Conduit pipe for transporting dihydrogen with a surface barrier layer and method for manufacturing such a conduit pipe

Abstract

The invention relates to a steel conduit pipe (10) configured to transport a gas comprising dihydrogen. On the inner wall (14), the steel comprises a surface barrier layer (20) having a thickness (22) starting from the inner wall (14) and within which the steel has different microstructural parameters than those of the steel outside the surface barrier layer (20) and configured to tend to oppose the passage of gas through the thickness (22) of the surface barrier layer (20). This layer is obtained by performing a mechanical nanostructuring surface treatment by ultrasonic shot peening under the effect of random impacts of spherical balls (26) which are moved in a vibratory manner by an ultrasonic power generator (28). The invention also relates to a method for manufacturing the conduit pipe (10).

Description

[0001] DESCRIPTION

[0002] TITLE: Pipe tube for transporting dihydrogen with surface barrier layer and method of manufacturing such a pipe tube

[0003] Technical field of the invention

[0004] The present invention relates to a pipeline tube configured to transport a gas comprising dihydrogen, formed in a steel, having a tubular-shaped internal wall delimiting a cavity in which a flow of said gas is intended to circulate.

[0005] The invention also relates to a method of manufacturing such a pipeline tube.

[0006] The manufacturing process can be implemented on line pipes at the end of their manufacturing process, but can also potentially be applied to line pipes that have already been put into service and that would be considered for improvement in terms of capacity, such as for example line pipes that would have been used for the transport of natural gas and that one would like to transform (via the manufacturing process) for conversion to a use dedicated to the transport of a gas containing dihydrogen, whether pure dihydrogen or a mixture between natural gas and dihydrogen.

[0007] The invention finds application in particular in the transport of dihydrogen in the gaseous state, whether it is pure dihydrogen or a gas mixture containing dihydrogen, such as for example dihydrogen mixed with natural gas.

[0008] State of the art

[0009] The development of the hydrogen sector requires the production, transport and storage of large quantities of dihydrogen under multiple implementation and operating conditions.

[0010] One of the major concerns for user safety and the environment is the embrittlement by hydrogen of the various components in the chain, such as reactor vessels, pipelines dedicated to transport and storage tanks, as well as potential explosion scenarios linked to the accumulation of hydrogen in enclosed spaces.

[0011] The present invention is solely concerned with the management of these problems at the level of pipeline tubes, dedicated to the transport of dihydrogen or gas mixtures containing dihydrogen.

[0012] It is known that the crystal lattices of metals frequently exhibit permeability to hydrogen by diffusion of hydrogen atoms into the interstitial spaces of the atomic lattice. This can be explained by the small size of the hydrogen atoms but also and above all due to their electronic affinity with the metal concerned. This permeation is broken down into several stages. The adsorption of hydrogen in a gaseous environment is explained by a physisorption of the dihydrogen molecule at the metal wall, then a dissociation of the dihydrogen molecule, then a chemisorption of the hydrogen atoms at the metal wall. After this adsorption of the hydrogen atom, its absorption follows, which corresponds to the migration of the atoms towards the interstitial sites in the sub-surface of the crystalline matrix of the metal. Then diffusion in the volume of the metal comes into play.It is known that hydrogen diffusion can be modified by the presence of traps, which are crystallographic or microstructural defects (vacancies, grain boundaries, dislocations, internal cracks, microcavities, etc.). Depending on whether hydrogen remains blocked or not on these defects at a given temperature, the traps are called irreversible or reversible, respectively. The behavior of these traps strongly depends on temperature and time: for an infinitely long time, all traps can be considered reversible.

[0013] The presence of hydrogen imparts hydrogen embrittlement by modifying the behavior and mechanical properties of steels, such as ductility, toughness, elasticity or fatigue resistance. Since these mechanical properties are essential to ensure the integrity of the transport infrastructure, it is therefore imperative to take these constraints into account in order to resolve the general problems mentioned above.

[0014] Currently, hydrogen is transported via pipeline networks. However, this network remains very limited, representing only a few thousand kilometers worldwide, mostly in Europe and the United States. For safety reasons, transport distances are relatively short and the network is located far from residential areas.

[0015] To address the risks of hydrogen embrittlement, the materials currently used for the transport of gaseous dihydrogen are generally either low-alloy ferritic (or ferrito-pearlitic) steels (with high safety coefficients), or stainless steels (for more specific or local applications).

[0016] Stainless steels are more expensive than low-alloy steels, which is a barrier to large-scale deployment of pipelines with large diameters, on the order of a meter, as is the case for natural gas transmission pipes.

[0017] On the other hand, feedback does not guarantee all risks of hydrogen embrittlement for periods of use of several decades. In particular, monitoring or maintenance programs, sometimes costly, of the tubes in service are necessary to overcome this problem also linked to a possible degradation / embrittlement of the steel over time. In parallel, research and development studies aim to improve the composition of these steels to allow the transport of dihydrogen at high pressure without risk.

[0018] In an attempt to address the above issues, recent studies have shown that a shot peening surface treatment process can mitigate the effects induced by hydrogen in low-alloy steels through the introduction of a high level of work hardening and residual surface compressive stresses. These include, for example:

[0019] Hitoshi Soyama et al, “Effect of compressive residual stress introduced by cavitation peening and shot peening on the improvement of fatigue strength of stainless steel”, Journal of Materials Processing Technology, Vol 288, February 2021, 116877,

[0020] Teng An et al, “Effect of shot peening on tensile properties and fatigue behavior of X80 pipeline steel in hydrogen environment”, International Journal of Fatigue, 2019,

[0021] Yanfei Wang et al, “Effect of shot peening coverage on hydrogen embrittlement of a ferrite, pearlite”, International Journal of Hydrogen Energy, 2020.

