API MPMS 3.1B:2001 pdf download

API MPMS 3.1B:2001 pdf download.Manual of Petroleum Measurement Standard Chapter 3- -Tank Gauging Section 1B- Standard Practice for Level Measurement of Liquid Hydrocarbons in Stationary Tanks by Automatic Tank Gauging.
3.18.6 Initial Setting of ATGs in the Field
3.IB.6.1 ULLAGE.BASED ATGS
a. With the tank contenLs static at a kvel between one third and two thirds full. record the stable ATG reading betore the gauger atmes at the tank. Ako record the ATG reading inunediately before making the manual reference measurements. Check whether the presence of the gauger on the tank top aflects the ATG reading. If the ATCJ reading varies by more than I mm (1116 inch). investigate the cause and evaluate the impact before proceeding.
b. Measure the tank Reference Height at the oIllcial gauging recess position until three consecutive measurements agree within a range of I mm (lila inch) or live consecutive Incasurernenis agree within a range of 3 mm (/ inch. Calctilate the arithmetic average value fur Reference Height (i.e. the average of the consecutive measurements) and compare with the calibration Relerence Height. If the measured and calibration Reference Heights differ by more than 2 mm (h/s mclii, then dilliculties may be espcnenced with the initial verification procedure. Investigate the cause before proceeding.
Nsc: This is not an inconsistency with oilier paragraphs. hut ,s ncc cw.wy to stay ss ithin the permissible tolerance.
c. Determine the reference manual ullage measurement of the tank contents from the same gauging access point (using the same measurement tape and weight i until three consecutise measurements agree within a range of I mm (1/16 inch) or livc consecutive measurements agree within a range of 4 mm inch. Calculate the arithmetic average value of the ullage measurement (i.e.. the average of the consecutive mcaureitlents I.
d. Determine the equivalent innage measurement by subtracting the average manual ullage measurement from the average measured tank Reference Height.
c. Record the ATh reading immediately after making the manual reference measurements and continn that no change has occurred during the manual gauging. If the ATG reading has changed from that recorded during Step a. check that there has been no transter either to or from the tank and that the tank valves are closed. Repeat the procedure from Step a.
f. Conipare the ATO reading with the calculated equivalent innage measurement. If the two do not agree (within the resoluuon of the AIG i. set the ATG so that it reati’. the same as the equivalent innage measurement.
3.1 8.6.2 INNAGE-BASED ATGS
a. With the tank contents static at a level between one third and two thirds full, record the stable A reading hctore the gauger arnves at the tank, Also record the ATG reading immediately before making the manual reference measurements. Check whether the presence of the gauger on the tank top affects the ATG reading. If the ATG reading vanes by more than 1 mm (h116 incht, inves*igate the cause and evaluate the impact before proceeding.
b. L)eterminc the level of the tank contents b reference manual innage measurements until three consecutive measurements agree within a range of I nun (1116 inch or live consecutive measurements agree within a range of 4 mni inch).
c. Calculate the arithmetic average value of the innage meatsurenlent (i.e.. the average of the consecutive measurements obtained in Step b.
d. Record the ATG reading immediately after making the manual reference innage measurements and confirm that no change has occurred during the manual gauging. If the ATG reading has changed from that recorded during Step a. check that there has been no transfer either to or front the tank and that the tank valves axe closed. Repeat the pencedure from Step a.
e. Compare the ATG reading with the average manual reference mnagc measurement. If the two do not agree (within the resolution of the ATG). set the ATCI so that it reads the same as the average manual reference itulage measUrement.
3.18.7 Initial Verification
3.1 B.7.1 INTRODUCTION
Ullage-based ATGs arc designed to measure the distance from the ATG reterence point to the liquid surface. Some types of ullage•based ATG may be able to compensate for tank reference datum movement I where such movement has been quantified and found to be repeatable). but most tradilionai types of ullage based ATG cannot compensate 11w many of the .ixuracy limitations of tank level measurement described in Section 3.1 B.4.3 of this standard
lnnage.based ATGs are designed to mcasure the liquid innage directly. They should be less prone to some of the tank stability problems that can cause level measurement errors with ullage-based ATOs. but they require the tank innage datum to be stable.