Hydrogen transport pipeline with surface barrier layer and method for surface treatment of such pipeline

Abstract

A steel pipeline (10) for transporting a gas comprising hydrogen is described. At 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 microstructural parameters different from 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). The latter is obtained by implementing a mechanical treatment of surface nano-structuring by ultrasonic shot peening under the effect of random impacts of spherical balls (26) set in vibrational motion by an ultrasonic power generator (28). A method for surface treatment of the pipeline (10) is also described. Figure 4

Description

Title of the invention: Hydrogen transport pipeline with surface barrier layer and method for surface treatment of such a pipeline Technical field of the invention

[0001] The present invention relates to a pipeline for transporting a gas comprising hydrogen, formed in a steel, having an internal wall of tubular shape delimiting a cavity in which a flow of said gas is intended to circulate.

[0002] The invention also relates to a method for surface treatment of such a pipeline tube.

[0003] The surface treatment method can be implemented on pipeline pipes at the end of their manufacturing process, but can also potentially be applied to pipeline pipes that have already been put into service and that would be considered for improvement in terms of capacity, such as for example pipeline pipes that would have been used for the transport of natural gas and that one would wish to transform (via surface treatment) for conversion to a use dedicated to the transport of a gas containing hydrogen, whether it is pure dihydrogen or a mixture between natural gas and dihydrogen.

[0004] The invention finds application in particular in the transport of hydrogen in the gaseous state, whether it is pure hydrogen or a gaseous mixture containing hydrogen, such as for example dihydrogen mixed with natural gas. State of the art

[0005] The development of the hydrogen sector requires the production, transport and storage of large quantities of hydrogen under multiple implementation and operating conditions.

[0006] One of the major concerns for the safety and environment of users is the embrittlement by hydrogen of the various components of the chain, namely the reactor vessels, the pipeline tubes dedicated to transport and the storage vessels, as well as the potential explosion scenarios linked to the accumulation of hydrogen in enclosed spaces.

[0007] The present invention is solely concerned with the management of these problems at the level of pipeline tubes, dedicated to the transport of hydrogen or gas mixtures containing hydrogen.

[0008] 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 atoms of hydrogen but also and above all because of the electronic affinity of these 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 wall of the metal, then a dissociation of the dihydrogen molecule, then a chemisorption of the hydrogen atoms at the wall of the metal. 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 the diffusion in the volume of the metal comes into play. It is known that the diffusion of hydrogen can be modified by the presence of traps, which are crystallographic or microstructural defects (vacancies, grain boundaries, dislocations, internal cracks, microcavities...).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 depends strongly on temperature and time: for an infinitely long time, all traps can be considered reversible.

[0009] The presence of hydrogen confers 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 guarantee 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.

[0010] Currently, hydrogen is transported via pipeline networks. However, this network remains very limited, representing only a few thousand kilometers worldwide, mainly in Europe and the United States. For safety reasons, transport distances are quite short and the network is located far from residential areas.

[0011] To address the risks of hydrogen embrittlement, the materials currently used for the transport of gaseous hydrogen are generally either low-alloy ferritic (or ferrito-pearlitic) steels (with high safety coefficients), or stainless steels (for more specific or local applications).

[0012] Stainless steels are more expensive than low-alloy steels, which is a barrier to large-scale deployment of pipelines with large diameters, of the order of a meter, as is the case for natural gas transmission pipes.

[0013] On the other hand, feedback does not allow us to guarantee all the risks of embrittlement by hydrogen for periods of use of several decades. In particular, monitoring or maintenance programs, sometimes expensive, in-service tubes are necessary to overcome this problem, which is also linked to possible degradation / embrittlement of the steel over time. At the same time, research and development studies aim to improve the composition of these steels to allow the transport of hydrogen at high pressure without risk.

[0014] In an attempt to address the above issues, recent studies have shown that a shot peening surface treatment process (also known as "shot peening" in the established Anglo-Saxon terminology) can mitigate the effects induced by hydrogen in low-alloy steels via the introduction of a high level of work hardening and residual surface compressive stresses at the surface. These include, for example, the following studies: - 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, - 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, - Yanfei Wang et al, “Effect of shot peening coverage on hydrogen embrittlement of a ferrite, pearllite”, International Journal of Hydrogen Energy, 2020.

[0015] 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.

