1、Designation: D 5540 94a (Reapproved 2003)Standard Practice forFlow Control and Temperature Control for On-Line WaterSampling and Analysis1This standard is issued under the fixed designation D 5540; the number immediately following the designation indicates the year oforiginal adoption or, in the cas
2、e 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 practice covers the conditioning of a flowing watersample for the precise measurement
3、 of various chemical andphysical parameters of the water, whether continuous or grab.This practice addresses the conditioning of both high- andlow-temperature and pressure sample streams, whether fromsteam or water.1.2 This practice provides procedures for the precise controlof sample flow rate to m
4、inimize changes of the measuredvariable(s) due to flow changes.1.3 This practice provides procedures for the precise controlof sample temperature to minimize changes of the measuredvariable(s) due to temperature changes.1.4 The values stated in either SI or inch-pound units are tobe regarded as the
5、standard. The values given in parenthesesare for information only.1.5 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 app
6、lica-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 Equipment for Sampling Waterand Steam in Closed Conduits3D 3370 Practices for Sampling Water from Closed Con-du
7、itsD 3864 Guide for Continual On-Line Monitoring Systemsfor Water Analysis3. Terminology3.1 DefinitionsFor definitions of terms used in this prac-tice, refer to Terminology D 1129.3.2 Definitions of Terms Specific to This Standard:3.2.1 crud depositiondeposition on interior surfaces ofsample tubing
8、or other hardware of fine insoluble particles ofiron oxides and other byproducts of metallic corrosion that arepresent throughout the system. The term “crud” is generallyused for all types of fouling.3.2.2 sample conditioningreduction of the temperatureand pressure of a flowing sample from process c
9、onditions to acontrolled temperature and pressure, and maintenance of aconstant flow rate both in incoming sample lines and throughon-line analyzers.3.2.3 sample coolera small heat exchanger designed tocool small streams of water or steam.3.2.4 temperature compensationadjustment of the ana-lyzer mea
10、sured value for variation in temperature of the samplefrom a preestablished value by the use of electronic adjustmentor data manipulation.4. Summary of Practice4.1 This practice covers the system design, operating pro-cedures, and selection of equipment to help ensure the appro-priate flow and tempe
11、rature control for analysis of water andsteam samples. This control is essential to ensure the accuracyand repeatability of on-line analyzers. Variations in types ofanalysis, sample characteristics, and their effect on sampleconditioning are included.4.2 The equipment and procedures described in thi
12、s practiceare intended to represent current state-of-the art technologyavailable from major manufacturers of sample conditioningequipment. Refer to Practices D 1066 and D 3370, Specifica-tion D 1192, and Guide D 3864 for additional information onsampling.5. Significance and Use5.1 Sample conditionin
13、g systems must be designed to ac-commodate a wide range of sample source temperatures andpressures. Additionally, efforts must be made to ensure that theresultant sample has not been altered during transport andconditioning and has not suffered excessive transport delay.1This practice is under the j
14、urisdiction of ASTM Committee D19 on Water andis 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 approved Sept. 15, 1994. Published
15、 November 1994. Originallyapproved in 1994. Last previous edition approved in 1994 as D 5540 94a.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 Docum
16、ent Summary page onthe ASTM website.3Withdrawn.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.Studies have shown that sample streams will exhibit minimaldeposition of ionic and particulate matter on wetted surfaces atspecific flow r
17、ates (15).45.1.1 To ensure that the physical and chemical properties ofthe sample are preserved, this flow rate must be controlledthroughout the sampling process, regardless of expectedchanges of source temperature and pressure, for example,during startup or changing process operating conditions.5.2
18、 The need to use analyzer temperature compensationmethods is dependent on the required accuracy of the measure-ment. Facilities dealing with ultra-pure water will require bothclosely controlled sample temperature and temperature com-pensation to ensure accurate measurements. The temperaturecan be co
