INNOVATIVE NONDESTRUCTIVE ULTRASONIC TESTING AND ANALYSIS

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additives can be added to the FRP piping when they are used to transfer high flammable. products such as oil and gas products, With the FRP pipes market growth and expansion inspection procedures must be. developed for pipes structural health monitoring However inspection of composite. materials is challenging compared to metals and alloys Composite materials are. anisotropic nature with poor electrical conductivity low thermal conductivity and high. acoustic attenuation 4 Defects can be introduced during different manufacturing stages. of composite materials These defects are commonly occurring because of misapplication. of materials improper installation practice and poor quality of manufacturing These. defects reflect on the fabricated FRP pipe stiffness and strength The most common. defects found in composite materials are foreign object damage fiber splitting fiber. fracture fiber waviness impact damage resin micro cracks pores and fiber matrix. debonding 6 7 In order to avoid any FRP pipe catastrophic failures that could lead to. life losses or environmental disaster these defects should be identified and characterized. at early stages The most common methods for FRP pipe inspection are either visual. inspection or pressure testing The former method often underestimates the risk as the. method is subjective and some defects can be missed In the pressure testing method the. system should be isolated which adds to the inspection cost FRP pipes can be inspected. and evaluated during their fabrication and in service life using Nondestructive Testing. NDT techniques 4, Low frequency Ultrasonic Testing UT systems and techniques specifically designed for. FRP provide rapid and accurate one sided measurements 8 UT technique is practical. and optimally used for inspecting FRP pipes when representative samples with the. laminate type weight fraction and fiber orientation are used in the calibration process. Special care should be taken during this process because the FRP pipe surface finish and. quality of coupling affects the interpretation of the results Single point assessment is not. entirely reliable and not recommended hence multiple point inspections are used to map. large areas that provide accurate information to characterize the FRP pipes Multiple. point inspections allow the distribution of defects to be represented using statistical. parameters In addition to identifying defects UT has also been shown to provide. information that relates to characteristics and properties of the FRP 8 The same. readings that may be used to identify defects can be used for the FRP mechanical. properties characterization This paper deals with the use of UT readings as a. nondestructive approach to determine modulus properties of FRP pipe sections. 2 TYPES OF DEFECTS IN FRP PIPES, Defects in FRP pipes occur at different stage of the FRP pipe service life These defects. are found commonly due to improper installation practice misapplication of materials. and poor manufacturing quality Common defects as porosity inadequate resin curing. Foreign Object Inclusion FOI and dry spot can be found in the fabrication stage. However defects as impact damage wear damage cracks and chalking can be found in. installation and service life stages Full review for typical defects types cause of the. defects and their time of occurrence can be found in 4 9 The fabrication and. manufacturing techniques affects the frequency of the defects occurrence in FRP pipes It. can be noticed that in the hand lay up process results in high levels of porosity. dimensional tolerance limitations and inconsistent fiber orientations It was found that. centrifugal casted pipes only can be used to process relatively low fiber content FRP. pipes when compared to other fabrication methods that limits the ultimate pressure. obtained at comparable wall thickness It is worth mention that the filament winding. process is the most common method for manufacturing FRP pipes as it is automated. processes that lead to low probabilities of defect existence. 3 FRP PIPES INSPECTION METHODS, There are several inspection technique that can be used for FRP piping health motoring. These techniques are listed in details in 4 10 Over estimated factor of safety i e up to. 10 1 were used for FRP pipes in early 1970s due to the absence of qualitative and. quantitative information at that time The main purpose for pipe inspection and. evaluation is to identify deviations from the design specifications and perform fast. corrective actions to prevent the pipe failure Common methods of inspection as pressure. testing and visual inspection are used to detect high porosity levels and cracks that lead to. flow leakage i e drop in the pressure of the transferred fluid or cracks visual to the. naked yes Methods such as Acoustic Emission AE can be used in identifying fiber. breakage and delamination in composite however the technique is considered to be an. active technique i e the FRP pipe should be under loading X ray radiography can be. used to detect FOI fiber waviness porosity and crack in FRP however high safety. precautions should be considered and special procedures should be performed if portable. X ray systems used to ensure that the induced vibration resulted from the operating. pipeline does not affect on the radiographic exposure Ultrasonic Testing UT technique. is the most common nondestructive method used in the inspection and characterization of. FRP pipes However it should be noticed that the inspection of FRP pipes difficult in. comparison to other metallic pipes as there are a wide variation of materials and. manufacturing procedures used in production of FRP pipes Low frequency pulse echo. UT systems can be specially designed for FRP pipes inspection that allows rapid and. accurate one sided inspection 8 There are several defects can be detected using UT. method such as plies disbands cracks porosity and delaminations 6 11 12 In this. paper we focus on UT as an inspection method for FRP pipes to evaluate its elastic. properties,4 CASE STUDY,4 1 FRP Pipe Materials and Fabrication.