[0016] There is therefore a need to have pipelines dedicated to the transport of a gas containing hydrogen which are more economical, while providing an increased level of safety with regard to risks linked to embrittlement by hydrogen. Subject of the invention

[0017] The present invention aims to propose a solution for the transport of a gas containing hydrogen, 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.

[0018] This aim can be achieved by means of a pipeline tube for transporting a gas comprising hydrogen, formed in a steel, having an internal wall of tubular shape 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 internal wall, this steel comprises a surface barrier layer having a thickness starting from the internal 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 motion in a vibratory manner by an ultrasonic shot peening device.

[0019] 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-blasting treatment specifically adapted to cause severe plastic deformation of the steel in question (such a process also being 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 gas 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 flux 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 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 nano-structuring treatment described here. Within the surface barrier layer, the mechanical nano-structuring 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 nano-structuring treatment, compared with the permeability coefficient of the same initial steel which has not undergone the mechanical nano-structuring 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.

[0020] In this document, the terms “nano-structured” and “nano-structuring” associated with a layer mean that the grains of this layer have a submicron size.

[0021] The pipeline tube may have the technical characteristics described below, taken individually or in combination with each other.

[0022] 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.

[0023] According to another non-limiting embodiment, the steel within the surface barrier layer has, moving away from the internal wall, an average grain size which increases over at least part of the thickness of the surface barrier layer, and the surface barrier layer comprises the following successive stack, starting from the internal wall:

[0024] - a nano-structured layer in which the steel has an average size of grains having a value less than 1 micron,

[0025] - a transition layer, within which the steel has an average size of grains gradually increasing away from the nano-structured layer.

[0026] 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 safety level.

[0027] 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 provides excellent resistance to embrittlement by hydrogen and significantly improves the behavior in service and durability, as well as the level of safety.

[0028] 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.

[0029] According to a non-limiting embodiment, within the surface barrier layer, the steel has residual superficial 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 yield strength or the advantageous presence of residual surface compressive stresses, a very significant advantageous effect on the gas 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 provide excellent resistance to hydrogen embrittlement and significantly improve in-service behavior and durability, as well as the level of safety.

[0030] According to a non-limiting embodiment, within the nano-structured layer, 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 outside the surface barrier layer, the average value of the shape factor of the grains of the steel is between 0.4 and 0.6. Once again, these arrangements make 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.

[0031] The invention also relates to a method for surface treatment of a pipeline tube for transporting a gas comprising hydrogen, formed in a steel, having an internal wall of tubular shape delimiting a cavity in which a flow of said gas is intended to circulate, comprising the following steps:

[0032] - providing an initial part to be treated, in the form of a tube having a wall initial interior tubular shape delimiting an initial cavity,

[0033] - installation, in the initial cavity, of all or part of a shot blasting device ultrasonic 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,

[0034] - placing, in the working enclosure, a plurality of free spherical balls to move within the work enclosure, the work enclosure being configured to ensure confinement of the balls within the work enclosure regardless of their movements,

[0035] - vibratory movement of the sonotrode, the vibration amplitude and the vibration frequency of this vibratory movement being adapted to communicate to the balls sufficient kinetic energy to carry out 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 the pipeline tube during which the initial interior wall becomes the internal wall of the pipeline tube and during which, in the steel, a surface barrier layer is formed 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 configured to tend to oppose the passage of said gas through the thickness of said surface barrier layer.

[0036] 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 also being 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 elastic limit 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 nano-structuring treatment described here. Within the surface barrier layer, the mechanical nano-structuring 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 nano-structuring treatment, compared with the permeability coefficient of the same initial steel which has not undergone the mechanical nano-structuring 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.

[0037] The surface treatment method may furthermore have the technical characteristics described below, taken individually or in combination with each other.

[0038] According to a non-limiting embodiment, the active vibrating wall has a concave shape. These arrangements promote easy implementation of the surface treatment method by essentially delimiting the working enclosure receiving the balls on the sonotrode side; this also makes it possible to adapt and execute the surface treatment method independently of a particular shape of the treated pipeline, ultimately offering the guarantee of a certain universality.

[0039] 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.

[0040] According to a non-limiting embodiment, 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 treatment process.

[0041] During the vibratory movement step, the average impact distance of the balls can be between 15 and 30 mm, and is preferably of the order of 17 mm. These arrangements 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 treatment process.

[0042] According to a non-limiting embodiment, 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 treated pipeline tube.

