Title of Invention

A MEASURING SYSTEM FOR ON-LINE MEASUREMENT OF CORROSION RATE OF METALS IN AN AQUEOUS MEDIUM

Abstract

A measurement system for on-line measurement of corrosion rate of metals in aqueous medium,. The device having a hydrogen doped argon source being connected through a mass flow controller for controlling the flow of hydrogen doped argon to a mixing chamber and an argon source being connected through a mass flow controller for controlling the flow or argon to the said mixing chamber, the mixing chamber being connected to a reaction chamber for receiving the mixed gas from the mixing chamber a hydrogen sensor being connected to the reaction chamber for continuously monitoring and measuring the hydrogen evolved in the reaction chamber and the output of the on chamber being connected to a matter for measuring the corrosion rate. By the use of the system the corrosion rate can be measured accruable.

Full Text

The Patent Act, 1970 (39 of 1970) Complete Specification (See section) 10) . A MEASURING SYSTEM FOR ON-LINE MEASUREMENT OF CORROSION RATE OF METALS IN AN AQUEOUS MEDIUM The following specification particularly describes the nature of this invention and the manner in which it is to be performed The invention relates to a measuring system for on-line measurement of corrosion rate of metals in an aqueous medium. Introduction On-line measurement of corrosion is of significant technological importance. The on¬line corrosion data can be us; ful in better understanding of the corrosion process so that necessary action can be taken to minimise the effect of corrosion. An example is the on line measurement of corrosion of carbon steel and oxide coated carbon steel in acid medium. Carbon steel is generally used as piping material for primary heat transport system in power plants. Different types of corrosion products are formed by corrosion of these pipelines with high temperature water. The coolant in power plants when operated under deoxygenated condition, the major corrosion product is found to be Fe304.The deposited oxide will affect the heat transport properties. One way of removing the oxide deposited on the surfaces is by dissolving the coated oxide using chemical formulation, which must be effective to remove the oxide without causing significant corrosion of the underlying metal. The chemical agents used are 1.37mM EDTA, 1.7mM Ascorbic acid and 1.4mM Citric acid or any formulation of similar kind, which will not cause much damage to the underlying metal. Complex-forming organic acids are normally used in low concentrations. The measurement of corrosion rate of base metal and the dissolution rate of magnetite has to be known to carry out the dissolution of magnetite coating in an effective manner since precautions has to be taken to prevent excessive corrosion of base metal. Similarly, there are situations where corrosion rate has to be measured as a function of time. The new invention is applicable to such cases. This can be used where hydrogen is product of corrosion and the corrosion rate can be estimated by measurement of evolved hydrogen on-line. Conventional methods used for measurement of corrosion rate V The conventional methods of measuring corrosion rate is by obtaining (I) the weight loss of the carbon steel specimen exposed to corroding medium (2) estimation of iron dissolved into the corroding medium for predetermined time period and (3) electrochemical methods. The popular electrochemical techniques are linear polarisation method and tafel method. The polarisation resistance can also be measured by impedance spectroscopy. Disadvantages of the conventional methods However the above mentioned conventional methods cannot be used for an on line monitoring and measuring of the corrosion rate as a function of time. In the first two techniques, to have the measurable weight loss and iron in solution needs some particular exposure time and hence time resolution below few minutes cannot be achieved. The electrochemical methods such as tafel method and polarisation method cannot be applied to coated specimens where the coating along with the underlying metal interacts with the corroding medium by a redox process. Principle of the new invention for the corrosion rate measurement The invention has been developed based on the principle that the corrosion rate can be measured accurately by simulating the corrosion reaction and measuring the evolved hydrogen. The hydrogen evolved by corrosion of carbon steel in corroding medium is measured online using hydrogen sensor. The invention provides a measuring system for on¬line measurement of corrosion rate of metals in an aqueous medium by measuring on-line, the hydrogen released during corrosion. The following reactions occur during corrosion: Fe ► Fe2+ + 2 e" 2H+ + 2e ► H2 The hydrogen released during the corrosion of carbon steel is collected by flowing argon and is measured online using a polymer electrolyte based hydrogen sensor. Since the amount of hydrogen released during the corrosion process is same as the amount of iron corroded, corrosion rate can be estimated from the rate of hydrogen release due to corrosion. Hydrogen released by interaction of carbon steel with a reacting medium is estimated as a function of time using a polymer electrolyte based amperometric hydrogen sensor. Acid 3 polymer blend of polyvinyl alcohol and phosphoric acid is used as proton conducting solid electrolyte. The electrolyte in sandwiched between two palladium film electrodes. The sensing side of the electrode is exposed to the gas containing hydrogen. The other side of the electrode is exposed to air. The electrodes are short-circuited and the short-circuit current is measured using a digital current in.cgrator interfaced to a computer. This current is found to be proportional to the concentration of hydrogen on the sensing side. The electrochemical processes proposed to be occurring at the electrodes are H2 >2H + + 2e- (1) 2H+ + 2e" + Vi 02 > H20 (2) The anodic oxidation reaction is a diffusion-controlled process under short-circuit condition. The amount of H+ produced by the anodic reaction is proportional to the concentration of hydrogen on the sensing side. Hydrogen liberated during the interaction of metal sample with the reacting medium is carried by argon flowing at steady rate through a mass flow controller. The concentration (C) of hydrogen in argon is given by C = E/F (3) Where, F is the flow rate of argon and E is the evolution rate of hydrogen. The total amount of hydrogen liberated during the time of exposure of the metal sample to the reacting medium is given by jEdt = F|Cdt (4) in which E, F and C are as defined above. Integral on the right hand side of the equation (4) corresponds to the area under the response curve in the plot of concentration of evolved hydrogen Vs time. The amount of hydrogen liberated is equivalent to the amount uf metal dissolved into the reaction mixture. The mass of metal (W) dissolved into the reacting medium per unit time is given by W = FCM/V (5) in which V is the standard volume, M is the atomic weight of metal and F and C are as defined above. Corrosion rate (R) can be calculated from the equation R - W/AD (6) in which A is the total surface area of the metal sample exposed to the reaction mixture, D is the density of the metal sample and W is as defined above in equation (5). The average corrosion rate (RAVC) of the metal sample is given by RAve = (FM/VADt)JCdt (7) in which t is the total time of exposure of the metal sample in the reacting medium. Based on the above principle, the