1、Designation: D5540 08D5540 13Standard Practice forFlow Control and Temperature Control for On-Line WaterSampling and Analysis1This standard is issued under the fixed designation D5540; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision
2、, 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 practice covers the conditioning of a flowing water sample for the precise measurement of various c
3、hemical andphysical parameters of the water, whether continuous or grab. This practice addresses the conditioning of both high- andlow-temperature and pressure sample streams, whether from steam or water.1.2 This practice provides procedures for the precise control of sample flow rate to minimize ch
4、anges of the measuredvariable(s) due to flow changes.1.3 This practice provides procedures for the precise control of 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 to be regarded as the standard
5、. The values given in parentheses arefor information only.mathematical conversions to inch-pound units that are provided for information only and are not consideredstandard.1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibi
6、lityof the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatorylimitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D1066 Practice for Sampling SteamD1129 Terminology Relating to WaterD3370 Practices for Sampling Wate
7、r from Closed ConduitsD3864 Guide for On-Line Monitoring Systems for Water Analysis3. Terminology3.1 DefinitionsFor definitions of terms used in this practice, refer to Terminology D1129.3.2 Definitions of Terms Specific to This Standard:3.2.1 approach temperaturetemperature, nthis is a term that is
8、 used in heat exchanger applications. It applies to all typesof heat exchangers and is defined as: the difference in outlet temperature in one stream and the inlet temperature on the otherstream.The definition as it applies to sample coolers used for cooling water or steam samples as noted in this s
9、tandard is as follows:Approach Temperaturethe difference in temperature temperature between cooling water temperature in and sample temperatureout.3.2.1.1 DiscussionThis term is used in heat exchanger applications and applies to all types of heat exchangers. The term is defined as: the differencebet
10、ween the outlet temperature in one stream and the inlet temperature in the other stream.1 This practice is under the jurisdiction ofASTM Committee D19 on Water and is the direct responsibility of Subcommittee D19.03 on Sampling Water and Water-FormedDeposits, Analysis of Water for Power Generation a
11、nd Process Use, On-Line Water Analysis, and Surveillance of Water.Current edition approved Oct. 1, 2008July 15, 2013. Published November 2008July 2013. Originally approved in 1994. Last previous edition approved in 20032008 asD5540 94aD5540 (2003). 08. DOI: 10.1520/D5540-08.10.1520/D5540-13.2 For re
12、ferencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.This document is not an ASTM standard and is intended only to provide
13、 the user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current versionof the sta
14、ndard as published by ASTM is to be considered the official document.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States13.2.2 crud depositiondeposition, ndepositionon interior surfaces of sample tubing or other hardware, the disposition
15、of fineinsoluble particles of(of iron oxides and other byproducts of metallic corrosioncorrosion) that are present throughout the system.The term “crud” is generally used for all types of fouling.3.2.2.1 DiscussionThe term “crud” is generally used for all types of fouling.3.2.3 sample conditioningco
16、nditioning, nreduction of the temperature and pressure of a flowing sample from processconditions to a controlled temperature and pressure, and maintenance of a constant flow rate both in incoming sample lines andthrough on-line analyzers.3.2.4 sample coolercooler, na small heat exchanger designed t
17、o cool small streams of water or steam.3.2.5 temperature compensationcompensation, nadjustment by the use of electronic adjustment or data manipulation, theadjustment of the analyzeranalyzers measured valuetemperature for variation in temperature of the sample sample temperaturefrom a preestablished
18、 value by the use of electronic adjustment or data manipulation. value.4. Summary of Practice4.1 This practice covers the system design, operating procedures, and selection of equipment to help ensure the appropriate flowand temperature control for analysis of water and steam samples. This control i
19、s essential to ensure the accuracy and repeatabilityof on-line analyzers. Variations in types of analysis, sample characteristics, and their effect on sample conditioning are included.4.2 The equipment and procedures described in this practice are intended to represent current state-of-the art techn
20、ologyavailable from major manufacturers of sample conditioning equipment. Refer to Practices D1066 and D3370 and Guide D3864for additional information on sampling.5. Significance and Use5.1 Sample conditioning systems must be designed to accommodate a wide range of sample source temperatures and pre
21、ssures.Additionally, efforts must be made to ensure that the resultant sample has not been altered during transport and conditioning andhas not suffered excessive transport delay. Studies have shown that sample streams will exhibit minimal deposition of ionic andparticulate matter on wetted surfaces
22、 at specific flow rates (11-55). 35.1.1 To ensure that the physical and chemical properties of the sample are preserved, this flow rate must be controlledthroughout the sampling process, regardless of expected changes of source temperature and pressure, for example, during startup,or changing proces
23、s operating conditions.5.2 The need to use analyzer temperature compensation methods is dependent on the required accuracy of the measurement.Facilities dealing with ultra-pure water will require both closely controlled sample temperature and temperature compensation toensure accurate measurements.