[0043] According to a non-limiting embodiment, during the step of setting into vibratory movement, the vibration amplitude is between 10 and 50 microns, preferably between 20 and 30 microns, and in particular of the order of 25 microns.

[0044] According to another non-limiting embodiment, during the step of setting into vibrational movement, the vibration frequency is of the order of 20 kHz.

[0045] According to a particular mode of implementation, the parameters used during the step of setting into vibratory movement, the Almen intensity of the treatment conferred 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 treatment process. Summary description of the drawings

[0046] 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:

[0047] [Fig-1] [Fig.l] is a longitudinal sectional view schematically showing partially an example of a pipeline tube according to a first aspect of the invention.

[0048] [Fig.2] [Fig.2] is a view illustrating in enlarged form the detail marked A in [Fig.l].

[0049] [Fig.3] [Fig.3] schematically represents the components of an ultrasonic shot blasting device usable for implementing a surface treatment method according to another aspect of the invention.

[0050] [Fig.4] [Fig.4] is a sectional view schematically representing a non-limiting example of implementation of an example of a treatment method according to one aspect of the invention.

[0051] [Fig.5] [Fig.5] is a flowchart representing the different stages of the surface treatment process.

[0052] [Fig.6] [Fig.6] is a principle view showing a method for testing hydrogen gas permeation. Detailed description

[0053] 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 can be combined with each other.

[0054] Unless otherwise stipulated, the terms “substantially” or “of the order of” mean, in this document, “exactly or to within 10% or 10°”.

[0055] In [Fig.l], a pipeline tube 10 is visible capable of transporting a gas comprising hydrogen. In other words, this gas is either pure hydrogen or a gas mixture containing hydrogen, such as for example dihydrogen mixed with natural gas. This pipeline tube 10 is typically an element forming part of a pipeline.

[0056] By way of 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.

[0057] 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 arrangements 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. It nevertheless remains that a person skilled in the art may possibly envisage other low-alloy steels as well as stainless steels conventionally used for the transport of hydrogen or gases containing hydrogen.

[0058] 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.

[0059] It is hereby specified that the person skilled in the art is able, by conventional micrographic analysis or examination, to determine whether such a mechanical nanostructuring treatment has been carried out or not.

[0060] 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.

[0061] 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:

[0062] - 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,

[0063] - a transition layer 34, within which the steel has an average size of grains gradually increasing away from the nano-structured layer 32.

[0064] The thickness 38 of the transition layer 34 is between 50 and 250 microns.

[0065] 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.

[0066] 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.

[0067] The size of the grains in the zone 40 located outside the surface barrier layer 20 is for example of the order of 5 microns while the average size of the grains within the nano-structured layer 32 is between 0.1 and 1 micron.

[0068] 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.

[0069] 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.

[0070] 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 grains of the steel 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 grains of the steel 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.

[0071] With reference to [Fig.5] now, reference is also made to a method of surface treatment of a pipeline tube 10 for the transport of a gas comprising hydrogen, formed in a steel, having an internal wall 14 of tubular shape delimiting a cavity 16 in which a flow 18 of this gas is intended to circulate, this method comprising the following steps:

[0072] - step El 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,

[0073] - step E2 of placing, in the initial cavity 161, all or part of a 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,

[0074] - step E3 of placing, in the working enclosure 286, a plurality of balls 26 spherical balls 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,

[0075] - step E4 of setting the sonotrode 282 into vibratory motion, the amplitude of vibration and the vibration frequency of this vibratory movement being adapted to communicate to the balls 26 sufficient kinetic energy to carry out 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 the pipe tube 10 during which the initial inner wall 141 becomes the internal wall 14 of the pipe tube 10 and during which, in the steel, a surface barrier layer 20 is formed having a thickness 22 starting from the internal wall 14 and within which the steel has microstructural parameters different from the steel located in the zone 40 outside the surface barrier layer 20, these parameters being configured to tend to oppose the passage of gas through the thickness 22 of the surface barrier layer 20.

[0076] The installation 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.

[0077] With reference to [Fig. 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 28 Id using this piezoelectric converter 281c. The ultrasonic power generator 281 also comprises a booster 281e: the weak mechanical signal 28 Id at the output of the piezoelectric converter 281c is routed to the booster 281e which allows it to be amplified to generate an amplified mechanical signal 28If transmitted to the input of the sonotrode 282.

