GPA STD 2198-2016 Selection Preparation Validation Care and Storage of Natural Gas and Natural Gas Liquids Reference Standard Blends.pdf

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1、 Selection, Preparation, Validation, Care and Storage of Natural Gas and Natural Gas Liquids Reference Standard Blends Adopted as a Standard 1998 Revised 2016 GPA Midstream Association Sixty Sixty American Plaza, Suite 700 Tulsa, Oklahoma 74135 GPA Midstream Standard 2198-16 DISCLAIMER GPA Midstream

2、 Association publications necessarily address problems of a general nature and may be used by anyone desiring to do so. Every effort has been made by GPA Midstream to assure accuracy and reliability of the information contained in this publication. Each person who uses or refers to this publication

3、will need to make their own decisions based on consideration of their own internal best practices, recommendations, and engineering judgment. GPA Midstream and its members do not guarantee the accuracy, completeness, efficacy, timeliness, or correct sequencing of such information, including without

4、limitation, the reference material and information of the various other industry associations that may be provided herein. Use of the information provided in this publication is voluntary, and reliance on it should only be undertaken after an independent review of its accuracy, completeness, efficac

5、y, timeliness, and consideration of the applicability of any local, state, and federal laws and regulations. It is not the intent of GPA Midstream to assume the duties of employers, manufacturers, or suppliers to warn and properly train employees, or others exposed, concerning health and safety risk

6、s or precautions. Reference herein to any specific commercial product, process, or service by trade name, trademark, service mark, manufacturer, or otherwise does not constitute or imply endorsement, recommendation, or favoring by GPA Midstream. GPA Midstream makes no representation, warranty, or gu

7、arantee in connection with this publication and hereby expressly disclaims any liability or responsibility for loss or damage resulting from its use or for the violation of any federal, state or municipal regulation with which this publication may conflict, or for any infringement of letters of pate

8、nt regarding apparatus, equipment, or method so covered. “Copyright2016 by GPA Midstream Association. All rights reserved. No part of this Report may be reproduced without the written consent of GPA Midstream Association.” Selection, Preparation, Validation, Care and Storage of Natural Gas and Natur

9、al Gas Liquids Reference Standard Blends 1. SCOPE 1.1. This method covers the recommended procedures for selecting the proper Natural Gas and Natural Gas Liquids (NGL) Reference Standards, preparing the standards for use, verifying the accuracy of composition as reported by the manufacturer, and the

10、 proper care and storage of those standards to insure their integrity and longevity as long as they are in use. 2. SUMMARY OF PROCEDURE 2.1. It is highly recommended that the proper reference standard blend be obtained for a particular application. The accuracy of its reported composition must be au

11、thenticated when received and periodically during its use. 2.2. Special care must be taken to ensure the integrity of any reference standard from the time it is received until it is taken out of service. 2.2.1. It is a good laboratory practice to order a replacement standard and confirm its validity

12、 well in advance of the depletion or deterioration of the reference standard blend that is presently in service. 2.3. A constant pressure cylinder used to obtain a NGL Reference Standard must be properly prepared and inspected to avoid contaminating, altering or losing its contents. 2.4. All necessa

13、ry Department of Transportation (DOT) requirements must be followed when transporting a Natural Gas or NGL Reference Standard blend. 3. SELECTION OF REFERENCE STANDARD BLENDS 3.1. The selection of a proper reference standard blend depends upon the composition of the samples that are to be analyzed.

14、A reference standard composition should resemble the samples that are to be analyzed. 3.1.1. A reference standard blend prepared gravimetrically, containing high purity components to a stated accuracy as shown in Table 1 and provided with the stated uncertainty per component as calculated by the man

15、ufacturer, is re-commended for instrument calibrations. The concentration of a component in the reference standard blend should not be less than one-half or more than double the concentration of the corresponding component in the unknown (unless linearity tests demonstrate otherwise). Corresponding

16、components in the reference standard blend and in the unknown should not differ by more than twenty (20) mol percent (of the total mixture) when the peak area calculation method is used. When applying these rules, the values for the hexanes and heavier components may be totaled and considered as a s

17、ingle component. Recommended Purity for Reference Standard Blend Components % Concentration in Reference Standard Blend Required Purity of Raw Component Stock 0.00 - 0.099% 95% Relative 0.10 - 9.999% 98% Relative 10.0 - 100% 99% Relative Table 1 3.1.2. On a thermal conductivity detector (TCD), it is