[0022] However, analysis of the bibliographic results shows that the "shot peening" treatment implemented on these samples only allows a limited appreciable gain during a hydrogen gas permeation test in terms of incubation time (threshold time before measuring a hydrogen flow through the sample) and the presence despite everything of a measurable hydrogen flow in permanent (or stabilized) regime.

[0023] There is therefore a need for pipelines dedicated to the transport of gas containing dihydrogen that are more economical, while providing an increased level of safety regarding risks linked to hydrogen embrittlement.

[0024] Subject of the invention

[0025] The present invention aims to propose a solution for the transport of a gas containing dihydrogen, which is economical, which is reliable in reducing the penetration of hydrogen into the material and thus significantly improving its behavior in service and its durability, as well as the level of safety.

[0026] This aim can be achieved by means of a pipe tube configured to transport a gas comprising dihydrogen, formed in a steel, having a tubular inner wall delimiting a cavity in which a flow of this gas is intended to circulate, in which at the level of all or part of the inner wall, this steel comprises a surface barrier layer having a thickness starting from the inner wall and within which the steel has microstructural parameters different from the steel outside said surface barrier layer and configured to tend to oppose the passage of said gas through the thickness of said surface barrier layer, the surface barrier layer having been obtained by implementing a mechanical treatment of surface nano-structuring by ultrasonic shot peening under the effect of random impacts of spherical balls set in vibrational motion by an ultrasonic shot peening device.

[0027] It has been discovered that the level of severe plastic deformation induced by such a mechanical treatment of surface nano-structuring, which has the specificity of being a very intense shot peening treatment specifically adapted to cause severe plastic deformation of the steel considered (such a process being also known by the acronym SMAT for "Surface Mechanical Attrition Treatment" in the appropriate Anglo-Saxon terminology), makes it possible to obtain, beyond an improvement in the mechanical properties in terms of hardness and yield strength or the advantageous presence of residual superficial compressive stresses, a very significant advantageous effect on the gas permeation of hydrogen, in particular dihydrogen, through the thickness of the line pipe. This makes it possible to drastically reduce, or even cancel, the permeation flux of the gas transported through the thickness of the line pipe.Indeed, the surface barrier layer has the effect of locally significantly reducing the diffusion capacity of the gas contained in the cavity towards the inside of the thickness of the barrier layer in comparison with its diffusion capacity towards the inside of the same steel when the latter has not undergone the mechanical nanostructuring treatment described here. Within the surface barrier layer, the mechanical nanostructuring treatment results in a reduction in the gas permeability coefficient, by a factor ranging from 20 to 1000 depending on the conditions of implementation of the mechanical nanostructuring treatment, compared with the permeability coefficient of the same initial steel which has not undergone the mechanical nanostructuring treatment.In conclusion, a pipeline tube is thus obtained in a possibly more economical manner for which the hydrogen permeation flow is greatly reduced, which makes it possible to greatly improve its resistance to hydrogen embrittlement.

[0028] In this document, the terms "nano-structured" and "nanostructuring" associated with a layer mean that the grains of this layer have a submicron size.

[0029] The pipeline may have the technical characteristics described below, taken individually or in combination with each other. According to a non-limiting embodiment, the ratio between the hardness of the steel within the surface barrier layer and the hardness of the steel outside the surface barrier layer is between 1.2 and 3, and preferably between 1.2 and 1.5.

[0030] According to another non-limiting embodiment, the steel within the surface barrier layer has, moving away from the inner wall, an average grain size which increases over at least a portion of the thickness of the surface barrier layer, and the surface barrier layer comprises the following successive stack, starting from the inner wall:

[0031] - a nano-structured layer in which the steel has an average grain size of less than 1 micron,

[0032] - a transition layer, within which the steel has a progressively increasing average grain size moving away from the nano-structured layer.

[0033] According to a non-limiting embodiment, the nano-structured layer has a thickness greater than 40 microns, in particular greater than 45 microns, and preferably greater than 50 microns. Such a thickness has the advantage of providing an excellent anti-gas permeation function for hydrogen, in particular dihydrogen, through the thickness of the pipeline tube, making it possible to drastically reduce, or even eliminate, the permeation of the gas transported through the thickness of the pipeline tube and provides excellent resistance to embrittlement by hydrogen and significantly improves the in-service behavior and durability, as well as the level of safety.

[0034] According to a non-limiting embodiment, the ratio between the average grain size within the nano-structured layer and the average grain size of the steel outside the surface barrier layer is between 5 and 50. These arrangements have the advantage of providing an excellent anti-gas permeation function for hydrogen, in particular dihydrogen, through the thickness of the pipeline tube, making it possible to drastically reduce, or even eliminate, the permeation of the gas transported through the thickness of the pipeline tube and providing excellent resistance to hydrogen embrittlement and significantly improving the in-service behavior and durability, as well as the safety level.

[0035] According to a non-limiting embodiment, the steel is a ferrite-pearlite type steel, in particular an X80 grade steel. As the tests carried out by the Applicant have shown, these provisions make it possible to promote an excellent response of the steel to the mechanical surface treatment applied, with a view to obtaining the anti-permeation function sought in the present invention.

