ASTM D6502-2010 6875 Standard Test Method for Measurement of On-line Integrated Samples of Low Level Suspended Solids and Ionic Solids in Process Water by X-Ray Fluorescence (XRF)《.pdf

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1、Designation: D6502 10Standard Test Method forMeasurement of On-line Integrated Samples of Low LevelSuspended Solids and Ionic Solids in Process Water byX-Ray Fluorescence (XRF)1This standard is issued under the fixed designation D6502; the number immediately following the designation indicates the y

2、ear 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.1. Scope1.1 This test method covers the operation, calibration, a

3、nddata interpretation for an on-line corrosion product (metals)monitoring system. The monitoring system is based on x-rayfluorescence (XRF) analysis of metals contained on membranefilters (for suspended solids) or resin membranes (for ionicsolids). Since the XRF detector is sensitive to a range ofem

4、ission energy, this test method is applicable to simultaneousmonitoring of the concentration levels of several metalsincluding titanium, vanadium, chromium, manganese, iron,cobalt, nickel, copper, zinc, mercury, lead, and others in aflowing sample. A detection limit below 1 ppb can be achievedfor mo

5、st metals.1.2 This test method includes a description of the equipmentcomprising the on-line metals monitoring system, as well as,operational procedures and system specifications.1.3 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstanda

6、rd.1.4 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.2. Reference

7、d Documents2.1 ASTM Standards:2D1066 Practice for Sampling SteamD1129 Terminology Relating to WaterD2777 Practice for Determination of Precision and Bias ofApplicable Test Methods of Committee D19 on WaterD3370 Practices for Sampling Water from Closed ConduitsD3864 Guide for Continual On-Line Monito

8、ring Systemsfor Water AnalysisD4453 Practice for Handling of Ultra-Pure Water SamplesD5540 Practice for Flow Control and Temperature Controlfor On-Line Water Sampling and AnalysisD6301 Practice for Collection of On-Line CompositeSamples of Suspended Solids and Ionic Solids in ProcessWater3. Terminol

9、ogy3.1 DefinitionsFor definitions of other terms used in thistest method, refer to Terminology D1129 and Practice D3864.3.2 Definitions of Terms Specific to This Standard:3.2.1 emission intensity, nthe measure of the amplitude offluorescence emitted by a sample element.3.2.1.1 DiscussionThis measure

10、ment is correlated with acalibration curve for quantitative analysis. The emission inten-sity generally is given in units of counts per second (c/s).3.2.2 excitation source, nthe component of the XRFspectrometer, providing the high-energy radiation used toexcite the elemental constituents of a sampl

11、e, leading to thesubsequent measured fluorescence.3.2.2.1 DiscussionThe excitation source may be an elec-tronic x-ray generating tube or one of a variety of radioisotopesemitting an x-ray line of a suitable energy for the analysis athand.3.2.3 integrated sample, nthe type of sample collected byconce

12、ntrating the metal constituents of a water sample using afilter or an ion-exchange resin.3.2.3.1 DiscussionThese samples typically are collectedover long time periods (up to several days). The result ofanalysis of the collection medium yields a single measurement,which, when divided by the total sam

13、ple volume, is interpretedas the average metals concentration during the time of collec-tion.3.2.4 ionic solids, nmatter that will pass through a 0.45m filter and may be captured on anion or cation ion-exchangemembranes, or both.1This test method is under the jurisdiction of ASTM Committee D19 on Wa

14、terand is the direct responsibility of Subcommittee D19.03 on Sampling Water andWater-Formed Deposits, Analysis of Water for Power Generation and Process Use,On-Line Water Analysis, and Surveillance of Water.Current edition approved May 1, 2010. Published June 2010. Originallyapproved in 1999. Last

15、previous edition approved in 2008 as D6502 08. DOI:10.1520/D6502-10.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM w

16、ebsite.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.2.5 suspended solids, nmatter that is removed by a 0.45m filter.3.2.6 x-ray fluorescence (XRF) spectroscopy, nan analyti-cal technique in which sample elements are irradiated b

17、y ahigh-energy source to induce a transition from the ground stateto an excited state.3.2.6.1 DiscussionThe excitation source is in the 5 to 50KeV x-ray range. The resulting transition elevates an inner-shell electron to one of several outer shells. The excited state isunstable and those excited ele