18、 known that a hexanes plus containing only normal alkanes will yield a different response than a blend that also contains isomers. The ideal hexanes plus composition will have a similar molecular weight and density to that of the unknown samples and produce a similar response. This reduces the error

19、 on determination of the hexanes plus concentration. Extended analyses of the potential sample streams can be utilized to determine the composition and concentration ranges of the hexanes plus for a reference standard. 3.1.3. A properly blended Reference Standard should be prepared gravimetrically b

20、y the manufacturer and its composition verified by chromatographic analysis before shipment to the user. 3.2. It may be necessary for the user to check the linearity of an instrument before a range of instrument accuracy can be determined. (Refer to section 6.3) 3.2.1. The linearity of the instrumen

21、t will determine the range of samples that can be analyzed with a single reference standard. It may be necessary to obtain more than one reference standard blend. NOTE: Hydrogen and/or Helium are more difficult to blend. Contact the manufacturer for the accuracy determination of these components. 4.

22、 INITIAL PREPARATION AND HANDLING OF REFERENCE STANDARD BLENDS 4.1. Before a reference standard can be used for calibrating instruments, it must be properly prepared and the contents must be verified. Improper preparation can lead to inaccurate calibrations and verifications. 4.2. If a Natural Gas R

23、eference Standard has (or is suspected to have) dropped below its hydrocarbon dew point it must be maintained above its hydrocarbon dew point for at least 4 hours before attempting to analyze it. Due to the uncertainty in measuring or calculating the hydrocarbon dew point, it is recommended that the

24、 standard be maintained at least 30F (17C) above the expected hydrocarbon dew point. (Refer to API MPMS Chapter 14.1) 4.3. The pre-charge end of a NGL Reference Standard cylinder should be pressured not less than 200 psi (1379 kPa) above the vapor pressure of the sample at the temperature of the chr

25、omatograph injection valve (A pressure of 1000-1200 psig should be sufficient for most liquids). CAUTION: Do not over-pressure the cylinder. 4.3.1. The contents of a NGL Reference Standard blend should be thoroughly mixed immediately before attempting to analyze it. (Refer to manufacturers informati

26、on for mixer type and proper mixing instructions.) 5. LONG TERM CARE AND HANDLING 5.1. Special care must be taken to ensure the integrity of a natural gas and NGLreference standard blend after it has been verified and placed into service. If improperly handled, the composition will begin to exhibit

27、noticeable deterioration as the pressure of the cylinder decreases, due to usage, and should be removed from service at that time. Experience dictates that a properly maintained reference standard blend containing no reactive compounds can be utilized until a variation is indicated by the fidelity p

28、lot and/or the control chart regardless of age. Reactive compounds are components that are incompatible with other components within the reference standard blend, the container material of construction, or material that may adsorb to the container wall. Consult the manufacturer to determine componen

29、t compatibility with your desired composition or container. A few outlined steps will help ensure the prolonged integrity of the original composition of the reference standard blend. 5.2. Natural Gas Reference Standard 5.2.1. After the gas reference standard blend has been verified as to the proper

30、composition for calibration purposes, it should be stored with the cylinder valve tightly closed, a plug inserted in the valve and tightly secured to eliminate possible leakage. Reference standard blends that contain hexane and heavier mole components should be stored at a stable temperature that is

31、 above the hydrocarbon dew point temperature of the gas composition (preferably heat blanketed, or in some type of heating cabinet). The cylinder temperature should be monitored on a routine basis and no product removed from the cylinder if it is not properly heated. 5.2.2. Fidelity plots (as descri

32、bed in section 6.4) should be made periodically on calibration run data. For a specific instrument, the plot slope should remain essentially constant. A change in the slope usually indicates a change in the gas composition. Should a Fidelity Plot indicate a change in composition, the reference stand

33、ard blend should be removed from service. 5.2.3. Comparison of recent component peak area ratios with corresponding peak area ratios of the original calibration will indicate if the reference standard blend is beginning to deteriorate. 5.2.4. Another good practice is the use of quality control chart

