1、Designation: C 537 87 (Reapproved 2004)e1Standard Test Method forReliability of Glass Coatings on Glassed Steel ReactionEquipment by High Voltage1This standard is issued under the fixed designation C 537; the number immediately following the designation indicates the year oforiginal adoption or, in
2、the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.e1NOTEKeywords were added editorially in September 2004.1. Scope1.1 This test method covers the
3、 determination of the reli-ability of glass coating on metal and is intended for use bymanufacturers of equipment that is designed to withstandhighly corrosive conditions where a failure of the coating inservice would cause extreme damage to the exposed metal. Itsuse outside the manufacturers plant
4、is discouraged becauseimproper or indiscriminate testing can cause punctures that aredifficult to repair without returning the equipment to themanufacturers plant. This test method detects not only exist-ing discontinuities in the glass coating, but also areas where theglass may be thin enough to be
5、 likely to result in prematurefailure in service.1.2 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of re
6、gulatory limitations prior to use. For specificprecautionary statements, see Section 7.2. Terminology2.1 Definition:2.1.1 glassed steel, glass-lined steel, or glass-coated steeldesignations generally applied to a class of porcelain enamelsthat have high resistance to chemical attack at elevatedtempe
7、ratures and pressures.3. Summary of Test Method3.1 This test method consists essentially of grounding themetal structure of the equipment to the ground side of adirect-current high-voltage generator and sweeping the glasssurface with a high-potential probe on the end of an insulatedhandle and cable.
8、 Wherever a discontinuity exists or thecoating is thin enough (by reason of a concealed bubble orconducting inclusion, etc.) so that the dielectric strength of theremaining glass is less than some preset desired amount, thedielectric strength of air-plus-remaining-glass breaks down anda discharge oc
9、curs. Built-in current-limiting devices ensureelectrical safety to the operator. A variable voltage controlallows selection of a voltage which assures a predeterminedminimum thickness of glass.4. Significance and Use4.1 The widespread use of glassed-steel equipment in highlycorrosive chemical proces
10、ses has made it necessary to detectweak spots in the coating and repair them before catastrophicfailure occurs in service. This test is intended to detectdiscontinuities and thin areas in a glass coating on metal toensure that the coating is defect free and has sufficientthickness to withstand the p
11、rescribed service conditions. A testvoltage may be selected at any desired value up to 20 000 V,thus making the test applicable to a wide range of thicknessrequirements. When, because of bubbles or defects, the thick-ness of glass at any spot is less than enough to withstand theapplied voltage, a pu
12、ncture results with an accompanyingindication of a defect. Remedial action is then required torepair the defect before the equipment can be used forcorrosive service. (When such defects are found before theequipment leaves the manufacturers plant another applicationof glass can usually be applied an
13、d fired to become an integralpart of the coating.)5. Interferences5.1 Since the test method is electrical, it is necessary to havea good ground connection between the instrument and themetal substrate of the equipment being tested. It is alsonecessary that the surface of the glass be reasonably clea
14、n anddry. A wet surface will conduct enough of the high voltage toany exposed metal, including the edges of the glass coating, sothat an indication of a “contact” may be obtained over a largearea instead of at localized spots that can be marked andidentified for repair.1This test method is under the
15、 jurisdiction of ASTM CommitteeB08 on Metallicand Inorganic Coatings and is the direct responsibility of SubcommitteeB08.12 onMaterials for Porcelain Enamel and Ceramic-Metal Systems.Current edition approved Aug. 1, 2004. Published September 2004. Originallyapproved in 1964. Last previous edition ap
16、proved in 1998 as C 537 87 (1998).1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.6. Apparatus26.1 The tester is composed of a source of high-voltage directcurrent with a suitable device to limit the current. A constant-voltage trans
17、former is used to supply a more uniform voltagesource than the usual 115-V, 60-Hz line to which it isconnected. The power supply unit consists of a suitable step-uptransformer along with a voltage-control device, a current-limiting rheostat, a rectifier, and appropriate safety and remotecontrol rela
18、ys, meters, as well as an insulated cable and probe(see Fig. 1 for schematic wiring diagram). The current outputis limited to 2.5 mA. The output voltage is variable up to20 000 V, and the level is indicated by a voltmeter. The handleis insulated and grounded and is designed to use either a wirebrush
19、-type or a point probe. The brush probe is used forsweeping larger surfaces of glass coating while the point probeis better adapted to interior corners and the more restrictedareas.7. Safety Precautions7.1 The instrument and equipment being tested should bewell grounded both to a good ground and to