24、The temperature can be controlled by adding a second or trim cooling stage. The temperaturecompensation must be based on the specific contaminants in the sample being analyzed. In other facilities in which some variationin water chemistry can be tolerated, the use of either trim cooling or accurate
25、temperature compensation may provide sufficientaccuracy of process measurements. This does not negate the highly recommended practice of constant temperature sampling,especially at 25C, as the most proven method of ensuring repeatable and comparable analytical results.5.3 A separate class of analysi
26、s exists that does not require or, in fact, cannot use the fully conditioned sample for accurateresults. For example, the collection of corrosion product samples requires that the sample remain at near full system pressure, butcooled below the flash temperature, in order to ensure a representative c
27、ollection of particulates. Only some of the primaryconditioning criteria apply in this case, as in others. Temperature compensation is not applicable since the material being analyzedis not in a liquid state.6. Interferences6.1 Samples can be degraded by the loss of ionic or particulate components,
28、introduction of contaminants by components orleaks, changes of sample flow rate through an analyzer, excessively long sample lines, sample temperature changes, and inaccuratetemperature compensation of on-line analysis equipment.6.2 Studies (33-55) have shown that the loss of ionic and particulate c
29、omponents is minimized by maintaining the water samplevelocity at 1.8 m/s in the sample tubing transporting the sample. The turbulent flow at 1.8 m/s (6 ft/s) presents a stable conditionof deposition and removal. Changes in sample flow rate or flow rates beyond a median range of approximately 1.8 m/
30、s can upsetthis equilibrium condition.3 The boldface numbers in parentheses refer to thea list of references at the end of this practice.standard.D5540 1326.3 Saturated steam and superheated steam samples present difficult transport problems between the source and the primarysample cooling equipment
31、 (4). Saturated steam samples with transport velocities typically above 11 m/s (36 ft/s) provide adequateturbulent flow to ensure the transport of most particulates and ionic components. Excessively large or small steam sample linescan affect the sample quality and quantity significantly. If the sam
32、ple tubing has too large an inside diameter, the steam velocitymay be too low to transport the condensed portion of the steam along with the vapor. If the sample tubing has too small an insidediameter, the pressure drop may be excessive, reducing the quantity of sample available at the sample panel.
