1、Designation: D 3370 95a (Reapproved 2003)e1Standard Practices forSampling Water from Closed Conduits1This standard is issued under the fixed designation D 3370; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revis
2、ion. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of the Department of Defense.e1NOTEWarning notes were editorially moved into the standa
3、rd text in January 2004.1. Scope1.1 These practices cover the equipment and methods forsampling water from closed conduits such as process streams atpower stations for chemical, physical, microbiological, andradiological analyses. It does not cover specialized equipmentrequired for and unique to a s
4、pecific test or method of analysis.The following are included:SectionsPractice AGrab Samples 9 to 17Practice BComposite Samples 18 to 23Practice CContinual Sampling 24 to 291.2 For information on specialized sampling equipment,tests or methods of analysis, reference should be made tovolumes 11.01 an
5、d 11.02 of the Annual Book of ASTMStandards, relating to water.1.3 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 applic
6、a-bility of regulatory limitations prior to use. For specific hazardsstatements, see 8.3 and 13.4.2. Referenced Documents2.1 ASTM Standards:2A 106/A 106M Specification for Seamless Carbon SteelPipe for High-Temperature ServiceA 179/A179M Specification for Seamless Cold-DrawnLow-Carbon Steel Heat-Exc
7、hanger and Condenser TubesA 269 Specification for Seamless and Welded AusteniticStainless Steel Tubing for General ServiceA 335/A335M Specification for Seamless Ferritic AlloySteel Pipe for High-Temperature ServiceD 1066 Practice for Sampling SteamD 1129 Terminology Relating to WaterD 1193 Specifica
8、tion for Reagent WaterD 3648 Practices for the Measurement of RadioactivityD 3694 Practices for Preparation of Sample Containers andfor Preservation of Organic ConstituentsD 3856 Guide for Good Laboratory Practices in Laborato-ries Engaged in Sampling and Analysis of WaterD 4453 Practice for Handlin
9、g of Ultra-Pure Water SamplesD 4515 Practice for Estimation of Holding Time for WaterSamples Containing Organic ConstituentsD 4840 Guide for Sampling Chain-of-Custody ProceduresD 4841 Practice for Estimation of Holding Time for WaterSamples Containing Organic and Inorganic ConstituentsD 5540 Practic
10、e for Flow Control and Temperature Controlfor On-Line Water Sampling and Analysis3. Terminology3.1 DefinitionsFor definitions used in these practices,refer to Terminology D 1129.3.2 Definitions of Terms Specific to This Standard:3.2.1 back pressure regulatora device designed to main-tain a constant
11、pressure upstream of itself (variable or fixedback pressure regulators are available) to maintain constantflow in analyzers in continual sampling.3.2.2 composite samplea series of grab samples inte-grated into a single sample or a sample collected at specifictime intervals and integrated into a sing
12、le sample. The goal ofa composite sample is to characterize a process weightedaverage in proportion to process parameters.3.2.3 grab samplea single sample from a process stream(flowing) or from a source of confined geometry (stagnant)withdrawn at a specific time. The goal of withdrawing a grabsample
13、 is to obtain a small portion of the process stream orconfined geometry source in order to characterize the entiresystem.3.2.4 head cupa method used to achieve constant pressure(see back pressure regulator). It incorporates plumbing of thesample to a selected height above the inlet to the analyzer i
14、nletline(s) to achieve the required inlet pressure for the analyzers.1These practices are under the jurisdiction of ASTM Committee D19 on Water,and are the direct responsibility of Subcommittee D19.03 on Sampling of Water andWater-Formed Deposits, Analysis of Water for Power Generation and Process U
15、se,On-Line Water Analysis, and Surveillance of Water.Current edition approved Sept. 10, 1995. Published November 1995. Originallyapproved in 1974. Last previous edition approved in 1995 as D 3370 95a.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Servic
16、e at serviceastm.org. For Annual Book of ASTMStandards volume 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.It is occasionally used downstream of colorime
