Ballast Tank & Void Space Monitoring on Tanker Ships
It has been generally recognised that the ballast tanks and the voids between double skin constructed tanker ships is potentially an area where there could be a build up of explosive gases. This is due to the potential of the cargo leaking into these areas and if undetected this will cause the formation of an explosive atmosphere.
It is now the industry accepted practice to install gas detection in these voids and tanks with all new ships now fitted with these systems. It is now common practice to measure for both lighter than air and heavier than air gasses in these areas, thus two sample points per tank are fitted. Additionally, several operating companies insist on measuring for Hydrogen Sulphide and Oxygen depletion in these areas. The number of ballast tanks and voids requiring monitoring vary between the design of the ships, however, there are always several tanks that require gas detection leading to the fitting of Multipoint systems.
Due to the conditions inside these tanks, a sampling system is the only suitable method to monitor for these gases. There is also a problem with water and mud inside the tanks that needs to be taken into consideration in the design of suitable systems.
It is also vital that any system is designed to meet the exacting nature of the shipping industry and meets the relevant shipping standards. Regular maintenance on board ship is not always practicable, so any solution needs to be very reliable with self-correcting mechanisms incorporated into the system as far as possible.
The GMI Seafarer system is specifically designed to meet and exceed all the requirements of the shipping industry and is type approved by TUV and has the MED (marine equipment directive) approval. The system has been designed to meet IACS (International association of classification societies) Unified Requirement UR F43 outline specification. The Seafarer has been designed to meet the unique challenges of void and ballast tank applications therefore it is capable of handling up to four gas sensors (flammable catalytic or infrared sensor, H2S, oxygen plus one other depending on application). The system is capable of drawing samples from up to 32 points and by using a fast flow manifold, cycle times are kept to a minimum.
The Seafarer will alert the operator if any of the pre-set alarm points are exceeded. The alphanumeric display clearly defines the nature and location of the problem enabling corrective action to be taken as quickly as possible. The system autosenses if a sample line becomes blocked and will try to clear it by using the optional blow back system if fitted, otherwise it raises an alarm. Any sample lines that are likely to be underwater, occasionally can be protected from water ingress by the use of the recommended GMI snorkel valve.
GMI recommend the use of the GMI infrared flammable sensor as this is a particularly good option for shipping applications for the following reasons: The GMI infrared sensor is far more stable than traditional gas sensors and therefore the regular calibration periods can be extended. These periods are always based on operational experience, however, experience shows that often periods of one year or better are achievable giving large cost savings due to the reduction of service visits required. Additionally, infrared sensors have expected lifetimes over three times longer than traditional catalytic sensors, thus increasing system availability and reducing the total operating costs over the lifetime of the vessel.
As an ISO 9001 approved company, GMI Ltd’s quality assurance programmes demand the continuous assessment and improvement of all GMI products. Information in this article could thus change without notification and does not constitute a product specification.
Please contact GMI or their representative if you require more details.