Expulsion from the Safety Valve of Drum Due to Blockage of Boiler Superheater Needle Valve

What happened

After entering dock and completing Docking work, the ship sailed out for sea trials.
While carrying out ballasting (operation of 2 cargo pumps) and after repeatedly increasing and decreasing the main engine speed for about 2.5 hours, the main engine speed was set to 50 rpm. At this time, the boiler was operated with AS-22 x 3 units at oil pressure 17kg/cm2. By an order from the bridge, the speed was increased to 55 rpm. Due to a rise of boiler load, the burner ignited. Immedi- ately afterward, the oil pressure increased to 20kg/cm2, the #2 boiler drum pressure rapidly increased, and finally resulted in expulsion from the safety valve of drum.
The main engine speed was immediately reduced and anchor was let go for safety reasons.
The following day, with assistance from the dock workers, various inspections were carried out to as- certain the cause of this breakdown. As blockage of the #2 boiler superheater needle valve was assumed, this boiler was stopped and overhaul inspection of the needle valve was carried out. Investiga- tion revealed that the superheater hand hole plug was caught which caused blockage.

Causes

The hand hole plug which was left inside the superheater header was pushed toward the needle valve due to the flow of steam during operation. This caused blockage of the valve.

Corrective actions

The later half of the docking period becomes very busy and there always seem to be a shortage of workers. As work continues late into the night, sufficient wariness is required.
Proper control and double ckeck from the ship’s crew side is essential to avoid such mistakes.