ASTM D2186-2005 Standard Test Methods for Deposit-Forming Impurities in Steam《蒸汽中沉积杂质的标准试验方法》.pdf

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1、Designation: D 2186 05Standard Test Methods forDeposit-Forming Impurities in Steam1This standard is issued under the fixed designation D 2186; 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 p

2、arentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 These test methods cover the determination of theamount of deposit-forming impurities in steam. Determinationsare made on condensed steam samples

3、 in all test methods. TestMethods A, B, and C give a measure of the amount of totaldeposit-forming material present; Test Method D deals withspecial constituents that may be present. Special precautionsand equipment, calculation procedures, and ranges of applica-bility are described. The following t

4、est methods are included:SectionsTest Method A (Gravimetric or Evaporative) 6 to 12Test Method B (Electrical Conductivity) 13 to 19Test Method C (Sodium Tracer) 20 to 26Test Method D (Silica and Metals) 27 to 301.2 Test Method A is applicable for determining totaldissolved and suspended solids in co

5、ncentrations normally notless than 0.4 mg/L (ppm). It is applicable only to long-timesteady-state conditions and is not applicable for transients.1.3 Test Method B will measure minimum impurity concen-trations varying from 3 mg/L (ppm) down to at least 0.005mg/L (ppm), depending on the means for rem

6、oving dissolvedgases from the steam condensate. The means for removingdissolved gases also affects the storage capacity of steamcondensate in the system and, thus, affects the response of thesystem to transients.1.4 Because of the high sensitivity of methods for measur-ing sodium in steam condensate

7、, Test Method C provides themost sensitive measure of impurity content for samples inwhich sodium is an appreciable percentage of the impuritiespresent. Concentrations as low as 4.0 g/L (ppb) can bedetected by inductively coupled plasma atomic emission spec-troscopy, 0.2 g/L (ppb) by atomic absorpti

8、on spectrophotom-etry, 0.1 g/L (ppb) by graphite furnace atomic absorptionspectroscopy, and as low as 0.5 g/L (ppb) by sodium ionelectrode. The apparatus can be designed with low volume,and, therefore, Test Method C is the most responsive totransient conditions.1.5 Test Method D covers the determina

9、tion of silica andmetals in steam, which are not included in Test Methods B andC and are not individually determined using Test Method A.1.6 This standard does not purport to address the safetyconcerns, if any, associated with its use. It is the responsibilityof the user of this standard to establis

10、h appropriate safety andhealth practices and determine the applicability of regulatorylimitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D 512 Test Methods for Chloride Ion in WaterD 516 Test Method for Sulfate Ion in WaterD 857 Test Methods for Aluminum in WaterD 859 Test Method fo

11、r Silica in WaterD 1066 Practice for Sampling Steam2D 1068 Test Methods for Iron in WaterD 1125 Test Methods for Electrical Conductivity and Re-sistivity of WaterD 1129 Terminology Relating to WaterD 1687 Test Methods for Chromium in WaterD 1688 Test Methods for Copper in WaterD 1886 Test Methods fo

12、r Nickel in WaterD 1976 Test Method for Elements in Water by Inductively-Coupled Argon Plasma Atomic Emission SpectroscopyD 2791 Test Method for Continuous Determination of So-dium in WaterD 3082 Test Method for Boron in Water2D 3370 Practices for Sampling Water from Closed ConduitsD 3867 Test Metho

13、ds for Nitrite-Nitrate in WaterD 4191 Test Method for Sodium in Water by AtomicAbsorption SpectrophotometryD 5542 Test Methods for TraceAnions in High Purity Waterby Ion ChromatographyD 5907 Test Method for Filterable and Nonfilterable Matterin WaterD 6071 Test Method for Low Level Sodium in High Pu

14、rityWater by Graphite Furnace Atomic Absorption Spectros-copy1These test methods are under the jurisdiction of ASTM Committee D19 onWater and are the direct responsibility of Subcommittee D19.03 on Sampling ofWater and Water-Formed Deposits, Analysis of Water for Power Generation andProcess Use, On-

15、Line Water Analysis of Water for Power.Current edition approved June 1, 2005. Published July 2005. Originally approvedin 1966. Last previous edition approved in 2005 as D 2186 84 (2005).2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceas

16、tm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3. Terminology3.1 DefinitionsFor definitions of terms used i

