Method for determining the degree of deterioration by thermal aging or creep of a tubular reactor made of high-temperature resistant alloy.

Abstract

The invention relates to a method for determining the degree of deterioration by thermal aging or creep of a tubular reactor (2) of a furnace (1) used in endothermic processes, the method comprising the steps of: a) performing non-destructive ultrasonic testing of a tubular reactor (2) to be tested and obtaining results in the form of at least one scan; b) comparing said at least one scan obtained in step a) with stored data correlating pre-recorded scans of different stages of deterioration of a tubular reactor with degrees of deterioration of tubular reactors; c) determining the degree of deterioration of the tubular reactor (2) to be tested, from the comparison performed in step b). (Short figure: Fig. 2)

Description

Title of the invention: Method for determining a degree of deterioration by thermal aging or creep of a tubular reactor made of high-temperature resistant alloy.

[0001] The invention belongs to the field of furnaces used in endothermic processes, such as the cracking of ammonia or hydrocarbon feedstocks carried out in externally heated reactors, in particular furnaces for steam reforming, steam reforming (in English "steam reforming") of hydrocarbons, essentially methane, or the cracking of ammonia.

[0002] The SMR process is essentially based on the methane reforming reaction which, in the presence of water vapor, leads to a mixture mainly comprising hydrogen and carbon monoxide. The slow and endothermic reaction takes place at pressure higher than atmospheric pressure and is carried out using a catalyst as well as an additional heat input.

[0003] The structural integrity of pressurized reactors is a key point for their safe operation. In practice, an SMR reformer comprises tubular reactors (also called reforming tubes or simply tubes) which are placed in a furnace, which contain catalyst - often in the form of pellets or granules - and are fed with a reaction gas mixture of methane (CH4) and water vapor at a pressure between 15 barg and 45 barg. Loss of integrity of a tubular reactor, induced by deterioration, such as the formation of cavities and cracks in its structure, leads to the shutdown of the reformer.

[0004] Eddy current reactor inspection methods are known. Such a method makes it possible to detect localized cracks near the outer surface of tubular reactors. The formation of cavities in the wall of a tubular reactor is a prerequisite for the formation of a crack. However, eddy current inspection is not very sensitive to the presence of said cavities. A crack crossing the thickness of the wall of the tubular reactor and detectable, because it has reached the outer surface, means that a gas leak is in progress. The detection of cracks by eddy currents therefore means that the tubular reactor is at the end of its life and a shutdown for replacement must be planned quickly. It is therefore difficult to plan the maintenance of tubular reactors using this inspection method.

[0005] Methods for ultrasonic testing of reactors are known, but none of these methods consider correlating the result of the testing with a degree of degradation of the material, in order to accurately determine the remaining operating life of the reactor. tubular reactor and plan furnace maintenance.

[0006] The present invention aims to solve all or part of the problems and / or drawbacks of known methods.

[0007] The invention then relates to a method for determining a degree of deterioration by thermal aging and / or fining of a tubular reactor of a furnace used in endothermic processes, the method comprising the steps of: (a) carry out non-destructive ultrasonic testing of a tubular reactor to be tested and obtain results in the form of at least one scan, in particular a type A, B, C or D scan; b) comparing said at least one scan obtained in step a), with stored data correlating pre-recorded scans of different stages of deterioration of a tubular reactor with degrees of deterioration of tubular reactors; (c) determine the degree of deterioration of the tubular reactor to be checked, based on the comparison made in step (b).

[0008] According to one embodiment, the tubular reactor is delimited by a wall.

[0009] According to one embodiment, step a) is carried out in situ on a tubular reactor arranged in a furnace used in an endothermic process, the reactor being supplied with a feed stream comprising, for example, a mixture of hydrocarbon and water vapor, or comprising ammonia in gaseous form (NH3). Of course, the invention can also be used with other feed streams provided that they are used in a tubular reactor implemented in the context of an endothermic process likely to damage tubular reactors over time, such as, for example, steam reforming of ethanol, steam reforming of naphtha or others.

[0010] In particular, the furnace comprises a combustion chamber, through which the tubular reactor extends and the wall of the tubular reactor delimits the reactor from the combustion chamber, the combustion chamber comprising at least one burner transferring heat to the feed stream, through the wall of the reactor.