34、s, as in Figure 5, with a chart for each component in the reference standard blend. Control charts may be plotted for components from verification runs. (Refer to section 6.5). 5.3. NGL Reference Standard 5.3.1. Valves should be securely sealed with PTFE tape, capped and plugged to eliminate any pos

35、sible leakage while the reference standard is being stored. 5.3.2. Fidelity plots (as described in section 6.4) should be made periodically on calibration run data. For a specific instrument, the angle of the plot should remain essentially constant. If there is a change in the angle, a change in com

36、position is indicated, and the reference standard blend should be removed from service until it is certain that the composition has not changed. 5.3.3. Another good practice is the use of quality control charts, as in Figure 5, with a chart for each component in the reference standard blend. Control

37、 charts may be plotted from verification runs. (Refer to section 6.5). 5.3.4. Comparison of recent component peak area ratios with corresponding peak area ratios of the original calibration will indicate if the reference standard blend is beginning to deteriorate. 6. QUALITY CONTROL PROCEDURES 6.1.

38、Natural Gas Reference Standard 6.1.1. Before a new reference standard blend can be used for calibrating instruments, it is highly recommended that the composition be authenticated. If the composition of the new reference standard blend does not match the gravimetric composition provided by the vendo

39、r, it should not be used for calibration purposes. To determine the accuracy of a new reference standard blend, these steps should be followed: 6.1.1.1. All regulators, gauges, and fittings attached to the cylinder should be tight and leak tested. The sample line between the cylinder and the gas sam

40、ple valve should be as short as practical and constructed of one size tubing only (no larger than 1/8” O.D.). 6.1.1.2. Analyze the composition of the reference standard blend at least two (2) times, as an unknown to determine the repeatability of the chromatograph. Repeatability can be confirmed by

41、comparing the component mol percent of the analyses from two repeatable runs. Component mol percent should agree within the repeatability requirements as stated in GPA Midstream Standard 2261. CAUTION: It may be necessary to heat and/or insulate the sample line from the cylinder to the sample valve

42、to prevent the loss of heavy ends. 6.1.1.3. Once the repeatability of the instrument has been confirmed, compare the composition of the latest analysis with the gravimetric composition supplied by the manufacturer. The two compositions should agree within the reproducibility values as stated in GPA

43、2261. If the two compositions do not agree, perform the Fidelity Plot (refer to section 6.4). 6.2. NGL Reference Standard 6.2.1. Before a new reference standard blend can be used for calibrating instruments, the accuracy must be determined. Liquid reference standards blends are difficult to prepare

44、and are subject to change in composition during use. It is highly recommended that the composition of the reference standard should be authenticated. If the composition of the new reference standard blend does not match the gravimetric composition provided by the manufacturer, it should not be used

45、for calibration purposes. To determine the accuracy of a new reference standard blend, these steps should be followed: 6.2.1.1. Connect a high pressure source (helium or nitrogen) to the pre-charge end of the constant pressure cylinder and slowly apply a pressure not less than 200 psi (1379 kPa) abo

46、ve the vapor pressure of the sample at the temperature of the sample injection valve (A pressure of 1000-1200 psig should be sufficient for most liquids). This pressure should be maintained on the cylinder at all times. CAUTION: Do not over-pressure the cylinder. NOTE: It is a good laboratory practi

47、ce to use a high pressure source that is not present in the sample. 6.2.1.2. Mix the sample thoroughly immediately before each use. There are several different types of mixers in the various constant pressure cylinders such as rods, balls, wafers, etc. Be sure to know the type of mixer in your cylin

48、der and how it operates. Failure to mix the contents of the cylinder thoroughly could eventually alter the composition of the reference standard blend. 6.2.1.3. When connecting the sample end of the cylinder to the inlet of the chromatograph liquid sample valve, the tubing must be kept the same diam

49、eter (no larger than 1/8” O.D.) and as short as practical. The liquid sampling valve must be capable of entrapping a fixed volume of sample at a pressure at least 200 psi (1379 kPa) above the vapor pressure of the sample at valve temperature (A pressure of 1000 2000 psig should be sufficient for most liquids). CAUTION: Do not over-pressure the cylinder. 6.2.1.4. Analyze the composition of the reference standard blend at least two (2) times as an unknown to determine the repeatability of the chromatograph. Repeatability can be confirmed by comparing the component mol percents of the analy