METHOD AND DEVICE FOR TESTING A MATERIAL SAMPLE IN A STANDARD TEST FOR INPLANE FRACTURE TOUGHNESS EVALUATION
1. A method of testing a material in a standard test for in-plane fracture toughness evaluation, the material sample of a type used in a wall of a structure, the method comprising:
- obtaining a sample of the wall of the structure;
shaping the sample into a notched component, the notched component including a flat bottom surface having a thickness dimension equal to a thickness of the wall of the structure, and a profiled top surface, the profiled top surface having a central notch oriented perpendicular to a plane of the bottom surface, a first socket on a first side of the central notch, and a second socket on a second side of the central notch;
assembling a test specimen which increases an effective thickness of the sample beyond the thickness of the bottom surface of the notched component by coupling a first lateral extension to the first socket and a second lateral extension to the second socket of the notched component; and
applying a standard fracture toughness test to the so-assembled test specimen in order to evaluate the fracture toughness of the material in an in-plane direction.
A method of testing a material sample of a type used in a wall of a structure in a standard test for in-plane fracture toughness evaluation. The method comprises obtaining a sample having a lateral length no larger than a thickness of the wall of the structure, shaping the sample to have (a) a bottom surface, (b) a profiled top surface having a central notch, (c) a first coupling feature on a first side of the central notch, and (d) a second coupling feature on a second side of the central notch, assembling a test specimen which increases the width of the sample beyond the lateral width by coupling a first lateral extension to the first coupling feature and a second lateral extension to the second coupling feature, and applying a standard fracture toughness test to the so-assembled test specimen and sample to evaluate the fracture toughness of the sample.
- 1. A method of testing a material in a standard test for in-plane fracture toughness evaluation, the material sample of a type used in a wall of a structure, the method comprising:
obtaining a sample of the wall of the structure; shaping the sample into a notched component, the notched component including a flat bottom surface having a thickness dimension equal to a thickness of the wall of the structure, and a profiled top surface, the profiled top surface having a central notch oriented perpendicular to a plane of the bottom surface, a first socket on a first side of the central notch, and a second socket on a second side of the central notch; assembling a test specimen which increases an effective thickness of the sample beyond the thickness of the bottom surface of the notched component by coupling a first lateral extension to the first socket and a second lateral extension to the second socket of the notched component; and applying a standard fracture toughness test to the so-assembled test specimen in order to evaluate the fracture toughness of the material in an in-plane direction.
- View Dependent Claims (2, 3, 4, 5, 6, 7, 9, 10, 15)
- 8. (canceled)
- 11-14. -14. (canceled)
- 16. An apparatus for testing a material used in a wall of a structure for fracture toughness, the apparatus comprising:
a notched component made from a sample of the material of the structure shaped to have (a) a bottom surface having a width equal to a thickness of the wall of the structure, (b) a profiled top surface, the profiled top surface having a central notch, (c) a first socket on a first side of the central notch, and (d) a second socket feature on a second side of the central notch; a first lateral extension coupled to the first socket of the notched component; and a second lateral extension coupled to the second socket of the notched component, wherein the first and second lateral extensions extend an effective width of the notched component to provide an assembled test specimen of sufficient length to be used in a standard fracture toughness test.
- View Dependent Claims (17, 18, 19, 20, 21)
- 22. (canceled)
The application claims priority to U.S. Provisional Application Ser. No. 62/520,489, filed on Jun. 15, 2017, having the same title, which is hereby incorporated by references as if set forth in its entirety herein.
The present invention relates to the testing of materials for structural fitness, and, more particularly, relates to a method and device for testing a material sample of relatively small thickness in a standard test for in-plane fracture toughness evaluation.
