API MPMS 3.1B: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
The use of ATGs in custody transfer application requires high accuracy. The use of ATGs for inventory control purposes often permits a lower degree of accuracy.
3.1B.4.4.1 Use of ATGs for Custody Transfer Purposes
3.1B.4.4.1.1 The ATG should meet the factory calibration tolerances prior to installation (refer to Section 3.1B.4.3.2).
3.1B.4.4.1.2 The ATG should meet the Þeld veriÞcation tolerance for custody transfer (refer to Section 3.1B.7.3.3), including the effects of installation methods and changes in operating conditions (refer to Section 3.1B.4.3.3).
3.1B.4.4.2 Use of ATGs for Inventory Control Purposes
3.1B.4.4.2.1 The ATG should meet the factory calibration tolerances prior to installation (refer to Section 3.1B.4.3.2).
3.1B.4.4.2.2 The ATG should meet the Þeld veriÞcation tolerance for inventory control (refer to Section 3.1B.7.3.3), including the effects of installation methods and changes in operating conditions.
3.1B.4.4.3 Remote Readout Custody Transfer The remote readout, if used, should meet the requirements of this standard (refer to Section 3.1B.4.6). 3.1B.4.5 INSTALLATION OF ATGs
3.1B.4.5.1 Manufacturer’s Requirements The ATG and the associated electronics should be installed and wired in accordance with the manufacturersÕ instructions, NFPA National Electrical Code and/or local standards.
3.1B.4.5.2 Mounting Location of Ullage-ATGs The mounting location of an ATG may affect its accuracy after installation. The mounting location of the ATG should be such that the ATG may be easily veriÞed by manual gauging from the ofÞcial gauge hatch. For custody transfer accuracy, it is essential that the mounting location should be stable, with minimal vertical move- ment with respect to the tank reference (which is typically the joint where the tank shell and bottom meet). If the datum plate is found to be stable, it may be used to verify the stabil- ity of ATG mounting. The stability of the mounting location is affected by the changes in liquid head, vapor pressure or loading of the roof or gauging platform. For best accuracy, an ullage-ATG should be mounted on a properly supported, slotted (or perforated) still pipe, as illustrated in Figures 1 and 2.
3.1B.4.5.2.1 Top Mounting With a Slotted Still Pipe Figure 1 shows an ullage-ATG mounted on a slotted still pipe supported by tank bottom. Figure 2 shows an ullageATG mounted on a slotted still pipe supported by a bracket. Ullage-ATGs mounted on properly supported slotted still pipes, as illustrated in Figures 1 and 2, deliver higher accu- racy because the slotted still pipe is supported on a stable location and ATG movement is minimized when the tank is Þlled or emptied.
3.1B.4.5.2.2 Top Mounting Without a Slotted Still Pipe Alternatively, an ullage-ATG may be supported on the roof of a Þxed-roof tank or on a ÒgallowsÓ on a Þxed or ßoating roof tank, as illustrated in Figure 3. This kind of mounting may cause the ATG to move vertically when the tank is Þlled or emptied. Ullage-ATGs mounted without slotted still pipes can be used for custody transfer or inventory control if the ATG as installed, can be veriÞed to meet the requirements set forth in Section 3.1B.4.3.4.
3.1B.4.5.2.3 Mounting Without a Slotted Still Pipe for Small Tanks For small (less than 5000 barrels) tanks, an ullage-ATG may be mounted without a slotted still pipe. The Reference Height variation should be measured with the tank full and empty.
3.1B.4.5.3 Mounting Location of Innage-ATGs The gauge head of an innage-ATG may be mounted in any suitable location. The mounting location of the ATG should be such that the ATG may be easily veriÞed by manual gaug- ing from the ofÞcial gauge hatch. The zero point of the measuring element should be mounted at a stable location on the tank bottom that has minimal vertical movement with respect to the bottom corner (which is the joint where the tank shell and bottom meet).
3.1B.4.5.3.1 Mounting Innage-ATGs Innage-ATGs usually do not require still pipes. If an innage-ATG is mounted on a still pipe, it should be slotted. Innage-ATGs should be mounted in accordance with the manufacturerÕs instructions. Refer to Figure 4.
3.1B.4.5.4 Avoiding Turbulence If the measuring element is subjected to excessive turbu- lence, certain types of ATGs may be thrown out of calibra- tion. The ATG should be located away from tank inlets, tank outlets and tank mixers. When this cannot be done, the level detecting element should be protected by means of a slotted still pipe to minimize the effect of turbulence and swirl.API MPMS 3.1B:2001 pdf free download
