1、Designation: D 4984 06Standard Test Method forCarbon Dioxide in Natural Gas Using Length-of-StainDetector Tubes1This standard is issued under the fixed designation D 4984; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of
2、 last revision. A number 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 test method covers a rapid and simple field deter-mination of carbon dioxide in natural gas pipelines. Availabl
3、edetector tubes provide a total measuring range of 100 ppm(parts per million) up to 60 % by volume, although the majorityof applications will be on the lower end of this range (that is,under 5 %).At least one manufacturer provides a special kit formeasurements from 10 to 100 % CO2, but the normal 10
4、0-cchand pump is not used. See Note 1.NOTE 1High-range carbon dioxide detector tubes will have measur-ing ranges in percent (%) CO2, and low-range tubes will be in parts permillion (ppm). To convert percent to ppm, multiply by 10 000(1%=10000ppm).1.2 The values stated in SI units are regarded as sta
5、ndard.The inch-pound units in parentheses are for information only.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 ap
6、plica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 Gas Processors Association Standard:2337 Test for Hydrogen Sulfide and Carbon Dioxide inNatural Gas Using Length-of-Stain Tubes23. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 detector tube pumpa ha
7、nd-operated pump of apiston or bellows type. It must be capable of drawing 100 mLper stroke of sample through the detector tube with a volumetolerance of 65 mL.3It must be specifically designed for usewith detector tubes.3.1.1.1 DiscussionA detector tube and pump togetherform a unit and must be used
8、 as such. Each manufacturercalibrates detector tubes to match the flow characteristics oftheir specific pump. Crossing brands of pumps and tubes is notpermitted, as considerable loss of system accuracy is likely tooccur.33.1.2 gas sampling chamberany container that providesfor access of the detector
9、 tube into a uniform flow of samplegas at atmospheric pressure and isolates the sample from thesurrounding atmosphere. A stainless steel needle valve (orpressure regulator) is placed between the source valve and thesampling chamber for the purpose of throttling the sampleflow. Flow rate should appro
10、ximate 1 to 2 volume changes perminute or, at minimum, provide exit gas flow throughout thedetector tube-sampling period.3.1.2.1 DiscussionA suitable sampling chamber may bedevised from a polyethylene wash bottle of nominal 500-mL(16-oz) or 1-L (32-oz) size. The wash bottles internal deliverytube pr
11、ovides for delivery of sample gas to the bottom of thebottle. A 14.7-mm (12-in.) hole cut in the bottles cap providesaccess for the detector tube and vent for the purge gas (see Fig.1). (An alternate flow-through sampler may be fashioned usinga 1-gal (3.8-L) “zipper”-type food storage bag. The flexi
12、bleline enters one corner of the bags open end and extends to thebottom of the bag. The opposite corner of the bags top issealed shut. The basic procedure for the sampler in Fig. 1applies.)3.1.2.2 DiscussionAn alternate sampling container is acollection bag made of a material suitable for the collec
13、tion ofnatural gas (for example, polyester film). The sampling bagshould have a minimum capacity of 2 L.3.1.3 length-of-stain detector tubea sealed glass tube withbreak-off tips sized to fit the tube holder of the pump. Thereagent layer inside the tube, typically a silica gel substancecoated with th
14、e active chemicals, must be specific for carbondioxide and produce a distinct color change when exposed to asample of gas containing carbon dioxide. Any substancesknown to interfere must be listed in the instructions accompa-nying the tubes. A calibration scale should be marked directlyon the tube;
15、however, other markings that provide for easyinterpretation of carbon dioxide content from a separatecalibration scale supplied with the tubes shall be acceptable.1This test method is issued under the jurisdiction of ASTM Committee D03 onGaseous Fuels and is the direct responsibility of Subcommittee
16、 D03.07 on Analysisof Chemical Composition of Gaseous Fuels.Current edition approved June 1, 2006. Published June 2006 Originally approvedin 1989. Last previous edition approved in 1999 as D 498489(1999).2Available from Gas Processors Association, 6526 East 60th St., Tulsa, OK74145.3Direct Reading C
17、olorimetric Indicator Tubes Manual , First ed., AmericanIndustrial Hygiene Association, Akron, OH 44311.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.The calibration scale shall correlate carbon dioxide concentra-tion to the length