[0011] The endothermic process is typically a hydrocarbon steam reforming process, an ammonia cracking process, or the like.

[0012] According to one embodiment, the tubular reactor extends vertically in the combustion chamber.

[0013] According to one embodiment, step a) is carried out on a tubular reactor arranged in a furnace adapted to implement in an endothermic process, said furnace being stopped.

[0014] According to one embodiment, the non-destructive testing is carried out over the entire thickness of the wall of the tubular reactor, in particular by a scanning method. sectoral.

[0015] According to one embodiment, the non-destructive testing is carried out on the external surface of the tubular reactor, over its entire length of the tubular reactor and over the entire thickness of the wall.

[0016] According to one embodiment, the non-destructive testing is carried out by a phased array ultrasonic device (PAUT). The device comprises in particular a plurality of multi-element transducer sensors, preferably at least 16, preferably at least 32, preferably at least 64 and preferably at least 128. Advantageously, the device implements an adaptive total focus method (ATFM). It is then possible to trace the geometry of the deterioration.

[0017] According to one embodiment, the comparison of step b) is carried out digitally within a computer system or computer means implementing one or more microprocessors.

[0018] According to one embodiment, the microprocessor(s) process the scans obtained in a) and carry out the comparison with the pre-recorded scans.

[0019] According to one embodiment, the degrees of deterioration of tubular reactors (thermal or finishing aging) are stored in the form of images, in particular metallography images.

[0020] According to one embodiment, the degrees of deterioration of the tubular reactor are stored in the form of several different criticality values ​​ranging from a degree corresponding to a new (never used) tubular reactor to a degree corresponding to a cracked tubular reactor that needs to be replaced. The degrees of deterioration take into account in particular a quantity of microcavities through the thickness of the wall of the tubular reactor and their degree of alignment. In particular, the criticality values ​​correspond to a class of the standard "Guidelines for the evaluation of the microstructure and damage development of materials exposed to finite element for pipes and boiler components", known as standard VGB-TW 507 1992.

[0021] The criticality values ​​according to the VGB-TW 507 1992 standard are described in the table below: [Tables 1] Assessed Class Structural and Deterioration Conditions 0 As new, not subjected to thermal loading under operating conditions 1 Exposed to fining, no cavities 2a Significant exposure to fining, isolated cavities 2b Greater exposure to fining, numerous cavities without particular orientation 3a Fining deterioration, numerous and oriented cavities 3b Significant fining deterioration, chains of cavities and / or grain boundary separations 4 Significant fining deterioration, microcracks 5 Significant fining deterioration, macrocracks

[0022] According to one embodiment, the pre-recorded scans were obtained by non-destructive ultrasonic testing on tubular reactors at different stages of deterioration. In particular, said tubular reactors were analyzed by cutting followed by observation, for example using a scanning electron microscope or an optical microscope, in order to determine their degree of deterioration and correlate the pre-recorded scans with said degrees of deterioration in the stored data. This is also referred to as a “post-mortem” analysis.

[0023] According to another embodiment, said tubular reactors were analyzed by observation under a microscope, in order to determine their degree of deterioration and to correlate the pre-recorded scans with said degrees of deterioration in the stored data. This is also referred to as a “post-mortem” analysis.

[0024] With the pre-recorded scans, it is possible to conclude on the severity of the deterioration of the tubular reactor, without having to resort to such a costly post-mortem analysis at each inspection. Said tubular reactors are in particular analyzed prior to their non-destructive testing by ultrasound. The non-destructive testing can be carried out on said tubular reactors at different stages of deterioration using a multi-element ultrasonic device, in the same way as for the tubular reactor checked in step a).

[0025] According to one embodiment, the criticality values ​​correspond to a thermal aging class, in particular established by observation under a microscope: - class 0: new equipment that has never been exposed to heat and has not undergone any thermal aging; primary eutectic precipitates are well cut, clean and delineated around the solidification cells and the austenitic matrix is ​​free of secondary precipitates, - class 1: presence of very fine secondary precipitates between the primary precipitates, - class 2: presence of fine secondary precipitates between the primary precipitates, - class 3: low presence of coarse secondary precipitates between the primary precipitates and signs of coalescence of the primary precipitates, - class 4: absence of secondary precipitates between the primary precipitates and presence of thick primary precipitates tending to agglomerate, - class 5: absence of secondary precipitates between the primary precipitates and presence of coarse agglomerated primary precipitates. Primary eutectic precipitates are larger than secondary precipitates. Primary precipitates are formed from the molten alloy and from the solidification of the alloy in the tubular reactors. Secondary precipitates are finer than primary precipitates; a new alloy does not have them: they only appear when the alloy is exposed to heat. However, if thermal aging is advanced, secondary precipitates disappear.

