Sensor for measuring the embrittlement of steels by hydrogen in an aggressive environment, said sensor comprising a metal cavity connected to a pressure-measuring device

Abstract

The present invention is a sensor for measuring a risk of hydrogen embrittlement of industrial equipment including a metallic wall in a reactor or in a pipeline comprising a body having a closed cavity including an end containing a pressure sensor which measures pressure within the closed cavity, the metallic wall having a wall thickness measured between inner and outer surfaces thereof, and wherein a ratio of thickness of the metallic wall to thickness of the industrial equipment ranges from 1/3 to 1/10.

Claims

1. A sensor for measuring a risk of hydrogen embrittlement of industrial equipment including a metallic wall in a reactor or in a pipeline comprising: a body having a closed cavity including an end containing a pressure sensor which measures pressure within the closed cavity; the metallic wall having a wall thickness measured between inner and outer surfaces thereof; and wherein a ratio of thickness of the metallic wall to thickness of the industrial equipment ranges from 1/3 to 1/10.

2. The sensor in accordance with claim 1 wherein the ratio of thickness of the metallic wall to the industrial equipment ranges from 1/4 to 1/50.

3. The sensor in accordance with claim 1 wherein the metal used to produce the sensor is the same metal used in the industrial equipment.

4. The sensor in accordance with claim 2 wherein the metal used to produce the sensor is the same metal used in the industrial equipment.

5. The sensor in accordance with claim 1 wherein the metallic wall is part of the reactor.

6. The sensor in accordance with claim 2 wherein the metallic wall is part of the reactor.

7. The sensor in accordance with claim 3 wherein the metallic wall is part of the reactor.

8. The sensor in accordance with claim 4 wherein the metallic wall is part of the reactor.

9. The sensor in accordance with claim 1 wherein the metallic wall is part of the pipeline.

10. The sensor in accordance with claim 2 wherein the metallic wall is part of the pipeline.

11. The sensor in accordance with claim 3 wherein the metallic wall is part of the pipeline.

12. The sensor in accordance with claim 4 wherein the metallic wall is part of the pipeline.

13. A method for measuring a risk of hydrogen embrittlement of industrial equipment including a metallic wall in a reactor or in a pipeline comprising: (1) performing cracking tests in hydrogenating environments having the risk of hydrogen embrittlement and obtaining from test conditions for which cracking is absent and for which cracking conditions are present; (2) in hydrogenating environments identical to step (1) performing pressure tests with a sensor in accordance with claim 1 containing a metal used in step (1) and measuring H.sub.2S equilibrium pressure (Pe) for each hydrogenating environment; (3) for each hydrogenating environment comparing results of the cracking tests of step (1) and pressure measurement tests of step (2) and determining a minimum pressure which is a threshold pressure for cracking resistance corresponding to conditions for which cracking is present; (4) exposing the sensor which includes a metal identical to the metal used for testing in step (2) in a given environment and monitoring a change over time of pressure in the sensor until the pressure reaches a constant plateau; and (5) comparing an equilibrium value with the threshold pressure obtained in step (3) to assess if the metal has a risk of hydrogen embrittlement in the hydrogenating environment.

14. The method in accordance with claim 13 comprising: assessing risk of hydrogen embrittlement of steel used in the reactor wall of a pipeline wall subject to environments containing H.sub.2 or H.sub.2S and having a pH from 3 to 8 with the sensor according to claim 1.

15. A method in accordance with claim 13 comprising: monitoring an environment of an industrial installation utilizing steel including an aqueous medium containing dissolved H.sub.2S to assess risk of embrittlement of the steel at the industrial installation.

16. A method for assessing risk of hydrogen embrittlement in accordance with claim 13 comprising: monitoring an environment of an industrial installation at which industrial equipment is located which uses steel including a gaseous medium found in refining processes to assess the risk of embrittlement of steel in the industrial equipment.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a diagrammatic view of the sensor according to the invention, which has a tubular shape and is connected to a pressure sensor. The tubular shape is practical, but other shapes could be used such as for example spherical or planar.

(2) FIG. 1A shows a diagrammatic view of the sensor according to the invention when it is directly integrated with the item of industrial equipment to be characterized. In this case the sensor according to the invention is arranged in a portion of the item of equipment to be characterized with this portion being provided if necessary with an additional thickness.