invention provides an accurate measuring system for on-line measurement of corrosion rate in an aqueous medium by measuring on-line, the hydrogen evolved during corrosion and computing the corrosion rate (R) using the equation R = W/AD in which W, A and D are as defined. The invention will now be described with reference to the drawing, accompanying this specification. The Fig.l of the figures accompanying the specification, shows showing the schematic representation of the measuring system according to the present invention. Description of the experimental set-up Accordingly, the present invention provides measuring system for on-line measurement of corrosion rate of metals in an aqueous medium which comprises a hydrogen doped argon source (1) being connected through a mass flow controller (3) for controlling the flow of hydrogen doped argon to a mixing chamber (5) and an argon source (2) being connected through another mass flow controller (4) for controlling the flow of argon to the said mixing chamber (5), the mixing chamber (5) being connected to a reaction chamber (6) for receiving the mixed gas stream from the mixing chamber (6). The measuring system of the present invention is calibrated before each measurement. A stream of hydrogen doped argon with predetermined quantity of hydrogen concentration (C) is passed through the mass flow controller (3), to the mixing chamber (5). A stream of argon is also passed through the other mass flow controller (4) to the mixing chamber (5). The two streams are mixed in the mixing chamber (5) and passed to the reaction chamber (6). The hydrogen content reaching the reaction chamber (6) is varied by controlling the mass flow controllers (3 and 4) and response of sensor is recorded in PC. Thus, the hydrogen sensor is calibrated. The flow of hydrogen doped argon is stopped. The metal sample of known weight to be tested is introduced into the reaction medium in reaction chamber (6) while (he argon stream is maintained in the reaction chamber (6). The hydrogen sensor (7) measures the hydrogen evolved over the required period of time continuously .The output from the hydrogen sensor (7) is measured by the integrator (8) and provided to the computer (9). The metal sample is removed from the reaction medium and immediately data acquisition from sensor output also stopped. The sample is washed with water and acetone. The final weight of the sample noted after drying. From the weight loss and exposure time of the sample the average corrosion rate is calculated using the formula R = W/ADt (8) in which W is weight loss of the metal sample, A&D are as defined above [in equation (6)]. The computer provides corrosion rate based on the data provided by the integrator (8.) using the equation (7). The mass flow controllers (3 and 4) may preferably be computer controlled for a programmed operation of the measuring system. This corrosion rate measurement is carried out at four different temperatures. Example-l A carbon steel sample coupon whose corrosion rate has to be measured was weighed first and found to be 1.2887g.The exposed area of thecoupon is 3.15cm2.The sample was held above the reaction medium (in this case was a mixture of EDTA, Ascorbic acid and Citric acid) in the reaction vessel and the temperature of the reaction medium was maintained at 50°C.The sensor was calibrated by passing Hydrogen in argon of known concentrations (25ppm,50ppm,75ppm,100ppm) at flow rate of 300sccmin"' through the reaction vessel into the sensor and noting the respective limiting current values. A linear calibration is obtained by plotting the limiting current against the concentration of hydrogen in argon. After the calibration, the flow of calibration gas is stopped and argon gas flow(carrier gas) is maintained at a flow rate of 300sccmhYl. The sample is introduced into the reaction medium. The hydrogen evolved due to the corrosion of the steel sample by the reaction medium is led into the sensor by the flowing argon carrier gas. The sensor response is continously logged to the computer. 6 After exposing the sample to the reaction medium for 1404 Seconds, the corroded sample was removed and Jogging of sensor response to the computer stopped. The sample was washed with water and acetone , dried and weighed and weight found to be 1.2880g. The corrosion rate C.R calculated using the equation C.R = W/Adt. Where, Weight loss W - 0.7 mg Aurfave area A = 3.15 cm2 Density D - 7.8 g/cm3 Exposure time = 1404 seconds Corrosion rate =0.7 To estimate the corrosion rate using the hydrogen sensor, the peak area for the response curve of the sensor was found out. Using the slope and intercept, that were obtained from the calibration graph for the hydrogen sensor, the response curve of the sensor for hydrogen evolved due to corrosion is transferred from sensor output vs time to hydrogen concentration vs time. The peak area was determined by integrating the area under the curve and was found to be.34191PPM S. From the peak area, exposure time(1404s), flow rate (400 sccmin*1), surface area of the sample (3.15 cm2) and density of Carbon steel (7.8 g/cc) the corrosion rate of carbon steel is calculated as follows. Corrosion rate (C.R) microns per hour = [34191 ppms 106.66sccsx x 55.85 gmor'x3600 sh'xl04ucm 'l [22400 sec mol*1 x 3.15 cm2x7.8 gec'1 x 1404s] = 0.54 u.m hour'1 Table 1 illustrates the examples of the measurement carried out by weight loss method and by the method using the hydrogen sensor as explicitly shown by example 1 above. 7 Table. I Method by direct weight Loss Method by present invention using H2 sensor Sl.No [1] Temp .C [2] Initial weight (g) '(3) Final weight (g) Weight Loss W(mg) [5] Exposure time T(s) [6] Surface Area of the sample A (cm2) [7] C.R = W/ADt (um/h) f81 Mean (um/h) [9] Area under the curve [10] (FM/V)|CDt [HI C.R = W*/Adt [12] Mean (um/h) I 50 1.2887 1.2880 0.7 1404 3.15 0.73 0.54 34191 0.57 0.59 0.53 2 50 1.2666 1.2658 0.8 2065 3.14 0.57 46468 0.77 0.55 3 50 1.2445 1.2438 0.7 2021 3.13 0.51 42687 0.71 0.52 4 50 1.3770 1.3764 0.6 2022 3.19 0.43 43481 0.72 0.52 5 50 1.2754 1.2747 0.7 2235 3.14 0.46 44959 0.75 0.49 1 85 1.5105 1.5074 3.1 1848 3.25 2.38 2.41 193679 3.25 2.50 2.50 2 85 1.5160 1.5129 3.1 1740 3.25 2.53 202375 3.36 2.74 3 85 1.5094 1.5061 3.3 1935 3.25 2.42 195999 3.25 2.38 4 85 1.5182 1.5149 3.3 1903 3.25 2.46 201691 3.35 2.50 5 85 1.5315 1.5284 3.1 1936 3.26 2.27 ' 193991 3.22 2.36 We claim: 1. An improved measuring system for on-line measurement of corrosion of rate of metals in aqueous medium, which comprises a hydrogen doped argon source (1) being connected through a mass flow controller (3) for controlling the flow of hydrogen doped argon to a mixing chamber (5) and an argon source (2) being connected through a mass flow controller (4) for controlling the flow of argon to the said mixing chamber (5), the mixing chamber (5) being connected to a reaction chamber (6) for receiving the mixed gas from the mixing chamber (5) a hydrogen sensor (7) being connected to the reaction chamber (6) for continuously monitoring and measuring the hydrogen evolved in the reaction chamber and (6) the output of the on chamber being connected to a meter (8) for measuring the corrosion rate. 2. An improved measuring system as claimed in claim 1 wherein the mass flow controllers (3&4) are computer controlled mass flow controllers. 3. An improved measuring system for on-line measurement of corrosion rate of metals in aqueous medium substantially as herein described with reference to the drawing accompanying this specification. Dated this 17th day of October 2001

