Most operators, including all those that Worldwide Turbocharger Guide has spoken with, have a planned maintenance (PM) strategy in place for turbochargers and closely follow original equipment manufacturer (OEM) recommendations, except where experience has shown that some extensions can be justified. Being rotating machines, turbochargers would appear to be ideal territory for condition-based maintenance (CBM) techniques, but of all the operators contacted by Worldwide Turbocharger Guide only one was currently trialling the concept and even then only on auxiliary engines.
None but those operators at the very bottom of the quality scale would contemplate the alternative of a ‘run to failure’ maintenance strategy, although every operator needs to be able to deal with a sudden failure. Freddy Homi Pavri, senior superintendent for technical services at Seaspan Ship Management told Worldwide Turbocharger Guide: “It is essential that turbochargers have a planned maintenance system rather than ‘breakdown maintenance’ because a breakdown in case of a main engine can be a very costly matter, including high-cost spares that are mostly not stocked in warehouses but made to order, damage to casings which will take even longer to procure, the very real danger of fatalities due to the high revolutions and incapacitation on the main engine leading to costly off-hire.”
Mr Pavri’s sentiments were echoed by London-based V Ships. In an emailed response to our questions, the shipmanager detailed additional reasons for ensuring the turbocharger is maintained to the highest condition possible, saying even fairly minor wear can cause a significant drop in performance and hence extra fuel consumption. This also leads to thermal overload of the engine itself with the consequent increase in wear and tear, and hence a further drop in performance and reliability.
V.Ships’ operating and maintenance policy sticks as closely as possible to the maker’s recommendations both for in-service cleaning of turbines and compressors, and for major inspections and overhauls. The company’s PM system is tailored to the needs of the specific equipment fitted, not a generic type. This is essential when operating and maintaining such highly rated equipment. The payback on this is better long-term engine efficiency and lower spares expenditure through the life of the engine.
Maren Schroeder, LPG fleet manager at Exmar Shipmanagement, is another whose company operates a PM strategy for the main and auxiliary engines of all vessels in the company’s fleet. She told Worldwide Turbocharger Guide that the turbochargers are overhauled at every special and intermediate survey, and also if any turbocharger experiences a problem in between.
Mr Pavri also commented on the need for operators and their engineers to ensure that they are fully up to date and aware of any changes in OEM recommendations. “One must also pay attention to any circulars and information from turbocharger makers.” He illustrated this by saying that in early 2013 MAN Diesel & Turbo had sent out a notice for their older generation of NA turbochargers that had grey cast-iron casings. Apparently there was a chance that these could not withstand the load from something such as a rotor failure and might disintegrate causing severe/fatal harm to any personnel in the area. As a precautionary measure, Mr Pavri said that until any such casings could be identified, ship staff had to keep away from the marked hazardous perimeter of this equipment in case failure were to occur.
Similar advice came from the superintendent of a major London-based bulk carrier operator, who said that, as well as information from the turbocharger and enginemakers, there was a steady stream of information from other sources such as protection and indemnity (P&I) clubs, and accident and incident reports. He added that a good safety management system would ensure that these were distributed throughout the fleet both as a reminder to crew of the need to be vigilant and to check that, where specific equipment problems were identified, the appropriate corrective action was applied.
Advice from P&I clubs would seem to be something that should be taken very seriously as many report that turbocharger failure is high on the list of machinery claims. Evidence from the clubs is that most failures occur at between five and 10 years of operation – a period that coincides with the special surveys.
Adopting a CBM strategy is something that a number of operators are considering, although some have said that the regular checks and maintenance their particular system requires might make it an unnecessary extra cost. One operator said they had carried out a trial using vibration tools and measurements which reported the turbocharger to be in good condition and yet, on opening it up for overhaul, its condition was found to be unsatisfactory.
V.Ships said condition monitoring of the turbocharger is advisable as another method of spotting when performance is dropping off or where minor damage has occurred and fast tracking of shut down and repair can save the shipowner the considerable time and expense of major repairs. Although not yet planning its introduction for main engines, another operator (who asked to be kept anonymous) is currently trialling CBM on the auxiliary engines of one or two ships.
Ms Schroeder told Worldwide Turbocharger Guide that this is a less risky trial because most ships have excess power-generating capacity in the auxiliary engines and therefore a turbocharger failure on one auxiliary engine does not carry the same consequences as it would on a main engine. Although the system is collecting data that will prove useful in time, Ms Schroeder said it was too early to comment on the merits of CBM.
Monitoring the condition of a turbocharger need not depend solely on sensors as there are plenty of visual and audible signs that crew can pick up on. As Mr Pavri points out, “Good watchkeeping is essential since many things can go wrong well before the planned maintenance date. Any sign of vibration, however slight, is a big red flag. If the revolutions of a turbocharger differ significantly from its twins, there is a problem. Any abnormal sound from the turbocharger is a big red flag. Essentially, for sound and vibration, it is wisest to stop the engine, blank off the suspect turbocharger and proceed to port.” There is almost never enough time in port for a major overhaul of a turbocharger that requires cleaning and balancing of the rotor, so many companies have one extra rotor for a batch of sister vessels and use that on an exchange basis.
