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【英文标准名称】:StandardTestMethodsforDeposit-FormingImpuritiesinSteam
【原文标准名称】:蒸汽中沉积杂质的标准试验方法
【标准号】:ASTMD2186-2005(2009)
【标准状态】:现行
【国别】:美国
【发布日期】:2005
【实施或试行日期】:
【发布单位】:美国材料与试验协会(US-ASTM)
【起草单位】:D19.03
【标准类型】:(TestMethod)
【标准水平】:()
【中文主题词】:
【英文主题词】:deposit-forming;electricalconductivity;evaporate;gravimetric;impurities;Larsen-Lane;sodiumtracer;steam;Conductanceandconductivity(electrical)--water;Dissolvedelements(ofwater);Evaporators/evaporation;Generatormaterials--turbine;
【摘要】:Limitingtheconcentrationofdeposit-formingimpuritiesinsteamisofsignificancetoprotectbothsteamgeneratorsandsteamturbinesfromdamageordegradationofperformance,orboth.Steamenteringsuperheatersandreheatersofsteamgeneratorsalwayscontainssomeimpurities.Iftheconcentrationofimpuritiesissufficientlylow,theimpuritiesaredissolvedinsuperheatedsteamandarecarriedoutofthesteamgenerator.However,ifthesteamcontainsasufficientamountofanysubstancetoexceeditssolubilitylimitinsteam,thesubstanceislikelytoformadepositontheheat-transfersurface.Becauseheattransferinsuperheatersandreheatersinfossil-fueledsteamgeneratorsiscontrolledprincipallybythelowheat-transfercoefficientonthegasside,theformationofsteam-sidedepositswillhavelittleeffectontheoverallheat-transferrate.However,steam-sidedepositswillincreasetheoperatingtemperatureoftheheat-transfersurface.Suchtemperatureincreasescanleadtoswellingandultimatelytoruptureofthetubing.Also,aggressivematerialscanconcentrateundersoliddepositsofporousmaterials,suchasmagnetite(Fe3O4),andcancauseseriouscorrosionofthetubing.Assteamflowsthroughturbines,itstemperatureandpressuredecreaserapidly.Becausetheabilityofsteamtodissolveimpuritiesdecreaseswithdecreasingtemperatureandpressure,impuritiesinsteammayexceedtheirsolubilitylimitandformdepositsontheturbine.Suchdepositsreducesteamflowarea,particularlyinthehigh-pressureportionoftheturbinewhereflowpassagesaresmall,andtheroughnessofdepositsandtheireffectonbladecontoursresultinlossesofturbineefficiency.Alloftheseeffectsleadtoreductionoftheplantmaximumcapacity,whichappreciablyreducesthefinancialreturnonthecapitalinvestmentinthepowerplant.Furthermore,aggressivematerials,suchassodiumhydroxide(NaOH)andsodiumchloride(NaCl),maycondenseanddepositonturbinesurfaces.Suchdepositsoccasionallycontributetofailureduetocrackingofhighlystressedturbinebladesandrotors.Repairsandoutagesareextremelycostly.Bymonitoringtheconcentrationofdeposit-formingimpuritiesinsteam,apowerplantoperatorcantakestepsnecessarytolimittheimpuritiestotolerableconcentrationsandthusminimizeoreliminatelossesduetoexcessivedeposits.1.1Thesetestmethodscoverthedeterminationoftheamountofdeposit-formingimpuritiesinsteam.Determinationsaremadeoncondensedsteamsamplesinalltestmethods.TestMethodsA,B,andCgiveameasureoftheamountoftotaldeposit-formingmaterialpresent;TestMethodDdealswithspecialconstituentsthatmaybepresent.Specialprecautionsandequipment,calculationprocedures,andrangesofapplicabilityaredescribed.Thefollowingtestmethodsareincluded:
Sections
TestMethodA(GravimetricorEvaporative)
6to12
TestMethodB(ElectricalConductivity)
13to19
TestMethodC(SodiumTracer)
20to26
TestMethodD(SilicaandMetals)
27to30