Oil in feedwater

Beware of fuel oil in the marine steam boilers feedwater system

The marine steam boilers on board in ships nowadays have become a less evident part of the engine room than they were in the old days. However, the marine steam boilers are still important parts of the system, especially if the main engines are running on heavy fuel oil that need to be heated. I don’t want to go through the entire instruction book for the marine boiler but just point out one important matter.

As we all know, a very thin layer of oil on the surface of the boiler tubes or any of the direct heated surfaces of a boiler might cause local overheating of the material and possible damage to the boiler. What we maybe not know is how very small quantity of oil it requires to get a dangerous situation. A tube break in a fuel oil heat exchanger is very easy to detect, a simple detector in the hotwell will manage that, but a small crack in a tube may cause you an even more serious problem.
A tiny oil leakage giving some 15 to 25 ppm of oil in the boiler feedwater would not be visible; the water is still limpid. Yet this apparently insignificant oil pollution might causes sever danger to the boiler. If a boiler has a capacity of 20 tons of steam per hour at full load and the feed water is polluted with 25 ppm of oil, then it will accumulate approximately 12 kg oil in the steam drum per day. A bucket of oil in the boiler every day; I suggest that you buy yourself a sensitive oil detector.
It will cost you, but it might save you from some future cost of repairs.

N.B. ppm = parts per million.
1 ppm = 1 kg per 1000 metric tons.

An oily ring inside the water gauge glasses at the water level is a serious warning.