Hydrogen-induced cracking (HIC) is encountered by oil and gas pipelines and related installations with sour environments having high hydrogen sulfide (H2S) concentrations. These defects are attributable to atomic hydrogen produced by sour corrosion that enters the bulk of the steel. The atomic hydrogen reacts and recombines to form high pressure molecular hydrogen cavities at the interface of nonmetallic spaces residing in the microstructure. HIC tends to propagate in a plane parallel to the pipe wall as shown in
When carrying out fracture toughness (FT) tests to characterize the ability of the material to resist crack propagation, the dimensions and orientation of the FT specimen are critical. The dimensions of a rectangular forged/rolled plate sample are defined as the longitudinal (L) which is parallel to the plate rolling/forging direction, the transverse dimension (T) and the short transverse or thickness dimension (S). A schematic model of a sample illustrating these planes is shown in
The directions of interest for HIC crack propagation and more generally, stepwise cracking, are the S-T or S-L directions shown in
The ASTM (American Society for Testing and Materials) 1820 fracture toughness test standard requires use of specific specimens, of either a single edge bending (SEB) or a compact tension (CT) type. However, such specimens are not suited for FT measurements in S-T and S-L directions because there is not enough material in the thickness direction to extract a full SEB or CT specimens. For example, to machine a typical SEB specimen of 10 millimeter thickness requires a minimum plate thickness of about 90 millimeters, which is well above common pipe thicknesses of pipe equipment used in the oil and gas industries.
While in-plane FT data is not required to design against fracture of metallic structures, it becomes of high interest when the equipment of interest may develop in-plane cracks such as HIC. Such data can help at the material selection stage to discriminate between different types of steel, the quality of metal provided by different manufacturers, and also can enable prediction of crack growth rate and their impact on the residual integrity of the equipment during their service life.
What is therefore need is a methodology to enable FT tests for in-plane fractures that can produce valid measurements (i.e., compliant with the Standard) of the in-plane fracture toughness of metallic plates. It is with respect to these and other considerations that the disclosure made herein is presented.
Embodiments of the present invention provide methods of testing a material in a standard test for in-plane fracture toughness evaluation, in which the material sample is of a type used in a wall of a structure. In certain embodiments, the method comprises obtaining a sample of the wall of the structure, shaping the sample into a notched component, the notched component including a flat bottom surface having a thickness dimension equal to a thickness of the wall of the structure, and a profiled top surface, the profiled top surface having a central notch oriented perpendicular to a plane of the bottom surface, a first socket on a first side of the central notch, and a second socket on a second side of the central notch, assembling a test specimen which increases an effective thickness of the sample beyond the thickness of the bottom surface of the notched component by coupling a first lateral extension to the first socket and a second lateral extension to the second socket of the notched component, and applying a standard fracture toughness test to the so-assembled test specimen in order to evaluate the fracture toughness of the material in an in-plane direction. The structure to be tested is preferably a material with a thickness between about 5 mm and about 70 mm, such as a steel pipe prevalently used in the oil and gas industry.
In some implementations, methods of the present invention further comprise machining the notched component such that the central notch is oriented to open in a T-L direction in a standard fracture toughness test. In other implementations, the methods further comprise machining the notched component is shaped such that the central notch is oriented to open in a S-L direction in a standard fracture toughness test.
To meet the requirements of standard fracture tests, it is preferable to form the first and second lateral extensions such that a sum of the lengths of the first and second lateral extensions and the thickness of the notched component is as great, or greater than, 4.5 times the width of the notched component as measured from the bottom surface to a tip of the profiled surface.
In some embodiments, the first and second sockets can be symmetrical about the central notch, while in other embodiments the first and second sockets can be asymmetrical about the central notch. The test specimen can be placed in a standard fracture toughness test apparatus such that force is applied the bottom surface of the notched component. The central notch of the notched component can be shaped to include a first section having a first width and a second section positioned beneath the first section having a second width that is smaller than the first width. The first and second sockets of the notched component can form elbow-shaped notches.
In some embodiments, the method further includes performing a finite element simulation of fracture toughness using a programmed computer and data from the standard fracture toughness test to determine optimal geometric parameters for the notched component.
