Problems caused by oil in boiler feed water system
01 NOV 2003
Industry statistics indicate that breakdowns can occur in a steam system. There have been cases reported to Gard Services whereby oil contaminated boiler feed water has caused the total breakdown of boilers. This article outlines the problem of oil contamination in the boiler feed water system.
Oil leakages can start as a result of minor cracks in HFO heating coils or in different heaters in the engine room, or in other places where steam is used for heating. In a complex engine room today there are several possibilities for oil leakage to occur. Thin layers of oil are not always visible. Experience shows that 15-20 ppm (parts per million) oil pollution will not be visible. With a boiler capacity of 20 tons of steam per hour and with 25-ppm oil pollution, approximately 12 kg of oil will accumulate in the steam drum each day. Thin layers of oil at the boiler tubes or any of the directly heated surfaces of the boiler might cause local overheating of the material and possible damage to the boiler.
There are many ways to prevent the entry of oil-contaminated feed water into the boilers, such as the use of observation tanks with detection-filter systems in hotwell tanks.
The vessel was equipped with one auxiliary boiler, one exhaust boiler and with a constantly-running circulating pump from auxiliary to exhaust boiler. Since this was a bulk carrier, the steam system was only for heating HFO and for the purifier system. During a routine inspection one of the engineers discovered excessive amounts of HFO in the observation tank and in the hotwell. Due to earlier problems with the detection system in the observation tank, no alarm was given (it had been disconnected a long time ago).
The engineer immediately stopped the auxiliary boiler and the circulating pump for the exhaust boiler. During inspection it was discovered that the feed water system was completely polluted by oil. As the circulating pump was running this also included the exhaust boiler. The investigation also revealed a feed water leakage into the flame chamber, since the wall panel in the auxiliary boiler was cracked, and some pin tubes were broken/melted due to local overheating. Because all the heating systems had to be shut down, the main engine fuel supply had to be changed over from HFO to DO (diesel oil).
There should also have been a better inspection during the yard work.
If the heating coils had been mounted properly with pipe clamps, possibly there would have been no incident at all.
Gard News is published quarterly by Gard Services AS, Arendal, Norway.
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