17、tric analyzers toincrease sample flow past the analyzer. The sample flows to anopen cup with an overflow. This fixed head provides theconstant pressure, assuming inlet flow to the head cup exceedsoutlet flow to the grab sample and analyzers.NOTE 1Contemporary designs of back pressure regulators prov
18、ideexcellent sensitivity to pressure change and have limited the need for headcups and the concurrent space and maintenance problems as well assample contamination potential.3.2.5 pressure reducera device designed to reduce pres-sure, and therefore control flow, of sample to a pressure levelwhere it
19、 can be regulated easily. This device shall be locateddownstream of the cooled sample where cooling is required.3.2.6 sample coolera small heat exchanger designed toprovide primary or secondary cooling, or both, of small processsampling streams of water or steam.3.2.7 time responsethe time required
20、for the system toreach 63.2 % of the total change between the state of initialequilibrium in response to a step change introduced at the inputto the system.3.2.8 variable rod in tube orificea type of pressure re-ducer for high pressure samples that uses a retractable taperedrod inside a reamed tube
21、to provide a variable orifice forpressure reduction that is parallel with the sample flow. Thiseliminates wear of the orifice and provides variable pressurereduction and flow.4. Summary of Practices4.1 These practices include three procedures for samplecollection. The first is for the collection of
22、a grab sample ofwater at a specific site representing conditions only at the timeof sampling. Grab sampling is the only procedure suitable forbacteriological analysis and some radiological test procedures.4.2 The second practice is for collection of a compositesample at a specific site, portions of
23、which are collected atvaried time intervals. Alternatively, the composite may consistof portions collected at various sites or a combination of bothsite and time variables.4.3 The third practice provides a continuously flowingsample from one or more sampling sites, suitable for on-lineanalyzers or f
24、or collecting grab samples from a continuouslyflowing sample stream.5. Significance and Use5.1 The goal of sampling is to obtain for analysis a portionof the main body of water that is representative. The mostcritical factors necessary to achieve this are points of sampling,and materials selection,
25、system design, time of sampling,frequency of sampling, and proper procedures to maintain theintegrity of the sample prior to analysis.5.2 Homogeneity of the process to be sampled is frequentlylacking, necessitating multiple-point sampling. If it is imprac-tical to utilize a most-representative sampl
26、ing point, it may bepractical to determine and understand interrelationships so thatresults obtained at a minimum number of points may be usedto characterize the system.5.3 Samples collected from a single point in a system arealways recognized as being non-representative to some degree.For this reas
27、on, total representativeness of samples cannot be aprerequisite to the selection of a sampling point. The degree ofrepresentativeness of the sample shall be assessed and theassessment made a part of the permanent record. This willprevent an artificial degree of accuracy from being assigned tothe dat
28、a derived from tests on the sample.5.4 The samples shall be of sufficient volume and shall betaken frequently enough to permit reproducibility of testingrequisite for the desired objective, as required by the method ofanalysis to be used.5.5 Laboratories or facilities conducting water samplingshould
29、 be in compliance with Guide D 3856.6. Interferences6.1 If chemicals are injected or other streams are introducedinto the medium to be sampled, the sample collection pointshould be placed far enough downstream to ensure a com-pletely mixed sample.Assuming turbulent flow (for example, aReynolds numbe
30、r of at least 4000), locating the samplecollection point an equivalent length of 25 diameters down-stream of the chemical injection point is considered acceptable.An equivalent length of 50 diameters is recommended forlaminar flow.6.2 The sampling of high-purity water requires specialconsideration.
