Turbochargers: Procedures for Safety and Care

Turbochargers are among the most advanced engine components of an onboard ship. The impeller blades of a medium sized turbocharger commonly rotate at speeds up to 400 revolutions per second, and the outer edges of the rotor blades therefore move at more than one and a half times the speed of sound. As turbochargers are critical components, it is important that proper procedures for safety and cleaning are always adhered to. In this blog, we will discuss the best practices for safety and turbocharger overhaul & cleaning.

Great care should be taken during the operation and maintenance of turbochargers. In terms of safety, it is critical to avoid the build up of fuel, cylinder oil, or lubricating oil in the exhaust trunking ahead of the turbochargers. If these are allowed to build up, it could result in combustion happening in the exhaust manifold. Under these conditions, the increase in the quantity of gas available to the turbocharger can result in dangerous overspeeding, wherein the engine is allowed or forced to turn faster than its design limits permit. The condition that most commonly leads to this is long periods of slow steaming. Slow steaming is a process of intentionally reducing the speed of the engine to reduce fuel consumption and emissions. In slow steaming, a ship will travel at speeds between 12 and 19 knots, rather than the normal 20 to 24 knots, resulting in lower engine power and fuel consumption.

Should your vessel be involved in extended periods of slow steaming (greater than 24 hours), the relevant entities should be notified and the following precautions should be taking at the appropriate intervals:

Subject to the permission of the deck officer, the main engine RPM should be gradually increased to the normal operating maximum for approximately 30 minutes.
Prior to the increase of the engine RPM, the exhaust trunking should be drained of any excess fuel, cylinder oil, and lubricant oil.
Sudden increases in inlet and exhaust gas temperature or RPM should be countered immediately, ideally by stopping or reducing the RPM to a minimum of the main engine.

When it comes to overhauls, it is never a good idea to extend far beyond the manufacturer’s recommended overhaul periods. In turbochargers that use ball or roller bearings, the overhaul period will generally be dictated by the need to change these bearings per manufacturer instructions. However, at each overhaul, all of the following should be done by an engineer:

Cleaning and inspection of all relevant parts and components.
Changing of bearings.
Changing of oil and lubricating oil pumps.
Balancing of rotor assembly.
Checking of the intake grid’s integrity.
Checking for erosion or cracks on the nozzle ring.
Ultrasonic testing of the casings, especially at the cooling water inlet.
Checking and re-securing of the silencer (if deemed necessary).
Cleaning of the air filter elements.
Inspection of bearing housings.
Measuring and recording of impeller, bearing, thrust, and seal clearances.

In order to ensure top performance, the turbocharger should be cleaned in accordance to manufacturer guidelines. This typically involves washing the compressor side with water or washing the turbine side with a combination of water and dry washing. Note that the washing process of the compressor side can leave deposits on the air cooler lines and therefore should be followed by cleaning of the cooler lines.

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