[0036] According to a non-limiting embodiment, within the surface barrier layer, the steel has residual surface compressive stresses of the order of -400 MPa at a depth, counted from the internal wall, greater than 100 microns, and in particular greater than 200 microns.These provisions make it possible to obtain, beyond an improvement in the mechanical properties in terms of hardness and elastic limit or the advantageous presence of residual surface compressive stresses, a very significant advantageous effect on the gaseous permeation of hydrogen, in particular dihydrogen, through the thickness of the pipeline tube, making it possible to drastically reduce, or even eliminate, the permeation of the gas transported through the thickness of the pipeline tube and confers excellent resistance to embrittlement by hydrogen and significantly improves the behavior in service and durability, as well as the level of safety.

[0037] According to a non-limiting embodiment, within the nano-structured layer, the grains are highly deformed, the average value of the grain shape factor of the steel being between 0.10 and 0.15, and outside the surface barrier layer, the average value of the grain shape factor of the steel is between 0.4 and 0.6. Once again, these arrangements not only make it possible to provide excellent mechanical properties but at the same time to oppose or even cancel the gaseous permeation of hydrogen through the wall of the treated pipeline.

[0038] The invention also relates to a method of manufacturing a pipeline tube as previously described, the manufacturing method comprising for this purpose the following steps:

[0039] - supply of an initial part to be treated, in the form of a tube having an initial interior wall of tubular shape delimiting an initial cavity,

[0040] - installation, in the initial cavity, of all or part of an ultrasonic shot blasting device comprising a sonotrode and an ultrasonic power generator, the sonotrode having an active vibrating wall delimiting a working enclosure in combination with the internal initial wall,

[0041] - placing, in the working enclosure, a plurality of spherical balls free to move in the working enclosure, the working enclosure being configured to ensure confinement of the balls within the working enclosure independently of their movements,

[0042] - setting the sonotrode into vibratory motion, the vibration amplitude and the vibration frequency of this vibratory motion being adapted to communicate to the balls sufficient kinetic energy to carry out a mechanical treatment of surface nano-structuring by ultrasonic shot peening generating, under the sole effect of the impacts of the balls against the initial interior wall, the conversion of the initial part into said pipeline tube, conversion during which the initial interior wall of the initial part becomes the internal wall of the pipeline tube and the surface barrier layer of the pipeline tube is formed.It has been discovered that the level of severe plastic deformation induced by a mechanical surface nano-structuring treatment as described above, i.e. by grain refinement by ultrasonic shot peening, which has the specificity of being a very intense shot peening treatment specifically adapted to cause severe plastic deformation of the steel in question (such a process being also known by the acronym SMAT for "Surface Mechanical Attrition Treatment" in the appropriate English terminology), makes it possible to obtain, beyond an improvement in the mechanical properties in terms of hardness and yield strength or the advantageous presence of residual superficial compressive stresses, a very significant advantageous effect on the gaseous permeation of hydrogen, in particular dihydrogen, through the thickness of the pipeline tube.This makes it possible to drastically reduce, or even cancel, the permeation flow of the gas transported through the thickness of the pipeline tube. Indeed, the surface barrier layer has the effect of locally significantly reducing the diffusion capacity of the gas contained in the cavity towards the interior of the thickness of the barrier layer in comparison with its diffusion capacity towards the interior of the same steel when the latter has not undergone the mechanical nanostructuring treatment described here. Within the surface barrier layer, the mechanical nanostructuring treatment results in a reduction in the gas permeability coefficient, by a factor ranging from 20 to 1000 depending on the conditions of implementation of the mechanical nanostructuring treatment, compared with the permeability coefficient of the same initial steel which has not undergone the mechanical nanostructuring treatment.In conclusion, a pipeline tube is thus obtained in a possibly more economical manner for which the hydrogen permeation flow is greatly reduced, which makes it possible to greatly improve its resistance to hydrogen embrittlement.

[0043] The manufacturing process may also have the technical characteristics described below, taken individually or in combination with each other.

[0044] According to a non-limiting implementation method, the active vibrating wall has a concave shape. These arrangements facilitate the easy implementation of the surface process by essentially delimiting the working enclosure receiving the balls on the sonotrode side; this also makes it possible to adapt and execute the manufacturing process independently of a particular shape of the treated pipeline, ultimately offering the guarantee of a certain universality.

[0045] According to a non-limiting embodiment, each of the balls has a diameter of between 400 microns and 10 mm, preferably between 1 and 4 mm, in particular of the order of 3 mm. These arrangements, where the projectiles have dimensions significantly greater than the dimensions (conventionally between 0.1 and 0.8 mm) of the projectiles used in the case of simple shot peening, guarantee the implementation of severe plastic deformation, these arrangements making it possible not only to confer excellent mechanical properties but at the same time to oppose or even cancel the gaseous permeation of hydrogen through the wall of the treated pipeline.

[0046] According to a non-limiting implementation method, the total mass of the balls present in the working enclosure is between 10 and 40 grams, preferably of the order of 20 grams. These provisions guarantee the implementation of severe plastic deformation, in order to oppose the gaseous permeation of hydrogen into the treated steel through the wall of the pipeline tube having undergone the surface treatment by ultrasonic shot blasting.

[0047] During the vibratory movement stage, the average impact distance of the balls can be between 15 and 30 mm, and is preferably of the order of 17 mm. These provisions guarantee the implementation of severe plastic deformation, in order to oppose the gaseous permeation of hydrogen into the treated steel through the wall of the pipeline tube having undergone the surface treatment by ultrasonic shot blasting.