[0026] According to one embodiment, the stored data is recorded in the form of a library.

[0027] According to one embodiment, the at least one scan obtained in step a) is compared in step b) to the pre-recorded scans.

[0028] According to one embodiment, the degree of deterioration of the tubular reactor determined in c) is displayed on a screen, such as a computer or smartphone screen.

[0029] According to one embodiment, the method comprises a step of comparing the degree of deterioration determined in step c) with a predetermined criticality threshold, for example a threshold corresponding to one or more micro or macro cracks having or not having crossed the entire thickness of the wall of the tubular reactor, and a step of triggering an alert when the degree of deterioration determined in step c) is greater than the criticality threshold. In particular, the method comprises a step of deciding to replace the tubular reactor checked in step a), in particular with a new tubular reactor, the replacement being subsequently carried out or planned.

[0030] According to one embodiment, the method comprises a step of calculating a remaining operating time of the reactor controlled in step a) before its replacement.

[0031] According to one embodiment, the length of the tubular reactor is between 10 and 15m.

[0032] According to one embodiment, an external diameter of the tubular reactor is between 90 and 150 mm.

[0033] According to one embodiment, the wall of the tubular reactor is made of an austenitic phase alloy of the high temperature resistant alloy type, such as Manaurite, preferably comprising Fe, Cr, Ni, Si, Mn, C and traces of additives such as Ti, Nb, W, V, Zr, Co.

[0034] According to one embodiment, the thickness of the wall of the reactor is between 5 and 20 mm.

[0035] The invention will be better understood upon reading the following description and examining the accompanying figures. These figures are given only for illustrative purposes but in no way limit the invention.

[0036] [Fig.l] is a schematic representation of a furnace used in endothermic processes;

[0037] [Fig.2] is a representation of images obtained under a microscope and classified according to the VGB-TW 507 1992 standard;

[0038] [Fig.3] is a representation of the different classes 0 to 5 of thermal aging, obtained by analysis.

[0039] [Fig.l] represents a furnace 1 for implementing a process for steam reforming of hydrocarbons, but the invention covers the field of other endothermic reactions. The furnace 1 comprises a combustion chamber 4, through which extends a plurality of tubular reactors 2, each being delimited by a wall. The combustion chamber 4 comprises a plurality of burners 3 implementing the combustion of a fuel and transferring heat to the feed stream, through the wall of the reactors. The fumes produced by the combustion are evacuated from the combustion chamber 4 by tunnels 5. In the embodiment shown, the burners 3 are located at the ceiling of the furnace 1. In another configuration not shown, the burners 3 can be located on the sides of the furnace 1, or even on the floor of the furnace 1. The burners 3 produce heat by the combustion of a fuel.The reactors are filled with a catalyst, for example nickel supported on alumina, whose function is to promote the endothermic steam reforming reaction. The reactors are fed from above with a feed stream F comprising a hydrocarbon, for example natural gas, and water vapor. The endothermic reaction converts the feed stream into a synthesis gas S which comprises a mixture of hydrogen, carbon monoxide and other gases. The endothermic reaction occurs in contact with the catalyst, typically at a temperature of 950°C and a pressure of 30 bar absolute. The pressure within the combustion chamber 4 is maintained slightly below atmospheric pressure (for example 5 mbar) for safety reasons.

[0040] The endothermic reaction is total or almost total in the most downstream section of the tubular reactors 2 considered in the direction of circulation of the feed flow F and of the synthesis gas S (lower section of the reactors in the embodiment shown). Since the reaction is less endothermic or no longer endothermic at all in this most downstream section, more heat is transmitted to the wall of the reactors. The most downstream section of the reactors is therefore the most subject to deterioration by fining and loss of structural integrity.

[0041] Advantageously, the control of the tubular reactors 2 of step a) is carried out using a piloted robot moving on the external surface of the tubular reactor using a pneumatic propulsion means (not shown). The robot may comprise a multi-element ultrasonic device.

