe Inspection Pipe Thickness. Measurement,1 Introduction, Ultrasonic testing is one of the important techniques of nondestructive testing NDT It uses ultra high fre. quency sonic energy to locate and identify discontinuities in materials that are both on and below the surface of. the material such as metals or plastic commonly used to make pipes depending on the application 1 5. In 2007 D S Caravaca et al 6 studied polyethylene pipe joints and detection of improper preparation of the. joints using a phased array technique PAT The problems that arise with the electrofusion type of bonding used. for the pipe are analogous to those that occur in metal welds for steel pipe This paper aims to offer an ultrasonic. method for evaluating polyethylene pipe welds in pipeline used for gas and water distribution along with re. sults from both laboratory and field experiments 6. The sonic energy passes through the substrate There is a reduction in energy intensity as well as reflection of. the waves by the back wall of the material and where discontinuities are encountered The returning signal is. captured mathematically analyzed and presented on a screen with the resultant waveform showing the location. of defects on or within the substrate 7 11, In 2006 Yi Mei Mao and Pei Wen Que investigated the possibility of using a then new sonic signal process. ing method for inspection of oil pipelines They compared ultrasonic signals reflected from defect free pipe. lines and from pipelines with defects 12 and treated the recaptured waveforms with the Hilbert Huang trans. form HHT The results demonstrated the feasibility of using the technique to successfully locate and determine. the extent of discontinuities in oil pipes 12, Reflected signals are attenuated to different degrees depending on the type of interface they encounter An in. terface between a metal and a liquid presents a reduced reflection of the sonic energy whereas an interface be. tween a gas and a metal causes nearly 100 reflection of the sonic waves 7 The actual percentage of reflec. tion is dependent on the ratio of the parameters of certain physical properties between the two types of material. for example the ratio between the metal and the liquid substance at the interface 13 16. Cracks holes laminations slags cavities porosities bursts lack of fusion flakes lack of penetration and. other discontinuities that produce sharp boundaries are easily identified by ultrasonic testing Other types of. discontinuities that produce a more diffuse boundary are still identifiable because they will disrupt the sonic. waves in a detectable manner 7 17, In 2015 Wissam Alobaidi et al surveyed seven types of defects commonly found in pipe joint welds and.
five often used types of welds in manufacturing The correlation between each defect type and the NDT tech. nologies which best reveal the defects is presented in a table 17 The ability and shortcomings of four NDT. techniques commonly used for testing pipe are compared one of which is ultrasonic testing and the table re. ports whether each technique can detect surface or subsurface flaws The paper examines ways in which new. quality assurance techniques can be incorporated alongside the standard methods in order to overcome the. shortcomings of current methods with the aim to reduce labor costs and increase line output 17. Because the sensing mode of ultrasonic evaluation is a mechanical process the frequency range is limited to. avoid permanent damage to the targeted objects Frequencies used most often range from 0 1 MHz to 25 MHz. Although Ultrasonic testing UT is capable of identifying surface defects it is primarily used to detect and lo. cate discontinuities that are below the surface especially in metal parts UT is useful for other types of inspec. tion including welds wall thinning and surface defects as mentioned above 1 7. This review paper presents applications of and limitations of some ultrasonic techniques we will demonstrate. the fundamental theory of ultrasound and type of waves used we will thoroughly examine the inspection ap. proaches of the contact and angle beam techniques Approaches discussed focus on the measurement of defects. in oil and gas pipe manufacturing Primarily we are interested in determining the depth of the defect DD below. the material surface We will also address the limitations of scanning pipe that depend on the transducers used. contact for pipe body and angle beam for welds Moreover the paper presents a literature survey for applica. W M Alobaidi et al, tions of ultrasonic techniques in the pipe industry The primary aim for this review is to investigate possible fu. ture coupling of one of the ultrasonic techniques with other NDE techniques to develop a hybrid detection sys. tem for discontinuities This research study is an accumulation of the practical experience of the authors as well. as the practical experience represented by the reviewed papers. 2 Fundamental Theory of Ultrasonic,2 1 Ultrasound, Ultrasonic inspection uses sound as the source for testing the medium under consideration This is the same kind. of sound that creates the motion of our eardrums and allows us to hear The vibrations used for Ultrasonic Test. ing UT are very much higher frequency than what we can hear But just like any sound wave that moves. through the air the ultrasonic waves that are sent into metal will propagate through the solid medium When. these vibrations encounter interfaces between discontinuous materials which represent defects in the materials. and welds of pipes for example they will be reflected in predictable ways UT is a commonly used method in. industries for quality control purposes It is useful for testing the integrity of metal parts both before and after. forming into pipes The roll stock can be tested for invisible defects using straight beam ultrasonic testing al. lowing the material to be categorized as acceptable repairable or scrap before it is incorporated into pipes 7. 17 18 Because air does not transmit ultrasound waves as well as solids or gels the difficulty of introducing. the signals into metals is overcome by using water or grease as a conducting medium between the transducer. and the material to be tested 13, Ultrasonic testing is used both during the manufacturing of pipe and for inspection of in service pipelines. The particulars of pipeline insulation may require ingenious ways of getting the ultrasonic transducers into con. tact with the pipe to be tested For example in 2009 H Lei et al 19 were interested in developing a device for. assessment of the inner walls of underwater oil pipeline The device called a pig uses ultrasonic testing to dis. cover and determine the extent of corrosion within the pipe while storing the data on a hard disk Following re. trieval of the pig the recorded data is analyzed in order to determine the reduction in the oil pipe wall and to. identify areas of wall thinning which are then categorized using the American Petroleum Institute API stan. dards The authors claim perfect performance of the device 19. Waves commonly used are, Longitudinal Waves LW Another name for these waves is compression waves LW is the type of. sound wave that we hear and that is used in manual UT for testing the front end and tail end of the pipe. body and in coil UT for testing the integrity of the plates before they are formed into pipe The LW pushes. the molecules of the tested material in the same direction as the movement of the wave as shown in Figure. The velocity of the ultrasonic LWs is different in different metals for example their velocity through copper. is roughly 4760 m s making them the most rapidly propagating ultrasonic waves used in NDT Through the. analysis of wave velocity the depth of defect DD can be found 7 20 21 This is what we demonstrated in. Section 4 1, Shear waves SW Shear waves also known as transverse waves propagate more slowly and at shorter.