FRP pipes with 457 2 mm 18 length and diameters ranging from 101 6mm 4 to. 203 2 mm 8 were used in this work The FRP pipes were manufactured from glass. fiber epoxy vinyl ester using filament winding process These pipes were fabricated. from three distinct layers The first layer is a liner a smooth layer with special additives. that comes with direct contact with the fluid The main objective of this layer is to. provide corrosion and wear resistance for the internal surface of the FRP pipe The. filament layer is the second layer that forms the pipe wall thickness and handles the. stresses resulting from the internal and external pressure Then a final layer of pure resin. coating is added to insure smooth surface finish and full fiber impregnation It is worth. mentioning that information about the fiber orientation and the fiber weight percentage. for the pipes received was not provided Prior knowledge of the fiber weight fraction ply. thickness and orientation is necessary to obtain reliable UT prediction for the elastic. modulus of the FRP pipes Hence burn off testing ply counting and micrographs were. performed to obtain this information Three samples were extracted out the. circumferential direction of each pipe and placed in the oven under 500 C for an hour. The samples were weighed before and after the burn off process and the fiber weight. fraction was calculated using the following relation 13. where is the total mass of the composite before burn off and is the mass of the. remaining constituent after burn off After burn off the number of the plies was counted. and stereomicroscope Carl Zeiss Stemi SV11 was used to determine the fiber. orientation as shown in Figure 1 Table 1 shows the burn off and plies counting results. The weight fraction values can be converted to volume fraction using the following. relation 13, where is the matrix density and is the fiber density The resulted data were used in. the theoretical and experimental calculation The FRP pipes were fabricated from a total. of 10 plies The first 6 plies were stacked in 57 57 6 configuration followed by 4 plies. of Chopped Strand Mats CSM with random orientation It showed be noticed that the. orientation angle values for the unidirectional laminates obtained experimentally has a. difference of 2 5 when compered to the reported value by the manufacturer i e. 54 5 54 5 At orientation angles greater than 45 a minor change in the orientation. angle i e 2 5 does not has a significant effect on the tensile modulus 3. 4 2 Theoretical Evaluation for Elastic Properties of FRP Pipes. Micro mechanical model can predict the composite stiffness properties from then. properties of its original constituents listed in Table 2 The elastic properties for. unidirectional continuous fiber can be calculated using the Rule of Mixture RoM 3. where is the fiber modulus is the matrix modulus is the matrix volume. fraction However in this study a modified version of the rule of mixture see Appendix. A were used to account for the change in the fiber angle In order to determine the. micro mechanical properties for the CSM with random orientation the following. equation was used 3, where and are the longitudinal and transverse tensile modulus for chopped. unidirectional fibers respectively obtained by Halpin Tsai theory 14 In this case the. properties are assumed to be the same in all directions in the plane of the lamina i e. Figure 1 Stereography images for the glass fiber constituent after burn off a Fibers. angle of 57 b Fibers angle of 57 and c Fibers with random orientation. Table 1 FRP pipe burn off and ply counting results. Pipe Calculated Fiber Average Fiber,Standard Number of. diameter volume fraction Weight fraction,Deviation Plies. 101 6 4 34 6 50 8 0 8 3 ply 57,4 ply Random,152 4 6 40 3 56 9 0 4 3 ply 57.
