1、UDC 669.35-4 : 020.194.2 : 620.193.461.711 DEUTSCHE NORM September 1985 Temperature Solution A OC PH 22 tl 10.0 f0.1 25 9.9 +0,1 27 +i 9,8 k0.1 30 21 9,7 t0,l Testing of copper alloys Stress corrosion cracking test using ammonia Testing of components Solution B PH 9,o 8.9 8,8 8,7 DIN 50 916 Part 2 P
2、rfung von Kupferlegierungen; Spannungsrikorrosionsprfung mit Ammoniak; Prfung von Bauteilen In keeping with current practice N, standards published by the International Organization for Standardization (ISO), a comma has been used throughout as the decimal marker, 1 General In the simultaneous prese
3、nce of ammonia, water or steam and oxygen, components of copper alloys, in particular of copper-zinc alloys which are under tensile stresses, may be subject to cracking often without corrosion products being visible. This type of corrosion is termed stress corrosion cracking as defined in DIN 50900
4、Part 1. 2 Scope This standard specifies a method of testing components of copper alloys, in particular copper-zinc alloys, in wet ammonia vapour. It serves to determine the stress conditions which may lead to stress corrosion cracking. Furthermore, this test can be used to investigate the following:
5、 - susceptibility of different copper alloys as component - protective effect of any existing coatings or of other materials to stress corrosion cracking; measures to protect components against stress corrosion cracking. 3 Apparatus Closeable glass vessels shall be used for the test. These may be, f
6、or example, desiccator vessels or simple glass troughs with ground rim and lid. The vessel volume should be at least 10 litres. A certain ratio of test space to volume of test solution shall be maintained (20 : 1 to 10 : 11, for example by using 0,5 to 1 I of test solution for a test vessel of 1 O l
7、itres capacity. 4 Test solution Two solutions which may be used alternatively are specified for testing in accordance with this standard. The solutions used shall be buffered solutions of am- monium chloride and sodium hydroxide with a pH value of 9 (solution B) or 10 (solution A) I. The test shall
8、be After the pH adjustment, make up to 1 litre with distilled or fully demineralized water. This does not change the pH value any more. Keep the temperature in any event constant to within k 1 OC during the pH adjustment, if necessary by means of a constant-temperature circulator. Carry out the pH m
9、easurement using an instrument which permits an adjustment of the pH value to within *0,02 (glass electrode). The test solutions may be used over a prolonged period, but the pH value, which represents a measure of the ammonia concentration in the vapour atmosphere, shall be checked at least every 3
10、weeks and adjusted if necessary. Continued on pages 2 and 3 Beuth Verlag GmbH, Berlin 30, has exclusive sale rights for German Standards (DIN-Normen) DIN 50 9 16 Part 2 Engl. Price group 5 Sales No. 0105 04.86 Page 2 DIN 50916 Part 2 5 Specimens 5.1 Type Specimens used shall be components of copper
11、alloys, e.g. clamps, gearwheels, pinions, screws, switching levers, punched bent parts or deepdrawn parts. The specimens shall be tested under stress conditions which also exist in practice. They shall be tested either individually or in combination with other components, in the assembled state, or
12、possibly also as a complete unit. The components may be produced from semi-f inished products, e.g. sheet metal, or they may be castings or forgings. 5.2 Number The number of specimens which can be tested simul- taneously in one test vessel depends on the size of the vessel and of the specimens and
13、has no bearing on the test result. Due to the unavoidable scatter of results, unless otherwise agreed, at least 6 parallel specimens shall be used. 5.3 Pretreatment The specimens shall be degreased before testing with ammonia. If further handling of the components (final assembly) is subsequently ne
14、cessary, this shall be carried out in such a way that renewed greasing is avoided. 6 Test duration The following test durations shall be used for the two test solutions. Table 2. I Soiution A I Soiution B I I Test duration I 4h 8h i6 h 24 h 2d 4d 7d 16h 24 h 2d 4d 7d 14 d 28 d 7 Procedure 7.1 Method
15、1 Introduce, preferably suspend, the specimens in the test vessel in such a way that the ammonia vapour can take effect unhindered. The specimens shall not dip into the test solution nor touch each other. Supports or suspension devices shall be made of materials which are not sus- ceptible to attack
16、 by ammonia vapour, e.g. glass or porcelain. Testing shall be carried out at a constant temperature of (30 * 1) OC to exclude visible condensed water formation caused by temperature fluctuations, which could severely falsify the test result. Prior to testing, the test vessel containing the test solu
17、tion shall be brought to a temperature of (30 1) OC. The test vessel shall subsequently be filled as quickly as possible with the specimens preheated to 30C and closed. This moment is to be considered the beginning of the test. 7.2 Method II Testing shall be carried out at a chosen temperature, whic
18、h shall be kept constant to within f 2OC. In choosing the temperature it shall be ensured that no visible condensate forms on the specimen. Otherwise, proceed as for method I. Method II is intended for a comparative materials test. 7.3 Assessment After the periods of time specified in table 2, remov
19、e the specimens from the test vessel for a short time and examine for cracks under a stereomicroscope at X6 to XI0 magnification. The moment when the first incipient crack occurs is to be considered the end of testing for a particular specimen. After each assessment, heat the undamaged specimens to
20、test temperature before re- introducing them into the test vessel. 8 Evaluation The median value shall be determined from the lifetime values of all specimens of the same type as a representative value. The maximum and minimum lifetime values shall also be recorded. The result of testing may then be
21、 specified as ”relative lifetime” with respect to a reference specimen. 9 Test report With reference to this standard, the following details shall be specified in the test report: type and designation of the specimen material; type of specimen, if applicable details of combination with other compone
22、nts (final assembly); number of specimens; type of test solution; test method applied; if applicable, test temperature; results of visual crack examination (lifetime; median; if applicable, relative lifetime; maximum and minimum lifetime values); if applicable, deviations from this standard; date of
23、 test. DIN 50916 Part 2 Page 3 Standards and other documents referred to DIN 50900 Part 1 I F. Aebi. Zeitschrift Metallkunde (Metallography) 49 (1958), pp. 63-68. Corrosion of metals; terminology; general concepts Explanatory notes This standard has been prepared by NMP Technical Committee 171 Korro
24、sion und Korrosionsschutz of the Norrnen- auschu Materialprfung (Materials Testing Standards Committee). Under otherwise identical circumstances, the danger of stress corrosion cracking depends particularly on the ammonia concentration, which may be greatly increased locally, e.g. inside housings wh
25、ich contain plastics releasing NI43 (e.g. phenolic resin, melamine resin). For example, the following concentrations have been measured. Table 3. I 1 Location Free atmosphere Closed moulded plastic housing at 2OoC (Phenolic resin) at 7OoC Testing over solution A at 3OoC Testing over solution B at 3OoC Concentration by mass up to 60 pg/m3 1 O00 mg/m3 (after 30 days) 5 O00 mg/m3 (after 4 days) 29 500 mglm3 5 500 mg/m3 International Patent Classification G O1 M 13/00 G O1 N 17/00