31、Contact with any material other than the originalcontainer subjects the sample to possible contamination oralteration. This includes contact with air. Additional require-ments are given in Practice D 4453.7. Materials and Apparatus7.1 Sample Lines:7.1.1 GeneralSample lines should be designed so that
32、 thesample is representative of the source. They shall be as short asfeasible and of the smallest practicable bore to facilitateflushing, minimize conditioning requirements, reduce lag timeand changes in sample composition, and provide adequatevelocity and turbulence. The lines shall have sufficient
33、 strengthto prevent structural failure. The designer is responsible forensuring that applicable structural integrity requirements aremet. Small tubing is vulnerable to mechanical damage andshould be protected.7.1.1.1 Traps and pockets in which solids might settle shallbe avoided, since they may be p
34、artially 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 means shall be provided toprevent undue buckling and bendin
35、g 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.NOTE 2Studies (15)3on particle transport in sampling lines haveindicated that sample velocity rate and stab
36、ility are important factors indetermining deposition and erosion rates on sample tube walls and timerequired to reach and maintain equilibrium. Although limited, other work3The boldface numbers in parentheses refer to the list of references at the end ofthis standard.D 3370 95a (2003)e12has also not
37、ed effects of sorption of dissolved species within tube walldeposits. Velocities near 1.8 m/s (6 f/s) seem to optimize these factors, but,other velocities can provide acceptable results. Sample velocity should beconsidered as a key design issue along with type of sample, lag time,pressure drop, new
38、or existing sample lines, etc. when determining sampleflow rates. Maintaining the selected velocity is necessary to achievesample representivity.7.1.2 MaterialsThe material from which the sample linesare made shall conform to the requirements of the applicablespecifications as follows:ASTM Designati
39、onPipe (seamless carbon steel for high-temperatureservice)Specification A 106Pipe (seamless ferritic alloy-steel for high-temperatureservice)Specification A 335Tubing (seamless carbon-steel for high-temperatureservice)Specification A 179Tubing (seamless or welded alloy-steel for high-temperature ser
40、vice)Specification A 269Tubing, Plastic (polyethylene), or equivalentnon-leaching inert materialsCarbon steel pipe or tubing may be satisfactory for samplinglines where levels of contaminants in the sample are high, orsample constituents require it. For sampling high-purity watersor corrosive waters
41、, the sampling lines shall be made ofstainless steel that is at least as corrosion resistant as 18 %chromium, 8 % nickel steel (AISI 304 or 316 austeniticstainless steels are commonly used (6).NOTE 3Plastic tubing should be avoided where low values of dis-solved oxygen are to be measured since atmos
42、pheric gases may diffusethrough the tubing and cause an analytical bias. The selection of thesample line material should be based on the parameters of interest.7.2 Valves and Fittings:7.2.1 MaterialsValve and fitting materials should be com-patible with the sample and the sample line material select
43、ed.AISI 316 austenitic stainless steel is commonly used. Pressureand temperature ratings should be selected based on thespecific service of the valve/fitting.7.2.2 Isolation Valves At least one shut off valve (com-monly referred to as a root valve) shall be placed immediatelyafter the point from whi
44、ch the sample is withdrawn so that thesample line may be isolated when desired. For safety purposes,an isolation valve should be placed at the sample cooler inlet (ifused) and be rated in accordance with the pressure andtemperature of the sample source.7.2.3 Pressure ReducersThe pressure reducer, in
45、 combi-nation with properly sized sample lines, is the primary com-ponent necessary to control the sample flow at the ratesrequired to give the most representative sample (see Note 2).Flow control is accomplished at the same time sample pressureis reduced.7.2.3.1 For samples equal to or greater than
46、 500 psig (3447kPa), the pressure reducer shall be a rod-in-tube type orifice orcapillary (variable or fixed). Variable rod-in-tube devices arerecommended since they offer two advantages: (a) they arecapable of varying the pressure drop and, therefore, the flow;and (b) they are cleanable in place (e
47、xercising the position ofthe tapered rod in the tube). Forepressure regulators are notrecommended for large pressure reductions because of suscep-tibility to erosion, plugging, and wire drawing of the stem orseat.7.2.3.2 For samples less than 500 psig (3447 kPa), thepressure reducer shall be a needl
48、e valve or forepressureregulator.Aneedle valve is preferred since it will not hunt withsmall pressure variations.7.2.4 Pressure RegulatorsSince most on-line analyzersare flow sensitive, as well as temperature sensitive, the flowrate in the branch circuits shall also be controlled to ensurerepeatable
49、 analytical results. This is achieved by establishing aconstant pressure zone where the sample line feeds theanalyzer branch lines. See Practice D 5540 for additionalinformation. Because of the relationship of pressure and flow,a zone of constant pressure will ensure that each analyzer fedfrom this zone gets a constant flow rate independent of actionstaken in the other branch lines while maintaining constant flowin the main sample line. Maintaining constant flow is alsoessential in regularly monitored grab samples. Two methodsare available to achieve this const
