ASTM_C_537_-_87_2014e1.pdf

Designation:C53787(Reapproved 2014)1Standard Test Method forReliability of Glass Coatings on Glassed Steel ReactionEquipment by High Voltage1This standard is issued under the fixed designation C537;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon()indicates an editorial change since the last revision or reapproval.1NOTEIntroduction added and unit abbreviation corrections made editorially in June 2014.INTRODUCTIONThis test method covers the determination of the reliability of glass coating on metal using highvoltage.It is intended for use by manufacturers of equipment that is designed to withstand highlycorrosive conditions where a failure of the coating in service would cause extreme damage to theexposed metal.The test method detects not only existing discontinuities in the glass coating,but alsoareas where the glass coating may be thin enough to be likely to result in premature failure in service.1.Scope1.1 This test method covers the 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 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 likely to result in prematurefailure in service.1.2 The values stated in SI units are to be regarded asstandard.No other units of measurement are included in thisstandard.1.3 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 regulatory limitations prior to use.For specificprecautionary statements,see Section 7.2.Terminology2.1 Definitions: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 elevatedtemperatures 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.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 occurs.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 processes 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 prescribed service conditions.A testvoltage may be selected at any desired value up to 20k V,thusmaking 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 puncture results with an accompanying1This test method is under the jurisdiction ofASTM Committee B08 on Metallicand Inorganic Coatings and is the direct responsibility of Subcommittee B08.12 onMaterials for Porcelain Enamel and Ceramic-Metal Systems.Current edition approved May 1,2014.Published June 2014.Originallyapproved in 1964.Last previous edition approved in 2009 as C537 87(2009).DOI:10.1520/C0537-87R14.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 indication 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 and 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