API MPMS 2.8B:1995 (R2014)

Scope and Field of Application This recommended practice is intended as a guide for establishing reference gauge heights during calibration of marine tank vessels. In many cases this calibration is carried out by shipyard engineers who may not be fully familiar with petroleum measurement requirements nor the use of such measurements by petroleum inspectors and tanker operating personnel. This procedure is also for recalibration of vessels. The importance of establishing an accurate reference gauge height for tanks on marine tank vessels cannot be overstressed. Such tanks are generally calibrated in ullages (outages) whereas in measuring quantities remaining onboard (ROB) or free water, it is frequently more convenient and accurate to measure innages. The reference gauge height is a necessity in converting ullage to innage. Also, in determining the volume of the ROB, the reference gauge height is a factor in every wedge formula, for the establishment of wedge tables. API MPMS Chapters 2.7 and 2.8A provide three methods of calibrating the volumes of tanks on marine tank vessels: calibration by linear measurement, liquid calibration, and calibration from vessel drawings. The measurement and establishment of the reference gauge height, however, can only be determined by direct linear measurement.