1、Designation: D 5540 08Standard 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 case of revision, the
2、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 practice covers the conditioning of a flowing watersample for the precise measurement of various chemical
3、 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 minimize changes of t
4、he 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 standard. The values
5、 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 applica-bility of regul
6、atory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D 1066 Practice for Sampling SteamD 1129 Terminology Relating to WaterD 3370 Practices for Sampling Water from Closed ConduitsD 3864 Guide for Continual On-Line Monitoring Systemsfor Water Analysis3. Terminology3.1 Definitions
7、For 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 approach temperaturethis is a term that is used inheat exchanger applications. It applies to all types of heatexchangers and is defined as: the difference in outlet t
8、empera-ture in one stream and the inlet temperature on the otherstream. The definition as it applies to sample coolers used forcooling water or steam samples as noted in this standard is asfollows: Approach Temperaturethe difference in temperaturebetween cooling water temperature in and sample tempe
9、ratureout.3.2.2 crud depositiondeposition on interior surfaces ofsample tubing 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.3.2.3 sample conditio
10、ningreduction of the temperatureand pressure of a flowing sample from process conditions to acontrolled temperature and pressure, and maintenance of aconstant flow rate both in incoming sample lines and throughon-line analyzers.3.2.4 sample coolera small heat exchanger designed tocool small streams
11、of water or steam.3.2.5 temperature compensationadjustment of the ana-lyzer measured 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-ced
12、ures, and selection of equipment to help ensure the appro-priate flow and temperature 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 sa
13、mpleconditioning are included.4.2 The equipment and procedures described in this practiceare intended to represent current state-of-the art technologyavailable from major manufacturers of sample conditioningequipment. Refer to Practices D 1066 and D 3370 and GuideD 3864 for additional information on
14、 sampling.1This practice is under the jurisdiction of ASTM Committee D19 on Water andis 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 editio
15、n approved Oct. 1, 2008. Published November 2008. Originallyapproved in 1994. Last previous edition approved in 2003 as D 5540 94a (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
16、information, refer to 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.5. Significance and Use5.1 Sample conditioning systems must be designed to ac-commodate a wide range of samp
17、le 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.Studies have shown that sample streams will exhibit minimaldeposition of ionic and particula
18、te matter on wetted surfaces atspecific flow rates (15).35.1.1 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 startu
19、p or changing process operating conditions.5.2 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 a
20、ccurate measurements. The temperaturecan be controlled 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 c
21、ooling or accurate temperature compen-sation may 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 separ
22、ate class of analysis exists that does not requireor, 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
23、 representative collection of particulates. Only 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 orparticula
24、te components, introduction of contaminants by 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 andpa
25、rticulate components is minimized by maintaining 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 approximate
26、ly 1.8m/s can upset this equilibrium condition.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 turbu
27、lent flow to ensure the transport of mostparticulates 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
28、of the steam along with the vapor. If thesample 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 stea
29、m desuperheats. This can affectsample analysis 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 becom
30、e contaminated by products intro-duced into the stream by the tubing, valves, or other associatedconditioning hardware. To minimize contamination of thesample, high-grade tubing, such as Type 316 SS, must be used.Cobalt contamination from valve hardening material can intro-duce significant error in
31、transition metal analysis by ionchromatography.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 an
32、alyz-ers. The accuracy of the analyses can 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-li
33、ne analyzer can alter the accuracy of the analysis.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 e
34、ffort should be made to ensure constant sampletemperature. 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 che
35、mical matrix(contamination). If an unknown 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 pre
36、ssure or cycling power plants, or both, inwhich 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 qual
37、ity such asType 316 SS and be sized to maintain appropriate flow to3The boldface numbers in parentheses refer to the list of references at the end ofthis practice.D5540082minimize sample analysis errors. The tubing inside diameter isthe critical dimension. Heavy-wall tube with an appropriateinside d
38、iameter size selected to provide proper flow rate (see6.2) can be used for construction strength.7.2 Primary Sample CoolersHeat exchangers, designedto handle high-pressure and high-temperature samples andprovide efficient cooling typically with approach temperaturesof below 1C (1.8F), should be sele
39、cted. Generally, Type 316SS is an appropriate sample tube material; however, othermaterial selections may be necessary based on incomingsample temperature and cooling water impurities, that is,chlorides.7.3 Pressure ReducersPressure reduction is accomplishedwith a variable orifice. A high-quality ne
40、edle valve performswell for source 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 constantsam
41、ple pressure at the inlet to each analyzer train, a variable orfixed back pressure regulating valve may be used.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 inco
42、ming cooling water 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 (analysi
43、s, grab,and bypass) 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
44、and confirm the efficiencyof the heat exchangers.7.8 Pressure IndicatorA mechanical or electronic indica-tion of the upstream pressure of the pressure regulating device(V4) to confirm proper operation of the device.8. Procedure8.1 Procedure for Establishing Constant Flow:8.1.1 Confirm that the sampl
45、e 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 alteration of the sample prior to the primarycooling point.8.1.2 Flow control of the sample streams involves twostages. The
46、 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 constant value so that flow through the analyzerswill remain constant.8.1.3 Hold the reduced sample pressure constant b
47、y 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 valve closesif the inlet pressure decreases, maintaining the inlet pressurebut reducing the flow through it. Use the c
48、onstantly flowingdischarge from the back pressure valve for grab samples. Pipethe analyzers in parallel to the constant pressure 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 press
49、ure remains constant.See Fig. 1.8.2 Procedure for Establishing Constant Temperature:8.2.1 Temperature reduction and control of 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 primarysample cooler. Using a second stage of cooling will bring thetemperature of all the samples to the same constant temperature(recom
