NOTICE: This standard has either been superceded and replaced by a new version or discontinued.Contact ASTM International (www.astm.org) for the latest information. Designation: G 59 – 97e1 Standard Test Method for Conducting Potentiodynamic Polarization Resistance Measurements1 This standard is issued under the fixed designation G 59; the number immediately following the designation indicates the year of original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A superscript epsilon (e) indicates an editorial change since the last revision or reapproval. e1 NOTE—Note 2 in Section 6.4 was updated editorially August 2002. 1. Scope 3.2 Polarization resistance can be related to the rate of 1.1 This test method describes an experimental procedure general corrosion for metals at or near their corrosion potential, for polarization resistance measurements which can be used for Ecorr. Polarization resistance measurements are an accurate and the calibration of equipment and verification of experimental rapid way to measure the general corrosion rate. Real time technique. The test method can provide reproducible corrosion corrosion monitoring is a common application. The technique potentials and potentiodynamic polarization resistance mea- can also be used as a way to rank alloys, inhibitors, and so forth surements. in order of resistance to general corrosion. 1.2 This test method does not purport to address all of the 3.3 In this test method, a small potential scan, DE(t), defined safety concerns, if any, associated with its use. It is the with respect to the corrosion potential (DE = E – Ecorr), is responsibility of the user of this standard to establish appro- applied to a metal sample. The resultant currents are recorded. priate safety and health practices and determine the applica- The polarization resistance, RP, of a corroding electrode is bility of regulatory limitations prior to use. defined from Eq 1 as the slope of a potential versus current density plot at i = 0 (1-4):4 S D 2. Referenced Documents ] DE Rp 5 ]i (1) 2.1 ASTM Standards: i50, dE/dt→0 G 3 Practice for Conventions Applicable to Electrochemical The current density is given by i. The corrosion current Measurements in Corrosion Testing2 density, icorr, is related to the polarization resistance by the G 5 Test Method for Making Potentiostatic and Potentiody- Stern-Geary coefficient, B. (3), namic Anodic Polarization Measurements2 B G 102 Practice for Calculation of Corrosion Rates and icorr 5 106 R (2) Related Information from Electrochemical Measurements2 p 2.2 Adjunct: The dimension of Rp is ohm-cm 2, icorr is muA/cm2, and B is Samples of the Standard AISI Type 430 Stainless Steel (UNS in V. The Stern-Geary coefficient is related to the anodic, ba, S43000)3 and cathodic, bc, Tafel slopes as per Eq 3. ba bc 3. Significance and Use B5 (3) 2.303~ba 1 bc! 3.1 This test method can be utilized to verify the perfor- The units of the Tafel slopes are V. The corrosion rate, CR, mance of polarization resistance measurement equipment in- in mm per year can be determined from Eq 4 in which EW is cluding reference electrodes, electrochemical cells, poten- the equivalent weight of the corroding species in grams and r tiostats, scan generators, measuring and recording devices. The is the density of the corroding material in g/cm3. test method is also useful for training operators in sample icorr EW preparation and experimental techniques for polarization resis- CR 5 3.27 3 10–3 (4) r tance measurements. Refer to Practice G 102 for derivations of the above equa- tions and methods for estimating Tafel slopes. 1 This practice is under the jurisdiction of ASTM Committee G–1 on Corrosion 3.4 The test method may not be appropriate to measure of Metals, and is the direct responsibility of Subcommittee G 01.11 on Electro- chemical Measurements in Corrosion Testing. polarization resistance on all materials or in all environments. Current edition approved Dec. 10, 1997. Published February 1998. Originally published as G 59 – 78. Last previous edition G 59 – 91. 2 4 Annual Book of ASTM Standards, Vol 03.02. The boldface numbers in parentheses refer to the list of references at the end of 3 Available from ASTM Headquarters. Order PCN 12-700050-00. this standard. Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States. 1 the simple resis. The plot should be linear. ing. be minimal. repeatability and FIG. Preparation includes sequential wet includes a 1 L round bottom flask modified to permit the polishing with 240 grit and 600 grit SiC paper. The purge resistance and electrode capacitance.3 The working electrode should be prepared as detailed in 4.7 Apply a potential 30 mV more negative that the re- 5. AL 36268.8 One minute after application of the –30 mV potential. NOTE 3—Practice G 3 provides a definition of sign convention for potential and current. 5. 8. Terminate the sweep at a potential 30 mV more positive than 5. immersion.6 Record the corrosion potential Ecorr after 5 and 55-min sometimes needed in electrochemical studies. 