[0048] According to a non-limiting implementation method, the vibratory movement step is implemented during a treatment duration of between 1 and 60 minutes, preferably between 5 and 20 minutes, in particular of the order of 10 minutes. These arrangements where the balls are projected for a period of time much longer than the treatment duration (conventionally of the order of 1 minute maximum) in the case of simple shot peening, guarantee the implementation of severe plastic deformation, these arrangements making it possible not only to confer excellent mechanical properties but at the same time to oppose or even cancel the gaseous permeation of hydrogen through the wall of the pipeline tube having undergone the surface treatment by ultrasonic shot peening.

[0049] According to a non-limiting embodiment, during the step of setting into vibrational movement, the vibration amplitude is between 10 and 100 microns, preferably between 20 and 30 microns, and in particular of the order of 25 microns.

[0050] According to another non-limiting embodiment, during the step of setting into vibrational movement, the vibration frequency is of the order of 20 kHz.

[0051] According to a particular mode of implementation, the parameters used during the vibratory movement step, the Almen intensity of the treatment imparted by the balls is greater than F 45 A, in particular of the order of F 49 A. These provisions guarantee the implementation of severe plastic deformation, in order to oppose the gaseous permeation of hydrogen into the treated steel through the wall of the pipeline tube having undergone the surface treatment by ultrasonic shot blasting.

[0052] Also presented is the principle of using a tube for transporting a gas comprising dihydrogen where the tube is formed from a steel, has a tubular-shaped inner wall delimiting a cavity in which a flow of said gas is intended to circulate, where at the level of all or part of the inner wall, this steel comprises a surface barrier layer having a thickness starting from the inner wall and within which the steel has microstructural parameters different from the steel outside said surface barrier layer and configured to tend to oppose the passage of said gas through the thickness of said surface barrier layer, the surface barrier layer having been obtained by implementing a mechanical treatment of surface nano-structuring by ultrasonic shot peening under the effect of random impacts of spherical balls set in vibrational motion by an ultrasonic shot peening device.

[0053] Summary description of the drawings

[0054] Other aspects, aims, advantages and characteristics of the invention will appear better on reading the following detailed description of preferred embodiments thereof, given by way of non-limiting example, and made with reference to the appended drawings in which:

[0055] Figure 1 is a longitudinal sectional view schematically showing in part an example of a pipeline tube according to a first aspect of the invention.

[0056] Figure 2 is a view illustrating in enlarged form the detail marked A in Figure 1.

[0057] Figure 3 schematically represents the components of an ultrasonic shot peening device usable for implementing a manufacturing method according to another aspect of the invention.

[0058] Figure 4 is a sectional view schematically representing a non-limiting example of implementation of an example of a manufacturing method according to one aspect of the invention.

[0059] Figure 5 is a flowchart representing the different stages of the manufacturing process.

[0060] Figure 6 is a schematic view showing a hydrogen gas permeation test method.

[0061] Figure 7 is an example of an ultrasonic shot peening device, as an alternative to Figure 4, suitable for implementing a manufacturing method according to one aspect of the invention.

[0062] Detailed description

[0063] In Figures 1 to 6 and in the remainder of the description, the same references represent identical or similar elements. In addition, the different elements are not shown to scale so as to enhance the clarity of the figures. Furthermore, the different embodiments and variants are not mutually exclusive and may be combined with each other. Unless otherwise stated, the terms "substantially" or "of the order of" mean, in this document, "exactly or to within 10% or 10°".

[0064] In Figure 1, a pipeline 10 is visible configured to transport a gas comprising dihydrogen. In other words, this gas is either pure dihydrogen or a gas mixture containing dihydrogen, such as for example dihydrogen mixed with natural gas. This pipeline 10 is typically an element forming part of a pipeline.

[0065] For example, this pipeline tube 10 has a length of several tens of meters and a diameter 12 of the order of 1 meter, even if this diameter 12 may possibly have a value lower than this if necessary depending on the needs or requirements. Its section is for example circular in shape for reasons of simplicity of manufacture, even if this is not limiting.

[0066] The pipeline tube 10 is formed from a steel. According to a non-limiting embodiment which has given excellent results and complete practical satisfaction, the steel is a ferrite-pearlite type steel, in particular a grade X80 steel. As the tests carried out by the Applicant have shown, these provisions make it possible to promote an excellent response of the steel to the mechanical surface treatment applied by ultrasonic shot peening, in order to obtain the anti-permeation function sought in the present invention. It remains nonetheless that the person skilled in the art may possibly envisage other low-alloy steels as well as stainless steels conventionally used for the transport of gases containing dihydrogen.

[0067] The pipeline tube 10 has an internal wall 14 of tubular shape delimiting a cavity 16 in which a flow 18 (symbolized by an arrow for simplicity of representation) of this gas is intended to circulate. In other words, the internal wall 14 delimits an internal surface which itself delimits the external contours of the cavity 16, the latter thus being of tubular shape extending essentially in a direction of extension 24 corresponding to the general direction of flow (except for turbulence) for the flow 18 of gas. The pipeline tube 10 has the particularity that at the level of all or part of the internal wall 14, the steel previously mentioned for the construction of the pipeline tube 10 comprises a surface barrier layer 20 having a thickness 22 which starts from the internal wall 14 and within which the steel has microstructural parameters different from the steel outside the surface barrier layer 20.These microstructural parameters are specifically configured so that the surface barrier layer tends to oppose the passage of gas through the thickness 22 of the surface barrier layer 20. The surface barrier layer 20 is obtained by implementing a mechanical treatment of surface nano-structuring by ultrasonic shot peening under the effect of random impacts of balls 26 of spherical shape previously set in motion in a vibratory manner by an ultrasonic shot peening device 28 which will be detailed later.