To investigate the effects of a harsh hydrogen environment on test specimens, in some embodiments the method further comprises charging the notched component with hydrogen prior to applying the standard fracture test. In such embodiments, the notched component can be charged with hydrogen over a duration until the hydrogen concentration reaches a desired level. The current density required to charge the notched component to a target steady-state hydrogen concentration can also be determined, as well as the difference in fracture properties between S-L and T-L directions at a plurality of hydrogen concentration levels.
Embodiments of the present invention also provide an apparatus for testing a material used in a wall of a structure for fracture toughness. Embodiments of the apparatus comprise a notched component made from a sample of the material of the structure shaped to have (a) a bottom surface having a width equal to a thickness of the wall of the structure, (b) a profiled top surface, the profiled top surface having a central notch, (c) a first socket on a first side of the central notch, and (d) a second socket feature on a second side of the central notch, a first lateral extension coupled to the first socket of the notched component, and a second lateral extension coupled to the second socket of the notched component. The first and second lateral extensions extend an effective width of the notched component to provide an assembled test specimen of sufficient length to be used in a standard fracture toughness test. The structure is preferably a material having a relatively small thickness between about 5 mm and about 70 mm, such as a wall of a pipe made of steel, such as X65.
In some embodiments, the central notch of the notched component is oriented to open in a T-L direction in a standard fracture toughness test. In other embodiments, the central notch of the notched component is oriented to open in a S-L direction in a standard fracture toughness test.
The first and second lateral extensions can be formed such that a sum of the lengths of the first and second lateral extensions and the thickness of the notched component is as great or greater than 4.5 times the width of the notched component as measured from the bottom surface to a tip of the profiled surface.
In some implementations, the central component is charged with hydrogen.
These and other aspects, features, and advantages can be appreciated from the following description of certain embodiments of the invention and the accompanying drawing figures and claims. The drawings are illustrative and exemplary, and do not necessarily accurately indicate the scale, either in an absolute sense, or a relative sense, of the elements depicted.
Embodiments of the present invention provide a method and device for enabling FT tests of samples in the S-L and S-T directions, which provides HIC information. An assembled test specimen is provided which has dimensions that are compatible and compliant with standard fracture toughness test requirements. The specimen comprises a sample taken from the material of interest (e.g., a mother steel plate) that is machined to include a notch that matches a crack orientation in the S-L or S-T directions.
In the embodiment depicted, the notched component 105, in addition to a central notch 107, a first half of the “W” shaped profile is formed, on a first side of the component (left side in
The end of the first lateral extension 210 shown adjacent to the notched component 105 includes a downward curving, hook-shaped tab 212 adapted to precisely and snugly fit into the first socket 122 of the notched component. Adjacent to tab 212 on lateral extension 210 is a socket 214 that is adapted to snugly receive the first tab 124 of the notched component. Similarly, the end of the second lateral extension 220 shown adjacent to the notched component 105 includes a downward curving, hook-shaped tab 222 adapted to precisely and snugly fit into the second socket 126 of the notched component. Adjacent to tab 222 on second lateral extension 220 is a socket 224 that is adapted to snugly receive the second tab 128 of the notched component.
The length of the lateral extensions can be configured so that the assembled test specimen complies with the following equation set forth in standard test requirements:
in which L represents the lengths of the lateral extensions (in embodiments in which the extensions are the same length), W measures the width of the notched component, measured as the distance from the top edge of the front face 106 to the back edge of the rear face 108 of the notched component, and T measures the thickness of the sample, which, as noted above, corresponds to the thickness of the structural material (e.g., pipe).
In addition to enabling measurement of in-plane fracture toughness (i.e., S-T and S-L directions), the test specimen according to the present invention provides additional advantages. Since, for a given structural material of interest (e.g., “mother plate”), only the relatively small notched components are machined from the material, while the lateral extensions can be machined from other structures having comparable mechanical properties (e.g., elastic modules and strength) as the original material of interest. For example, if the structure of interest is carbon steel, then the extensions should also be made of steel (e.g., HSLA, carbon steel, mild steel), and should not be made of a metal with distinctly different properties such as aluminum. In this manner, raw material can be economized. For example, the maximum number of samples that can be machined from a unit area of mother plate is about (1/W*B) for the S-L configuration, compared to (1/4.5 W*W) for the T-L configuration and (1/4.5*W*B) for the L-S configuration, where B is a constant stipulated by the standard test requirements. Given that some standards require that B=0.5 W, up to 9 more specimens per unit area can be produced by economizing on raw material in this manner.