(3) FIG. 2 shows an example of the change over time of the internal pressure in a hollow sensor made from low-alloy, high elastic limit steel according to the invention. This sensor is subject to a corrosive environment constituted by water at 35 g/L NaCl at pH 4.5 and containing 10 then 50 mbar dissolved H.sub.2S. This type of environment is known to promote the entry of hydrogen into the steel. It originates in this case from the electrochemical proton reduction reaction (H++e−.fwdarw.H).

(4) FIG. 3 shows an example of measurements of equilibrium pressure in the hollow sensor according to the invention made from low-alloy ferrito-pearlitic steel exposed to corrosive solutions at different pHs and under 100 mbar of H.sub.2S. This type of environment is known to promote the entry of hydrogen into the steel. It originates in this case from the electrochemical proton reduction reaction (H++e−.fwdarw.H).

(5) FIG. 4 shows an example of the connection between the crack area and equilibrium pressure for a low-alloy ferrito-pearlitic steel exposed to a solution of water at different pH levels and under H.sub.2S at 100 mbar.

(6) FIG. 5 shows an example of the change in the internal pressure in a hollow sensor made from low-alloy ferrito-pearlitic steel according to the invention. This sensor is subject to a corrosive environment constituted by water at 35 g/L NaCl at pH 6 and containing dissolved H.sub.2S at 10 mbar. This type of environment is known to promote the entry of hydrogen into the steel. It originates in this case from the electrochemical proton reduction reaction (H++e−.fwdarw.H).

(7) FIG. 6 shows in diagrammatic form an example of the methodology followed in order to carry out Example 2 with a first part of the experiment using coupons of the steel to be investigated (B), and a second part of the experiment using the sensor according to the invention (C), both being submerged in an aggressive medium containing hydrogen (A).

DETAILED DESCRIPTION OF THE INVENTION

(8) The present invention is a sensor and a method of use of this sensor, for assessing the risk of hydrogen embrittlement for a given metal in an aggressive environment promoting the penetration of hydrogen into the metal.

(9) The sensor according to the invention is constituted by a metal body containing a closed cavity connected to a device for measuring pressure. This sensor is intended to be exposed to an aggressive environment capable of causing hydrogen embrittlement for the metal constituting the metal body.

(10) The penetration of hydrogen from the external medium leads to the diffusion of hydrogen into the metal of the sensor, then recombination thereof as gaseous hydrogen inside the closed cavity.

(11) The measurement of the steady-state pressure (Pe) reached within this cavity is thus indicative of the hydrogen activity in the steel. If the acceptable threshold for hydrogen content in the metal in question is known (Ps), the sensor then allows real-time verification that this level has not been reached in service.

(12) The present invention therefore describes an embrittlement sensor the main constituents of which are shown diagrammatically in FIG. 1 or in FIG. 1A, according to the version used.

(13) This sensor contains:

(14) (1) a metal portion, chosen in the same grade of metal as the installation for which it is desired to assess the risk of hydrogen embrittlement. In normal use, this metal portion is exposed to the hydrogenating corrosive medium.

(15) (2) a cavity having a small volume, arranged inside the metal portion (1).

(16) (3) a device for measuring pressure inside the cavity.

(17) The approach of the present invention is very different in nature than the data used and in the interpretation of the data than compared to the prior art.

(18) In fact, while currently normal practice determines the flow of hydrogen, herein direct use of the measurement of the equilibrium pressure within the cavity is performed in order to assess the absorbed hydrogen activity in the steel.

(19) In fact, by application of Sieverts' law, the activity of a gaseous element dissolved in a metal is directly proportional to the square root of the pressure of this same gas in equilibrium with the metal, therefore corresponding to the equilibrium pressure (Pe) generated by this gas within the measurement cavity. As a result, the equilibrium pressure measurement inside the cavity of the sensor can be directly correlated with the hydrogen activity or concentration in the steel at equilibrium (Ce). Now, the risk of internal cracking of the “blistering” or “hydrogen-induced cracking (HIC)” type is directly linked to the hydrogen activity in the steel. This pressure measurement therefore corresponds to a direct measurement of the severity of the risk of hydrogen embrittlement.