[0042] [Fig.2] shows metallographic images obtained with an electron microscope at scan of the wall of a tubular reactor subjected to post-mortem analysis, at different degrees of degradation. The images were associated with a class of the standard "Guidelines for the assessment of microstructure and damage development of creep-exposed materials for pipes and boiler components" (VGB-TW 507 1992) to correlate images with the deterioration degrees of a tubular reactor. This classification method takes into account the quantity of microcavities throughout the wall thickness of the tubular reactor and their degree of alignment. A significant number of aligned microcavities leads to the formation of a crack. This is an example of classification by degree of deterioration, but the invention is in no way limited to this particular standard. The invention also considers the deterioration of tubular reactors by thermal aging.

[0043] [Fig.3] shows metallographic images representing the different classes 0 to 5 thermal aging obtained by microscopic observation, of the wall of a tubular reactor subjected to post-mortem analysis, at different degrees of degradation.

[0044] It is understood that this invention based on the ultrasonic analysis of the furnace tubes, if necessary in situ, is more efficient than the state of the art because once the method or process is well calibrated, it is possible to obtain the degree of aging of the tube without having to remove the tube if necessary, take samples and carry out post-mortem analyses to evaluate the health of the tubes. This method makes it possible to shorten the intervention times on site and to obtain the desired final result quickly.

Claims

Claims

1. Method for determining a degree of deterioration by thermal aging and / or fining of a tubular reactor (2) of a furnace (1) used in endothermic processes, the method comprising the steps of a) carrying out a non-destructive ultrasonic testing of a tubular reactor (2) to be tested and obtaining results in the form of at least one scan; b) comparing said at least one scan obtained in step a), with stored data correlating pre-recorded scans of different stages of progress of the deterioration of a tubular reactor with degrees of deterioration of tubular reactors; c) determining the degree of deterioration of the tubular reactor (2) to be tested, from the comparison carried out in step b).

2. Method according to the preceding claim, characterized in that step a) is carried out in situ on a tubular reactor (2) arranged in a furnace (1) used in an endothermic process, the reactor (2) being supplied with a feed stream (F) comprising for example a mixture of hydrocarbon and water vapor or ammonia in gaseous form.

3. Method according to one of the preceding claims, characterized in that the non-destructive testing is carried out over the entire thickness of a wall of the tubular reactor (2), in particular by a sector scanning method.

4. Method according to one of the preceding claims, characterized in that the non-destructive testing is carried out by a multi-element ultrasonic device.

5. Method according to one of the preceding claims, characterized in that the degrees of deterioration of tubular reactors are stored in the form of images, in particular metallographic images.

6. Method according to one of the preceding claims, characterized in that the degrees of deterioration of the tubular reactor are stored in the form of several different criticality values ​​ranging from a degree corresponding to a new tubular reactor to a degree corresponding to a cracked tubular reactor which must be replaced.

7. Method according to one of the preceding claims, characterized in that the pre-recorded scans were obtained by non-destructive ultrasonic testing on tubular reactors at different stages of deterioration progress, said tubular reactors having been analyzed by cutting followed by observation, for example under a scanning electron microscope or an optical microscope, in order to determine their degree of deterioration and to correlate the pre-recorded scans with said degrees of deterioration in the stored data.

8. Method according to one of the preceding claims, characterized in that the at least one scan obtained in step a) is compared in step b) with the pre-recorded scans.

9. Method according to one of the preceding claims, characterized in that the degree of deterioration of the tubular reactor (2) determined in c) is restored by display on a screen, such as a computer or smartphone screen.

10. Method according to one of the preceding claims, comprising a step of comparing the degree of deterioration determined in step c) with a predetermined criticality threshold, for example a threshold corresponding to one or more micro or macro cracks having or not crossed the entire thickness of a wall of the tubular reactor (2), and a step of triggering an alert when the degree of deterioration determined in step c) is greater than the criticality threshold.

11. Method according to the preceding claim, comprising a step of deciding to replace the tubular reactor (2) controlled in step a), in particular with a new tubular reactor, the replacement being subsequently carried out or planned.

12. Method according to the preceding claim, comprising a step of calculating a remaining operating time of the tubular reactor (2) checked in step a) before its replacement.

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