In addition, the test specimens according to the present invention are particularly suited for environmental FT testing. Since the notched component is machined separately, there is more flexibility for carrying out FT tests in harsh environments. For example, when carrying out FT tests in a hydrogen-rich environment, one can select a material for the lateral extensions that has less sensitivity to hydrogen absorption (e.g., austenitic stainless steel) in order to concentrate the hydrogen embrittlement into the machined sample only. Additionally, the machined notched component can be exposed to the harsh environment of interest prior to coupling the sample to the lateral extensions and FT testing.
Since the notched component according to the certain embodiments present invention has a complex “W” shape, it important to select the dimensional parameters of the shape to ensure that the test specimen, when fully assembled with lateral extensions, behaves mechanically like a single-part, integral test specimen.
The following discussion describes an exemplary geometric parameter optimization that may be performed for the notched component according to the present invention using program code executed on a processor of a computer system. The optimization uses a finite element analysis which simulates and compares the mechanical behavior, under a fracture toughness test, of assembled and integral test specimens having different values of the six tested parameters. The optimization seeks to find parameter values for which the assembled test specimen behaves as closely to an integral, single-part specimen as possible.
The following example describes a parameter optimization for two different planar structures, having thicknesses of 10 mm and 20 mm, common for structures in the oil & gas industry. The parameter optimization was obtained using a finite element simulation program (e.g., ANSYS® v16 “simulator”) executed on a computer system. The simulation generated four separate models. Two of the models represent integral, single-part specimens, one of a 10 mm thick specimen, and the other of a 20 mm thick specimen. The two models represent assembled test specimens according to the present invention, similarly one of 10 mm thickness and the other of 20 mm thickness. As the test specimens are symmetric about their respective horizontal centers, the finite element simulations were performed on half-specimens from the center to the periphery. Schematic illustrations of the finite element models are shown in
In the four finite element models, the simulator used a plane strain formulation for both the integral and assembled FT test specimens. This formulation is a fair approximation in order to compare the force-displacement curves and fracture toughness parameter KQ of the two types of specimens. In addition, for all the models, a static non-linear analysis was performed using large displacement theory and employing a Newton-Raphson incremental-iterative scheme. For the integral test specimens, eight node 2D structural shell elements were used, while the roller supports were modeled as rigid objects. Contact between the specimen and roller supports was modeled using three node 2D surface to surface contact elements, with a friction coefficient equal to about 0.3.
The simulator modeled material behavior using the stress-strain curve of a High Strength Low Alloyed steel (HSLA), more particularly, FCA (Fatigue Crack Arrester) steel, which has a ferritic-bainitic structure. Boundary conditions were imposed at the rollers. Specifically, translations in either the x-direction (direction of compression) or the y-direction (along the length of the specimens) at the roller ball elements were set to zero with rotation allowed. Translations at the point of application of ball element 405 in the y-direction and rotations were also set to zero. For deriving the force-displacement curve from the simulations, a displacement (Ux) and was imposed at the pilot node of ball element 405 (the point at which the ball element 405 contacts the notched component). For evaluating the fracture toughness KQ, a Force load (FX) was imposed at the pilot node of ball element 405.
Using the boundary conditions and material behavior, the finite element simulator evaluated of the J integral parameter around the crack tip of each test specimen. The J-integral represents a way to calculate the strain energy release rate, or work (energy) per unit fracture surface area, in a material. The J-integral was evaluated through integration around closed paths around the crack using identical element edge lengths facilitating convergence of the J-integral value. The fracture toughness parameter KQ was then evaluated via J integral. The J integral can be converted to the fracture toughness parameter according to the following equation:
in which E is the material elastic modulus of the FCA material, J is the J integral, and K is the fracture toughness parameter.