18、ments will spontaneously dropback to their ground state with a concurrent emission offluorescent radiation. The energy (or wavelength) of thefluorescence is unique for each element, so the position of theemission lines on the energy scale serves to identify theelement(s). Then, the intensity of an e

19、mission peak may beused, with proper calibration methods, to determine the con-centration of an element in the sample.3.3 Symbols:3.3.1 WDXRF = Wavelength-Dispersive X-ray Fluores-cence3.3.2 EDXRF = Energy-Dispersive X-ray Fluorescence4. Summary of Test Method4.1 The concentrations of particulate, o

20、r dissolved metals,or both, in water streams are determined through accumulationon appropriate collection media (filters or ion exchange mate-rials) and detection by x-ray fluorescence spectroscopy, pro-viding real time determination of iron and other metals foundin water streams. The water sample d

21、elivered into the moni-toring system passes through a flow sensor, and then, to a flowcell assembly containing a membrane or resin filter, dependingon the application of interest. For an application where onlydissolved metals are to be analyzed, the sample needs to befiltered upstream of the sample

22、chamber to prevent particulatecontamination of the resin membrane surface.Asample bypassvalve is used for flow control through the sample chamber. Twosample chambers in sequence can be used to determine bothparticulate and dissolved components of the metal(s) of inter-est. X-ray fluorescence is used

23、 to determine the concentrationof the captured material. XRF analysis gives a measure of totalelemental concentration independent of the oxidation state ormolecular configuration of the element. Elements with atomicnumbers 13 through 92 can be detected.4.2 The filter chamber is essentially a variati

24、on of thetraditional corrosion product sampler used to collect integratedsamples (see Practice D6301). The main difference in thedesign of the flow cell in the on-line monitor is that the sampleenters the filter chamber in a way that allows an x-ray probe tobe positioned in close proximity to the fi

25、lter or resin membranesurface.4.3 Since even a small quantity of water covering a samplesignificantly attenuates both the excitation and emission radia-tion, a computer controlled valve switching system is incorpo-rated into the monitor. In one position, this valve allows sampleflow to proceed throu

26、gh the monitoring unit and metals toaccumulate on the filter or resin membrane while the flow totalis monitored. In the other position, the valve introduces air orother gas to purge the filter chamber of liquid while the sampleis diverted to drain. It is during the air purge that the x-raymeasuremen

27、t takes place. In this way, the monitor operates bycontinuously alternating between two modes: a sample accu-mulation mode and an analysis mode. Typical time assign-ments for these modes for sample concentrations in the lowppb range are five minutes each; thus, in one cycle, sampleaccumulates for fi

28、ve minutes followed by a five minute x-raymeasurement. With various delays for valve switching opera-tions, computer extraction of x-ray data, and date manipula-tion, the measurement cycle in this case lasts approximately 14minutes. Sample accumulation and analysis times are programvariables, which

29、may be adjusted prior to each monitoringsession. A monitoring session typically lasts several days forhigh purity water such as secondary feedwater for nuclearsteam generators.5. Significance and Use5.1 Corrosion products, in the form of particulate anddissolved metals, in the steam and water circui

30、ts of electricitygenerating plants are of great concern to power plant operators.Aside from indicating the extent of corrosion occurring in theplant, the presence of corrosion products has deleterious effectson plant integrity and efficiency. Deposited corrosion productsprovide sites at which chemic

31、als, which are innocuous at lowlevels, may concentrate to corrosive levels and initiate under-deposit corrosion. Also, corrosion products in feedwater enterthe steam generating components where deposition on heattransfer surfaces reduces the overall efficiency of the plant.5.2 Most plants perform so

32、me type of corrosion productmonitoring. The most common method is to sample for longtime periods, up to several days, after which laboratoryanalysis of the collected sample gives the average corrosionproduct level over the collection time period. This methodol-ogy is referred to as integrated sampli

33、ng. With the morefrequent measurements in the on-line monitor, a time profile ofcorrosion product transport is obtained. Transient high corro-sion product levels can be detected and measured, whichcannot be accomplished with integrated sampling techniques.With this newly available data, plant operat