[0078] According to a non-limiting embodiment, the active vibrating wall 284 has a concave shape. These arrangements, visible in [Fig. 4], promote easy implementation of the treatment 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 treatment 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 [Fig. 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).

[0079] 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 treated pipe tube 10.

[0080] 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 pipe tube 10 having undergone the treatment process.

[0081] According to another non-limiting embodiment, during step E4 of setting into 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 to the gaseous permeation of hydrogen into the treated steel through the wall of the pipeline 10 having undergone the treatment process.

[0082] 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.

[0083] 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 much longer than the treatment duration (of the order of 1 minute at most) 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 pipe tube 10.

[0084] According to a non-limiting embodiment, during step E4 of setting into vibratory movement, the vibration amplitude is between 10 and 50 microns, preferably between 20 and 30 microns, and in particular of the order of 25 microns.

[0085] According to another non-limiting embodiment, during step E4 of setting into vibrational movement, the vibration frequency is of the order of 20 kHz.

[0086] According to a particular mode of implementation, the parameters used during the step of setting into vibratory movement, 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 a 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 treatment process. The Almen intensity is a characterization of the intensity of the mechanical treatment of surface nano-structuring. 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.

[0087] The parameters mentioned in the preceding 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 ambient temperature, but it is possible to work under a controlled temperature and / or atmosphere).

[0088] The balls 26 impact the surface to be treated in a random and multidirectional manner, which makes it possible to achieve high coverage rates.

[0089] The material of the balls 26 may in particular be 100C6 steel, which in practice gives great satisfaction and excellent results. It remains nonetheless that the person skilled in the art may envisage using, for the implementation of the surface treatment method, balls 26 formed in other grades of hard steel or tungsten carbide.

[0090] The line pipe 10 and the surface treatment method, both described in detail above, have numerous advantages which have already been explained previously. The surface treatment method can be implemented on line pipes at the end of their manufacturing process, but can also potentially be applied to line pipes which have already been put into service and which would be considered for improvement in terms of capacity, such as for example line pipes which would have been used for the transport of natural gas and which it would be desired to transform (via the surface treatment) for conversion to a use dedicated to the transport of a gas containing hydrogen, whether it is pure dihydrogen or a mixture between natural gas and dihydrogen.

[0091] 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 [Fig.6] now.

[0092] 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 [Fig. 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. Since . outside the frame, an inlet flow Fl 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.

[0093] To conduct comparative tests, four different test discs 300 were prepared: a first test disc called sample 1 whose central part 300a underwent a simple polishing, a second test disc called sample 2 whose central part 300a underwent a sandblasting treatment, a third test disc called sample 3 whose central part 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 called sample 4 whose central part 300a underwent a surface treatment 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.

[0094] 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.

[0095] [Tables 1] Parameters used for the preparation of sample 4 (intense ultrasonic peening) Material for the balls Steel 100C6 Diameter of the balls 3 mm Total mass of the balls 20 grams Impact distance 17 mm Treatment time 10 minutes Vibration amplitude + / - 25 microns (i.e. a total amplitude of 50 microns) at 20 KHz Treatment intensity (in arrow Alm en) F 49 A

[0096] It should be noted that the parameters listed above are particular values ​​which fall within the ranges of values ​​listed above when describing the general principles of the surface treatment process.

[0097] Table 2 below lists the set of parameters that were applied to prepare Sample 2.

[0098] [Tables2] Parameters used for the preparation of sample 2 (sandblasting technique) Material for the beads Glass Diameter of the beads Between 100 and 200 microns Impact distance 50 mm Treatment time 30 seconds Pressure 4 bars

[0099] Finally, Table 3 below indicates the set of light shot peening treatment parameters that were applied to prepare Sample 3.

[0100] [Tables3] Parameters used for the preparation of sample 3 (light ultrasonic peening) Material for the balls Steel 100C6 Diameter of the balls 3 mm Total mass of the balls 20 grams Impact distance 17 mm Treatment time 10 minutes Vibration amplitude + / - 12.5 microns (i.e. a total amplitude of 25 microns) at 20 KHz Treatment intensity (in arrow Alm en) F 22 A

[0101] Table 4 below provides a comparison of the results of the gas permeation tests of dihydrogen, obtained when the principles of [Fig.6], at a temperature of 80°C and when the inlet flow Fl of dihydrogen has a pressure of 8 bars, were applied respectively to samples 1 to 4.

