1、 Low-Pressure Field Method for Determining Ethyl Mercaptan Odorant in LP-Gas Using Length of Stain Tubes Adopted as a Standard 2001 Revised 2014 Gas Processors Association 6526 East 60th Street Tulsa, Oklahoma 74145 GPA Standard 2194-14 DISCLAIMER GPA publications necessarily address problems of a g
2、eneral nature and may be used by anyone desiring to do so. Every effort has been made by GPA to assure accuracy and reliability of the information con-tained in its publications. With respect to particular circumstances, local, state, and federal laws and reg-ulations should be reviewed. It is not t
3、he intent of GPA to assume the duties of employers, manufactur-ers, or suppliers to warn and properly train employees, or others exposed, concerning health and safety risks or precautions. GPA makes no representation, warranty, or guarantee in connection with this publication and hereby expressly di
4、sclaims any liability or responsibility for loss or damage resulting from its use or for the vio-lation of any federal, state, or municipal regulation with which this publication may conflict, or for any infringement of letters of patent regarding apparatus, equipment, or method so covered. Copyrigh
5、t2014 by Gas Processors Association. All rights reserved. No part of this Report may be reproduced without the written consent of the Gas Processors Association. Impact Statement Low Pressure Field Method for the Determination of Ethyl-Mercaptan Odorant in LP Gas Using a Length of Stain Tube GPA 219
6、4-14 Purpose This standard covers the determination of the concentration of Ethyl-Mercaptan in low pressure LP Gas using a length of stain tube. While other mercaptans and sulfur species may be indicated in a stain tube it is important to remember that the tubes are calibrated for and intended to be
7、 used to determine the con-centrations specifically of Ethyl Mercaptan in LP gas. This standard has not seen any revisions since its adoption as a Tentative Standard in 1994. It was then reapproved in 2001. This revision updates some materials used in the procedures which by todays best practices wo
8、uld be found obsolete in terms of what we would use to collect or transport a sample to the stain tube. i.e. gum rubber tubing etc. The most significant addition to the standard is a “Cautionary Statement”. The intention of the statement is to inform the user that it is critical that manufacturers i
9、nstructions be followed implicitly. Each lot of stain tubes is tested by the manufacturer for compliance to stated accuracy and each lot or box of stain tubes quite possibly is slightly different in terms of how they are to be used i.e. exposure times, indicat-ing colors or contaminants etc. Further
10、 the manufacturers instructions will state the exponent to be used for multiple or partial testing “pulls” of the pump or if these are allowed at all. This information may vary from lot to lot and from one brand of tube to another. Also of significance is the concept that if high accuracy and repeat
11、ability is required and chromatog-raphy is not indicated or feasible then there is many portable handheld electronic devices which offer these things as well as low power usage and intrinsic safety. So the user should consider if a length of stain tube is really the best commercially available optio
12、n based on their situation and requirements. Impact It is not expected that the use of this Standard will have any new or further impact. The users of this Standard should perform their own economic evaluation to include the use of handheld portable electronic devices as applicable. 1 Low-Pressure F
13、ield Method for Determining Ethyl Mercaptan Odorant in LP-Gas Using Length of Stain Tubes CAUTIONARY STATEMENT The need to determine the concentration of Ethyl Mercaptan in Propane can be driven by numerous fac-tors, including safety related incidents. The user should be aware that if definitive, hi
14、ghly accurate and repeatable readings are needed, length of stain tubes may not be the first choice as a commercially viable solution. In recent years there have been advancements in the determination of components of interest in various gases and liquids by means of portable or handheld electronic
15、devices which are outside the scope of this document. Concentration level accuracies can be greatly enhanced by the use of these electronic de-vices and of course chromatographic analysis can be the most accurate means of determining the con-centration levels of components of interest. The analytica
16、l results from a length of stain tubes are highly dependent on many factors. Therefore, it is imperative that the user read, understand and follow the instructions in each box of tubes implicitly since every box or lot of tubes potentially has its own individual characteristics. Interferences may in
17、clude temperature and moisture content of the product under test, ambient conditions, and a number of other diluents and contaminants. Ambient or operational conditions may preclude the use of a stain tube. It may be too hot or humid outside or the conditions in the propane may not be appropriate fo