34、ors may begin tocorrelate periods of high corrosion product levels with control-lable plant operating events. In this way, operators may makemore informed operational decisions with respect to corrosionproduct generation and transport.6. Interferences6.1 Coincidence of Certain Emission LinesIn XRF,

35、eachelement emits fluorescence at characteristic wavelengths whichmakes element identification unambiguous; however, certainpairs of emission lines from different elements occur suffi-ciently close in energy that the resulting overlap causesdifficulties in quantitative analysis. An example of this i

36、s theKa line of cobalt, which occurs at 6.925 keV (average) and theKb line of iron, which occurs at 7.059 keV (average). In thecase of a small amount of cobalt in the presence of a largeamount of iron, which is a typical case among corrosionproduct samples from steam generating plants, the cobaltana

37、lysis is hindered by the iron in the sample. Note that iron isnot similarly affected by the presence of cobalt since the ironKa line may be isolated to extract iron emission intensity.D6502 1026.1.1 There are three strategies which may be used toameliorate the type of interference described above. F

38、irst, theratio of Ka to Kb emission intensity is constant and known foreach element; thus, from a higher than expected intensity ofiron Kb emission, relative to the Ka emission, the presence ofcobalt may be inferred and measured. Second, the use of acryogenically cooled, solid-state detector greatly

39、 improves theresolution (by reducing the band width of individual emissionpeaks) such that direct measurement of cobalt is possible.Third, the use of wavelength dispersive XRF (WDXRF)instrumentation provides the optimum line separation; how-ever, WDXRF instrumentation is much more expensive, andless

40、 robust for on-line use, than energy dispersive XRF(EDXRF) spectrometers.7. Apparatus7.1 The on-line metals analyzer3consists of the followingmain components: x-ray probe and associated electronics, flowcell and filter chamber, flow totalizer, valve switching system,and instrument control and data a

41、cquisition system.7.2 The volume of sample delivered to the flow cell assem-bly is monitored using a flow totalizer. Several varieties ofthese are available including piston, turbine, and Coriolistypes. The flow totalizer should have capability for computercommunication.7.3 The water sample is passe

42、d through a specially designedfilter chamber containing a membrane filter (typically 0.45micron, to remove particulates) or an ion exchange resinmembrane (for dissolved components).Above the filter or resinmembrane surface, an x-ray transparent material, for example,kapton or beryllium, fitted with

43、O-rings, confines the watersample within the filter cavity and provides the windowthrough which x-ray analysis proceeds. In this way, frequentmeasurements (several per hour) are made of the incrementalaccumulation of metals while the filter or resin membraneremains in service.7.4 The x-ray probe con

44、sists of both the excitation source toirradiate the sample and the detection device for returningfluorescence. The excitation source may be an electronic x-raytube or a suitably chosen radioisotope. For efficient excitation,the excitation energy should be 1.5 to 2 times the fluorescentenergy of the

45、element(s) being monitored. For example, ironwhich fluoresces at 6.4 keV should be irradiated with a sourcein the range of 10 to 13 keV. Many x-ray tubes have variablepower capability so voltage and amperage may be adjusted tooptimize the analysis at hand. Alternatively, for iron analysis,an appropr

46、iate choice of radioisotope as an excitation source iscurium-244 (Cm-244), which emits a line at approximately 12keV.7.5 For each measurement cycle, the following informationis recorded in a continuously updated data file in the control-ling personal computer (PC): date, time, mass measurement forea

47、ch metal of interest, volume increment, and raw intensitydata. The on-line control program, as well as several auxiliaryprograms, operate under the Microsoft Windows platform. ThePC controls all aspects of monitor operation and stores allcollected data. Monitoring results appear on the PC screen inr

48、eal time during a monitoring session, as well as, being storedin continuously updated files in a subdirectory of the userschoice.7.6 The data files generated during an on-line sessionrepresent a record of cumulative metal mass as a function ofcumulative sample volume during the course of the session

49、.Since the units of these parameters are micrograms and litersrespectively, the slope through the data at any point gives themetal concentration in ppb. A separate program, residing in thesame Windows group as the on-line control program, automati-cally converts the raw data to ppb values as a function of time.7.7 Aschematic diagram of a typical configuration is shownin Fig. 1. This configuration shows only one channel orsampling system. Additional channels can be incorporatedreadily into the monitoring system.7.8 Each channel comprises a separate flow cell, x-raypro