17、n these testmethods, refer to Terminology D 1129.4. Significance and Use4.1 Limiting the concentration of deposit-forming impuri-ties in steam is of significance to protect both steam generatorsand steam turbines from damage or degradation of perfor-mance, or both.4.1.1 Steam entering superheaters a

18、nd reheaters of steamgenerators always contains some impurities. If the concentra-tion of impurities is sufficiently low, the impurities are dis-solved in superheated steam and are carried out of the steamgenerator. However, if the steam contains a sufficient amountof any substance to exceed its sol

19、ubility limit in steam, thesubstance is likely to form a deposit on the heat-transfersurface. Because heat transfer in superheaters and reheaters infossil-fueled steam generators is controlled principally by thelow heat-transfer coefficient on the gas side, the formation ofsteam-side deposits will h

20、ave little effect on the overallheat-transfer rate. However, steam-side deposits will increasethe operating temperature of the heat-transfer surface. Suchtemperature increases can lead to swelling and ultimately torupture of the tubing. Also, aggressive materials can concen-trate under solid deposit

21、s of porous materials, such as magne-tite (Fe3O4), and can cause serious corrosion of the tubing.4.1.2 As steam flows through turbines, its temperature andpressure decrease rapidly. Because the ability of steam todissolve impurities decreases with decreasing temperature andpressure, impurities in st

22、eam may exceed their solubility limitand form deposits on the turbine. Such deposits reduce steamflow area, particularly in the high-pressure portion of theturbine where flow passages are small, and the roughness ofdeposits and their effect on blade contours result in losses ofturbine efficiency. Al

23、l of these effects lead to reduction of theplant maximum capacity, which appreciably reduces the finan-cial return on the capital investment in the power plant.Furthermore, aggressive materials, such as sodium hydroxide(NaOH) and sodium chloride (NaCl), may condense anddeposit on turbine surfaces. S

24、uch deposits occasionally con-tribute to failure due to cracking of highly stressed turbineblades and rotors. Repairs and outages are extremely costly.4.1.3 By monitoring the concentration of deposit-formingimpurities in steam, a power plant operator can take stepsnecessary to limit the impurities t

25、o tolerable concentrations andthus minimize or eliminate losses due to excessive deposits.5. Sampling5.1 Collect the samples in accordance with Practice D 1066and Practices D 3370 as applicable.5.2 The concentrations of sodium and silica in steamsamples are usually well below 1 mg/L (ppm). Because t

26、hesematerials exist in relative abundance in normal plant andlaboratory environments, even in atmospheric dust, extremecaution must be used when collecting and handling samples toavoid contamination. The use of a continuously flowingsample, which eliminates the need for collecting, handling, andstor

27、ing individual samples, is preferred.TEST METHOD AGRAVIMETRIC OREVAPORATIVE6. Scope6.1 The gravimetric test method is recommended for appli-cations for which an average value of impurities over a periodof several days or weeks is desired. It is particularly useful forsamples in which a large percent

28、age of the impurities areinsoluble, do not contain sodium, or do not contribute appre-ciably to the electrical conductivity of the samples, because theother methods are not satisfactory for these conditions. Ex-amples of such impurities are metals and metal oxides. It is notapplicable when short-tim

29、e trends are of interest or whenimmediate results are desired. The test method is useful for thedetermination of concentrations of impurities of 0.25 mg/L(ppm) or greater when a previously collected sample is usedand for impurities concentrations of 0.1 mg/L (ppm) or greaterwhen continuous sampling

30、is used. Concentrations less than0.1 mg/L (ppm) can be determined if a continuously flowingsample is evaporated for an extremely long period of time.7. Summary of Test Method7.1 This test method involves the evaporation of a quantityof steam condensate at a temperature below the boiling pointand the

31、 weighing of the residue to determine the amount ofimpurities in the sample. The evaporation process may becarried out on a steam condensate sample previously collected,or the sample may be taken continuously as the evaporationprocess is continued.8. Interferences8.1 Possible interferences for this

32、test method are describedin Test Methods D 5907.9. Apparatus9.1 Apparatus shall be provided in accordance with theapplicable test method of Test Methods D 5907.10. Procedure10.1 Proceed in accordance with Test Method D 5907 todetermine filterable and nonfilterable matter in the sample.11. Calculatio

33、n11.1 Calculate the concentration of impurities in the samplefrom the sum of the filterable and nonfilterable matter.11.2 Dissolved matter and total matter are usually of great-est interest in the determination of impurities in steam. Thedetermination of fixed solids after ignition at some temperatu