4 ply Random,203 2 8 39 8 56 4 0 7 3 ply 57,4 ply Random. The elements in the stiffness matrix for an angle ply lamina were determined and. then the extensional stiffness matrix and bending stiffness matrix for the laminate was. calculated using the Composite Lamination Theory CLT For simplicity the sample. assumed to be free from any geometrical curvatures and a perfect interlaminar bond. exists between various laminas The extensional stiffness matrix A and the bending. matrix D were calculated using the following relations 3. where N is the total number of laminas in the laminate elements of the stiffness. matrix of the jth lamina and 1 is the distance from the mid plane to the top of the jth. lamina The A matrix for the FRP pipes can be presented in a matrix form as. 21 22 23 8, Table 3 shows the theoretical elastic modulus values obtained using the CLT 3 It. should be noticed that an increase of 4 5 in the calculated theoretical modulus values. for the 4 pipe was observed when compared to the value of 8 FRP this is attributed to. the increase of the fabricated FRP pipe wall thickness. Table 2 FRP pipes constituent properties, Density Diameter Tensile Modulus Tensile Strength Poisson s. g cm3 m GPa GPa Ratio,Glass Fiber,2 54 10 round 72 4 3 45 0 2. Epoxy Vinyl,1 3 3 2 0 86 0 35, Table 3 Calculated theoretical properties of the FRP pipes.
Pipe Diameter Total Thickness Tensile Modulus Shear Modulus. mm mm GPa GPa,101 6 4 5 18 8 04 4 43,152 4 6 6 04 8 24 5 07. 203 2 8 7 09 8 42 5 72,4 3 Ultrasonic Testing and Evaluation. In order to obtain a systemic process for measuring and distinguishing the data for each. of the given points a template of a grid system was developed and applied to the. provided pipes The grid system consists of the x axis identified by numbers and y axis. identified by alphabets with the origin at the top right 38 1 mm 1 5 distance between. the grid points in both of the circumferential and the longitudinal direction was adapted. Different pipe diameters will result in additional data points of scan in the circumferential. direction i e hoop direction of the pipe A total of 120 168 and 228 point were scanned. for pipe diameters of 101 6mm 4 152 4 6 and 203 2 mm 8 respectively Pulse. echo ultrasonic system Olympus Epoch 4 was used to scan the FRP pipes across the. pipe hoop direction Low frequency flat transducer 0 5 MHz with an element diameter. of 32 mm 1 coupled with a zero degree vulcanized rubber delay line were used. Readings were taken by holding the transducer in place on the pipe surface and then. saving the reading into the memory of the Epoch 4 After all readings were taken the. raw reading data was extracted from the instrument using communications software. provided by UTComp The ultrasonic data was then processed and analyzed remotely. using proprietary software owned by UTComp Inc that calculates the ratio of expected. actual modulus to the theoretical modulus from CLT calculations The ratio is known as. the Percentage of Design Strength PDS Mathematically PDS is expressed as. The UT readings that were taken in the scans of the pipes were combined with pipe ID. location and assembled into a data file that could be processed remotely The raw data. was scaled normalized and filtered to account for variables in the collection process such. as transducer characteristics pipe geometry and surface conditions and environmental. conditions The original A scan was transformed to allow quantitative analysis An. ultrasonic nondestructive testing technology to acquire data for heal th monitoring of FRP structures This data gathered is then evaluated through custom software and analysis In the present work FRP pipes ranging from 8 to 24 length and 6 to 8 diameter supplied from number of sources was evaluated by ultrasonic NDE The FRP

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