ANSI ASTM D1066-2011 Standard Practice for Sampling Steam.pdf

1、Designation: D1066 11Standard Practice forSampling Steam1This standard is issued under the fixed designation D1066; the number 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 ye

2、ar of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of the U.S. Department of Defense.1. Scope1.1 This practice covers the sampling of saturated andsuperheated steam. It is applicable t

3、o steam produced in fossilfired and nuclear boilers or 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 repr

4、esentative flow.1.2 For information on specialized sampling 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 asstandard. The values given in parentheses ar

5、e for informationonly.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 applica-bility of regulatory limitations prior

6、to use.2. Referenced Documents2.1 ASTM Standards:2A269 Specification for Seamless and Welded AusteniticStainless Steel Tubing for General ServiceA335/A335M Specification for Seamless Ferritic Alloy-Steel Pipe for High-Temperature ServiceD1129 Terminology Relating to WaterD3370 Practices for Sampling

7、 Water from Closed ConduitsD5540 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 D1129.3.2 Definitions of Terms Specific to This Standard:

8、3.2.1 isokinetic sampling, na condition wherein thesample entering the port (tip) of the sampling nozzle has thesame as the velocity vector (velocity and direction) as thestream being sampled. Isokinetic sampling ensures a represen-tative sample of dissolved chemicals, solids, particles, chemi-cals

9、absorbed on solid particles, and in the case of saturatedand wet steam, water droplets are obtained.3.2.2 sample cooler, na small heat exchanger designed toprovide cooling/condensing of small process sampling streamsof water or steam.3.2.3 sampling, nthe withdrawal of a representative por-tion of th

10、e 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 steam, na vapor whose temperature cor-responds to the boiling water temperature at the particularexisting pressure.3.2.5 s

11、uperheated steam, na 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 of saturated and superheated steam. Ex

12、traction nozzleselection and application, line sizing, condensing requirementsand optimization of flow rates are all described. Condensedsteam samples should be handled in accordance with PracticesD3370 and D5540.5. Significance and Use5.1 It is essential to sample steam representatively in orderto

13、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 D19.03 on Sampling Water andWater-Formed Deposits, Analysis

14、 of Water for Power Generation and Process Use,On-Line Water Analysis, and Surveillance of Water.Current edition approved June 15, 2011. Published July 2011. Originallyapproved in 1949. Last previous edition approved in 2006 as D1066 06. DOI:10.1520/D1066-11.2For referenced ASTM standards, visit the

15、 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.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. Un

16、ited StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barrie

17、rs to Trade (TBT) Committee.1droplets) in it (1).3An 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 particle erosion,flow-accelerated corrosion,

18、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 parameters aresodium, silica, iron, copper,

19、 and cation conductivity.6. Interferences6.1 Saturated SteamSampling 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 direction) of the fluid entering the sample noz

20、zleport (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 illustrated in Fig. 1 and can make the sample

21、unrepresentative. 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 velocities above 11 m/s (36 ft/s) were considered top

22、rovide adequate turbulent flow to ensure transport of mostparticulates and ionic components. More recent studies (2,3)found that because many sample lines are long anduninsulated, steam samples are frequently fully condensedprior to reaching the sample station. Partially or fully con-densed samples

23、usually have a velocity too low to preventexcessive deposition and the sample becomes nonrepresenta-tive of the source. Detailed design of the sample line to controlvapor and liquid velocity can minimize this interference butcooling of saturated steam samples at the source is recom-mended to assure

24、a representative sample. See Practices D3370and D5540 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 the solubility of many contaminants isdecre

25、ased 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.6.2.1 Interference also occurs when the tr

26、ansport 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 samplenozzle or immediately after extraction to e

27、nsure 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 steam is normallysampled as a two-phase fluid

28、, 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.3The boldface numbers given in parentheses refer to a list of references at theend of this

29、standard.FIG. 1 Effect of Non-Isokinetic SamplingD1066 112Normally, the load of interest is full load or a guaranteedoverload. The sampling system shall be designed to provideisokinetic sampling at this design load.7.1.1.1 At low velocities, the moisture in wet steam forms afilm along the inside sur

30、face 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 solublespecies (Na, Cl, SO4) that are of interest an

31、d 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 pressuresuperheated steam deposit on the inner surfaces of t

32、he 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 the composition of thesteam samples. To mi

33、nimize 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 pipe should be near the top ofthe pipe (2,7) .

34、 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 of its distance from the upstreamdisturba

35、nce 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). This also ensures that the sample isextrac

36、ted 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 superheated steam, some experts recommended

37、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 acceptable alternative is to condense the sampl

38、eimmediately 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-induced vibration, thermal stress, and oth

39、er 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 austeniticstainless steels or superalloys (

40、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 cleanly, using thestandard drill size nearest to

41、 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 !/4 (1)where:S = sampling rate (by mass) of the steam

42、,ID = size of the sample port,v = velocity of the steam in the pipe being sampled, and = 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 is withdrawn so that thesample line may be is

43、olated. 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 inspected forcracking, and other forms of da

44、mage. 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 cracking, particu-larly in the weld areas sho

45、uld 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. See 6.1 and 7.1.1.They shall be as short as fe

46、asible 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 applicablestructural integrity requirements

47、are met to prevent structuralfailure. Small tubing is vulnerable to mechanical damage andFIG. 2 Isokinetic Sampling NozzleD1066 113should be protected. Once the sample is condensed it may betreated as a water sample and Practices D3370 and D5540should be followed.7.2.1.1 Traps and pockets in which s

48、olids 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 preventing particulates fromcollecting. Expansion loops or other mean

49、s 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 temperatures.7.2.2 MaterialsThe material from which the sample linesare made shall conform to the requirements of the applicablespecifications as follows: Specification A335/A335M for pipeand Specification A269 for tubing.7.2.2.1 For sampling steam, the sampling lines shall bemade of stainless steel that is at least as corrosion