Documents:

1029-mum-2001-abstract(21-4-2004).doc

1029-mum-2001-abstract(21-4-2004).pdf

1029-mum-2001-abstract.doc

1029-mum-2001-abstract.pdf

1029-mum-2001-cancelled pages(21-4-2004).pdf

1029-mum-2001-claims cancelled.pdf

1029-mum-2001-claims(granted)-(21-4-2004).doc

1029-mum-2001-claims(granted)-(21-4-2004).pdf

1029-mum-2001-claims.doc

1029-mum-2001-claims.pdf

1029-mum-2001-correpondence.pdf

1029-mum-2001-correspondence(5-3-2007).pdf

1029-mum-2001-correspondence(ipo)-(5-1-2004).pdf

1029-mum-2001-correspondence(ipo).pdf

1029-mum-2001-description(granted).doc

1029-mum-2001-description(granted).pdf

1029-mum-2001-drawing(21-4-2004).pdf

1029-mum-2001-form 1(22-10-2001).pdf

1029-mum-2001-form 1.pdf

1029-mum-2001-form 19.pdf

1029-mum-2001-form 2(granted)-(21-4-2004).pdf

1029-mum-2001-form 2(granted).doc

1029-mum-2001-form 2(granted).pdf

1029-mum-2001-form 2(title page)-(21-4-2004).doc

1029-mum-2001-form 2(title page).pdf

1029-mum-2001-form 3(22-10-2001).pdf

1029-mum-2001-form 3.pdf

1029-mum-2001-power of attorney(22-10-2001).pdf

1029-mum-2001-power of attorney.pdf

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