With reference to chemical tankers:

Sketch: The cargo pumping system consists of a cargo pump (a centrifugal or positive-displacement pump) in each cargo tank (or a deep-well pump), connected to the cargo piping (a main cargo line and a stripping line). The system includes:

• The cargo tanks, each with a suction line to the cargo pump.
• The cargo pump (e.g. a deep-well centrifugal pump or a hydraulic-driven pump) that discharges the cargo through the cargo line to the manifold (the loading/discharge connection).
• A stripping system (a stripping pump or an eductor) to remove the last of the cargo (the residue) from the tank, so that the tank is stripped down.
• Valves (cargo valves, isolating valves, non-return valves) and the manifold.
• The direction of fluid flow: from the tank suction, through the pump, to the manifold (discharge), and during loading, from the manifold through the line to the tank.
• The system is designed for the chemical cargoes (corrosion-resistant materials, suitable seals, and the ability to handle the specific cargo).

• The cargo quantity (the volume/level in each tank, the ullage, the temperature, and the density) for the cargo calculation.
• The cargo type and the properties (the chemical, its hazards, the IBC Code requirements).
• The pump operation (the pump speed, the discharge pressure, the flow rate).
• The tank level/ullage and the cargo temperature during loading/discharge.
• The stripping operation (the residue quantity).
• The cargo handling records (the loading/discharge plan, the times, the quantities, the tank cleaning).
• The safety records (the gas monitoring, the inerting, the tank atmosphere).
• The records are kept in the cargo log and the relevant records (e.g. the Oil Record Book for oil cargoes, or the cargo records for chemicals).

The oil monitoring system (the ODMCS - Oil Discharge Monitoring and Control System, or the oil content monitor) on a tanker faces difficulties:

• The oil-in-water content measurement can be affected by the type of oil, the emulsion, the temperature, and the presence of other substances (e.g. chemicals, solids), giving inaccurate readings.
• The sensor (e.g. an optical or ultrasonic sensor) can be fouled by oil, sludge or scale, reducing its accuracy.
• The calibration can drift, and the system must be calibrated regularly.
• The flow rate and the discharge conditions can affect the measurement.
• The system must be maintained and the sample line kept clean; a blocked or contaminated sample line gives false readings.
• The system must be operated correctly (the sample taken at the right point, the flow controlled) to give a reliable reading.
• The automatic stopping device and the alarm must operate correctly to prevent an over-limit discharge.

These difficulties can lead to inaccurate monitoring, the risk of an over-limit discharge, and non-compliance, so the system must be maintained, calibrated and operated correctly.