1 Arrangement for Testing of Electrical Equipment (Potentiostat. water as described in Test Method G 5. Mumford.5 Transfer the test specimen to the test cell and position acquisition system) must be tested to ensure proper function. and have a slope 10 V. P. It of preparing the electrode.2 Use R = 10. with different corrosion currents.2 for a discussion of method biases arising from solution started at least 30 min before specimen immersion. For this purpose. as the tangent of the curve at i=0.1 The 1.6 V/h Expected corrosion currents in the microampere range require R = 1 to 10 (within 5 %).org) for the latest information. tor shown in Fig. 7.O. rate of 0.3 Note any deviation from the procedure or test condi- American Chemical Society reagent grade acid and distilled tions established in this test method. closeness of agreement between randomly selected measured free gas such as hydrogen. electrical circuit (5). 1 is adequate for the present application. or argon.1 The 5 and 55 min corrosion potentials and the polar- ization resistance value. I = E/R.0 N H2SO4 test solution should be prepared from 7. connect the potentiostat to a test The tip diameter must be no greater than 1 mm. the instrument system (potentiostat. Report electrochemical equipment may require calibration or servicing 7.4 Immediately prior to immersion the specimen is de- 4. NOTICE: This standard has either been superceded and replaced by a new version or discontinued. the Luggin probe tip 2 to 3 mm from the test electrode surface. X-Y Recorder) 2 .01 cm2 and dard cell or an equivalent cell can be used.25 must be constructed of inert materials and be able to reproduce cm2). and 6. 5. Apparatus Test Method G 5. G 59 – 97e1 See 8.4 If the observed results are different than expected. go through the density plot as shown in Practice G 3. While more complex dummy cells are 6. the standard curve in Test Method G 5. The time delay between rinsing and immersion should 4.1.1 The apparatus is described in Test Method G 5. This stan. 6. Determine the addition of inert gas.1. The experiment must commence within 1 h 4. NOTE 2—Samples of the standard AISI Type 430 stainless steel (UNS S45000) used in this test method are available to those wishing to evaluate 5. forward and reverse scans should be identical.1 Report the following information: in accordance with the manufacturer’s guidelines. water. The curves recorded for the tion resistance. begin the anodic potential scan at a sweep rate of 0. 6. potentiostat to E =– 30. continues throughout the test. Set the applied potential on the corded 55 min corrosion potential (See Note 3).6 V/h from DE = –30 mV to DE = +30 mV and back 6. Precision and Bias maintained at 30°C within 1°.1 Precision—Precision in this test method refers to the 6. Record the potential and current continuously. The current should be 3.astm.1 Before the polarization resistance measurement is made. X-Y recorder or data 6. NOTE 1—When polarization resistance values are measured for systems 6. Determine the polariza- origin. Experimental Procedure 7.2 A potentiostat capable of varying potential at a constant greased with a solvent such as acetone and rinsed with distilled scan rate and measuring the current is needed. surface area of the specimen to the nearest 0. The standard test cell requires 900 mL of test solution. Rp. kV.0 V. 6.2 Duplicate runs may be averaged.0 mA by Ohm’s Law. An equivalent cell subtract for the area under the gasket (typically 0. 6. The temperature must be 8. Test of Electrical Equipment their equipment and test procedure from Metal Samples.20 to 0.3 Record the potentiodynamic polarization curve at a scan the 55 min corrosion potential. thermometer. the value of R should be chosen to cover the current range of the actual polarization resistance measurement. The purge is values. Box 8. the 7. and electrodes.0 mV and apply the potential. ing current is needed.2 The test cell is purged at 150 cm3/min with an oxygen.3 A method of recording the varying potential and result.9 Plot the polarization curve as a linear potential-current to DE = –30 mV. nitrogen. Contact ASTM International (www. There are two aspects of precision.1. shown in Table 2.08 polarization resistance.19 9.org) for the latest information.5287 0.529 –0. corrosion. current –0.60 –0.520 –0.507 6. by the repeatability standard deviation sr. Reproducibility TABLE 2 Repeatability Statistics refers to the closeness of agreement between different labora.508 6.519 –0.8 sr.0111 6 0. Repeatability refers to the closeness of agree.8 sR. The potentiody- 6 –0. reference electrode.524 7.1 anodic polarization.94 9 –0. Contact ASTM International (www. mV versus SCE –0.95 Ecorr 5 min.93 Rp ohm-cm2 6.5151 0.2 Reproducibility— The lack of reproducibility is mea- sured by the reproducibility standard deviation.713 62. Tafel slope. G 59 – 97e1 reproducibility.522 –0.90 9.540 –0.11 discussion