[0068] It is hereby specified that the person skilled in the art is able, by analysis or conventional micrographic examination, to determine whether such mechanical nano-structuring treatment has been carried out or not.

[0069] According to a non-limiting embodiment, the ratio between the hardness of the steel within the surface barrier layer 20 and the hardness of the steel in the zone 40 located outside the surface barrier layer 20 is between 1.2 and 3, and preferably between 1.2 and 1.5.

[0070] According to another non-limiting embodiment, the steel within the surface barrier layer 20 has, moving away from the internal wall 14, an average grain size which increases over at least a portion of the thickness 22 of the surface barrier layer 20, and the surface barrier layer 22 comprises the following successive stack, starting from the internal wall 14:

[0071] - a nano-structured layer 32 (which contains submicron-sized grains, as already mentioned above) in which the steel has an average grain size having a value of less than 1 micron,

[0072] - a transition layer 34, within which the steel has a progressively increasing average grain size moving away from the nano-structured layer 32.

[0073] The thickness 38 of the transition layer 34 is between 50 and 250 microns. According to a non-limiting embodiment, the nano-structured layer 32 has a thickness 36 greater than 40 microns, in particular greater than 45 microns, and preferably greater than 50 microns.

[0074] According to a non-limiting embodiment, the ratio between the average grain size within the nano-structured layer 32 and the average grain size of the steel in the zone 40 located outside the surface barrier layer 20 is between 5 and 50.

[0075] The grain size in the zone 40 located outside the surface barrier layer 20 is for example of the order of 5 microns while the average grain size within the nano-structured layer 32 is between 0.1 and 1 micron.

[0076] According to a non-limiting embodiment, within the surface barrier layer 20, the steel has residual surface compressive stresses of the order of -400 MPa up to a depth, counted from the internal wall 14, which is greater than 100 microns, and in particular greater than 200 microns.

[0077] If the maximum residual compressive stress depends essentially on the impact speed of the balls 26, it appears that the depth reached by this residual compressive stress depends both on the impact speed of the balls 26 and on the diameter of the balls 26.

[0078] According to a non-limiting embodiment, within the nano-structured layer 32, the grains are highly deformed, the average value of the shape factor of the steel grains being between 0.10 and 0.15, while in the zone 40 located outside the surface barrier layer 20, the average value of the shape factor of the steel grains is between 0.4 and 0.6. In the above, the shape factor is defined as the ratio between the maximum length of a grain and the orthogonal width (or thickness). A shape factor of 1 corresponds to an isotropic grain of maximum symmetry (similar to a circle, a sphere, a square or a cube). This is an important macroscopic criterion for differentiating the different zones after shot peening.Any optical microscopic analysis method that can determine, for each grain viewed, the form factor thus defined, and then average these values ​​for all grains viewed, can be used, for example using a magnification of between 500 and 1000 times. There are many microscopes equipped with suitable software, known to those skilled in the art, capable of carrying out these operations.

[0079] Referring now to Figure 5, reference is also made to a method of manufacturing a pipeline 10 as previously described. This manufacturing method comprises the following steps:

[0080] - step E1 of providing an initial part 101 to be treated, in the form of a tube having an initial interior wall 141 of tubular shape delimiting an initial cavity 161,

[0081] - step E2 of placing, in the initial cavity 161, all or part of an ultrasonic shot peening device 28 comprising a sonotrode 282 and an ultrasonic power generator 281, the sonotrode 282 having an active vibrating wall 284 delimiting a working enclosure 286 in combination with the internal initial wall 141,

[0082] - step E3 of placing, in the working enclosure 286, a plurality of spherical balls 26 free to move in the working enclosure 286, the working enclosure 286 being configured to ensure confinement of the balls 28 within the working enclosure 286 independently of their movements,

[0083] - step E4 of setting the sonotrode 282 into vibratory motion, the vibration amplitude and the vibration frequency of this vibratory motion being adapted to communicate to the balls 26 sufficient kinetic energy to carry out a mechanical treatment of surface nano-structuring by ultrasonic shot peening generating, under the sole effect of the impacts of the balls 26 against the initial inner wall 141, the conversion of the initial part 101 into said pipe tube 10, conversion during which the initial inner wall 141 of the initial part 101 becomes the internal wall 14 of the pipe tube 10 and the surface barrier layer 20 of the pipe tube 10 is formed. The positioning of the sonotrode 282 in the initial cavity 161 is shown diagrammatically by the arrow marked 30 in FIG. 4, for reasons of ease of understanding. Prior to this insertion, the balls 26 are placed within the working enclosure 286.

[0084] With reference to Figure 3, the ultrasonic power generator 281 of the ultrasonic shot peening device 28 comprises a frequency generator 281a which makes it possible to generate a signal 281b of a given frequency (for example here of the order of 20 KHz) for a given amplitude which remains adjustable. The ultrasonic power generator 281 comprises a piezoelectric converter 281c: the signal 281b delivered by the frequency generator 281a is converted into a mechanical signal 281d using this piezoelectric converter 281c. The ultrasonic power generator 281 also comprises a booster 281e: the weak mechanical signal 281d at the output of the piezoelectric converter 281c is routed to the booster 281e which makes it possible to amplify it to generate an amplified mechanical signal 281f transmitted to the input of the sonotrode 282.

