ASTM D1066-2006 Standard Practice for Sampling Steam《取样蒸汽的标准实施规程》.pdf

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1、Designation: D 1066 06An American National StandardStandard Practice forSampling Steam1This standard is issued under the fixed designation D 1066; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number

2、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 sampling of saturated andsuperheated steam. It is applicable to steam produced in fossilfired and nuclear boilers or

3、 by any other process means that isat a pressure sufficiently above atmospheric to establish theflow of a representative sample. It is also applicable to steam atlower and subatmospheric pressures for which means must beprovided to establish representative flow.1.2 For information on specialized sam

4、pling equipment,tests or methods of analysis, reference should be made to theAnnual Book of ASTM Standards, Vols 11.01 and 11.02,relating to water.1.3 The values stated in SI units are to be regarded as thestandard. The values given in parentheses are for informationonly.1.4 This standard does not p

5、urport 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 regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2

6、A 269 Specification for Seamless and Welded AusteniticStainless Steel Tubing for General ServiceA 335/A 335M Specification for Seamless Ferritic Alloy-Steel Pipe for High-Temperature ServiceD 1129 Terminology Relating to WaterD 1192 Guide for Equipment for Sampling Water andSteam in Closed Conduits3

7、D 3370 Practices for Sampling Water from Closed ConduitsD 5540 Practice for Flow Control and Temperature Controlfor On-Line Water Sampling and Analysis3. Terminology3.1 Definitions:3.1.1 For definitions of terms used in this practice, refer todefinitions given in Practice D 1129.3.2 Definitions of T

8、erms Specific to This Standard:3.2.1 isokinetic sampling (representative sampling)a con-dition wherein the sample entering the port (tip) of thesampling nozzle has the same as the velocity vector (velocityand direction) as the stream being sampled. Isokinetic sam-pling ensures a representative sampl

9、e of dissolved chemicals,solids, particles, chemicals absorbed on solid particles, and inthe case of saturated and wet steam, water droplets areobtained.3.2.2 sample coolera small heat exchanger designed toprovide cooling/condensing of small process sampling streamsof water or steam.3.2.3 samplingth

10、e withdrawal of a representative portionof the steam flowing in the boiler drum lead or pipeline bymeans of a sampling nozzle and the delivery of this portion ofsteam in a representative manner for analysis.3.2.4 saturated steama vapor whose temperature corre-sponds to the boiling water temperature

11、at the particularexisting pressure.3.2.5 superheated steama vapor whose temperature isabove the boiling water temperature at the particular existingpressure.4. Summary of Practice4.1 This practice describes the apparatus, design conceptsand procedures to be used in extracting and transportingsamples

12、 of saturated and superheated steam. Extraction nozzleselection and application, line sizing, condensing requirementsand optimization of flow rates are all described. Condensedsteam samples should be handled in accordance with PracticesD 3370 and D 5540, and Guide D 1192.5. Significance and Use5.1 I

13、t is essential to sample steam representatively in orderto determine the amount of all impurities (dissolved chemicals,solid particles, chemicals absorbed on solid particles, water1This practice is under the jurisdiction of ASTM Committee D19 on Water, andis the direct responsibility of Subcommittee

14、 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 Dec. 15, 2006. Published January 2007. Originallyapproved in 1949. Last previous edition approved in 2001 as D 1066 97

15、 (2001).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.1Copyright ASTM International, 100 Barr Ha

16、rbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.droplets) in it (1).4An accurate measure of the purity of steamprovides information, which may be used to determine whetherthe purity of the steam is within necessary limits to preventdamage or deterioration (corrosion, solid p

17、article erosion,flow-accelerated corrosion, and deposit buildup) of down-stream equipment, such as turbines. Impurities in the steammay be derived from boiler water carryover, inefficient steamseparators, natural salt solubility in the steam and other factors.The most commonly specified and analyzed

18、 parameters aresodium, silica, iron, copper, and cation conductivity.6. Interferences6.1 Saturated Steam Sampling of steam presents difficultextraction and transport problems that affect the representative-ness of the sample.6.1.1 Isokinetic sampling requires that the velocity vector(velocity and di

19、rection) of the fluid entering the sample nozzleport (tip) be the same as the stream being sampled at thelocation of the sample nozzle. When the sample is not extractedisokinetically the contaminants in the steam are not properlyrepresented in the sample. The effects of non-isokinetic sam-pling are