19、ntrolled by adding a second or trim cooling stage. Thetemperature compensation must be based on the specificcontaminants in the sample being analyzed. In other facilitiesin which some variation in water chemistry can be tolerated,the use of either trim cooling or accurate temperature compen-sation m
20、ay provide sufficient accuracy of process measure-ments. This does not negate the highly recommended practiceof constant temperature sampling, especially at 25C, as themost proven method of ensuring repeatable and comparableanalytical results.5.3 A separate class of analysis exists that does not req
21、uireor, in fact, cannot use the fully conditioned sample for accurateresults. For example, the collection of corrosion productsamples requires that the sample remain at near full systempressure, but cooled below the flash temperature, in order toensure a representative collection of particulates. On
22、ly some ofthe primary conditioning criteria apply in this case, as in others.Temperature compensation is not applicable since the materialbeing analyzed is not in a liquid state.6. Interferences6.1 Samples can be degraded by the loss of ionic orparticulate components, introduction of contaminants by
23、 com-ponents or leaks, changes of sample flow rate through ananalyzer, excessively long sample lines, sample temperaturechanges, and inaccurate temperature compensation of on-lineanalysis equipment.6.2 Studies (35) have shown that the loss of ionic andparticulate components is minimized by maintaini
24、ng the watersample velocity at 1.8 m/s in the sample tubing transporting thesample. The turbulent flow at 1.8 m/s (6 ft/s) presents a stablecondition of deposition and removal. Changes in sample flowrate or flow rates beyond a median range of approximately 1.8m/s can upset this equilibrium condition
25、.6.3 Saturated steam and superheated steam samples presentdifficult transport problems between the source and the primarysample cooling equipment (4). Saturated steam samples withtransport velocities typically above 11 m/s (36 ft/s) provideadequate turbulent flow to ensure the transport of mostparti
26、culates and ionic components. Excessively large or smallsteam sample lines can affect the sample quality and quantitysignificantly. If the sample tubing has too large an insidediameter, the steam velocity may be too low to transport thecondensed portion of the steam along with the vapor. If thesampl
27、e tubing has too small an inside diameter, the pressuredrop may be excessive, reducing the quantity of sampleavailable at the sample panel. In the case of super-heatedsteam, significant ionic deposition can occur in the sampletubing transport as the steam desuperheats. This can affectsample analysis
28、 accuracy significantly. Superheated samplesshould use a process to inject cooled sample into the sampleline at or near the nozzle outlet to desuperheat the sample so asto minimize deposition in the initial portion of the tubing run.6.4 Samples may become contaminated by products intro-duced into th
29、e stream by the tubing, valves, or other associatedconditioning hardware. To minimize contamination of thesample, high-grade tubing, such as AISI Type 316 SS, must beused. Cobalt contamination from valve hardening material canintroduce significant error in transition metal analysis by ionchromatogra
30、phy.6.5 Air leakage into sample lines can affect pH, conductivity(specific, cation, and degassed), and especially dissolved oxy-gen measurements.6.6 The operation of a sample system includes periodicallytaking grab samples and adding and removing on-line analyz-ers. The accuracy of the analyses can
31、be affected if the flow ratethrough any on-line analyzer changes because of these proce-dures. The same is true if these actions change the flow rate inthe incoming sample line to the system.6.7 Changing the temperature of the sample flowing throughan on-line analyzer can alter the accuracy of the a
32、nalysis.Sample temperature can change because of a change in flowrate through the heat exchangers, because of a change of flowrate of the cooling water in the heat exchangers, or from achange in temperature of the heat exchanger cooling watersupply. Every effort should be made to ensure constant sam
33、pletemperature. The ideal sample temperature is 25 6 0.5C(77 6 1F) because this is the standard for comparing readingsof temperature-sensitive analyses.6.8 Electronic compensation is able to compensate for thedeviations in sample temperature for a known chemical matrix(contamination). If an unknown
34、source of contamination isintroduced, the analyzer may not be programmed, or program-mable, to respond to the new solution.An error is introduced asa result. The further the sample temperature deviates from25C (77F), the greater the error.6.9 In sliding pressure or cycling power plants, or both, inw
