API MPMS 2.8B:1995(R2005) pdf download.Manual of Petroleum Measurement Standards Chapter 2—Tank Calibration
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 oper- ating 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 conve- nient 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 establish- ment 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.
Prior to entering any compartment, permission must be obtained from the vessel’s master, senior deck officer, autho- rized shipyard official, or other responsible person in charge. This responsible person should be able to supply information regarding particular materials and conditions or the appli- cable Material Safety Data Sheet. Before entering the compartment, a valid marine chemist’s certificate must be obtained indicating that the compartment is “Safe for Workers” and/or “Safe for Hot Work,” as prescribed in National Fire Protection Association 306, Control of Gas Hazards on Vessels. Regulations of the U.S. Coast Guard, the Occupational Safety and Health Administration (OSHA), or other international, federal, state, or local regulations may also apply. Such testing must be made at least every 24 hours or more often when changing conditions warrant. When entering a compartment, another person should stand watch at the compartment entrance for the duration of such entry to sound an alarm should an emergency occur. Normal safety precautions with respect to staging and ladders are to be observed.However, if a swash bulkhead or transverse web frame is fitted at the mid length of the tank, the reference gauge point must be sufficiently forward of the mid length so that the zero gauge point clears the swash bulkhead or web frame at the bottom under the normal direction of maximum trim. This location will permit obtaining an ullage for a quick close approximation of tank content volume without the necessity of applying a trim correction. For complete accuracy, a trim correction is necessary inasmuch as the gauge point has been displaced longitudinally from the geometric tank center. The secondary reference gauge point or points on a vessel tank should be located at the aft and/or forward end of the tank, depending on the varying operating trim conditions. Note: In the course of normal operations involving a barge that operates with trim by the bow and stern, the primary gauge point at the geometric center is not required since secondary gauge points are required at both forward and aft locations.