34、regreater than 103C (217F) may be of more significance thanthe measurement taken at 103C, depending on the type ofsolids in the sample and the maximum temperature to whichthe steam is to be heated in the application.12. Precision and Bias12.1 The precision of the analytical results is given in TestM

35、ethods D 5907. Because of the uncertainties involved insampling steam, it is not possible to state the overall precisionof this test method.D 2186 052TEST METHOD BELECTRICAL CONDUCTIVITY13. Scope13.1 Ion-Exchange DegasserAn ion-exchange degasserconsists of an ion-exchange resin that exchanges hydrog

36、en ionsfor all cations in the sample, thereby eliminating all basicdissolved gases, including volatile amines. By convertingmineral salts to their acid forms, it also increases the specificconductance of the impurities. As a result, the linear relation-ship between conductivity and impurity content

37、is extended toa much lower level, depending on the carbon dioxide content.The test method is very useful for measuring low concentra-tions of impurities, such as condenser cooling water leakage, insteam condensate, and it is especially useful, for indicatingsmall or intermittent changes in impurity

38、content from somenormal value. The test method is not satisfactory for thedetermination of impurities in steam condensate samples thatcontain acidic gases, such as carbon dioxide, large percentagesof insoluble matter, or substances that ionize weakly. Thesensitivity and accuracy of the method are de

39、creased forsamples in which hydroxides represent an appreciable percent-age of the impurities, because hydroxides, which contribute tothe formation of deposits, are converted to water by theion-exchange resin. This characteristic is particularly signifi-cant when steam is generated at sufficiently h

40、igh pressure tocause appreciable vaporization of sodium hydroxide from theboiler water.13.2 Mechanical and Ion-Exchange DegasserBy combin-ing mechanical and ion-exchange degassing of steam orcondensed steam, or both, effective elimination of both acidicand basic dissolved gases is attained. This arr

41、angement has thesame advantages and limitations as the ion-exchange degasseralone, except that it will remove acidic gases, and the greatersensitivity afforded by measuring the conductance at atmo-spheric boiling water temperature extends the linear relation-ship between conductivity and the ionized

42、 impurity contentdown to about at least 0.005 mg/L (ppm). Although therelationship becomes somewhat nonlinear, the conductance issensitive to concentration changes down to at least 0.005 mg/L(ppm).314. Summary of Test Method14.1 Because the concentrations of impurities in steamcondensate are usually

43、 very low, most impurities are assumedto be completely dissolved and completely ionized. Therefore,the electrical conductivity of the condensate sample is ameasure of the concentration of ionized impurities in thesample.14.2 Most steam contains gases from decomposition ofcertain substances in boiler

44、 feedwater and from the addition ofchemicals to boiler water or boiler feedwater for the control ofcorrosion. These gases dissolve and ionize in the condensedsteam samples. Since such gases normally do not form depos-its, their contribution to conductivity should be eliminated bydegassing the sample

45、 before its electrical conductivity ismeasured. Because mechanical degassing is not completelyeffective, the amount of residual gases must be determined andthe measured conductivity value must be corrected for theireffect. Although mechanical degassers may still be used to alimited extent, they are

46、no longer available commercially. Theuse of mechanical degassers should be considered obsolete.14.3 Basic dissolved gases, many of which are not effec-tively removed by mechanical degassing, are converted towater by an ion-exchange degasser. The ion-exchange degasseralso converts mineral salts to th

47、eir acid form by exchanginghydrogen ions for the metallic cations. Since the specificconductance of the acid form is roughly three times that of theoriginal mineral salts at 25C (77F), the sensitivity of mea-surement is increased. If the conductance measurement is madeat the atmospheric boiling poin

48、t (approximately 100C(212F), the specific conductances of the ions are increasedand the sensitivity of measurement is improved still further.15. Interferences15.1 Residual gases remaining in steam condensate samplesafter mechanical degassing constitute interference with theconductivity measurement.

49、The concentrations of these gasesremaining in the samples shall be determined, and appropriatecorrections shall be subtracted from the measured conductivityvalues.16. Apparatus16.1 Apparatus shall be provided in accordance with TestMethods D 1125.16.2 Ion-Exchange DegasserThe ion exchange columnshall consist preferably of sulfonated styrenedivinyl-benzeneresin in a container of plastic or other corrosion-resistantmaterial. A column of approximately 38-mm (1.5-in.) internaldiameter and 305 mm (12 in.) in length, containing about 272g (0.6 lb) of resin, is satisfactor