18、 of the color stain. Shelf life of the detectortubes must be a minimum of two years from the date ofmanufacture when stored according to manufacturers recom-mendations.4. Summary of Test Method4.1 The sample is passed through a detector tube filled witha specially prepared chemical. Any carbon dioxi
19、de present inthe sample reacts with the chemical to produce a color changeor stain. The length of the stain produced in the detector tube,when exposed to a measured volume of sample, is directlyproportional to the amount of carbon dioxide present in thesample. A hand-operated piston or bellows-type
20、pump is usedto draw a measured volume of sample through the tube at acontrolled rate of flow. The length of stain produced isconverted to parts per million (ppm) or percent (%) carbondioxide by comparison to a calibration scale supplied by themanufacturer for each box of detection tubes. The system
21、isdirect reading, easily portable, and completely suited to makingrapid spot checks for carbon dioxide under field conditions.(See Note 1.)5. Significance and Use5.1 The measurement of carbon dioxide in natural gas isimportant, because of the gas quality specifications, the corro-sive nature of carb
22、on dioxide on pipeline materials, and theaffects of carbon dioxide on utilization equipment.5.2 This test method provides inexpensive field screening ofcarbon dioxide. The system design is such that it may be usedby nontechnical personnel with a minimum of proper training.6. Interferences6.1 Detecto
23、r tubes are usually subject to interferences fromgases and vapors other than the target substance. Such inter-ferences may vary among brands as a result of the use ofdifferent detection methods. Some detector tubes will have a“precleanse” layer designed to remove interferences up tosome maximum inte
24、rferent level. Consult manufacturers in-structions for specific interference information.7. Procedure7.1 Select a sampling point that provides access to arepresentative sample of the gas being tested (source valve onthe main line). The sample point should be on top of thepipeline and equipped with a
25、 stainless steel sample probeextending into the middle third of the pipeline. Open the sourcevalve momentarily to clear the valve and connecting nipple offoreign materials.7.2 Install needle valve (or pressure regulator) at the sourcevalve outlet. Connect sampling chamber using the shortestlength of
26、 flexible tubing possible (see Fig. 1). Most flexibletubing material will be suitable for carbon dioxide sampling;however, if the sampler is also used for other constituents suchas hydrogen sulfide, then choose tubing materials carefully.Avoid using tubing that reacts with or absorbs hydrogensulfide
27、, such as copper or natural rubber. Use materials such asTFE-fluorocarbon, vinyl, polyethylene, or stainless steel.7.3 Open source valve. Open needle valve enough to obtainpositive flow of gas through chamber, in accordance with 3.1.2.Purge the container for at least 3 min (see Fig. 1).NOTE 2If a co
28、llection bag is used instead of a sampling chamber,follow 7.1 and 7.2, substituting the bag for the chamber. Follow 7.3,disconnecting the bag when filled. Deflate the bag to provide a purge, andfill a second time to provide a sample. The bag must be flattenedcompletely before each filling (see secon
29、d Discussion in 3.1.2).7.4 Before each series of measurements, test the pump forleaks by operating it with an unbroken tube in place. Consultmanufacturers instructions for leak check procedure detailsand for maintenance instruction if leaks are detected. The leakcheck typically takes 1 min. A leakin
30、g pump used in fieldtesting will bias sample results low.7.5 Select the tube range that best encompasses carbondioxide concentration. Reading accuracy is improved when thestain length extends into the upper half of the calibration scale.Consult manufacturer guidelines for using multiple strokes toac
31、hieve a lower range on a given tube.7.6 Break off the tube tips and insert the tube into the pump,observing the flow direction indication on the tube. Place thedetector tube into the sampling chamber through the accesshole, such that the tube inlet is near the chamber center (seeFig. 1).NOTE 3Detect
32、or tubes have temperature limits of 0 to 40C (32 to104F), and sample gases must remain in that range throughout the test.Cooling probes are available for sample temperatures exceeding 40C.7.7 Operate the pump to draw the measured sample volumethrough the detector tube. Observe tube instructions when
