Content Gauging System for Seawater displaced Fuel Oil Tanks onboard British Naval Destroyers

Replacement of original equipment and enhanced display / reporting capabilities. System to incorporate additional Tanks which were to be converted to Seawater displaced type.

Reliable Tank gauging on any ship especially a Naval Vessel is essential. When that gauging system is monitoring the content of tanks needing to be controlled within certain limits to maintain trim and hence sailing characteristics, reliability and performance become vital. The equipment originally fitted to the Frigates in question was technologically outmoded, proving unreliable, and expensive / difficult to maintain. The quality of information it provided was also of limited value. In practice Ships staff were having to rely upon manual readings by checking discharge from petcocks on each of the tanks, a hazardous, time consuming, and, what should have been unnecessary process. PSM were initially invited to survey the installation and propose a solution based upon current instrumentation practice. Following this a specifically constructed differential pressure transmitter was proposed and subsequently fitted to all "end bays" across all ships in the fleet. The end bay was considered most critical to avoid inadvertent discharge of emulsion into the Sea during refilling. After an extended successful trial period a contract was awarded to equip all of the bays on all ships in the fleet. This contract also included for a complete distributed data acquisition and monitoring package to monitor and display tank information from both the original and newly converted Seawater displaced fuel oil tanks.

Click here for  an illustration of the sensor design and principle of operation. The measurement principle of Diaphragm / LVDT is proven in countless thousands of liquid level monitoring duties and is renowned for its combination of sensitivity, reliability, and ruggedness.

• Special constructional materials were used and earthing constraints were imposed to prevent corrosion of the ships Hull due to galvanic action.
• The entire "in Tank" installation was engineered to make use of original fitting points making replacement a simple "bolt for bolt" operation
• Placing the DP sensor and reference chamber within the Tank itself eliminated one of the fundamental issues with the original sensor, which was externally mounted above the tank. With the original it often occurred that the Seawater primed reference lines would become contaminated with oil resulting in an immediate loss of calibration. The internal arrangement of the PSM system is entirely self-replenishing.

The data Acquisition system comprises of two main units which receive the DP transmitters level signal and process this to calculate the current volume of oil in each tank. This is both displayed locally, and transmitted via an RS485 data bus to remote display modules sited throughout the ship. The system has facilities for keying in the SG value of whatever oil is in use.