20、illustrated in Fig. 1 and can make the sampleunrepresentative. The sample should be removed at a positionaway from the pipe wall, located at a point of average velocitywhich can be calculated for both laminar and turbulent flows.6.1.2 Traditionally, saturated steam samples with initialsteam velociti

21、es above 11 m/s (36 ft/s) were considered toprovide adequate turbulent flow to ensure transport of mostparticulates and ionic components. More recent studies (2,3)found that because many sample lines are long and uninsu-lated, steam samples are frequently fully condensed prior toreaching the sample

22、station. Partially or fully condensedsamples usually have a velocity too low to prevent excessivedeposition and the sample becomes nonrepresentative of thesource. Detailed design of the sample line to control vapor andliquid velocity can minimize this interference but cooling ofsaturated steam sampl

23、es at the source is recommended toassure a representative sample. See Practices D 3370 andD 5540 for further information on factors that affect liquidsample transport.6.2 Superheated SteamMost contaminants can be dis-solved in superheated steam. However, as steam pressure andtemperature are reduced

24、the solubility of many contaminants isdecreased and the contaminants precipitate and deposit on theinner surfaces of the sample line (4). This condition has beenfound to be prevalent only in regions of dry wall tube where thetemperature of the tube wall exceeds the saturation temperatureof the steam

25、.6.2.1 Interference also occurs when the transport tube tem-perature is at or below the saturation temperature. The steamloses superheat and dissolved contaminants deposit on the tubewall. The sample is no longer representative. Superheatedsteam samples shall be cooled or desuperheated in the sample

26、nozzle or immediately after extraction to ensure a representa-tive sample. Cooling the sample within the sample nozzle maycause thermal fatigue. All necessary precautions should betaken. See 7.1.3.4 and 7.2.4.7. Materials and Apparatus7.1 Extracting the Sample:7.1.1 Saturated SteamSince saturated st

27、eam is normallysampled as a two-phase fluid, made up of steam and smalldroplets of water, isokinetic sampling shall be employed. Sincesteam velocities vary with boiler load it normally is notpractical to sample isokinetically throughout the load range.Normally, the load of interest is full load or a

28、 guaranteed4The boldface numbers given in parentheses refer to a list of references at theend of this standard.FIG. 1 Effect of Nono-Isokinetic SamplingD1066062overload. The sampling system shall be designed to provideisokinetic sampling at this design load.7.1.1.1 At low velocities, the moisture in

29、 wet steam forms afilm along the inside surface of the steam line that entrainsimpurities (5). Samples should be extracted at a position awayfrom the pipe wall (Fig. 2). See 7.1.3.1.7.1.2 Superheated SteamParticulates are often present insuperheated steam and these particulates can contain solublesp

30、ecies (Na, Cl, SO4) that are of interest and should besampled (1,6,7). Therefore, an isokinetic sampling nozzleshould be used for sampling superheated steam in order toobtain a representative sample of both the gas and solid phases.7.1.2.1 Because the dissolved contaminants in high pressuresuperheat

31、ed steam deposit on the inner surfaces of the nozzleand sample lines as the sample desuperheats, superheatedsteam samples shall be rapidly desuperheated or condensednear the point of extraction. See 7.2.4.7.1.3 Sampling NozzlesStratification of suspended solidsin horizontal steam pipes can influence

32、 the composition of thesteam samples. To minimize the effects of stratification it isrecommended that steam sampling nozzles be located in longvertical pipes. To ensure that all water droplets are carried inthe flow stream, downward flow is preferred. Nozzles whichmust be located in a horizontal pip

33、e should be near the top ofthe pipe (2,7). Ideally, the nozzle should be installed at least 35internal pipe diameters downstream and 4 internal pipe diam-eters upstream of any flow disturbance (elbow, tee, valve,orifice, etc.). If this is not possible, the nozzle should beinstalled so that the ratio

34、 of its distance from the upstreamdisturbance to the downstream disturbance is about 9:1.7.1.3.1 Nozzles are most frequently located at a distancefrom the pipe wall where the actual velocity equals the averagevelocity under laminar flow, typically 0.12 times the pipe innerdiameter (Fig. 2) (1,2,7).