35、hich sample inlet pressures vary, the sample flow methodol-ogy detailed in this practice should be modified to automate theflow control process to ensure constant sample flow forhigh-accuracy analysis.7. Apparatus7.1 Sample Tubing Tubing should be high quality such asAISI Type 316 SS and be sized to
36、 maintain appropriate flow tominimize sample analysis errors. The tubing inside diameter isthe critical dimension. Heavy-wall tube with an appropriateinside diameter size selected to provide proper flow rate (see6.2) can be used for construction strength.7.2 Primary Sample CoolersHeat exchangers, de
37、signedto handle high-pressure and high-temperature samples and4The boldface numbers in parentheses refer to the list of references at the end ofthis practice.D 5540 94a (2003)2provide efficient cooling with approach temperatures of below1C (2F), should be selected. Generally, AISI Type 316 SS isan a
38、ppropriate sample tube material; however, other materialselections may be necessary based on incoming sample tem-perature and cooling water impurities, that is, chlorides.7.3 Pressure ReducersPressure reduction is accomplishedwith a variable orifice. A high-quality needle valve performswell for sour
39、ce pressure less than 34.5 bar (500 psig). Avariable rod-in-tube device performs well for pressures 34.5bar and greater because it is basically non-wearing andminimizes sample dissociation during pressure reduction.7.4 Pressure Regulating DeviceTo maintain constantsample pressure at the inlet to eac
40、h analyzer train, a variable orfixed back pressure regulating valve or a head cup may beused.7.5 Secondary or Trim Sample CoolerSimilar to theprimary sample cooler, this heat exchanger should be a devicecapable of maintaining a sample outlet temperature within0.5C (1F) of the incoming cooling water
41、temperature toensure constant outlet temperature, even with significant varia-tions in sample flow or heat load.7.6 Sample Flow Indicator(s)A non-valved rotameter orother flow indication device in the main sample line or flowindication device, or both, in all branch lines (analysis, grab,and bypass)
42、 is typically used. A method of measuring totalsample flow in accordance with recommended velocities mustbe used (see 6.2 and 8.4 ).7.7 Temperature IndicatorA mechanical or electronic in-dication of sample temperature must be provided to help theoperator monitor sample conditions and confirm the eff
43、iciencyof the heat exchangers.8. Procedure8.1 Procedure for Establishing Constant Flow:8.1.1 Confirm that the sample tube transporting the sampleis sized properly to ensure the sample velocities noted in 6.2and 6.3. Keep the sample lines as short as possible (particularlysteam) to eliminate alterati
44、on of the sample prior to the primarycooling point.8.1.2 Flow control of the sample streams involves twostages. The first is reduction of the pressure from the source toa lower value and establishment of the desired flow in theincoming line. The second is maintenance of the reducedpressure at a cons
45、tant value so that flow through the analyzerswill remain constant.8.1.3 Hold the reduced sample pressure constant by passingit through a back pressure regulating valve that maintains theinlet pressure constant. The valve opens to let more waterthrough if the inlet pressure tends to increase. The val
46、ve closesif the inlet pressure decreases, maintaining the inlet pressurebut reducing the flow through it. A head cup will also achievesimilar constant flow results. Use the constantly flowingdischarge from the back pressure valve for grab samples. Pipethe analyzers in parallel to the constant pressu
47、re zone. Thus,once the valved flow meter (FICV) controlling the flow to ananalyzer sensor is set, the flow through the analyzer willremain constant as long as the inlet pressure remains constant.See Fig. 1.8.2 Procedure for Establishing Constant Temperature:8.2.1 Temperature reduction and control of
48、 the sample isbest accomplished in two stages: primary and secondarycooling. If only one stage of cooling is used, the temperature ofeach sample will be constant with constant flow, but eachsample will have a different temperature because of differentsource temperatures and pressures supplied to the
49、 primarysample cooler. Using a second stage of cooling will bring thetemperature of all the samples to the same constant temperature(recommended at 25C (77F). Refer to 6.7 and 6.8.8.2.2 Refer to the first stage of cooling as primary cooling.The bulk of the heat in each sample is removed in this samplecooler (heat exchanger). A highly efficient sample cooler isdesirable so that the temperature of the sample leaving thecooler will be as close as possible to the cooling watertemperature. This is particularly true of the steam samples withshort sample lines, sin
