API 31B06:2001 pdf free download.Manual of Petroleum Measurement Standards Chapter 3—Tank Gauging Section 1B—Standard Practice for Level Measurement of Liquid Hydrocarbons in Stationary Tanks by Automatic Tank Gauging
3.1B.4.3 ACCURACY
3.1B.4.3.1 Intrinsic Accuracy of ATGs The level measurement accuracy of all ATGs is affected by the intrinsic accuracy of the ATG, i.e., the accuracy of the ATG when tested under controlled conditions as speciÞed by the manufacturers.
3.1B.4.3.2 Calibration Prior to Installation (Factory Calibration) The reading of an ATG to be used for custody transfer application should agree with a certiÞed measurement instru- ment within ±1 mm or (± 1 / 16 inch) over the entire range of the ATG. The certiÞed measurement instrument should be traceable to the national standards and should be provided with a calibration correction table. The uncertainty of the ref- erence should not exceed 0.5 mm or ( 1 / 32 inch), with the cali- bration correction applied. The reading of an ATG to be used for inventory application should agree with a certiÞed measurement instrument within ±3 mm (± 1 / 8 inch) over the entire range of the ATG. The certiÞed measurement instrument should be traceable to the national standards and should be provided with a calibration correction table. ATGs installed prior to the effective date of this document may not have factory calibration documentation. These ATGs are not required for re-test at the factory, but the installed accuracy of these ATGs should meet the requirements in 3.1B.7.3.3 for their intended application.
3.1B.4.3.3 Error Caused by Installation and Operating Conditions The total error of an ATG in custody transfer service should not be affected by more than ±3 mm (± 1 / 8 inch) due to installation, to variation of operating conditions (refer to Sec- tion 3.1B.4.3.5) or variation of physical and electrical proper- ties of the liquid and/or vapor, provided that these conditions are within the limits speciÞed.
3.1B.4.3.4 Overall Accuracy of the Installed ATG The overall accuracy of the installed ATG includes both the intrinsic accuracy of the ATG, as veriÞed by factory calibra- tion, and those effects caused by installation and operating conditions. The overall accuracy of an ATG in custody trans- fer service should be within ±4 mm (± 3 / 16 inch). The overall accuracy of an ATG in Inventory control service should be within ±25 mm (±1 inch).
3.1B.4.3.5 Accuracy Limitations of Tank Measurement ATGs (and measurements derived therefrom, e.g., volume) are affected by the same inherent accuracy limitation as man- ual tank gauging measurements. It is imperative that the user understand these limitations, which are addressed in more detail in MPMS Chapter 3.1.A, but are listed here for conve- nience. Other limitations unique to ATGs are also listed.
3.1B.4.3.5.1 Accuracy limitations Inherent to both Manual Tank Measurement and ATGs a. Accuracy of tank capacity table, including the effect of tank tilt and hydrostatic pressure.
b. Bottom movement.
c. Incrustation.
d. Movement of the manual gauging reference point or the ATG reference point during tank transfers or because of thermal expansion. Both affect ullage gauging.
e. The accuracy of measurements using innage-based ATGs is affected by vertical movement of the datum plate used to calibrate the ATG or vertical movement of the ATG reference point during tank transfers.
f. Random and system errors in level, density, and tempera- ture measurement.
g. Expansion of the tank diameter due to temperature.
h. Operational procedures used in the transfer.
i. Minimum difference between opening and closing levels (parcel size).
j. Errors in measured level caused by sticking and/or cock- ing of ßoating roofs.
3.1B.4.3.5.2 Accuracy Limitations Unique to ATG Systems
a. Errors caused by the improper installation of the ATG.
b. Errors in transmitting the tank level and temperature information to the remote readout.
c. Errors in tank capacity table, physical property and other data input into the tank gauging system computer.
3.1B.4.4 USE OF ATGs FOR CUSTODY TRANSFER OR INVENTORY CONTROL
The overall accuracy of level measurement by ATGs, as installed (Òinstalled accuracyÓ), is limited by the intrinsic error of the ATG equipment, the effect of installation methods and the effect of changes in the operating conditions. Depending on the overall accuracy of the ATG, as installed, ATGs may be used either for custody transfer or for inventory control purposes. The use of ATGs for custody transfer normally requires mutual contractual agreement between the buyer and the seller and may be subject to federal, state and local regulations.API 31B06 pdf download.API 31B06:2001 pdf free download
