Turbochargers are the most high-technology engine component on board ship. Regularly, impeller blades of a medium sized turbocharger rotate at as much as 400 revolutions per second. The outer edges of the rotor blades thereby move at 1.5 times the speed of sound.
In the process, the turbocharger digests contaminated exhaust gases of up to 700° C. Thus, the turbocharger is a very sensitive piece of high-speed machinery, continuously serving in harsh conditions and under extremely high strain. Being on the receiving end of gas flows, turbocharger damage is many times caused by the failure of various upstream components.
As shipowners and ship managers are aware, damage to main engine and auxiliary engine turbochargers have a significant impact on the vessel's ability to trade. Damage can lead to costly repairs, significant reductions in speed while at sea and can be a significant safety hazard.
These damages are costly to shipowners and ship managers as well as underwriters. For ships insured for Hull and Machinery between 1996 and 2001, there have been 192 incidents of turbocharger damage with total gross claims of USD 24.7 million. Taking into account deductibles, these turbocharger damages have cost shipowners and ship managers in excess of USD 25 million. Additional costs are accrued by shipowners and ship managers for turbocharger damage that falls below the deductible levels.
ABB TPL Turbocharger
Some major contributors to turbocharger breakdowns:
Late maintenance and overhauls
In many cases, the service life of major components is disregarded. Not only bearings, but also compressor wheels and turbine blades/discs can have service life limitations. Compressor wheels, for instance, can be limited to between 50,000 and 100,000 work-hours depending upon the use and configuration. This is equivalent to 7.5 to 15 years of use between exchange intervals. Due to operational and economic constraints, overhauls are sometimes postponed until dry-docking rather than overhauling while the ship is in service.
Sometimes, obvious signals indicating that there are problems are disregarded. Surging of the turbocharger can point to a clogged air cooler or fouled nozzle ring. Continued surging at full load might, by the way, cause breakdown. Further, rising exhaust gas temperatures may indicate that an inspection with service is required.
Pirate parts used in place of manufacturer's parts
To reduce the costs of maintenance and parts, owners will use "pirate" or "alternative source" parts in place of manufacturer's parts. Due to the rough service environment of a turbocharger, inferior quality parts with slight discrepancies in material, design and dimensions can easily lead to damage.
Maintenance not performed by manufacturer
Maintenance costs for turbochargers can be significant. Maintenance by the crew, shipyard personnel, or other personnel not qualified by the manufacturer to perform such servicing, can lead to improper maintenance and servicing. Here are a few examples of small mistakes that can eventually lead to total breakdown:
- Failure to observe the right fitting sequence may pre-damage components.
- Failure to exchange key wear parts may lead to loss of functionality, for instance to loss of bearing lubrication.
- Failure to observe the correct clearances of the assembly and to adjust the right true run of rotors may lead to rubbing of the rotor with consequential imbalance.
- Improper cleaning of cover rings can lead to blade rubbing and consequent blade failure when installing overhauled rotors.
- Lack of or improper balancing of a rotor may damage bearings (due to high speed tolerances are extremely low).
Missing service letters
When there is a change of ownership of a vessel, the service letters and logbooks for the turbocharger (as well as other critical pieces of machinery and equipment) can be missing. This break in information does not allow the new owners or ship managers the opportunity to assess the maintenance and services needs of the turbochargers.
Depending upon the ship's trade and operation, engines and turbochargers are sometimes specified for "slow steaming". When greater load demands are again made on such equipment, some components may need to be replaced to match the new operating conditions. If disregarded, the result may be operational problems and/or reduced life cycle of the rotating parts of the turbocharger due to elevated speed.
Actual turbocharger not appropriately matched to engine
During vessel construction, turbochargers are rated for specified operating conditions. Engine conversions and changes to increase the power output put a greater load demand on the turbocharger and thus reduce the reliability and service time of turbocharger turbine wheel, compressor wheel and bearings.
