1、Designation: D 6502 99 (Reapproved 2003)Standard Test Method forOn-Line Measurement of Low Level Particulate andDissolved Metals in Water by X-Ray Fluorescence (XRF)1This standard is issued under the fixed designation D 6502; the number immediately following the designation indicates the year oforig
2、inal adoption or, in the case of revision, the year of 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.1. Scope1.1 This test method covers the operation, calibration, anddata in
3、terpretation 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 particulate forms) or resin membranes (for dissolvedforms). Since the XRF detector is sensitive to a range ofemissio
4、n 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 most me
5、tals.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 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibil
6、ity 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. Referenced Documents2.1 ASTM Standards:2D 1066 Practice for Sampling SteamD 1129 Terminology Relating to WaterD 1192 Specification for Equ
7、ipment for Sampling Waterand Steam in Closed Conduits3D 2777 Practice for Determination of Precision and Bias ofApplicable Methods of Committee D19 on WaterD 3370 Practices for Sampling Water from Closed ConduitsD 3864 Guide for Continual On-Line Monitoring Systemsfor Water AnalysisD 4453 Practice f
8、or Handling Ultra-Pure Water SamplesD 5540 Practice for Flow Control and Temperature Controlfor On-Line Water Sampling and AnalysisD 6301 Practice for Collection of Samples of Filterable andNonfilterable Matter in Water3. Terminology3.1 DefinitionsFor definitions of other terms used in thistest meth
9、od, refer to Terminology D 1129 and Practice D 3864.3.2 Definitions of Terms Specific to This Standard:3.2.1 emission intensity, nthe measure of the amplitude offluorescence emitted by a sample element. This measurementis correlated with a calibration curve for quantitative analysis.The emission int
10、ensity generally is given in units of counts persecond (c/s).3.2.2 excitation source, nthe component of the XRFspectrometer, which provides the high energy radiation used toexcite the elemental constituents of a sample leading to thesubsequent fluorescence which is measured. The excitationsource may
11、 be an electronic x-ray generating tube or one of avariety of radioisotopes which emit an x-ray line of a suitableenergy for the analysis at hand.3.2.3 integrated sample, nthe type of sample collected byconcentrating the metal constituents of a water sample using afilter or an ion exchange resin. Th
12、ese samples typically arecollected over long time periods (up to several days). The resultof analysis of the collection medium yields a single measure-ment, which, when divided by the total sample volume, isinterpreted as the average metals concentration during the timeof collection.3.2.4 x-ray fluo
13、rescence (XRF) spectroscopy, nan analyti-cal technique in which sample elements are irradiated by a highenergy source which induces a transition from the ground stateto an excited state condition. Using an excitation source in the5 to 50 KeV x-ray range, the resulting transition elevates aninner she
14、ll electron to one of several outer shells. The excitedstate condition is unstable and elements so excited willspontaneously drop back to their ground state with a concurrentemission of fluorescent radiation. The energy (or wavelength)of the fluorescence is unique for each element, so the position1T
15、his test method is under the jurisdiction of ASTM Committee D19 on Waterand is the direct responsibility of Subcommittee D19.03 on Sampling of Water andWater-formed Deposits, Analysis of Water for Power Generation and Process Use,On-Line Water Analysis, and Surveillance of Water.Current edition appr
16、oved Dec. 10, 1999. Published March 2000.2For 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 website.3Withdrawn.1Copyrigh
17、t ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.of the emission lines on the energy scale serves to identify theelement(s). Then, the intensity of an emission peak may beused, with proper calibration methods, to determine the con-centration o
18、f 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, or dissolved metals,or both, in water streams are determined through accumulationon appropri
19、ate 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 delivered into the moni-toring system passes through a flow sensor, and then, to a flowcell
20、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 chamber to prevent particulatecontamination of the resin membrane surface.Asample bypassval
21、ve 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 to determine the concentrationof the captured material. XRF analysis gives a measure of to
22、talelemental 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 variation of thetraditional corrosion product sampler used to collect integratedsamples (see Pract
23、ice D 6301). 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 filter or resin membranesurface.4.3 Since even a small quantity of water covering a samplesi
24、gnificantly 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 through the monitoring unit and metals toaccumulate on the filter or resin membrane while the f
25、low 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-raymeasurement takes place. In this way, the monitor operates bycontinuously alternating between two mo
26、des: 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 five minutes followed by a five minute x-raymeasurement. With various delays for valve switc
27、hing 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 may be adjusted prior to each monitoringsession. A monitoring session typically lasts seve
28、ral 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 circuits of electricitygenerating plants are of great concern to power plant operators.Aside fro
29、m 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 chemicals, which are innocuous at lowlevels, may concentrate to corrosive levels and initiate un
30、der-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 some type of corrosion productmonitoring. The most common method is to sample for longtime p
31、eriods, 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 sampling. With the morefrequent measurements in the on-line monitor, a time profile ofcorrosion
32、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 operators may begin tocorrelate periods of high corrosion product levels with control-lable plan
33、t 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, eachelement emits fluorescence at characteristic wavelengths whichmakes element identifica
34、tion 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 is theKa line of cobalt, which occurs at 6.925 keV (average) and theKb line of iron, which
35、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 cobaltanalysis is hindered by the iron in the sample. Note that iron isnot similarly affected by th
36、e presence of cobalt since the ironKa line may be isolated to extract iron emission intensity.6.1.1 There are three strategies which may be used toameliorate the type of interference described above. First, theratio of Ka to Kb emission intensity is constant and known foreach element; thus, from a h
37、igher 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 improves theresolution (by reducing the band width of individual emissionpeaks) such that direct m
38、easurement 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, andD 6502 99 (2003)2less robust for on-line use, than energy dispersive XRF(EDXRF) spectrometers.7. Appara
39、tus7.1 The on-line metals analyzer4consists of the followingmain components: x-ray probe and associated electronics, flowcell and filter chamber, flow totalizer, valve switching system,and instrument control and data acquisition system.7.2 The volume of sample delivered to the flow cell assem-bly is
40、 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 passed through a specially designedfilter chamber containing a membrane filter (typical
41、ly 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 O-rings, confines the watersample within the filter cavity and provides the window
42、through 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 consists of both the excitation source toirradiate the sample and the detection devic
43、e 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 element(s) being monitored. For example, ironwhich fluoresces at 6.4 keV should be
44、 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 appropriate choice of radioisotope as an excitation source iscurium-244 (Cm-244), which e
45、mits 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 foreach metal of interest, volume increment, and raw intensitydata. The on-line control
46、 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 inreal time during a monitoring session, as well as, being storedin continuously upda
47、ted 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.Since the units of these parameters are micrograms and litersrespectively, the sl
48、ope 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. T
49、his 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-rayprobe, flow totalizer, and valve switching system. Through theuse of a multiplexer, several channels may share commonelectronics and software control. With a multi-channel system,several separate process streams may be monitored simulta-neously. Another application of a multi-channel system is toseparately monitor particulates (using a filter in one channel)and dissolved metals (using a resin
