API MPMS 14.1:2006(2011) pdf download
API MPMS 14.1:2006(2011) pdf download.Manual of Petroleum Measurement Standards Chapter 14- -Natural Gas Fluids Measurement Section 1- -Collecting and Handling of Natural Gas Samples for Custody Transfer.
6.2 FLOW CHARACTERISTICS
6.2.1 General
Piping elements, such as salve’s and orifices, can create re-circulation epons (eddies) in (he flowing sample source stream. The gas composition in thcse eddies may be measurably different from the gas composition of 11w bulk flow. 11w gas downstream of a gas-liquid separator will he near its hydrocarbon dew point, and a reduction in line temperature will likely cause sonic condcnsalion to occur. In other cases, a pipeline may be operating with both gas and liquid continually present in the pipe. Obtaining an accurate gas sample under these condiuons is diflicult and outside the scope of this standard. See Appendix C. Lessons Learned During Sampling in Hvdrvearbon Saturated and 2-Phase Natural Gas Streams. Also see Appendix B. Fluid MechanEcl (‘rmsiderouons in Gas Sampling for a detailed discussion of fluid incehanics.
Users arc cautioned not to interpret liquids condensed by the metering or sampling system as free liquids flowing through the pipeline.
6.2.2 Single-Phase Flow
Single-phase flow is natural gas flowing at a teniperature above the hydrocarbon dew point and free of conwrexcor oil, water, or other contaminants in the flowing sample source stream. In general. it is preferred that the single phase gas in the pipeline be in the turbulent flow regime. because the fluid turbulence creates a well-mixed, representative fluid.
6.3 CAUSES OF GAS SAMPLE DISTORTION
Since natural gas is a mixture of organic and Inorganic pure gases. its integrity will be sacnticcd if any components of the sample gas are depleted or augmented (e.g., air-contamination, dc-sorption of hydrocarbons). This section identifies fundamental mechanisms of sample distortion. An understanding of these mechanisms will reduce the likelihood of poorly designed sampling systcms.
11 is important to rewgmze that only sample collection distortion mechanisms are identified in this section. Poor gas analysis techniques can also distort the indicated composition (see Scetion 16, Guidelines (or Macis).
6.3.1 Phase Changes
Condensation and revaporiianon of hydrocarbons within the sampling system can cause significant distortions in a gas sample. These type’s of sample distortions can occur tender both flowing and non.tlowing conditions (i.e.. in a flowing sample delivery system or in sample containers), or if the sample comes in contact with sampling equipment that is below the hydrocarbon dew point. Sec Appendix A. The Phase Diagram. for a detailed discussion of the thermod namics of these phase changes.
Accurate sampling from gas streams with temperatures at the hydrocarbon dew point temperature is more difficult than sampling from streams with temperatures above the hydrocarbon dew point temperature. Additionally, depending on the pipeline pressure, retrograde condensation may occur if the pressure is reduced. Some gas mixtures will have a hydrocarbon dew point that is high enough to cause condensation at ambient temperatures commonly experienced during the year. If condensation does occur, and only the gaseous phase of the partially condensed sample is analysed, the heating saluc and density of the sample will he ineorrect. Furthermore, the remaining sample will no longer be representative of the sample source.
The integrity of gas samples (and calibration standards) with condensed components can be recovered by revaporizing the condensed liquids. provided that no fluid (gas or liquid) has been released from the sample container prior to revaporization. Sce 6.4, Resuporiatian, and Appendix A, The Phaw Diagram.
6.3.1.1 FlowIng and Sampling Conditions
A gas sample flowing through a sampling system may experience temperature and pressure changes. Pressure and temperature reductions occur when the gas accelerates through tubing elements within the sampling system. If the gas is near the hydrocarbon.