The modeling for the assembled test specimens shown in
Table 1 shows a summary of fracture toughness parameter results of the finite element simulation of fracture toughness tests on the integral and assembled models at the two thickness. The KQ results were obtained by using an applied force Fx of 2.2 kN and a notch plus crack length (a0) of 4.1 mm for the 10 mm specimens and applied force Fx of 6.09 kN and a0 length of 10 mm for the 20 mm specimens. Table 1 provides evidence that the predicted fracture toughness indicators (J and KQ) for the assembled specimens are in excellent agreement with those of the conventional single-part integral specimens.
In addition to the finite element study, several fracture toughness tests were performed on physical specimens to validate the assembled specimen designs. The fracture toughness tests were performed specifically on FCA (Fatigue Crack Arrester) steel, which was also modeled in the finite element simulations. FCA steel is a high strength ferritic-bainitic steel with following composition listed in below Table 2.
As with the finite element simulation, tests were conducted on both integral and assembled test specimens at 10 mm and 20 mm thicknesses, totaling four tests. In addition, each of the 4 tests was repeated 3 times (12 tests in total) to assess the standard deviation of FT measurements. Prior to fracture toughness testing, the machined samples were notched, and fatigue pre-cracked, following the guidelines of testing standard ASTM E1820. The length of the fatigue pre-crack was measured using a MATELECT CM 7 ACPD (AC potential drop). All tests were performed on a 100 kN MTS hydraulic testing machine. A photograph showing the test apparatus 600 used for the tests is shown in
Table 3 lists measured FT values for integral and assembled test specimens of 20 mm thickness. Table 4 lists corresponding measured FT values for integral and assembled test specimens of 10 mm thickness. Tables 3 and 4 show close agreement between FT values of the integral and assembled test specimens.
With respect to the thin 10 mm specimens, the data of Tables 3 and 4 indicates that the difference between the average KQ values of the integral and the assembled specimens is (ΔKQ) is 0.08 (table 4), which is substantially less than the standard deviation of the integral specimens (0.91). The same is true of the value of J0 integral for which the difference (ΔJ0) is 16.24 and the standard of the integral specimens is 38.63. These experimental results demonstrate that the geometric design implemented for the notched component and assembled test specimen as a whole, according to the present invention, is well suited to evaluate the fracture toughness properties of relatively thin steel plates.
A second set of experiments was performed to determine the effect of hydrogen on the fracture toughness properties of API X65 pipeline steel under simulated H2S conditions prevalent in pipelines while in service. Specifically, fracture toughness properties KIH and CTOD¬0 in air and at three levels of hydrogen were studies for the S-L and T-L crack directions. The fracture toughness experiments were performed on 300 mm thick X65 low carbon steel extracted from a field pipeline. A standard HIC qualification test was first performed and the results showed that the pipeline steel used in this study is HIC resistant.
The first procedure in the second set of experiments was simulating the in-service, harsh environment conditions by charging the specimen with hydrogen. Three different hydrogen concentrations (CH) were established by electrolytic hydrogen charging in a 30 gm NaCl and 3 gm NH4SCN aqueous solution in which the X65 steel specimen served as the cathode with a platinum anode. The NH4SCN was used as a hydrogen recombination poison and during hydrogen charging the solution was de-aerated with N2. Hydrogen pre-charging was performed for a duration of for 48 hours which has been shown to be sufficient to achieve a stable hydrogen concentration in the metal lattice of a pipeline steel.
This initial set of charging tests determines the current densities which can produce the desired CH in the X65 samples. The hydrogen content was measured in notched X65 specimens of 20 mm length, 20 mm width and 10 mm thickness, with a notch depth of 5 mm. The X65 steel samples were polished using a 600-grade emery paper, cleaned with distilled water and acetone and dried. This ex-situ hydrogen charging protocol is representative of actual conditions relevant to crack initiation and propagation in oil and gas pipelines in the field. The charging protocol allows slow hydrogen uptake and diffusion inside notched X65, simulating the uptake in the bulk of the X65 steel material and the slow hydrogen accumulation rate that occurs in the oil field.