33、applying multiple strokes. Ensure that a positive flow ismaintained throughout the sample duration at the samplingchamber gas exit vent. Observe tube instructions for properFIG. 1 Apparatus SchematicD4984062sampling time per pump stroke. The tube inlet must remain inposition inside the sampling cham
34、ber until sample is com-pleted. Many detector tube pumps have stroke finish indicatorsthat eliminate the need to time the sample.NOTE 4If a collection bag is used, draw the sample from the bag viaa flexible tubing connection. Do not squeeze the bag during sampling.Allow the bag to collapse under pum
35、p vacuum, so that the pumps flowcharacteristics are not altered.NOTE 5It is very important to ensure that ambient air is not beingdrawn into the sample. Intrusion of ambient air into the sample will tendto bias the carbon dioxide readings low.7.8 Remove the tube from the pump and immediately readcar
36、bon dioxide concentration from the tubes calibration scaleor from the charts provided in the box of tubes. Read the tubeat the maximum point of the stain. If “channeling” hasoccurred (nonuniform stain length), read the maximum andminimum stain lengths and average the two. Consult tubeinstructions fo
37、r any special information in the event of multi-colored stains.NOTE 6If the calibration scale is not printed directly on the detectortube, be sure that any separate calibration chart is the proper match for thetube in use.7.9 If the number of strokes used differs from the number ofstrokes specified
38、for the calibration scale, correct the reading asfollows:ppm corrected!5ppm reading!3specified strokesactual strokes7.10 Record the reading immediately, along with the gastemperature and the barometric pressure. Observe any tem-perature corrections supplied in the tube instructions. Altitudecorrecti
39、ons become significant at elevations above 2000 ft.Correct for barometric pressure as follows:ppm corrected!5 ppm reading!3760 mm Hgbarometric pressure in mm HgNOTE 7Even though the amount of chemicals contained in detectortubes is very small, the tubes should not be disposed of carelessly. Ageneral
40、 disposal method includes soaking the opened tubes in water beforetube disposal. The water should be treated to a neutral pH before itsdisposal.8. Quality Assurance8.1 Detector tubes from each batch or lot of tubes should betested to conform the published accuracy, (generally 6 25 %).8.2 The tubes s
41、hould continue to meet the published accu-racy until the expiration date, if the tubes are shipped andstored per manufacturer instructions.9. Precision and Bias9.1 The accuracy of detector tube systems is generallyconsidered to be 625 %. This is based mainly on programsconducted by the National Inst
42、itute of Occupational Safety andHealth (NIOSH) in certifying detector tubes for low-levelcontaminants in air adapted to worker exposure monitoring.4NIOSH tested tubes at12 , 1, 2, and 5 times the threshold limitvalue (TLV) requiring 625 % accuracy at the three higherlevels and 35 % at the12 TLV leve
43、l. (For example, CO2, witha TLV of 5000 ppm, was tested at levels 2500, 5000, 10 000,and 25 000 ppm.) The higher tolerance allowed at the low levelwas due to the loss of accuracy for shorter stain lengths.3NIOSH discontinued this program in 1983, and it was pickedup by the Safety Equipment Institute
44、 (SEI) in 1986.9.2 The Gas Processors Association reports an observederror of 68 % or better in tests of two brands of carbon dioxidedetector tubes (see 2.1, 2337).10. Keywords10.1 gaseous fuels; natural gasASTM International takes no position respecting the validity of any patent rights asserted in
45、 connection with any item mentionedin this standard. Users of this standard are expressly advised that determination of the validity of any such patent rights, and the riskof infringement of such rights, are entirely their own responsibility.This standard is subject to revision at any time by the re
46、sponsible technical committee and must be reviewed every five years andif not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional standardsand should be addressed to ASTM International Headquarters. Your comments will receive care
47、ful consideration at a meeting of theresponsible technical committee, which you may attend. If you feel that your comments have not received a fair hearing you shouldmake your views known to the ASTM Committee on Standards, at the address shown below.This standard is copyrighted by ASTM Internationa
48、l, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org).4“NIOSH Certification Requirements for Gas Detector Tube Units,” NIOSH-TC-012, 1978.D4984063
