Tank storage facilities are often operating close to full storage. Tank maintenance programs are therefor often delayed or minimized to support storage demand. For example, an old tank with a floating roof that needs repairs, exposed to heavy rain combined with partial clogging of the drainpipes can end up with roof sinking and oil spill through the drain. This poses an ever-growing risk of oil spills, in addition to problems of overfill and leaks from related infrastructure. In this situation, automatic or manual failures and errors might result in unnecessary and costly outcome of spills, water contamination and cleanup. Now, when oil price are not low, is the right time to re-evaluate possible consequences from operational risks and have another look at early warning instruments of oil spills and leaks.

FM Class 7745 standard defines a requirement of 30 seconds detection response time of oil leak/spill detection systems. This seems like a quick response, but it refers only to the detection system itself from the time that oil reaches the exact location where the detector is installed. To allow the earliest possible oil spill detection, the selected system should be decided upon after considering the following points:

• The oil spill detector should be installed as close as possible to the spill source.
• The oil spill detector should be installed in a sump to which the spilled oil will reach quickly.
• Sump area should be small to allow significant oil layer formation from a minimal volume of spilled oil.
• Water should be drained from the sump from time to time to allow oil layer formation inside the sump and avoid sump overflow due to water accumulation. Emptying the sump can be done automatically by taking a feedback signal from the oil detection system and closing the drain if oil was detected.
• Select an oil detection system which provides the optimal performance, looking at the following points:
  • Proven field reliability.
  • Ability to detect oil instantly in the sump and not after 15 to 30 seconds.
  • Ability to detect a thin oil layer of 0.5 mm or less to achieve an early alarm, with a second alarm point at a thicker oil layer. Thin- oil layer detection is important especially when the sump overflows during heavy rain. The detection threshold, however, shouldn’t be too low, in order to avoid false alarms caused by a single drop of oil.
  • Ability to provide a continuous indication of the oil layer thickness, thus indicating spill progress rate and severity of the spill.
  • Ability to detect Aromatic and Aliphatic hydrocarbons, in addition to oil emulsion detection, so the same system can be used for different oil products stored in the tank farm.
  • Ability to operate in sumps which can be either dry or contain water.
  • Ability to operate even with floating debris in the sump.
  • Ability to give the same sensitive detection performance also when the water in the sump is turbulent.
  • Ability to follow a large water level change and monitor correctly even if tank dike is full of liquid during extreme circumstances.
  • A system which doesn’t often require maintenance, or factory refurbishments and continues to operate after multiple oil spills without the need to replace consumables and without a special cleaning / resetting procedure. Such additional expenses are accumulating over time beyond the system purchase cost.
  • No sensitivity to water properties, such as level changes, conductivity / salinity, turbidity, and temperature.
  • Ability to operate continuously in 100% humidity and condensation.
  • A system which will not be damaged by lightning surges through the water.
  • A system which will not give a false alarm or miss a true alarm due to rain, fog, mist or ambient temperature and light changes.
  • A system which can operate during winter above an ice layer in the sump.
  • A system that has a comprehensive self-diagnostic.
  • A system which can also indicate that the sump is dry. This can serve as feedback that water was drained from the sump and the drain valve should be closed.
  • A system that, if necessary, can be installed without spare wiring infrastructure in the tanks area.

Leakwise oil-on-water detection and monitoring systems were designed to address all the above issues successfully and are the optimal solution for long term operation.