Upstream maintenance resulting in damage to the turbocharger
In many cases, damage to turbochargers may occur when maintenance has been conducted on other machinery components or systems upstream of the turbocharger. Since the turbocharger is downstream of most other engine machinery, any foreign objects, loose parts, forgotten equipment or pieces of machinery equipment that may have not been properly reassembled may eventually move downstream to damage the turbocharger. Such items include loose bolts, injection nozzle fragments, compensator bellow bits, welding electrode stumps, wrenches and screwdrivers, rags or any other foreign objects. Due to the extreme service speed of a turbocharger, even minute particles may damage vital parts and lead to severe damage.
Improper operation and maintenance by the crew
Improper maintenance and operation by the crew can lead to damage to the turbocharger. The following is a list of some of the types of causes and events that can lead to more serious damage:
Dirt on compressor and turbine blades -
Improperly implemented or neglected washing routines can let dirt accumulate on both compressor and turbine blades. This will lead to imbalances in the rotor and consequentially it can cause bearing damage and even total breakdown.
Improper lubricating oil -
The use of lubricating oils not recommended by the manufacturer, or contaminated oil, can lead to reduced performance and eventual damage to the bearings.
Improper cleaning and maintenance of filtration rings -
The intake air quality can be affected when air filters are not properly cleaned and/or changed. A clogged filter may lead to surging. In some cases, it has been observed that the crew, to keep from having to maintain and clean the filters, have removed the filtration rings.
Turbocharger over-speed -
Due to incorrect maintenance or operational activities, turbochargers are in some cases over-sped. When continuously over-sped by only a few percent, turbocharger components are quickly damaged and their service life is reduced. An over-speed of 30-40 per cent very likely blows up the turbocharger instantly.
- Only qualified manufacturer-approved maintenance personnel should perform maintenance to turbochargers. In most cases, the most qualified to perform maintenance and overhauls are the manufacturers themselves, where repairs can be performed while the ship is in service or at dry-dock. Some companies and shipyards are willing to perform turbocharger maintenance and overhaul at a "cheaper" cost than the manufacturer. Although these reduced costs may be attractive to shipowners and ship managers, they may represent a false economy if damage occurs due to inadequate maintenance - this can, in the end, be very costly to the owner and/or underwriter. When qualified personnel perform the work, workmanship is normally under warranty.
- Use the correct manufacturer's replacement parts. The turbocharger is a highly loaded, high technology engine component. Therefore, it is imperative to maintain and overhaul it with the correct parts. As with the maintenance work, the parts will also normally be under warranty.
- Ensure that proper records are obtained and turbocharger service documents and letters kept. This is to ensure that proper maintenance and service can be scheduled. In cases where the service documents and letters are not available upon sale of the ship, the equipment manufacturer can often help with proper documentation and sometimes even with the turbocharger service history.
- Operate the turbocharger within the operational design parameters. Damage incurred due to improper use can be very costly by leading to operation at reduced speed, or a total breakdown of the turbocharger, loss of hire due to the need for maintenance and repair. Therefore, important parameters such as turbocharger speed and exhaust gas temperatures should be routinely monitored and if possible used as input to trigger alarms.
- Ensure proper care and maintenance of the turbocharger. Turbocharger care and maintenance are required at regular intervals and should be in accordance with the manufacturer's recommendations. If in doubt, contact the equipment manufacturer for information on component service life. Proper care and maintenance include:
- Water cleaning of compressors and turbines to remove dirt and other residual material from the rotor to ensure proper balance.
- Regular cleaning and changing of air intake filters to prevent foreign objects entering and dirt and residue build-up on the rotor blades. Furthermore, contamination of air intake filters results in a higher inlet restriction and may cause turbocharger overspeed or surging.
- In case of turbocharger separate lubricating system: regular changing of lubricating oil (consult manual for approved oil) and cleaning of centrifuges as well as filters.
- Regular inspection of turbocharger parameters while in operation.
We thank ABB Turbo Systems Ltd of Baden, Switzerland and the turbocharger service station in Oslo, Norway for providing valuable information on which this article is based.