33、 In the case ofsuper-heated steam, significant ionic deposition can occur in the sample tubing transport as the steam desuperheats. This can affectsample analysis accuracy significantly. Superheated samples should use a process to inject cooled sample into the sample line ator near the nozzle outlet
34、 to desuperheat the sample so as to minimize deposition in the initial portion of the tubing run.6.4 Samples may become contaminated by products introduced into the stream by the tubing, valves, or other associatedconditioning hardware. To minimize contamination of the sample, high-grade tubing, suc
35、h as Type 316 SS, must be used. Cobaltcontamination from valve hardening material can introduce significant error in transition metal analysis by ion chromatography.6.5 Air leakage into sample lines can affect pH, conductivity (specific, cation, and degassed), and especially dissolved oxygenmeasurem
36、ents.6.6 The operation of a sample system includes periodically taking grab samples and adding and removing on-line analyzers.Theaccuracy of the analyses can be affected if the flow rate through any on-line analyzer changes because of these procedures. Thesame is true if these actions change the flo
37、w rate in the incoming sample line to the system.6.7 Changing the temperature of the sample flowing through an on-line analyzer can alter the accuracy of the analysis. Sampletemperature can change because of a change in flow rate through the heat exchangers, because of a change of flow rate of theco
38、oling water in the heat exchangers, or from a change in temperature of the heat exchanger cooling water supply. Every effortshould be made to ensure constant sample temperature. The ideal sample temperature is 25 6 0.5C (77 6 1F) because this is thestandard for comparing readings of temperature-sens
39、itive analyses.6.8 Electronic compensation is able to compensate for the deviations in sample temperature for a known chemical matrix(contamination). If an unknown source of contamination is introduced, the analyzer may not be programmed, or programmable,to respond to the new solution. An error is i
40、ntroduced as a result. The further the sample temperature deviates from 25C (77F),the greater the error.6.9 In sliding pressure or cycling power plants, or both, in which sample inlet pressures vary, the sample flow methodologydetailed in this practice should be modified to automate the flow control
41、 process to ensure constant sample flow for high-accuracyanalysis.7. Apparatus7.1 Sample TubingTubing should be high quality such as Type 316 SS and be sized to maintain appropriate flow to minimizesample analysis errors. The tubing inside diameter is the critical dimension. Heavy-wall tube with an
42、appropriate inside diametersize selected to provide proper flow rate (see 6.2) can be used for construction strength.7.2 Primary Sample CoolersHeat exchangers, designed to handle high-pressure and high-temperature samples and provideefficient cooling typically with approach temperatures of below 1C
43、(1.8F), should be selected. Generally, Type 316 SS is anappropriate sample tube material; however, other material selections may be necessary based on incoming sample temperature andcooling water impurities, that is, chlorides.7.3 Pressure ReducersPressure reduction is accomplished with a variable o
44、rifice. A high-quality needle valve performs wellfor source pressure less than 34.5 bar (500 psig). A variable rod-in-tube device performs well for pressures 34.5 bar and greaterbecause it is basically non-wearing and minimizes sample dissociation during pressure reduction.7.4 Pressure Regulating De
45、viceTo maintain constant sample pressure at the inlet to each analyzer train, a variable or fixedback pressure regulating valve may be used.7.5 Secondary or Trim Sample CoolerSimilar to the primary sample cooler, this heat exchanger should be a device capableof maintaining a sample outlet temperatur
46、e within 0.5C (1F) of the incoming cooling water temperature to ensure constant outlettemperature, even with significant variations in sample flow or heat load.7.6 Sample Flow Indicator(s)A non-valved rotameter or other flow indication device in the main sample line or flowindication device, or both
47、, in all branch lines (analysis, grab, and bypass) is typically used. A method of measuring total sampleflow in accordance with recommended velocities must be used (see 6.2 and 8.4 ).7.7 Temperature IndicatorAmechanical or electronic indication of sample temperature must be provided to help the oper
48、atormonitor sample conditions and confirm the efficiency of the heat exchangers.7.8 Pressure IndicatorA mechanical or electronic indication of the upstream pressure of the pressure regulating device (V4)to confirm proper operation of the device.D5540 1338. Procedure8.1 Procedure for Establishing Con
49、stant Flow:8.1.1 Confirm that the sample tube transporting the sample is sized properly to ensure the sample velocities noted in 6.2 and6.3. Keep the sample lines as short as possible (particularly steam) to eliminate alteration of the sample prior to the primary coolingpoint.8.1.2 Flow control of the sample streams involves two stages. The first is reduction of the pressure from the source to a lowervalue and establishment of the desired flow in the incoming line. The second is maintenance of the reduced pressure at a constantvalue so that fl
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