After the X65 steel specimen was hydrogen-charged for 48 hours, it was immersed in liquid nitrogen (77K) in order to avoid fast hydrogen desorption and then transferred to a thermal desorption spectroscopy (TDS) measuring cell and inserted into a furnace. Argon flow (around 60 ml/min) was supplied and monitoring of the spectrometer signal was initiated. The duration o from immersion in the nitrogen bath to the signal monitoring was about 10 minutes. operation (from liquid N2 bath to MS monitoring of signals) lasted around 10 min. Sample signals were recorded for 6 minutes at room temperature, i.e. the sample was kept at room temperature for 6 minutes, in order to allow for flow/pressure equilibration, followed by a temperature ramp (3° C./min) up to 700° C. was initiated. After reaching 700° C. the sample was maintained at this temperature for around 3 hours. At the end of the 3-hour period, the furnace was turned off and natural cooling commenced. The results of the TDS measurements are used to establish the current densities required to achieve the target bulk. hydrogen concentrations
After charging the X65 specimen, in-service conditions were simulated by establishing a steady state CH in the bulk of the X65 steel. The following empirical formula was used to evaluate the steady-state CH in the bulk of the steel after the conclusion of the hydrogen charging based on pH and H2S partial pressure:
CHmeasured=3.1+0.56 log(pH2S)−0.17 pH (2)
In which the units of CHmeasured are ppmw and pH2S the partial pressure of H2S expressed in MPa.
Three levels of H2S partial pressure and pH were selected in order to cover the three different regions of environment severity specified in ISO 15156-2.
The hydrogen concentrations for the three levels of environmental severity selected in this study are shown in Table 5. Proposed hydrogen concentration values, after evaluation for the three levels of pH and H2S partial pressure are CH-1 at 0.5 ppmw, CH-2 at ppmw, and CH-3 at 2 ppmw.
The current densities (established by TDS) that correspond to the three target CH levels were used to pre-charge fracture toughness SEB (Single Edge-notch Bending) specimens for 48 hours, prior to ex-situ fracture toughness testing. TDS experiments were performed to determine the current densities. In the experiments, the current density was varied from 0.2 mA/cm2 to 5 mA/cm2.
In the fracture toughness tests of X65 specimens for the T-L direction, the parameter KQ was used as the maximum stress intensity factor for fracture toughness testing in air, and Km for the maximum value of the stress intensity factor of hydrogen pre-charged specimens. Furthermore, the K values specified the hydrogen concentrations, for example, KIH0.5 for the case of hydrogen charged specimens with 0.5 ppmw hydrogen concentration, KIH1 for hydrogen charged specimens with 1 ppmw hydrogen concentration and finally KIH2 for hydrogen charged specimens with 2 ppmw. Similarly, the maximum CTOD (crack tip opening displacement) parameter was distinguished in this manner. The X65 specimens tested in air yielded an average of KQ=50.38 MPa m½ and CTOD0=0.78 mm; the X65 specimens with 0.5 ppmw hydrogen concentration, yielded an average of KIH0.5=50.78 MPa m½ and CTOD0H0.5=0.52 mm; the X65 specimens with 1 ppmw CH, yielded an average of KIH1=50.99 MPa m½ and CTOD0H1=0.17 mm; and the X65 specimens with 2 ppmw CH, show an average of KIH2=50.36 MPa m½ and CTOD0H2=0.14 mm. Similarly, with respect to cracks oriented in the S-L direction, the X65 specimens tested in air yielded an average of KQ=52.43 MPa m½ and CTOD0=0.98 mm; the X65 specimens with 0.5 ppmw CH yielded an average of KIH0.5=47.25 MPa m½ and CTOD0H0.5=0.90 mm; the X65 specimens with 1 ppmw CH, yielded an average of KIH1=46.81 MPa m½ and CTOD0H1=0.32 m; and the X65 specimens with 2 ppmw hydrogen concentration yielded an average of Km=45.96 MPa m½ and CTOD0H2=0.39 mm.