[0085] According to a non-limiting embodiment, the active vibrating wall 284 has a concave shape. These arrangements, visible in Figure 4, promote easy implementation of the manufacturing method by essentially delimiting the working enclosure 286 receiving the balls 26 on the side of the sonotrode 282; this also makes it possible to adapt and execute the manufacturing method independently of a particular shape of the pipeline tube 10 being treated, ultimately offering the guarantee of a certain universality. It should be noted that the diagram in Figure 4 is a schematic diagram but the design and organization of the ultrasonic shot blasting device 28 could be adapted according to the size of the pipeline tubes being treated (size of the sonotrode 282 in particular).

[0086] To achieve an active vibratory wall 284 of concave shape allowing good angular distribution of the effects obtained by the balls 26 at 360° around the direction of extension 24, the active vibratory wall 284 can in particular be shaped in the form of a surface of revolution, which is mathematically defined by the 3-dimensional surface generated by the 360° revolution around an axis of revolution of a basic generator.

[0087] In the example of Figure 4, we can see that the basic generator is in the form of an arched profile. In other words, the active vibrating wall 284 is in the general form of a diabolo.

[0088] On the other hand, in the example of Figure 7, which shows a very efficient example of an ultrasonic shot peening device 28, the basic generator comprises over a majority (greater than 60 mm for example) of its total length (for example 83 mm) a rectilinear profile, oriented parallel to said axis of revolution. Thus, over a majority of its axial length, the active vibratory wall 284 has a cylindrical shape of circular section 287, for example with a diameter of 30 mm, the two ends of which are connected to the rest of the ultrasonic shot peening device 28 by respective connection fillets 288, for example having radii of curvature of 10 mm.

[0089] The shape of the active vibrating wall 284 of Figure 7 is advantageous compared to that of Figure 4. It has a significant length, which makes it possible to cover a large working area without the need for an extension cord. Tests have shown that a gain of 2.6 in efficiency is obtained when using the ultrasonic shot peening device 28 of Figure 7 compared to a gain of 1.0 when using the ultrasonic shot peening device of Figure 4. The shape of Figure 7 in fact makes it possible to optimize the random movement of the balls 26 during the ultrasonic shot peening treatment and thus to increase the efficiency of the treatment (i.e. the gain of 2.6 corresponding to the amplification of the ultrasonic signal).

[0090] According to a non-limiting embodiment, each of the balls 26 has a diameter of between 400 microns and 10 mm, preferably between 1 and 4 mm, in particular of the order of 3 mm. These arrangements, where the projectiles have dimensions significantly greater than the dimensions (generally between 0.1 and 0.8 mm) of the projectiles used in the case of simple shot peening, guarantee the implementation of severe plastic deformation, these arrangements making it possible not only to confer excellent mechanical properties but at the same time to oppose or even cancel the gaseous permeation of hydrogen through the wall of the pipeline tube 10 thus manufactured.

[0091] According to a non-limiting embodiment, the total mass of the balls 26 present in the working enclosure 286 is between 10 and 40 grams, preferably of the order of 20 grams. These provisions guarantee the implementation of severe plastic deformation, in order to oppose the gaseous permeation of hydrogen into the treated steel through the wall of the pipeline tube 10 having undergone the mechanical treatment of surface nanostructuring by ultrasonic shot peening.

[0092] According to another non-limiting embodiment, during step E4 of vibratory movement, the average impact distance (this is the distance between the active vibratory wall 284 and the initial interior wall 141) of the balls 26 is between 15 and 30 mm, and is preferably of the order of 17 mm. These provisions guarantee the implementation of severe plastic deformation, in order to oppose the gaseous permeation of hydrogen into the treated steel through the wall of the pipeline tube 10 having undergone the mechanical treatment of surface nano-structuring by ultrasonic shot peening.

[0093] During step E4 of vibratory movement, the average impact speed of the balls is less than or equal to 20 m / s. The balls 26 are projected at an impact speed significantly lower than the impact speed (conventionally between 40 and 120 m / s) of the projectiles used in the case of simple shot peening. According to a non-limiting embodiment, step E4 of vibratory movement is implemented during a treatment duration of between 1 and 60 minutes, preferably between 5 and 20 minutes, in particular of the order of 10 minutes.These arrangements, where the balls are projected for a period of time well in excess of the treatment time (of the order of 1 minute maximum) in the case of simple shot peening, guarantee the implementation of severe plastic deformation, these arrangements making it possible not only to confer excellent mechanical properties but at the same time to oppose or even cancel the gaseous permeation of hydrogen through the wall of the manufactured pipeline tube 10.

[0094] According to a non-limiting embodiment, during step E4 of vibratory movement, the vibration amplitude is between 10 and 100 microns, preferably between 20 and 30 microns, and in particular of the order of 25 microns.

[0095] According to another non-limiting embodiment, during step E4 of vibratory movement, the vibration frequency is of the order of 20 kHz.

[0096] According to a particular implementation mode, the parameters used during the vibratory movement step, the Almen intensity of the treatment imparted by the balls is greater than F 45 A, in particular of the order of F 49 A. These provisions guarantee the implementation of severe plastic deformation, in order to oppose the gaseous permeation of hydrogen in the treated steel through the wall of the pipe tube 10 having undergone the manufacturing process. The Almen intensity is a characterization of the intensity of the mechanical treatment of surface nano-structuring by ultrasonic shot peening. This intensity is directly linked to the vibration amplitude, therefore to the energy transmitted to the material during the treatment. It is therefore possible to imagine treating with low powers, which would lead to a low Almen intensity (or arrow), and vice versa.

