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1、BRITISH STANDARD BS ISO 17864:2005 Corrosion of metals and alloys Determination of the critical pitting temperature under potientiostatic control ICS 77.060 ? Licensed Copy: sheffieldun sheffieldun, na, Sun Nov 26 11:39:43 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS ISO 17864:2005 This British Sta
2、ndard was published under the authority of the Standards Policy and Strategy Committee on 17 January 2006 BSI 17 January 2006 ISBN 0 580 47099 7 National foreword This British Standard reproduces verbatim ISO 17864:2005 and implements it as the UK national standard. The UK participation in its prepa
3、ration was entrusted to Technical Committee ISE/NFE/8, Corrosion of metals and alloys, which has the responsibility to: A list of organizations represented on this committee can be obtained on request to its secretary. Cross-references The British Standards which implement international publications
4、 referred to in this document may be found in the BSI Catalogue under the section entitled “International Standards Correspondence Index”, or by using the “Search” facility of the BSI Electronic Catalogue or of British Standards Online. This publication does not purport to include all the necessary
5、provisions of a contract. Users are responsible for its correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. aid enquirers to understand the text; present to the responsible international/European committee any enquiries on the interpreta
6、tion, or proposals for change, and keep UK interests informed; monitor related international and European developments and promulgate them in the UK. Summary of pages This document comprises a front cover, an inside front cover, the ISO title page, pages ii to v, a blank page, pages 1 to 13 and a ba
7、ck cover. The BSI copyright notice displayed in this document indicates when the document was last issued. Amendments issued since publication Amd. No. DateComments Licensed Copy: sheffieldun sheffieldun, na, Sun Nov 26 11:39:43 GMT+00:00 2006, Uncontrolled Copy, (c) BSI Reference number ISO 17864:2
8、005(E) INTERNATIONAL STANDARD ISO 17864 First edition 2005-08-01 Corrosion of metals and alloys Determination of the critical pitting temperature under potientiostatic control Corrosion des mtaux et alliages Determination de la temprature critique de piqration des aciers inoxydables sous contrle pot
9、entiostatique BS ISO 17864:2005 Licensed Copy: sheffieldun sheffieldun, na, Sun Nov 26 11:39:43 GMT+00:00 2006, Uncontrolled Copy, (c) BSI ii Licensed Copy: sheffieldun sheffieldun, na, Sun Nov 26 11:39:43 GMT+00:00 2006, Uncontrolled Copy, (c) BSI iii Contents Page Foreword iv Introduction v 1 Scop
10、e . 1 2 Normative references. 1 3 Terms and definitions. 1 4 Principle. 1 5 Apparatus 2 6 Specimens. 3 7 Calibration of specimen temperature vs. solution temperature 4 8 Procedure 4 9 Assessment of results 5 10 Test report . 6 Annex A (informative) Guidelines for selecting the test parameters 7 Anne
11、x B (informative) Method of preventing a crevice attack. 9 Annex C (informative) Potential difference of selected reference electrodes at 25 C with respect to the standard hydrogen electrode (SHE) 13 BS ISO 17864:2005 Licensed Copy: sheffieldun sheffieldun, na, Sun Nov 26 11:39:43 GMT+00:00 2006, Un
12、controlled Copy, (c) BSI iv Foreword ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Standards is normally carried out through ISO technical committees. Each member body intereste
13、d in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical Com
14、mission (IEC) on all matters of electrotechnical standardization. International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2. The main task of technical committees is to prepare International Standards. Draft International Standards adopted by the techni
15、cal committees are circulated to the member bodies for voting. Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote. Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. ISO sh
16、all not be held responsible for identifying any or all such patent rights. ISO 17864 was prepared by Technical Committee ISO/TC 156, Corrosion of metals and alloys. BS ISO 17864:2005 Licensed Copy: sheffieldun sheffieldun, na, Sun Nov 26 11:39:43 GMT+00:00 2006, Uncontrolled Copy, (c) BSI v Introduc
17、tion Stainless steel is susceptible to pitting corrosion, crevice corrosion, and stress-corrosion cracking, etc., although it is used as generally a corrosion-resistant material. Pitting phenomenon is generally of a random nature, therefore its measurement requires at least a couple of values. Criti
18、cal pitting temperature defines the lowest potential-independent temperature, below which pitting does not occur. The basic methodology was first standardized in ASTM G150, Standard test method for electrochemical critical pitting temperature testing of stainless steels. BS ISO 17864:2005 Licensed C