18、r stain tube use. Manufacturers instructions will direct the user. Stain tube accuracies as stated by most manufacturers is 25%. While GPA testing shows 10% accu-racy in controlled conditions, it is important for the user to determine if the stated accuracy by the stain tube manufacturer is acceptab
19、le, based on the operational conditions, ambient conditions and safety re-quirements for the determination of the concentration level of Ethyl Mercaptan in Propane. 2 Low-Pressure Field Method for Determining Ethyl Mercaptan Odorant in LP-Gas Using Length of Stain Tubes 1.0 Scope 1.1 This method cov
20、ers the determination of ethyl mercaptan in LP-Gas vapors when those vapors are at a pressure of eleven (11) inches of water column. The time specified for the test is one minute (see manufacturers instructions). The stain tube suggested is calibrated to read directly in parts per million (2.5 40) a
21、t the specified condition. This test method is a field method to generally determine if an LP-Gas sample contains adequate odorization to meet the minimum requirements of NFPA58. A chromato-graphic method should be used for a more precise, quantitative determination. CAUTION: This test procedure req
22、uires the release of very small volumes of combustible LP-Gas vapors. The user is warned to take proper safety precautions to prevent the accumulation of a combustible mixture and prevent ignition. This procedure should never be performed in an enclosed building unless a properly designed vapor reco
23、very exhaust hood is provided. Liquid propane evaporates rapidly and can freeze flesh quickly. If any liquid propane is encoun-tered, avoid any skin contact. 2.0 Summary of Method 2.1 A sample of LP-Gas vapors is pressured through the detector tube with the pressure available at a consumer location,
24、 typically a service line, which is usually eleven (11) inches of water column pres-sure. This is normally the standard final pressure regulator setting for LP-Gas vapors at the point of con-sumption; however, field settings may be found 3”wc of this standard. The sample is pressured through the det
25、ector tube by the line pressure thereby eliminating the need for a proportioning pump. If the pressure and flow are maintained for one minute, or the specified time interval, the suggested detec-tor tube is designed to read directly in parts per million of ethyl mercaptan. Since the detector tube is
26、 the only piece of apparatus necessary, portability is convenient. 3.0 Apparatus 3.1 Low-Pressure Connection. A suitable soft seal and non-reactive connection must be provided for field application of the detector tube. A valve connection with a short piece of 3/16 inch non-reactive soft tubing atta
27、ched provides an adequate soft seal for the attachment of the detector tube. The down-stream end of the detector tube is open to the atmosphere. (See Figure 1.) The connection must be kept as short as possible to reduce the possibility of odorant reaction or adsorption with the sampling appa-ratus.
28、Figure 1 - Low Pressure Testing Connection 3 3.2 Detector Tubes. Tubes must be made of glass with breakoff tips. Tubes must be sealed and un-damaged prior to use, stored per manufacturers recommendations and not past the expiration date. The chemically treated material in the tube must be specifical
29、ly for ethyl mercaptan and produce a distinct color change when exposed to a sample of LP-Gas containing ethyl mercaptan. Any substance known to interfere must be listed in instructions accompanying the tubes. A calibration scale should be etched or printed directly on the tube to provide quantitati
30、ve indication of the ethyl mercaptan content. Maximum shelf life of the detector tubes must be stated in the manufacturers instructions and shall not be exceed-ed by the user. Note 1: At the time of this procedure preparation, only one manufacturer was known to have a commercial tube available speci
31、fically designed to read directly in parts per million of ethyl mercaptan in LP-Gas vapors if such vapors are allowed to pass for one minute at an upstream pressure of eleven (11) inches of water column. The tube is Sensidynel Gastec Tube No. 72P. If other manufacturers provide a tube that will oper
32、ate at the same time and pressure criteria, that tube would be ac-ceptable following verification testing. Note 2: Avoid reactive components anywhere in the sampling process including fittings, tubing and collection devices as ethyl mercaptans are readily absorbed. Note 3: Avoid any moisture in the
33、sampling process as this will ultimately affect the reading. CAUTION: Stain tubes may contain a very small amount of reactive chemicals. Care should be taken in the disposal of used tubes. 3.3 Alternate Connection. A self-contained non-reactive pressure regulator with a soft seal sample port and pre
