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2、 84 (Reapproved 1999)e1An American National StandardStandard 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 o
3、f 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.e1 NOTEFootnotes were editorially removed in June 1999.1. Scope1.1 These test methods cover the determination of the amount of
4、deposit-forming impurities in steam. Determinations are made on condensed steam samples in all test methods. Test Methods A, B, and C give a measure of the amount of total deposit-forming material present; Test Method D deals with special constituents that may be present. Special precautions and equ
5、ipment, calculation procedures, and ranges of applica- bility are described. The following test 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
6、.2 Test Method A is applicable for determining total dissolved and suspended solids in concentrations normally not less than 0.1 mg/L (ppm). It is applicable only to long-time steady-state conditions and is not applicable for transients.1.3 Test Method B will measure minimum impurity concen- tration
7、s varying from 3 mg/L (ppm) down to at least 0.005 mg/L (ppm), depending on the means for removing dissolved gases from the steam condensate. The means for removing dissolved gases also affects the storage capacity of steam condensate in the system and, thus, affects the response of the system to tr
8、ansients.1.4 Because of the high sensitivity of methods for measur- ing sodium in steam condensate, Test Method C provides the most sensitive measure of impurity content for samples in which sodium is an appreciable percentage of the impurities present. Concentrations as low as 0.6 g/L (ppb) can be
9、detected by flame photometry and as low as 0.5 g/L (ppb) by sodium ion electrode. The apparatus can be designed with low volume, and, therefore, Test Method C is the most responsive to transient conditions.1 These test methods are under the jurisdiction of ASTM Committee D-19 on1.5 Test Method D cov
10、ers the determination 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 safety concerns, if any, associated with its use. It is the responsibility of the user of this s
11、tandard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:D 512 Test Methods for Chloride Ion in Water2D 515 Test Methods for Phosphorus in Water2D 516 Test Method for Sulfate Ion in W
12、ater2D 857 Test Methods for Aluminum in Water2D 859 Test Method for Silica in Water2D 992 Test Method for Nitrate Ion in Water3D 1066 Practice for Sampling Steam2D 1068 Test Methods for Iron in Water2D 1125 Test Methods for Electrical Conductivity and Re- sistivity of Water2D 1129 Terminology Relati
13、ng to Water2D 1339 Test Methods for Sulfite Ion in Water4D 1428 Test Methods for Sodium and Potassium in Water and Water-Formed Deposits by Flame Photometry4D 1687 Test Methods for Chromium in Water2D 1688 Test Methods for Copper in Water2D 1886 Test Methods for Nickel in Water2D 1888 Test Methods f
14、or Particulate and Dissolved Matter, Solids, or Residue in Water2D 2791 Test Method for Continuous Determination of So- dium in Water2D 3082 Test Method for Boron in Water2D 3370 Practices for Sampling Water from Closed Con- duits2Water and are the direct responsibility of Subcommittee D19.03 on Sam
15、pling of Water and Water-Formed Deposits, and Surveillance of Water.Current edition approved Oct. 26, 1984. Published January 1985. Originally published as D 2186 66. Last previous edition D 2186 79.2 Annual Book of ASTM Standards, Vol 11.01.3 DiscontinuedSee 1983 Annual Book of ASTM Standards, Vol
16、11.01.4 DiscontinuedSee 1989 Annual Book of ASTM Standards, Vol 11.02.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.1D 2186 84 (1999)e13. Terminology3.1 DefinitionsFor definitions of terms used in these test methods, refer to Termin
17、ology D 1129.4. Significance and Use4.1 Limiting the concentration of deposit-forming impuri- ties in steam is of significance to protect both steam generators and steam turbines from damage or degradation of perfor- mance, or both.4.1.1 Steam entering superheaters and reheaters of steam generators
18、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 steam generator. However, if the steam contains a sufficient amount of any substance to exceed its solubility limit in steam, the
19、substance is likely to form a deposit on the heat-transfer surface. Because heat transfer in superheaters and reheaters in fossil-fueled steam generators is controlled principally by the low heat-transfer coefficient on the gas side, the formation of steam-side deposits will have little effect on th
20、e overall heat-transfer rate. However, steam-side deposits will increase the operating temperature of the heat-transfer surface. Such temperature increases can lead to swelling and ultimately to rupture of the tubing. Also, aggressive materials can concen- trate under solid deposits of porous materi
21、als, such as magne- tite (Fe3O 4), and can cause serious corrosion of the tubing.4.1.2 As steam flows through turbines, its temperature and pressure decrease rapidly. Because the ability of steam to dissolve impurities decreases with decreasing temperature and pressure, impurities in steam may excee
22、d their solubility limit and form deposits on the turbine. Such deposits reduce steam flow area, particularly in the high-pressure portion of the turbine where flow passages are small, and the roughness of deposits and their effect on blade contours result in losses of turbine efficiency. All of the
23、se effects lead to reduction of the plant 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 and deposit on turbine surfaces. Such
24、deposits occasionally con- tribute to failure due to cracking of highly stressed turbine blades and rotors. Repairs and outages are extremely costly.4.1.3 By monitoring the concentration of deposit-forming impurities in steam, a power plant operator can take steps necessary to limit the impurities t
25、o tolerable concentrations and thus 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 steam samples are usually well below 1 mg/L (ppm). Because