To better understand the failure mechanism underlying hydrogen induced fracturing, fractured surfaces of X65 steel in the S-L and T-L directions were analyzed using a scanning electron microscope (SEM). Specimens tested in air and at extreme hydrogen environment (2 PPM) were selected for SEM analysis.
To further investigate the mechanisms by which specimens fracture in air and under hydrogen environment, electron backscatter diffraction (EBSD) mapping was conducted at the edge of the notched region and the crack propagation path. All tested samples whether in air or hydrogen-charged showed similar crack propagation features, confirming that the main crack of a fracture propagates through the grains with random orientation and in the presence of fine grain structures.
To shed light on the hardness properties of the X65 test specimens near and distal from the notched regions of the specimens, micro indentation tests were performed on the specimens prior to fracture toughness tests. The results obtained indicate that the Vickers hardness of the matrix region (distal from the notch) is about 236 and in the notch region the Vickers hardness is about 193. These values are in the same order of magnitude relative to the standard deviation and therefore it can be concluded that there is no noticeable change in the Vickers hardness in the tested specimens whether in air or after charged with hydrogen.
The overall results demonstrate a reduction of maximum CTOD in both T-L and S-L directions by increasing CH in the bulk of the X65 steel, which is more pronounced for the T-L direction. On the other hand, it is observed that maximum K is not affected in the T-L direction by increasing CH, while in the S-L direction there is a noticeable reduction in K caused by increased CH. Furthermore, when fracture toughness results are compared between the two directions, a 3.9% difference in maximum KQ and a 20% difference in maximum CTOD0 between the T-L and S-L direction is shown for measurements in air. A similar trend is also evident for the hydrogen-charged specimens, where in the T-L direction there is no reduction of maximum K but in the S-L direction there is reduction up to 14.4%. The same trend can be noticed when comparing the maximum CTOD values in different directions. Although in both directions they have been reduced, they have different reduction rates for each direction. It is noteworthy to point out that in many Engineering Critical Assessment (ECA) tools, the most widely used fracture toughness parameter for assessing reaming life time or limit is the stress intensity factor (e.g., critical stress intensity factor or the maximum K). Nevertheless, it has been shown in this work that in tests, while the maximum K remains unaffected the CTOD is greatly reduced. It is of great interest to accommodate CTOD in the ECA tools in order to assess the complete effect of a hydrogen environment in the assessment tool, since CTOD encompasses maximum K. In conclusion, the experiments performed showed that crack in the S-L direction develop with unique characteristics different from other directions. Development of an assembled test specimen target for testing hydrogen-induced fracturing in this direction is therefore an important tool for assessing pipe metal condition in harsh environments.
It is to be understood that any structural and functional details disclosed herein are not to be interpreted as limiting the systems and methods, but rather are provided as a representative embodiment and/or arrangement for teaching one skilled in the art one or more ways to implement the methods.
It is to be further understood that like numerals in the drawings represent like elements through the several figures, and that not all components and/or steps described and illustrated with reference to the figures are required for all embodiments or arrangements. For the purpose of brevity certain elements of which there are a large number have been referred to by subset including the initial use of “e.g.” which in subsequent cases are referred to without the use of “e.g.” It is to be understand that the subset referred to by “e.g.” refers to all similar elements, and that the later use of the subset without “e.g.” should not be limiting but should also be understood to represent all such similar elements.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising”, when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.
Terms of orientation are used herein merely for purposes of convention and referencing, and are not to be construed as limiting. However, it is recognized these terms could be used with reference to a viewer. Accordingly, no limitations are implied or to be inferred.
Also, the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having,” “containing,” “involving,” and variations thereof herein, is meant to encompass the items listed thereafter and equivalents thereof as well as additional items.
While the invention has been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes can be made and equivalents can be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications will be appreciated by those skilled in the art to adapt a particular instrument, situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.