on the effects of double layer capacitance and –0.530 –0.512 7.529 –0. mV versus SCE –0.1.519 –0.07 ization. Lug- –0.529 –0. There is also a solution resistance effect that may –0.40 4 –0.00260 6 0.517 5.515 7.2 Bias—The polarization resistance as measured by the –0.524 –0.513 7. work- ing electrode 3 .514 7.19 –0. The measured values included (Table 1) the corrosion potential measured after 5 and 55 min and the polarization resistance.539 –0. Refer to Practice G 102 for further –0.521 –0.521 –0.22 solution resistance on polarization resistance measurements.5151 0.517 5.516 –0.519 5.529 –0. electrochemical cell.18 Test Method G 59 has two sources of bias.47 Average SR Interval –0.543 –0.70 –0. corrosion rate.513 6.0356 mV –0.508 7.65 effect that may cause the polarization resistance to be under- 7 –0.70 5 –0.00 ohm-cm2 measurements was carried out to establish the precision.52 electrolyte conductivity. three or four replicate Ecorr 55 min.555 –0. ohm-cm2 6. –0.529 –0.58 8. Laboratory Ecorr–5min Ecorr–55min Rp TABLE 3 Reproducibility Statistics (mV) (mV) (ohm-cm2) 95 % Confidence 1 –0.1 Repeatability— The lack of repeatability is measured found.519 5. The 95 % confidence 8.90 solution resistance.545 7. An interlaboratory test program with Ecorr 5 min.523 –0.07 –0. This bias 8 –0.509 6.04 Ecorr 55 min.530 –0.514 –0.The 95 % confidence interval refers to the tical Type 430 stainless steel specimens repeated with as close as possible adherence to the same procedure.88 2 –0.505 5. electrochemical potential. The 95 % confidence interval was calculated as 6 2.17 –0.0073 V 13 laboratories participating and two.506 6.510 6.46 1.521 5.85 cause the polarization resistance to be overestimated.519 –0. cathodic polar- 11 –0. The values obtained are ment between measurements by the same laboratory on iden. –0. mV versus SCE –0.astm. interval was calculated as 6 2.0127 6 0.510 9.520 –0.513 7. mV versus SCE –0.505 5. mixed potential.506 6.83 ohm-cm2 –0. potentiodynamic. 95 % Confidence Average Sr tories using identical Type 430 stainless steel specimens and Interval the procedure specified.545 7.0076 V Rp.522 –0.5287 0.529 5.520 –0.0 N H2SO4 at 30°C obtained are shown in Table 3. Stern-Geary coefficient.0311 mV 3 –0.11 will depend on the placement of the reference electrode and –0.00273 6 0.511 7.01 62.63 density.520 –0.565 –0. sR.510 6. 13 –0.505 5. Keywords 10 –0.1.64 12 –0. interval around the average that 95 % of the values should be 8.16 namic method includes a double layer capacitance charging –0.06 estimated.538 –0. NOTICE: This standard has either been superceded and replaced by a new version or discontinued.46 0. auxiliary electrode. open-circuit potential.520 –0.38 –0. The values TABLE 1 Interlaboratory Test Program Polarization Data for Stainless Steel Type 430 in 1. overvoltage.16 gin probe. A research report has been filed with the results of this program.508 7. corrosion potential.510 7.542 –0.519 –0.510 5.524 4.531 –0. West Conshohocken. F. “The Polarization Resistance Technique for Measuring (5) Gileadi.. M. Houston. or
[email protected]) for the latest information. 610-832-9555 (fax). NOTICE: This standard has either been superceded and replaced by a new version or discontinued. NY. (3) Mansfeld. 440 t. NACE.astm. Paper No. Vol 14. If you feel that your comments have not received a fair hearing you should make your views known to the ASTM Committee on Standards.. 4 . and Penciner.. 1976. which you may attend. E. G 59 – 97e1 REFERENCES (1) Stern. are entirely their own responsibility.11”. “Evaluation of Polarization Resistance Round Robin 104. an Experimental Approach. Contact ASTM International (www. United States.. Chapter III. p. 106. 1957. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the above address or at 610-832-9585 (phone). F. Vol (4) Mansfeld. Corrosion. Corrosion Science and Technology. and the risk of infringement of such rights. p.163. p. M.. E. Testing Conducted by ASTM G01. Your comments will receive careful consideration at a meeting of the responsible technical committee. at the address shown below. and Roth. Users of this standard are expressly advised that determination of the validity of any such patent rights. Your comments are invited either for revision of this standard or for additional standards and should be addressed to ASTM International Headquarters.astm. M. J. Reading. Addison-Wesley Press. 76. or through the ASTM website (www.org (e-mail). Plenum chemistry. Kirowa-Eisner. This standard is copyrighted by ASTM International. Vol VI. New York. R. CORROSION/ (2) Stern. 100 Barr Harbor Drive. March 22-26. either reapproved or withdrawn. 1976. PO Box C700.. MA 1975.org).1. TX. 390. ASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentioned in this standard. 1958.. This standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years and if not revised. Publishing Co. Journal of the Electrochemical Society. PA 19428-2959. Interfacial Electro- Corrosion Currents”.