26、 these materials exist in relative abundance in normal plant and laboratory environments, even in atmospheric dust, extreme caution must be used when collecting and handling samples to avoid contamination. The use of a continuously flowing sample, which eliminates the need for collecting, handling,
27、and storing 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 period of several days or weeks is desired. It is particularly useful for samples in which a la
28、rge percentage of the impurities are insoluble, do not contain sodium, or do not contribute appre- ciably to the electrical conductivity of the samples, because the other methods are not satisfactory for these conditions. Ex- amples of such impurities are metals and metal oxides. It is not applicabl
29、e when short-time trends are of interest or when immediate results are desired. The test method is useful for the determination of concentrations of impurities of 0.25 mg/L(ppm) or greater when a previously collected sample is used and for impurities concentrations of 0.1 mg/L (ppm) or greater when
30、continuous sampling is used. Concentrations less than0.1 mg/L (ppm) can be determined if a continuously flowing sample is evaporated for an extremely long period of time.7. Summary of Test Method7.1 This test method involves the evaporation of a quantity of steam condensate at a temperature below th
31、e boiling point and the weighing of the residue to determine the amount of impurities in the sample. The evaporation process may be carried out on a steam condensate sample previously collected, or the sample may be taken continuously as the evaporation process is continued.8. Interferences8.1 Possi
32、ble interferences for this test method are described in Test Methods D 1888.9. Apparatus9.1 Apparatus shall be provided in accordance with the applicable test method of Test Methods D 1888.10. Procedure10.1 Proceed in accordance with Test Method A or B of TestMethods D 1888, as applicable.11. Calcul
33、ation11.1 Calculate the concentration of impurities in the sample in accordance with Test Methods D 1888.11.2 Dissolved matter and total matter are usually of great- est interest in the determination of impurities in steam. The determination of fixed solids after ignition at some temperature greater
34、 than 103C (217F) may be of more significance than the measurement taken at 103C, depending on the type of solids in the sample and the maximum temperature to which the steam is to be heated in the application.12. Precision and Bias12.1 The precision of the analytical results is given in Test Method
35、s D 1888. Because of the uncertainties involved in sampling steam, it is not possible to state the overall precision of this test method.2D 2186 84 (1999)e1TEST METHOD BELECTRICAL CONDUCTIVITY13. Scope13.1 Ion-Exchange DegasserAn ion-exchange degasser consists of an ion-exchange resin that exchanges
36、 hydrogen ions for all cations in the sample, thereby eliminating all basic dissolved gases, including volatile amines. By converting mineral salts to their acid forms, it also increases the specific conductance of the impurities. As a result, the linear relation- ship between conductivity and impur
37、ity content 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, in steam condensate, and it is especially useful, for indicating small or intermittent chan
38、ges in impurity content from some normal value. The test method is not satisfactory for the determination of impurities in steam condensate samples that contain acidic gases, such as carbon dioxide, large percentages of insoluble matter, or substances that ionize weakly. The sensitivity and accuracy
39、 of the method are decreased for samples in which hydroxides represent an appreciable percent- age of the impurities, because hydroxides, which contribute to the formation of deposits, are converted to water by the ion-exchange resin. This characteristic is particularly signifi- cant when steam is g
40、enerated at sufficiently high pressure to cause appreciable vaporization of sodium hydroxide from the boiler water.13.2 Mechanical and Ion-Exchange DegasserBy combin- ing mechanical and ion-exchange degassing of steam or condensed steam, or both, effective elimination of both acidic and basic dissol
41、ved gases is attained. This arrangement has the same advantages and limitations as the ion-exchange degasser alone, except that it will remove acidic gases, and the greater sensitivity afforded by measuring the conductance at atmo- spheric boiling water temperature extends the linear relation- ship
42、between conductivity and the ionized impurity content down to about at least 0.005 mg/L (ppm). Although the relationship becomes somewhat nonlinear, the conductance is sensitive to concentration changes down to at least 0.005 mg/L(ppm). 514. Summary of Test Method14.1 Because the concentrations of i
43、mpurities in steam condensate are usually very low, most impurities are assumed to be completely dissolved and completely ionized. Therefore, the electrical conductivity of the condensate sample is a measure of the concentration of ionized impurities in the sample.14.2 Most steam contains gases from
44、 decomposition of certain substances in boiler feedwater and from the addition of chemicals to boiler water or boiler feedwater for the control of corrosion. These gases dissolve and ionize in the condensed steam samples. Since such gases normally do not form depos- its, their contribution to conduc
45、tivity should be eliminated bydegassing the sample before its electrical conductivity ismeasured. Because mechanical degassing is not completely effective, the amount of residual gases must be determined and the measured conductivity value must be corrected for their effect. Although mechanical dega
46、ssers may still be used to a limited extent, they are no longer available commercially. The use 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 to water by an ion-exchange degasser. The ion-exchange degasser also converts mineral salts to their acid form by exchanging hydrogen ions for the metallic cations. Since the specific conductance of the acid form is roughly thr