wavelengths than LWs at equal frequencies The particle motion is at right angles to the movement of the. wave as shown in Figure 2 SW is usually used for angle beam UT for example to detect discontinuities in. both the inner diameter and outer diameter of the weld in pipes As with LW the SW velocity varies with. the type of metal Some example velocities and corresponding metal types are Aluminum roughly 3040 m s. Steel 347 Stainless roughly 3100 m s When SWs reflect from an interface they sometimes become LWs 7. 20 22 23 This is demonstrated in Section 4 2, Rayleigh waves RW These waves which penetrate the material only to the sub surface distance of one. wavelength at any given frequency are also called Surface waves RW travels along the surface of the. tested material at velocities equal to those of SWs RWs are useful for detecting cracks that break the surface. of the tested part They are also useful for testing pieces with intricate rounded surface features Any defect. in zone as shown in Figure 3 would rest deeper than the wavelength of the test signal and would like. ly not be detectable by RW 7 20 22,W M Alobaidi et al. Figure 1 Graphical depiction of parallel motion response of material particles subjected to longitudinal ultrasonic. waves showing compression and rarefaction regions, Figure 2 Graphical depiction of perpendicular motion response of material particles subjected to shear ultrasonic. waves showing wavelength, Figure 3 Graphical depiction of limited detection area of Rayleigh waves showing how they are confined mostly to. the surface of a material,W M Alobaidi et al, In 2014 N P Aleshin et al examined various methods and devices for proficiently introducing ultrasonic.
signals into pipelines with thicknesses ranging between 6 mm to 20 mm They covered the choice between Sur. face and Plate wave modes for conducting these assessments 24. Lamb waves LMW Lamb waves are vibrations that occur from the upper to the lower surface up to sev. eral wavelengths in thickness of the tested material usually a plate composites or metals so they are also. called Plate waves They propagate not only through the full thickness of the tested material but are capable. of propagating from a single point of excitation over significant distances within the material as shown in. Figure 4 Because the LMWs travel through the solid in a way that is significantly like the behavior of elec. tromagnetic waves within a waveguide the characteristics of transmission vary from material to material. The velocity of LMWs is dependent on many factors including density plate thickness and the elastic. properties of the material being tested 7 25, In 2005 Kevin R Leonard et al explored use of helically propagating Lamb waves transmitted and recap. tured with longitudinal transducers They describe a meridional array scheme 26 used to test the concept of. using tomography to detect location and extent of discontinuities in pipes The research sample used wall thin. ning as the defect to be detected The study also investigated improved reconstruction programs for assessment. of helical array signals where the transmitters and receivers lie along circumferential parallel rings confirming. that frequency compounding reduces noise and artifacts leading to clearer imagery 26. Figure 4 Graphical depiction of ultrasonic lamb waves plate waves showing how they move through a test object. of a certain thickness which is directly related to the wavelength. 3 Transducers, There are five general categories of ultrasonic transducers used in NDE straight beam angle beam dual ele. ment delay line and immersion transducers Straight beam and angle beam transducers are used in pipe manu. facturing NDE procedures Usually the standardized inspection codes will determine the type of transducer the. manpower operator uses for a particular test In the case where there is no specification or customer require. ments the operator will select a suitable transducer based on prior experience and knowledge 27 29 Many. studies investigated ways to reduce the manpower needed for inspection of pipes by using ultrasonic waves and. also ways to reduce the number of transducers required for an inspection protocol in order to save capital ex. In 1998 M J S Lowe et al 30 studied the use of a single transducer for pulse echo testing of in service. pipeline in order to reveal corrosion in insulated pipes including oil pipes They removed only part of the pipe. insulation in order to reduce labor cost The study focused on selection of the most effective wave modes and. understanding the relationships between the size of a flaw and the signal strength when reflected The technique. was in field trials at the time of publication 30, In 2004 M H S Siqueira et al investigated the use of a single transducer to replace groups of transducers. that are used for rapidly inspecting pipe The research assessed the use of guided wave pulse echo conforma. tions with low ultrasonic signal to noise ratios S N together with processing via frequency bandpass filters. W M Alobaidi et al, and wavelet analysis 31 Their results confirmed the practicality of the concept showing up to 12 dB S N en. hancement of the recaptured signal allowing analysis even with otherwise unusably noisy signals 31. In 2006 Younho Cho et al 32 carried out a feasibility study of using guided sonic signals for remote moni. toring of stainless steel pipe They report that their experimental approach intended to allow them to optimize. Merging various NDE inspection techniques into the testing of objects is discussed Eventually it is hoped to find a suitable technique combined with ultra sonic inspection to deliver highly effective remote testing Corresponding author W M Alobaidi et al 275 Keywords Ultrasonic Testing Guided Waves Nondestructive Testing NDT Pipe Inspection Pipe Thickness Measurement 1

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