[0097] The parameters mentioned in the previous paragraph are in particular the following: the vibration amplitude, the duration of the treatment, the impact distance separating the sonotrode 282 and the surface to be treated, the mass of the balls 26, the diameter of the balls 26, the treatment temperature (for example at room temperature, but it is possible to work under a controlled temperature and / or atmosphere).

[0098] The 26 balls impact the surface to be treated in a random and multidirectional manner, which allows high coverage rates to be achieved.

[0099] The material of the balls 26 may in particular be 100C6 steel, which in practice gives great satisfaction and excellent results. It remains the case that the person skilled in the art may consider using, for the implementation of the manufacturing method, balls 26 formed from other grades of hard steel or tungsten carbide. The pipe tube 10 and the manufacturing method, both described in detail above, have numerous advantages which have already been explained previously.The manufacturing process can be implemented on line pipes that have never been used, but can also potentially be applied to line pipes that have already been put into service and that would be considered for improvement in terms of capacity, such as for example line pipes that would have been used for the transport of natural gas and that one would like to transform (via the manufacturing process) for conversion to a use dedicated to the transport of a gas containing dihydrogen, whether it is pure dihydrogen or a mixture between natural gas and dihydrogen.

[0100] To achieve the invention and prove its object, its operation, its effects and its advantages, the Applicant carried out tests which will be detailed below, with reference to figure 6 now.

[0101] In order to determine the effect of the ultrasonic shot peening detailed above on increased resistance to hydrogen embrittlement, it was chosen to focus on the reduction of its permeation. Tests in this sense were carried out using a test disc 300 made of X80 steel having a diameter of 49 mm and a thickness of approximately 1 mm, the test disc having a circular central part 300a surrounded by an annular periphery 300b. The purpose of the device illustrated in Figure 6 was to evaluate the gaseous permeation of dihydrogen, which is the phenomenon resulting in the passage of this fluid through the solid wall materialized by the central part 300a of the test disc 300. A two-part frame 302, 304 compressing against each other was used.A first O-ring 306 was interposed and compressed between the annular periphery 300b of the test disc 300 and the first part 302 of the frame and a second O-ring 308 was interposed and compressed between the annular periphery 300b of the test disc 300 and the second part 304 of the frame. The O-rings 306, 308 ensured a perfect seal between the two parts 302, 304 of the frame for the gaseous dihydrogen used. The two parts 302, 304 respectively comprise channels 302a, 304a opening on the one hand towards the outside of the frame, and on the other hand towards a cavity 310 delimited internally by the frame, this cavity 310 being separated in two by the central part 300a of the test disc 300 placed in the frame.From outside the frame, an inlet flow F1 of gaseous dihydrogen was directed towards the cavity 310 via the channel 302a of the first part 302 of the frame at a constant pressure and a fixed temperature, while a possible outlet flow F2 of gaseous dihydrogen coming from the channel 304a delimited by the second part 304 of the frame was monitored via a mass spectrometer outside the frame.

[0102] To conduct comparative tests, four different test discs 300 were prepared: a first test disc named sample 1 whose central portion 300a underwent a simple polishing, a second test disc named sample 2 whose central portion 300a underwent a sandblasting treatment, a third test disc named sample 3 whose central portion 300a underwent insufficient ultrasonic shot peening to create a surface barrier layer previously explained in connection with the pipe tube 10, and finally a fourth test disc named sample 4 whose central portion 300a underwent a manufacturing process as described above, the parameters of which imply that the ultrasonic shot peening is sufficiently intense to create, unlike sample 3, the surface barrier layer previously explained in connection with the pipe tube 10.

[0103] More specifically and in particular, Table 1 below indicates the set of parameters of the intense shot peening treatment which were applied to prepare sample 4.

[0104] [Table 1]

[0105] It should be noted that the parameters listed above are specific values ​​that fall within the ranges of values ​​listed above when describing the general principles of the manufacturing process.

[0106] Table 2 below lists the set of parameters that were applied to prepare Sample 2.

[0107] [Table 2]

[0108] Finally, Table 3 below shows the set of light shot peening treatment parameters that were applied to prepare Sample 3. [Table 3]

[0109] Table 4 below provides a comparison of the results of the hydrogen gas permeation tests obtained when the principles of Figure 6, at a temperature of 80°C and when the hydrogen inlet flow F1 has a pressure of 8 bars, were applied to samples 1 to 4 respectively.

[0110] [Table 4]

[0111] It follows that at a temperature of 80°C, while a permeation threshold with the detection of a dihydrogen flow is observed after a few minutes on samples 1 to 3, on the contrary no dihydrogen flow is detected on sample 4 after more than a week.

[0112] This test was carried out twice to verify the accuracy of the observed trend. Then an additional test was carried out, raising the temperature to 120°C: for sample 4, a stabilized regime was obtained after a very long time of approximately 500,000 seconds, which is still significantly longer than the times recorded at 80°C for samples 1 to 3.

[0113] In conclusion, the intense ultrasonic shot peening treatment described herein advantageously blocks or significantly delays the penetration of hydrogen into the steel.

