ASTM D6502-2008 752 Standard Test Method for Continuous Measurement of On-line Composite Samples of Low Level Filterable Matter (Suspended Solids) and Non-Filterable Matter (Ionic .pdf

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1、Designation: D 6502 08Standard Test Method forContinuous Measurement of On-line Composite Samples ofLow Level Filterable Matter (Suspended Solids) and Non-Filterable Matter (Ionic Solids) in Process Water by X-RayFluorescence (XRF)1This standard is issued under the fixed designation D 6502; the numb

2、er immediately following the designation indicates the year 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

3、.1 This test method covers the operation, calibration, anddata 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 particulate forms) or resin membranes (for dissolve

4、dforms). Since the XRF detector is sensitive to a range ofemission 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

5、 sample. A detection limit below 1 ppb can be achievedfor most 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 asstanda

6、rd. No other units of measurement are included in thisstandard.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 applic

7、a-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D 1066 Practice for Sampling SteamD 1129 Terminology Relating to WaterD 2777 Practice for Determination of Precision and Bias ofApplicable Test Methods of Committee D19 on WaterD 3370 Practices for Sampling Wa

8、ter from Closed ConduitsD 3864 Guide for Continual On-Line Monitoring Systemsfor Water AnalysisD 4453 Practice for Handling of Ultra-Pure Water SamplesD 5540 Practice for Flow Control and Temperature Controlfor On-Line Water Sampling and AnalysisD 6301 Practice for the Collection of Samples of Filte

9、rableand Nonfilterable Matter in Water3. Terminology3.1 DefinitionsFor definitions of other terms used in thistest method, 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

10、 by a sample element. This measurementis correlated with a calibration curve for quantitative analysis.The emission intensity 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 t

11、he elemental constituents of a sample leading to thesubsequent fluorescence which is measured. The excitationsource may 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

12、of sample collected byconcentrating the metal constituents of a water sample using afilter or an ion exchange resin. These 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 t

13、he total sample volume, isinterpreted as the average metals concentration during the timeof collection.3.2.4 x-ray fluorescence (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 s

14、tate condition. Using an excitation source in the5 to 50 KeV x-ray range, the resulting transition elevates aninner shell 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 concurrent1This t

15、est method is under the jurisdiction of ASTM Committee D19 on Waterand 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

16、 1, 2008. Published May 2008. Originallyapproved in 1999. Last previous edition approved in 2003 as D 6502 99 (2003).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

17、 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.emission of fluorescent radiation. The energy (or wavelength)of the fluorescence is unique for each element, so the positionof th

18、e 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 of an element in the sample.3.3 Symbols:3.3.1 WDXRF = Wavelength Dispersive X-ray Fluores-cence3.3.2 EDXRF = Ene

19、rgy 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 appropriate collection media (filters or ion exchange mate-rials) and detection by x-ray fluorescence spectroscopy, pro

20、-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 assembly containing a membrane or resin filter, dependingon the application of interest. For an application whe

21、re 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 bypassvalve is used for flow control through the sample chamber. Twosample chambers in sequence can be used to determine

22、 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 totalelemental concentration independent of the oxidation state ormolecular configuration of the element. Element

23、s 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 Practice D 6301). The main difference in thedesign of the flow cell in the on-line monitor is that the sampleenters

24、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 samplesignificantly attenuates both the excitation and emission radia-tion, a computer controlled valve switching syste

25、m 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 flow totalis monitored. In the other position, the valve introduces air orother gas to purge the filter chamber

26、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 modes: a sample accu-mulation mode and an analysis mode. Typical time assign-ments for these modes for sample con

27、centrations 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 switching opera-tions, computer extraction of x-ray data, and date manipula-tion, the measurement cycle in this case

28、 lasts approximately 14minutes. Sample accumulation and analysis times are programvariables, which 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.

29、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 from indicating the extent of corrosion occurring in theplant, the presence of corrosion products has deleterious

30、effectson plant integrity and efficiency. Deposited corrosion productsprovide sites at which chemicals, 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 deposit

31、ion 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 periods, up to several days, after which laboratoryanalysis of the collected sample gives the average corrosionp

32、roduct 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 product transport is obtained. Transient high corro-sion product levels can be detected and measured, whichcann

33、ot 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 plant operating events. In this way, operators may makemore informed operational decisions with respect to corrosio

34、nproduct generation and transport.6. Interferences6.1 Coincidence of Certain Emission LinesIn XRF, eachelement emits fluorescence at characteristic wavelengths whichmakes element identification unambiguous; however, certainpairs of emission lines from different elements occur suffi-ciently close in

35、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 occurs at 7.059 keV (average). In thecase of a small amount of cobalt in the presence of a largeamount of iron,

36、 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 the presence of cobalt since the ironKa line may be isolated to extract iron emission intensity.6.1.1 There are t

37、hree 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 higher than expected intensity ofiron Kb emission, relative to the Ka emission, the presence ofcobalt may be inf

38、erred 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 measurement of cobalt is possible.Third, the use of wavelength dispersive XRF (WDXRF)instrumentation provides th

39、e optimum line separation; how-ever, WDXRF instrumentation is much more expensive, andD6502082less 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, flo

40、wcell 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 monitored using a flow totalizer. Several varieties ofthese are available including piston, turbine, and Coriolistypes.

41、 The flow totalizer should have capability for computercommunication.7.3 The water sample is passed 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 r

42、esinmembrane 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 windowthrough which x-ray analysis proceeds. In this way, frequentmeasurements (several per hour) are made of the incrementala

43、ccumulation 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 device for returningfluorescence. The excitation source may be an electronic x-raytube or a suitably chosen radioisotope. For

44、 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 irradiated with a sourcein the range of 10 to 13 keV. Many x-ray tubes have variablepower capability so voltage and amp

45、erage 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 emits a line at approximately 12keV.7.5 For each measurement cycle, the following informationis recorded in a continuousl

46、y 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 program, as well as several auxiliaryprograms, operate under the Microsoft Windows platform. ThePC controls all aspects

47、 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 updated files in a subdirectory of the userschoice.7.6 The data files generated during an on-line sessionrepresent a record

48、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 slope through the data at any point gives themetal concentration in ppb. A separate program, residing in thesame Windows g

49、roup 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-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 ma