20、each other. Allgrounding contacts should be clean bare metal and not rustedor painted metal.7.2 Handle the insulated probe handle so that the handcontacts the ground ring to prevent build-up of a static chargewhich causes an unpleasant (although not dangerous) sensationon discharge.7.3 Keep the prob
21、e electrode at least 305 mm (12 in.) awayfrom conducting surfaces or personnel. Remember that con-ducting surfaces may lead to personnel at some distance fromthe probe. Discharge the probe tip by grounding it after turningoff the instrument and before changing probe tips. Although thecurrent is low
22、enough to be electrically safe, the involuntaryreaction from a surprise discharge might cause injury.7.4 Unless the surface to be tested is clean and dry, theremay be sufficient conduction along the surface to cause acapacitance discharge even if there is no direct path to ground.Such a capacitance
23、discharge is recognizable from a truefailure because the discharge spark is not confined to certainspots but is a general discharge to a large area of the moist glasssurface. Continuous application of the probe to such areasserves only to build up a capacitance charge on the surface ofthe vessel eve
24、ntually resulting in a discharge through theoperator to his discomfort.7.5 A d-c tester should never be used in a chemical plant fordiscontinuity testing because of the possibility that a capacitivecharge will be developed in the dielectric coating, resulting inan explosion hazard.8. Procedure8.1 Th
25、e following procedure is applicable to commerciallyavailable test equipment:8.1.1 Install ground connections to the instrument and to theequipment to be tested. Provide a separate ground connectionbetween the instrument and the equipment.8.1.2 Set the voltage-control knob near the minimum set-ting,
26、connect the instrument to the voltage stabilizer, andconnect the latter to the appropriate power line. Turn the poweron and allow the test equipment to warm up for 2 to 3 min toensure stabilization of the voltage.8.1.3 Engage the overload relay and then the “DC On”switch to apply voltage to the prob
27、e.8.1.4 Hold the probe by the handle with a firm grip on theground ring and with the electrode well away from all objectsand personnel, and slowly raise the voltage until the voltmeterindicates the desired value. Maintain hand contact with theground ring of the handle all through the test to avoid a
28、 buildupof static electricity in the operator that might result in anuncomfortable and annoying (although not dangerous) sparkdischarge. Pass the test probe across the coating surface at aspeed not to exceed 40 cm/s.NOTE 1The instrument is set to discharge across an internal gap at2When requesting i
29、nformation, specific reference should be made to the ASTMdesignation.FIG. 1 Circuit Diagram, 20 000-V D-C TesterC 537 87 (2004)e12slightly over 20 000 V. If the voltage is set high enough to cause such adischarge, ionization of the air usually causes the arc to persist until thevoltage is reduced to
30、 approximately 5000 V. Shortly after the arc hasextinguished, the voltage can be reset to the desired value.8.1.5 When a point of failure in the coating is approached,a spark will jump to the point of failure with a visible andaudible discharge or arc. As the path of the arc is shortened, bybringing
31、 the electrode close to the point of failure, the currentin the arc builds up. At a 2.5-mA current in the arc, theoverload relay will trip and the d-c current will cut off. Whenthis happens it is necessary to engage first the overload relayand then the “DC On” switch before the tester is againoperat
32、ive.8.1.6 Mark the point of failure with suitable chalk (orcrayon) for subsequent repair.9. Report9.1 The report shall include the following:9.1.1 Title of test, ASTM designation and issue,9.1.2 Date of test,9.1.3 Description or identification of equipment beingtested,9.1.4 Voltage used in the test,
33、 and9.1.5 Number and location of failures.10. Precision and Bias10.1 No justifiable statements can be made regarding theprecision and bias of this test method due to the fact that thismethod is designed for application to full-sized productionvessels and reactors with the result that variables due t
34、o design,metal composition, fabrication, and metal processing, as wellas porcelain enameling, are introduced into the results.11. Keywords11.1 glass coated steel equipment; glass coating; high volt-age test; porcelain enamel; reliability of coatingsASTM International takes no position respecting the
35、 validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly advised that determination of the validity of any such patent rights, and the riskof infringement of such rights, are entirely their own responsibility.This standard is
36、 subject to revision at any time by the responsible technical committee and must be reviewed every five years andif not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional standardsand should be addressed to ASTM International Hea
37、dquarters. Your comments will receive careful consideration at a meeting of theresponsible technical committee, which you may attend. If you feel that your comments have not received a fair hearing you shouldmake your views known to the ASTM Committee on Standards, at the address shown below.This st
38、andard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org).C 537 87 (2004)e13