[0114] In parallel with the advantages obtained with regard to the permeation of a gas containing dihydrogen thanks to the invention, it should also be noted that the surface treatment by intense ultrasonic shot peening has metallurgical effects on the surface of the internal wall 14 of the pipeline tube 10: a refinement and a flattening of the grains at the level of the internal wall 14 where the surface treatment by ultrasonic shot peening is applied, to a depth of approximately 50 microns; a significant increase in hardness: the micro-hardness, close to the area having undergone the surface treatment by intense ultrasonic shot peening, 30 microns from the edge, is 310 HV0.01 compared to 235 HV0.01 for the initial steel; the depth hardness profiles show that the effect is noticeable over a depth of 300 microns from the inner wall 14; the surface treatment by intense ultrasonic shot peening creates maximum residual superficial compressive stresses having a similar order of magnitude (approximately -400 MPa) to those obtained by implementing conventional shot peening, but the depths affected are higher in the case of the intense ultrasonic shot peening described in this document: in the first case, almost zero residual superficial stresses are measured at a depth of 200 microns, while in the second case, compressive stresses with values ​​of -400 MPa are measured at this depth.

Claims

CLAIMS 1. A pipe tube (10) configured to transport a gas comprising dihydrogen, formed in a steel, having an inner wall (14) of tubular shape delimiting a cavity in which a flow of said gas is intended to circulate, wherein at all or part of the inner wall, said steel comprises a surface barrier layer having a thickness starting from the inner wall and within which the steel has microstructural parameters different from the steel outside said surface barrier layer and configured to tend to oppose the passage of said gas through the thickness of said surface barrier layer, said surface barrier layer having been obtained by implementing a mechanical treatment of surface nano-structuring by ultrasonic shot peening under the effect of random impacts of spherical balls set in vibrational motion by an ultrasonic shot peening device (28).

2. A pipeline (10) according to claim 1, wherein the ratio of the hardness of the steel within the surface barrier layer (20) to the hardness of the steel outside the surface barrier layer (20) is between 1.2 and 3.

3. A pipeline (10) according to one of claims 1 or 2, wherein the steel within the surface barrier layer (20) has, moving away from the inner wall (14), an average grain size increasing over at least a portion of the thickness (22) of the surface barrier layer (20), and wherein the surface barrier layer (20) comprises the following successive stack, starting from the inner wall (14): a nano-structured layer (32) in which the steel has an average grain size having a value less than 1 micron, a transition layer (34), within which the steel has an average grain size gradually increasing moving away from the nano-structured layer (32).

4. Pipe tube (10) according to claim 3, in which the nano-structured layer (32) has a thickness (36) greater than 40 microns.

5. Pipe tube (10) according to one of claims 3 or 4, in which the ratio between the average grain size within the nano-structured layer (32) and the average grain size of the steel outside the surface barrier layer (20) is between 5 and 50.

6. Pipe tube (10) according to one of claims 1 to 5, in which the steel is a ferrite-pearlite type steel, in particular a grade X80 steel.

7. A pipeline (10) according to one of claims 1 to 6, wherein within the surface barrier layer (20), the steel has surface residual stresses of compression of the order of -400 MPa at a depth, counted from the internal wall (14), greater than 100 microns.

8. Pipe tube (10) according to one of claims 1 to 7, wherein within the nano-structured layer (32), the grains are highly deformed, the average value of the shape factor of the grains of the steel being between 0.10 and 0.15, and wherein outside the surface barrier layer (20), the average value of the shape factor of the grains of the steel is between 0.4 and 0.

6.

9. A method of manufacturing a pipeline tube (10) according to any one of the preceding claims, comprising the following steps: (E1) providing an initial part (101) to be treated, in the form of a tube having an initial inner wall (141) of tubular shape delimiting an initial cavity (161), (E2) placing, in the initial cavity (161), all or part of an ultrasonic shot blasting device (28) comprising a sonotrode (282) and an ultrasonic power generator (281), the sonotrode (282) having an active vibrating wall (284) delimiting a working enclosure (286) in combination with the internal initial wall (141), (E3) placing, in the working enclosure (286), a plurality of spherical balls (26) free to move in the working enclosure (286), the working enclosure (286) being configured to ensure confinement of the balls (26) within the working enclosure (286) independently of their movements, (E4) vibratory movement of the sonotrode (282), the vibration amplitude and the vibration frequency of this vibratory movement being adapted to communicate to the balls (26) sufficient kinetic energy to carry out a mechanical treatment of surface nano-structuring by ultrasonic shot peening generating, under the sole effect of the impacts of the balls (26) against the initial inner wall (141), the conversion of the initial part (101) into said pipe tube (10) according to any one of the preceding claims, conversion during which the initial inner wall (141) of the initial part (101) becomes the internal wall (14) of the pipe tube (10) and the surface barrier layer (20) of the pipe tube (10) is formed.

10. Manufacturing method according to claim 9, wherein the active vibratory wall (284) has a concave shape.

11. Manufacturing method according to one of claims 9 or 10, in which each of the balls (26) has a diameter of between 400 microns and 10 mm.

12. Manufacturing method according to one of claims 9 to 11, in which the total mass of the balls (26) present in the working enclosure (286) is between 10 and 40 grams.

13. Manufacturing method according to one of claims 9 to 12, in which during step (E4) of setting into vibratory movement, the average impact distance of the balls (26) is between 15 and 30 mm.

14. Manufacturing method according to one of claims 9 to 13, in which the step (E4) of vibratory movement is implemented during a treatment duration of between 1 and 60 minutes.

15. Manufacturing method according to one of claims 9 to 14, in which during step (E4) of setting into vibratory movement, the vibration amplitude is between 10 and 100 microns.

16. Manufacturing method according to one of claims 9 to 15, in which during step (E4) of setting into vibratory movement, the vibration frequency is of the order of 20 kHz.

17. Manufacturing method according to one of claims 9 to 16, in which the parameters used during step (E4) of vibratory movement, the Almen intensity of the treatment conferred by the balls (26) is greater than F 45 A.

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