[0102] [Tables4] Threshold time to detect the appearance of an F2 output flow Time to reach a stabilized F2 output flow regime Value of the F2 output flow in stabilized regime Sample 1 270 seconds Approximately 10,000 seconds 3.6 x 109Amp Sample 2 290 seconds Approximately 10,000 seconds 4.8 x 10 9Amp Sample 3 400 seconds Approximately 20,000 seconds 7.2 x 10 10Amp Sample 4 No flow after one week of monitoring No flow after one week of monitoring No flow after one week of monitoring

[0103] 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.

[0104] This test was carried out twice, in order 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 nevertheless remains significantly longer than the times recorded at 80°C for samples 1 to 3.

[0105] In conclusion, the intense ultrasonic shot blasting treatment described in the present document advantageously blocks or significantly delays the penetration of hydrogen into the steel.

[0106] In parallel with the advantages obtained with regard to the permeation of a gas containing hydrogen thanks to the invention, it should also be noted that the surface treatment by intense ultrasonic shot blasting has metallurgical effects on the surface of the internal wall 14 of the pipeline tube 10: - a refinement and flattening of the grains at the level of the internal wall 14 where the surface treatment by ultrasonic shot blasting is applied, to a depth of approximately 50 microns; - a significant increase in hardness: the micro-hardness, close to the area having undergone surface treatment by intense ultrasonic shot blasting, 30 microns from the edge, is 310 HV0.oi, compared to 235 HVo.oi for the initial steel; the depth hardness profiles show that the effect is noticeable over a depth of 300 microns from the internal wall 14; - surface treatment by intense ultrasonic shot peening creates maximum residual compressive surface stresses of 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 intense ultrasonic shot peening described in this document: in the first case, almost zero surface residual 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

1.

2.

3. Claims Pipe tube (10) for transporting a gas comprising hydrogen, 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, in which at the level of 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),pipeline (10) in which within the surface barrier layer (20), the steel has residual surface compressive stresses of the order of -400 MPa at a depth, counted from the internal wall (14), greater than 100 microns., The line pipe (10) of 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. A pipeline (10) according to either of claims 1 and 2, wherein the steel within the surface barrier layer (20) has, moving away from the inner wall (14), an average grain size which increases 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 a progressively increasing average grain size moving away from the nano-structured layer (32).

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

5. A pipeline (10) according to one of claims 3 or 4, wherein 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. A conduit tube (10) according to one of claims 1 to 5, wherein the steel is a ferrite-pearlite type steel.

7. A pipe tube (10) according to one of claims 1 to 6, 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.

8. A method of surface treatment of a pipeline tube (10) according to any one of claims 1 to 7, 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 vibratory wall (284) delimiting a working enclosure (286) in combination with the initial inner 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) setting the sonotrode (282) into vibratory movement, 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 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 the pipeline tube (10) during which the initial inner wall (141) becomes the internal wall (14) of the pipeline tube (10) and during which, in the steel, a surface barrier layer (20) is formed having a thickness (22) starting from the internal wall (14) and within which the steel has microstructural parameters different from the steel outside said surface barrier layer (20) configured to tend to oppose the passage of said gas through the thickness (22) of said surface barrier layer (20).

9. A surface treatment method according to claim 8, wherein the active vibratory wall (284) has a concave shape.

10. Surface treatment method according to one of claims 8 or 9, in which each of the balls (26) has a diameter of between 400 microns and 10 mm.

11. Surface treatment method according to one of claims 8 to 10, in which the total mass of the balls (26) present in the working enclosure (286) is between 10 and 40 grams.

12. Surface treatment method according to one of claims 8 to 11, in which during the step (E4) of vibratory movement, the average impact distance of the balls (26) is between 15 and 30 mm.

13. Surface treatment method according to one of claims 8 to 12, in which the step (E4) of vibratory movement is carried out during a treatment duration of between 1 and 60 minutes.

14. Surface treatment method according to one of claims 8 to 13, in which during step (E4) of vibratory movement, the vibration amplitude is between 10 and 50 microns.

15. Surface treatment method according to one of claims 8 to 14, wherein during step (E4) of setting into vibratory movement, the vibration frequency is 20 kHz, to within 10%. 23

16. Surface treatment method according to one of claims 8 to 15, in which the parameters used during step (E4) of vibratory movement, the Almen intensity of the treatment imparted by the balls (26) is greater than F 45 A.

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