19、opy: sheffieldun sheffieldun, na, Sun Nov 26 11:39:43 GMT+00:00 2006, Uncontrolled Copy, (c) BSI blank Licensed Copy: sheffieldun sheffieldun, na, Sun Nov 26 11:39:43 GMT+00:00 2006, Uncontrolled Copy, (c) BSI 1 Corrosion of metals and alloys Determination of the critical pitting temperature under p
20、otientiostatic control 1 Scope This International Standard describes the procedure for determining the critical pitting temperature for stainless steels (austenitic, ferritic/austenitic, ferritic stainless steel) under potentiostatic control. The principal advantage of the test is the rapidity with
21、which the critical pitting temperature can be measured in a single test. The critical pitting temperature, as determined in this International Standard, can be used as a relative index of performance, for example, to compare the relative performance of different grades of stainless steel. The test d
22、escribed in this International Standard is not intended to determine the temperature at which pitting will occur in service. 2 Normative references The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For und
23、ated references, the latest edition of the referenced document (including any amendments) applies. ISO 8044:1999, Corrosion of metals and alloys Basic terms and definitions 3 Terms and definitions For the purposes of this document, the following terms and definitions apply. 3.1 critical pitting temp
24、erature CPT lowest temperature on the surface of the specimen at which stable propagating pitting occurs under specified test conditions 3.2 temperature ramp rate rate at which the temperature of the surface of the specimen is increased during the test NOTE The temperature ramp rate is expressed in
25、degrees Celsius per second (C s1). 4 Principle 4.1 The test involves increasing the temperature of the surface of the specimen at a specified rate, whilst exposing the specimen to a specified environment and maintaining the potential of the specimen at a specified value. The temperature of the surfa
26、ce of the specimen is increased by heating the solution. BS ISO 17864:2005 Licensed Copy: sheffieldun sheffieldun, na, Sun Nov 26 11:39:43 GMT+00:00 2006, Uncontrolled Copy, (c) BSI 2 4.2 The critical pitting temperature is defined as the temperature of the specimen at which the current density exce
27、eds a specified value for 60 s. A 60 s delay is used in order to ensure that the observed current increase originates from stable propagating pitting, and not short-lived current peaks originating from metastable pitting. 4.3 The specimen holder is designed to ensure that crevice corrosion does not
28、occur at the seal between the specimen and the holder. 4.4 There may be a temperature gradient between the bulk of the solution and the surface of the specimen, the magnitude of which will depend on the geometry and dimensions of the specimen. Guidelines for calibrating the temperature of the surfac
29、e of the specimen relative to the temperature of the solution are given in Clause 7. 4.5 The temperature ramp rate, environment and applied potential may be varied, depending on the material. Guidelines for selecting the test parameters for austenitic and duplex stainless steels are given in Annex A
30、. 4.6 The critical pitting temperature is specific to the method of testing and should only be used as a comparative measure of performance. 5 Apparatus 5.1 Potentiostat The potentiostat shall be capable of controlling the electrode potential to within 1 mV of a preset value. 5.2 Electrode potential
31、-measuring instrument The instrument should have a high input impedance of the order of 1011 to 1014 , to minimize current drawn from the system during measurement. The sensitivity and accuracy of the instrument should be sufficient to detect a change of 1,0 mV. 5.3 Current-measuring instruments The
32、 current in the circuit is evaluated from the potential drop measured across a known resistor. In many potentiostats, this measurement is made internally, but measurements can also be made externally by locating a resistor in the current line from the auxiliary electrode to the auxiliary connection
33、on the potentiostat. The instrument shall be capable of measuring a current to within 2 % of the actual value. 5.4 Temperature controller The temperature controller shall be capable of increasing the temperature of the surface of the specimen from 0 C to 100 C at a controlled rate. This is achieved
34、by heating or cooling the solution. Above 10 C, the average rate of temperature change of the specimen shall be controlled to within 30 % of the desired value, where the average is calculated over a temperature range of 10 C. Guidelines for calculating the temperature of the specimen relative to the