35、This also ensures that the sample isextracted from a flow region removed from the pipe innersurface.7.1.3.2 Sampling Nozzles for Superheated SteamThenozzles described for use with saturated steam can also be usedfor superheated steam.7.1.3.3 In order to minimize the deposition of contaminantsfrom su

36、perheated steam, some experts recommended injectingcondensed and cooled sample directly into the superheatedsteam sampling nozzle (2). This rarely used method mayinduce thermal stresses and all necessary precautions should betaken and the nozzle should be periodically inspected forcracking. An accep

37、table alternative is to condense the sampleimmediately after extraction. See 7.2.4 for sample line andcondensing design criteria.7.1.3.4 Design, Materials, and InstallationSamplingnozzles shall be adequately supported and shall be designedaccording to applicable codes to prevent failure due to flow-

38、induced vibration, thermal stress, and other possible causes (8).A conical shape rather than cylindrical will reduce the effectsof vortex shedding, which can lead to fatigue failures. Strengthof the attachment to the pipe must also be considered. Nozzlesare most often made of AISI 316 (9) or other a

39、usteniticstainless steels or superalloys (1,2,7). Weld joints used fordissimilar metals are subject to high thermal stresses due todifferent coefficients of thermal expansion. Care should be usedin weld rod selection and inspection of all weld joints.7.1.3.5 Sample port (tip) shall be drilled cleanl

40、y, using thestandard drill size nearest to the calculated port diameter. Thesmallest recommended port diameter is 3.18 mm (18 in.). Portdiameters of less than 2.38 mm (332 in.) are subject to pluggingand shall not be used. The size of the sample port is determinedby the equation:S 5 ID2v rp!/4 (1)wh

41、ere:S = sampling rate (by mass) of the steam,ID = size of the sample port,v = velocity of the steam in the pipe being sampled, andr = density.7.1.3.6 At least one shut off valve (commonly referred to asa root valve or isolation valve) shall be placed immediatelyafter the point from which the sample

42、is withdrawn so that thesample line may be isolated. In high pressure applications tworoot valves are often used. The valve(s) selected should berated for the pressure/temperature of the sample source.7.1.3.7 InspectionsThe nozzle, pipe attachment, valves,tubing, and all welds should be periodically

43、 inspected forcracking, and other forms of damage. For sampling wet steam,the piping section after the nozzle should be periodicallyinspected for thinning by flow-accelerated corrosion (erosion-corrosion). For steam cycles where steam is contaminated withsodium hydroxide or chloride, inspection for

44、cracking, particu-larly in the weld areas should be performed more frequently.During operation, the nozzle and valve assembly should bechecked for any vibration problems.7.2 Transporting the Sample:7.2.1 GeneralSample lines should be designed so that thesample remains representative of the source. S

45、ee 6.1 and 7.1.1.They shall be as short as feasible to reduce lag time andchanges in sample composition. The bore diameters of thesampling nozzle, isolation valve(s), and downstream sampletubing before the sample cooler or condenser should be similar(7). The designer is responsible for ensuring that

46、 applicablestructural integrity requirements are met to prevent structuralfailure. Small tubing is vulnerable to mechanical damage andshould be protected. Once the sample is condensed it may betreated as a water sample and Practices D 3370 and D 5540 andGuide D 1192 should be followed.FIG. 2 Isokine

47、tic Sampling NozzleD10660637.2.1.1 Traps and pockets in which solids might settle shallbe avoided, since they may be partially emptied with changesin flow conditions and may result in sample contamination.Sample tubing shall be shaped so that sharp bends, dips, andlow points are avoided, thus preven

48、ting particulates fromcollecting. Expansion loops or other means shall be provided toprevent undue buckling and bending when large temperaturechanges occur. Such buckling and bending may damage thelines and allied equipment. Routing shall be planned to protectsample lines from exposure to extreme te

49、mperatures.7.2.2 MaterialsThe material from which the sample linesare made shall conform to the requirements of the applicablespecifications as follows: Specification A 335/A 335M for pipeand Specification A 269 for tubing.7.2.2.1 For sampling steam, the sampling lines shall bemade of stainless steel that is at least as corrosion resistant as18 % chromium, 8 % nickel steel (AISI 304 or 316 austeniticstainless steels are commonly used (9).7.2.3 Saturated SteamMany power generating stationscool their steam samples at a central sampling station, mostfrequently locate