(20) Another differentiating element of this invention is based on the use of the same metal for the body of the sensor as that of the item of industrial equipment to be monitored. In fact, for measurements of the hydrogen flow according to the prior art, the nature of the metal constituting the steel membrane can equally well be selected from a metal grade close to that of the metal of the item of equipment to be monitored, but not necessarily identical thereto. Now, the nature of the metal can affect the hydrogen diffusion and solubility properties, and in particular the acceptable threshold content before cracking occurs.

(21) The values for threshold concentration (Cs) or threshold pressure (Ps) defining the absorbed hydrogen value above which the metal is likely to crack, are in fact specific to each metal or each grade of steel. The same applies for steady-state concentrations and pressure (Ce and Pe).

(22) It is therefore important to use a representative metal for the device, preferably the same metal as will be used for the item of industrial equipment.

(23) The use of the sensor according to the invention is thus based on prior knowledge of the hydrogen embrittlement resistance range of the metal in question, which can be determined by any hydrogen embrittlement test method well known to a person skilled in the art.

(24) Among these methods there may be mentioned for example the test described in NACE TM0284 (NACE International) which describes carrying out tests for the HIC cracking behavior of low-alloy steels in an aqueous medium containing dissolved H.sub.2S.

(25) This pressure threshold value (Ps) can be characterized by using a sensor device according to the invention, as illustrated in Example 2. Once the threshold value for hydrogen activity or pressure (Cs or Ps) is known for a given metal, the sensor device according to the invention can be used in order to ensure that this limit value is not exceeded in service.

(26) In order to pre-empt risks, it is important for the thicknesses of the walls of the sensor to be less than the thicknesses of metal of the installation to be monitored, and for the volume of the cavity to be as small as possible. Under such conditions, the time taken to reach the equilibrium pressure (Pe) in the sensor is faster than the time taken to reach the same pressure level in the actual installation, thus making it possible to pre-empt risks.

EXAMPLES ACCORDING TO THE INVENTION

(27) Example 1 according to the prior art: low-allow steel with high elastic limit In this example, the body of the sensor was produced from low-alloy steel with a high elastic limit Its micro-structure is ferrito-pearlitic. This type of steel is very susceptible to internal hydrogen cracking when used in the presence of water containing dissolved H.sub.2S.

(28) These risks depend mainly on the pH of the solution and the H.sub.2S content.

(29) Two tests for crack-resistance (HIC or “hydrogen-induced cracking”) were conducted on this steel in an aqueous solution with 35 g/L NaCl at pH 4.5 under an H.sub.2S partial pressure of 10 mbar (test 1) and 50 mbar (test 2). These tests were conducted according to the NACE TM 0284 method well known to a person skilled in the art, and with immersion periods of 1 month. For test 2 (50 mbar of H.sub.2S) they showed significant cracking of the steel, while for test 1 (10 mbar of H.sub.2S), no cracking was noted.

(30) Tests according to the prior art, utilizing a pressure sensor used in order to determine a hydrogen flow through the steel, were then conducted in an aqueous solution of the same composition as for the previous tests (35 g/L NaCl, at pH 4.5) and varying the H.sub.2S composition from 10 to 50 mbar during the test. These test conditions thus correspond to starting the test in an environment in which the material is not susceptible to internal cracking (pH 4.5 and 10 mbar of H.sub.2S), then passing to an environment in which the material is susceptible to cracking (pH 4.5 and 50 mbar of H.sub.2S).

(31) The curve of the change in internal pressure measured throughout this test is shown in FIG. 2.

(32) This curve reveals that the change in H.sub.2S content from 10 to 50 mbar is not reflected in a change in the rate of pressure increase. This rate of pressure increase is a direct reflection of the hydrogen flow passing through the metal wall. This flow value is quoted in the prior art for characterizing the risk of hydrogen embrittlement. This example thus shows that the use of a simple flow measurement sensor as described in the state of the art does not make it possible to detect a difference between these two corrosive environments, since the first, under 10 mbar of H.sub.2S, does not present a cracking risk for this steel, while conversely the second, under 50 mbar of H.sub.2S, leads to significant cracking of this steel.

(33) This illustrates the limits of the current practices described in the prior art, of using only flow measurements. The second example is intended to illustrate more directly the benefit of the equilibrium pressure measurements by using the sensor according to the invention.