35、 temperature of the solution are given in Clause 7. 5.5 Temperature-measurement instrumentation The temperature-measurement instrumentation shall be capable of measuring the temperature of the test solution with an accuracy of 0,4 C. BS ISO 17864:2005 Licensed Copy: sheffieldun sheffieldun, na, Sun
36、Nov 26 11:39:43 GMT+00:00 2006, Uncontrolled Copy, (c) BSI 3 5.6 Specimen holder 5.6.1 Any part of the specimen holder coming into contact with the test solution shall be made of an inert material. 5.6.2 The specimen holder shall be designed to ensure that crevice corrosion does not occur at the con
37、tact area between the specimen holder and the specimen. A method of preventing such crevice attack, using a flushed-port cell or a flushed specimen holder, is outlined in Annex B. 5.7 Test cell 5.7.1 The test cell shall contain the test specimen, a Luggin capillary probe connected to an external ref
38、erence electrode for measuring the electrode potential, an auxiliary electrode, a port for insertion of a temperature-measuring device and a facility for stirring the solution in a repeatable manner. This can be achieved using a mechanical stirring device or simply by bubbling gas through the soluti
39、on at a controlled rate. 5.7.2 A double-walled cell is commonly used to enable the solution to be cooled or heated by recirculating a liquid from an external heating bath to the outer chamber of the cell. 5.7.3 The tip of the Luggin capillary probe shall be positioned so that it is at a distance fro
40、m the specimen of about, but not closer than, twice the diameter of the tip. 5.7.4 Any part of the test cell or specimen holder that comes into contact with the solution shall be constructed from an inert material. Polycarbonate, glass and polytetrafluoroethylene (PTFE) are suitable materials. 5.7.5
41、 The ratio of the volume of solution in the test cell to the specimen area shall be at least 100 ml/cm2. 5.8 Auxiliary electrode The auxiliary electrode is commonly prepared from high-purity platinum. Other materials may be used provided they are inert. The auxiliary electrode may be constructed in
42、the form of sheet or rod, or in the form of a gauze supported on a glass frame. The area of the auxiliary electrode should be at least the area of the specimen. NOTE Graphite may be used as a auxiliary electrode but care must be taken to avoid contamination; desorption of species retained in the gra
43、phite may be necessary prior to use. 5.9 Reference electrode 5.9.1 The reference electrode shall be maintained at ambient temperature external to the test cell and connected to the test cell via a Luggin capillary probe. 5.9.2 Commonly used electrodes include the silver/silver chloride electrode and
44、 the saturated calomel electrode. The potentials of these electrodes at 25 C relative to the standard hydrogen electrode at 25 C are given in Annex C. 6 Specimens 6.1 Any specimen geometry compatible with the specimen holder may be used. 6.2 A minimum test area of 1 cm2 shall be used. 6.3 The surfac
45、e finish shall be reproducible. BS ISO 17864:2005 Licensed Copy: sheffieldun sheffieldun, na, Sun Nov 26 11:39:43 GMT+00:00 2006, Uncontrolled Copy, (c) BSI 4 7 Calibration of specimen temperature vs. solution temperature 7.1 There may be a temperature gradient between the bulk solution and the surf
46、ace of the specimen. A test shall be conducted to calibrate the temperature of the specimen relative to the temperature of the solution. The calibration shall be performed using the procedure for the CPT test, given in Clause 8, except that no control or measurement of the electrode potential of the
47、 specimen is required. 7.2 The specimen size and geometry, solution volume, stirring rate and temperature ramp rate shall be the same for the calibration test as for the CPT test. 7.3 The specimen temperature shall be measured by installing a suitable temperature-measuring device inside the specimen
48、, as close as possible ( 40 C, the temperature ramp shall start at 30 C. 8.4.4 The specimen, counter electrode and salt bridge shall be placed in the test cell. The test cell shall then be filled with the solution. It is important to ensure that the salt bridge is filled with the test solution and i
49、s free of air bubbles, particularly in the restricted space at the tip. A wick, or equivalent device, may be placed in the salt bridge to ensure electric contact, even when small gas bubbles are formed during the test. 8.4.5 The solution shall be stirred continuously throughout the test. This can be achieved using a mechanical stirring device, or simply by bubbling an inert gas through the solution at a controlled rate. 8.4.6 The electrodes shall be connected to the potentiostat and d
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