34、ssure gauge can be utilized if a sample is to be analyzed from the vapor space of an LP-Gas tank at the vapor pressure of the product. This device can be applied to a suitable valved connection and must always be in the vapor phase. The pressure regulator must be calibrated at the upstream pressure
35、to provide an eleven (11) inch water column pressure downstream. (See Figure 2 for a typical self-contained pressure regulator/sample port combination.) Figure 2 - Quick Connect Test Fitting For Stain Tube Low RangePressure GaugeStain TubePressure RegulatorQuick ConnectFitting (Female)Quick ConnectF
36、itting (Male)HighPressureGasSource4 4.0 Sampling 4.1 Before connecting a stain tube or a regulator/sample port to an LP-Gas system, confirm the in-ternal pressure of the system where the sample is to be taken and eliminate all dirt or other foreign mate-rial from the connection point. CAUTION: Never
37、 connect a stain tube directly to a high pressure source of LP-Gas. 5.0 Procedure 5.1 Confirm the sample source is at or near a pressure of eleven (11) inches water column (approxi-mately 0.4 psig) by use of a water manometer or calibrated low pressure gauge. 5.2 Allow the gas to flow through the sa
38、mple connection at least 60 seconds before applying the stain tube. 5.3 Break off tube tips and insert upstream end into the soft seal connection. Flow should be in the same direction as the flow arrow on the tube. 5.4 Time the flow for one minute as precisely as possible using a second-hand or digi
39、tal watch. A stop-watch can be used, but is not necessary. 5.5 At the end of one minute or specified time interval, immediately remove the tube, then shut off the source of LP-Gas. 5.6 Immediately record the value indicated by the stain length. Note 4: There is tremendous variation in recommended us
40、age, instructions, time intervals, interferences, cross sensitivities, and temperature corrections between different model tubes, including different models from a particular manufacturer. It is the users responsibility to assure they are using the proper tube and strictly conforming to the manufact
41、urers instructions. Failure to do so can dramatically impact accuracy of the results. Note 5: The color of the stain may crawl or fade when exposed to air for a period of time. 6.0 Procedure Using Alternate Connection Method 6.1 Connect the sampling apparatus (see Figure 2) containing a non-reactive
42、 pressure regulator, down-stream pressure gauge or water manometer, and the sample port to the valve on the high pressure source. 6.2 Before opening the high pressure valve, make sure the regulator is in the closed position where no gas will pass when the valve is opened. 6.3 Open the high pressure
43、vapor valve. 6.4 Slowly adjust the regulator until the down-stream pressure is eleven (11) inches of water column while pinching the soft tubing outlet to restrict the flow. 5 6.5 When pressure adjustment is set, remove flow restriction and allow sample port to purge for at least 60 seconds. 6.6 Bre
44、ak off tube tips and insert upstream end into the non-reactive soft seal connection. Flow should be in the same direction as the flow arrow on the tube. 6.7 Time the flow for one minute or specified time interval as precisely as possible using a second-hand or digital watch. A stop-watch can be used
45、, but is not necessary. 6.8 At the end of one minute or specified time interval, immediately remove the tube and shut off the sample source. 6.9 Immediately record the concentration indicated by the stain length. Note 6: The color of the stain may crawl or fade when exposed to air for a period of ti
46、me. 7.0 Calculations 7.1 Since the tube is calibrated to read directly in parts per million by volume, no calculations are necessary. 8.0 Interpretation 8.1 This test is a direct measure of the concentration of ethyl mercaptan in low-pressure propane va-pors. It is also an indirect measure of the co
47、ncentration of ethyl mercaptan in the propane liquid that is in equilibrium with the sampled propane vapor. Ethyl mercaptan is very soluble in propane, but has much lower vapor pressure. Therefore, the equilibrium concentration of ethyl mercaptan in the vapor phase is much lower than its concentrati
48、on in the liquid phase. The exact ratio of concentration is dependent on the temperature of the fluids in the tank. 9.0 Interferences 9.1 The manufacturers application instructions should be consulted for possible interfering sub-stances. Most detector tubes for ethyl mercaptan will react with most
49、other mercaptans if they are pre-sent. 10.0 Accuracy 10.1 The accuracy indicated by the detector tube manufacturer is usually 25% of the reading. This test procedure can be used to generally determine if a system contains adequate odorant or if additional odorant is indicated. If a more accurate analysis is desired, a complete chromatographic analysis is rec-ommended. 6 11.0 Precision 11.1 The following precision statement is representative of the precision data attached to the test method. Precision Statement Ethyl Mercaptan in Propane, ppmv Material X SrSRr R Tank 1 6.3 1