Example 2 According to the Invention: Low-Alloy Steel for Pipeline Plate of API 5 L X65 Type

(34) In this example, the tested steel is a low-alloy steel of API 5 L X65 type, commonly used for the manufacture of oil and gas transportation pipelines. This steel presents risks of hydrogen embrittlement when it is used in the presence of water containing dissolved H.sub.2S.

(35) These risks depend mainly on the pH of the solution and the H.sub.2S content.

(36) Tests for crack-resistance (HIC or “hydrogen-induced cracking”) were conducted on this steel in solutions with a pH varying between 4.5 and 6.5, under a partial pressure of H.sub.2S of 100 mbar.

(37) These tests were conducted on steel coupons of 100 mm long, 20 mm wide, and thickness equivalent to the thickness of the plate (i.e. 17 mm) according to the NACE TM 0284 method well known to a person skilled in the art, and with immersion periods of 1 month.

(38) These tests according to the prior art make it possible to verify, for a given corrosive environment, if the steel presents risks of internal cracking. In the case of cracking, this can be quantified for example by ultrasound non-destructive testing. The extent of the cracking is then expressed as a percentage of surface area cracked in a given plane, and denoted by the abbreviation CAR (“Crack Area Ratio”).

(39) The CAR criterion, well known to a person skilled in the art, makes it possible to quantify the extent of internal cracking, which can vary between 0% for an absence of cracking, to 100% for a sample that is completely cracked. These tests are denoted “cracking tests” in the remainder of the example.

(40) For the same test conditions (same pH and same partial pressure of H.sub.2S), tests according to the invention were conducted using a hollow sensor produced from the same steel, in order to determine the hydrogen equilibrium pressure (Pe) reached under the test conditions. These tests are denoted “pressure measurement tests” in the remainder of the example.

(41) FIG. 6 illustrates the two types of tests carried out.

(42) The crack area results for this steel, obtained from cracking tests under different test conditions, are given in Table 1 below.

(43) As expected, the harshness of the test environment varies significantly with the pH of the solution, with a threshold at pH 6 above which no cracking is detected.

(44) TABLE-US-00001 TABLE 1 Correlation between the pH of the test environment and the CAR (measured by cracking tests) as well as the H.sub.2 equilibrium pressure (Pe) (measured by pressure measurement tests) pH 4.5 5.5 6 6.5 CAR (%) 25 5 0 0 Pe (bar) >500 160 40 3

(45) For this steel, and in the test medium containing 100 mbar of H.sub.2S, a series of pressure measurement tests was conducted using a hollow sensor device according to the invention, in order to determine the equilibrium pressures (Pe) corresponding to the different pH levels.

(46) In order to avoid cracking the steel bodies during pressure measurement tests, the sampling was carried out in an area of steel at a distance from the center of the plate, which is the most susceptible with respect to hydrogen embrittlement due to a higher concentration of inclusions.

(47) Despite these precautions, certain pressure measurement tests carried out at pH 4.5 had to be interrupted due to leaks associated with cracks in the body of the sensor.

(48) Table 1 thus correlates the crack area (CAR) with the equilibrium pressure (Pe) for this low-alloy steel with a ferrito-pearlitic microstructure exposed to aqueous media containing 35 g/L of NaCl under 100 mbar of H.sub.2S and at different pH values.

(49) The results are illustrated by FIGS. 3 and 4.

(50) By comparing these equilibrium pressure measurements (pressure measurement tests) with the measurements of the crack area (cracking tests), the conclusion can be reached that for this steel, the crack-resistance limit corresponds to a hydrogen pressure threshold Ps of 40 bar, as shown in FIG. 4. FIG. 4 establishes the link existing for a given steel between the crack area and the H.sub.2 pressure in the embrittlement sensor.

(51) An embrittlement sensor constructed in this grade of steel can thus now be used in any hydrogenating environment, in order to verify that the threshold pressure (Ps) of 40 bar is not exceeded.

(52) This principle was therefore used for a test at 10 mbar of H.sub.2S and at pH 6.

(53) The pressure change curve is shown in FIG. 5.

(54) It is very clearly apparent that the equilibrium pressure (Pe) is established under these conditions at 7 bar, well below the threshold of 40 bar established for this material. In this case, the use of the sensor according to the invention leads to the prediction of an absence of the risk of cracking.

(55) Cracking tests conducted under these same conditions have confirmed the absence of cracking, as predicted by the measurements carried out using the embrittlement sensor.