201261 Incorrect connections on boiler clogged the economiser

When the exhaust gas boiler on one of our vessels was opened up for inspection and survey in drydock, it was noticed that the smoke space within the water tube nest was badly choked and heavily encrusted with hard residue. The cleaning operation required much time and effort.
On further investigation, it was discovered that the hard residue was leaked fuel oil that had been carried over from the auxiliary boiler’s furnace. The problem was finally traced to an inadvertent mix-up in the three flexible fuel pipe connections on the burner unit along with their associated solenoid valves; i.e. high pressure, low pressure and circulating fuel lines. It was noticed that the low pressure and circulating fuel lines had been interchanged some time in the past. While there was no apparent problem in the subsequent operation of the boiler, unknown to the crew, a substantial quantity of circulating fuel oil continued to flow through the low pressure nozzle even when the flame was off. Over time, much of this unburnt fuel was carried up the uptakes, coating the internal surfaces of the economiser.

Lessons learnt
All pipes and couplings must be appropriately tagged so that they cannot be wrongly connected.