API MPMS 3.1B pdf 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 requireshigh accuracy.The use of ATGs for inventory control pur-poses often permits a lower degree of accuracy.
3.1B.4.4.1 Use of ATGs for Custody Transfer
3.1B.188.8.131.52 The ATG should meet the factory calibratioantolerances prior to installation (refer to Section 3.1B.4.3.2).
3.1B.184.108.40.206The ATG should mcet the ficld verificationtolerance for custoy transfer (refer to Section 3.1B.7.3.3),including the effects of installation methods and changes inoperating conditions (refcr to Section 3.1B.4.3.3).
3.1B.4.4.2Use of ATGs for Inventory Control
3.1B.220.127.116.11 The ATG should meet the factory calibrationtolerances prior to installation (refer to Section 3.1B.4.3.2).
3.1B.18.104.22.168The ATG should mcet the ficld werificationtolerance for inventory control (refer to Section 3.1B.7.3.3).including the effects of installation methos and changes inopcrating conditions.
3.1B.4.4.3 Remote Readout Custody Transfer
The remote readout, if used, should meet the requirementsof this standard (refer to Section 3.1B.4.6).
3.1B.4.5INSTALLATION 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 manufacturers’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 accuracyafter installatioan.The mounting location of the ATG should
be such that theATG may be easily verified by manual gaug-ing from the official gauge hatch.
For custody transfer accuracy, it is essential that the mount-ing location should be stable,with minimal vertical move-
ment with respect to the tank reference (which is typically thejoint where the tank shell and bottom mect). If thc datumplate 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 thechanges in liquid head, vapor pressure or loading of the roofor gauging platform.
For best accuracy, an ullage-ATG should be mounted on aproperly supported, slotted (or perforatedy still pipe, as illus-trated in Figures 1 and 2.
3.1B.22.214.171.124Top Mounting With a Slotted Still PipeFigure 1 shows an ullage-ATG mounted on a slotted stillpipe supported by tank bottom. Figure 2 shows an ullage-ATG mounted on a slottcd still pipe supportcd by a bracket.Ullage-ATGs mounted on properly supported slotted stillpipes, as illustrated in Figures 1 and 2, deliver higher accu-racy because the slotted still pipe is supported on a stablelocation and ATG movement is minimized when the tank isfilled or emptied.
3.1B.126.96.36.199Top Mounting Without a Slotted Still
Alternatively, an ullage-ATG may be supported on the roofof a fixed-roof tank or on a “gallows” on a fixed or floatingroof tank,as illustrated in Figure 3.This kind of mountingmay cause the ATG to move vertically when the tank is filledor emptied. Ullage-ATGs mounted without slotted still pipescan b used for custody transfer or inventory control if theATG as installed, can be verified to meet the requirements setforth in Section 3.1B.4.3.4.
3.1B.188.8.131.52 Mounting Without a Slotted Still Pipe
for Small Tanks
For small (less than 5000 barrels) tanks. an ullage-ATGmay be mounted without a slotted still pipe.The ReferenceHeight variation should be measured with the tank full andempty.
3.1B.4.5.3 Mounting Location of lnnage-ATGsThe gauge head of an innage-ATG may be mounted in anysuitable location.The mounting location of the ATG shouldbe such that the ATG may be easily verified by manual gaug-ing from the official gauge hatch.
The zero point of the measuring element should bemounted at a stable location on the tank bottom that has mini-mal vertical movement with respect to the bottom corner( which is the joint where the tank shell and bottom meet).3.1B.184.108.40.206 Mounting lnnage-ATGs
Innage-ATGs usually do not require still pipes.If aninnage-ATG is mounted on a still pipe, it should be slotted.Innage-ATGs should be mountedi in accordance with thcmanufacturer”s instructions.Refer to Figure 4.
3.1B.4.5.4 Avoiding Turbulence
lf the measuring clement 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,tankoutlets and tank mixers. When this cannot bc done, the leveldetecting element should be protected by means of a slottedstill pipe to minimize the effect of turbulence and swirl.