The precaution of blanking off a faulty turbocharger has been a fairly standard procedure over the years and would of course mean a loss of speed. Fortunately for ships that are operating a slow-steaming strategy and which have engines equipped with multiple turbochargers, it may be the case that one turbo has already been fitted with a turbocharger cut-out with swing gate valves. In such cases, that turbocharger can quickly be brought back into service in place of the faulty one.
As part of the OEM recommendations, regular checks are usual on most turbochargers. This would involve inspection of the general condition of the nozzle ring and the turbine blades. In the case of some makes, other checks might also be possible. In a Mitsubishi turbocharger, for example, extraction of the journal and thrust bearings without removal of the rotor is a standard procedure. In case any anomaly is noticed, then this is immediately taken care of.
Under general service conditions, turbocharger maintenance is restricted to keeping the nozzle ring and turbine clean and free of soot. For camshaft engines, a lazily rotating shaft, at say 60 rpm, will not do too much for optimum atomisation. Where the engine is not run at high loads, there will be fouling due to incomplete combustion or poor atomisation of the fuel.
This fouling will deposit on the exhaust manifold grids and on the blades/nozzle ring of the turbocharger, causing a drop in performance and surging of the turbocharger at higher loads. This does not apply to electronically controlled engines because the hydraulic drive for the plunger has a very high pressure with no real relation to the rpm of the engine. Good atomisation and combustion are thus assured. However, fouling cannot be completely eradicated.
If a vessel is slow steaming, there must be frequent inspections of the exhaust-gas receiver and the grids before the turbocharger. Exhaust-gas boilers may also have a coating of soot which drops performance. Hidden soot in the exhaust passages may stay ignored until such time that the engine rpm is rapidly increased for some reason and the soot catches fire. What is used as a fairly effective measure to prevent this, is slowly increasing the engine load to about 75 per cent of MCR power every three days to ‘blow out’ soot deposits before they get a chance to harden and coat the exhaust system.
Modern engine fuels tend to be of lower quality and this requires an increased amount of monitoring of the engine and the turbocharger system. Some operators, V Ships and Exmar are two from those that Worldwide Turbocharger Guide spoke with, either recommend or have had good experience using fuel additives.
Both companies believe the use of fuel treatments can help reduce turbocharger fouling along with certain fuel problems. Ms Schroeder told Worldwide Turbocharger Guide that where Exmar had used fuel additives there was some evidence that the turbocharger had performed better, but this was not the main reason for using the additive in the first place. She said there had been no scientific testing of the effect on the turbocharger but it was something that would be kept under review.
Cleaning of the turbocharger in service is a procedure that must be diligently followed. Mr Pavri said that on ships in the Seaspan fleet, the blades used to be water-washed until a few years ago, but this has now been stopped. He explained that when this was done not only was there a chance of thermal shock on the blades even if hot water was used, but sometimes when the cleaning operation was ignored for a few weeks and then washing carried out, a large clump of soot could get dislodged and imbalance the unit.
Dry washing is carried out now with crushed walnut shells of a suitable size. Even though some makers like Mitsubishi advise that cleaning is okay at even 2,500 rpm, it is preferable to carry this out every three days at the optimum rpm when at 75 per cent load, Mr Pavri said. Other operators also said that they had ceased washing, but water cleaning is still recommended by most turbocharger makers. Effective cleaning will help prevent surging as this phenomenon is mainly due to dirty air intake filters or clogged nozzle rings, although there are other causes such as running too fast in heavy seas when the propeller is often out of the water.
Almost all of the operators questioned said that, on smaller auxiliary engine turbochargers, the frequency of accidents is more than for the larger two-stroke engine turbochargers because there is no grid in place to protect the blades and any foreign object, such as a broken valve piece, can find its way into the system and disintegrate the turbocharger.
The weak link in these systems is the very badly contaminated trunk engine oil that is used as lubrication and which tends to wear down the bearings quickly if not filtered well and purified. Nozzle ring wear is also a common issue and, if the design permits, it can be rotated 120 degrees but, if not, it has to be renewed.
With regard to major overhauls of main engine turbochargers, most of the operators were content to entrust this to turbocharger specialists, with the rotor assembly being taken ashore for ash blasting and re-balancing. Only one operator could point to an instance where problems had occurred after servicing by a specialist and that was due to the method used for re-balancing.
There are several specialists located around the globe, some of whom are approved by the OEM and others independent. Most are well known and have earned a good reputation for work on different makes. The superintendent of the London-based bulk carrier operator did, however, point out that some new models of turbochargers sometimes created problems for the independents. In particular he said that the new generation of ABB turbochargers made use of a cartridge system that must be exchanged and prevents work being done on the rotor. He also said that these turbochargers employed a new bearing type.
In recent months ABB has opened new service centres worldwide and has also just updated its website, giving easier access to some useful technical information and service options such as the customer exchange programme.
On the matter of spares, Seaspan’s Mr Pavri said consideration is needed to ensure availability. If one has to source spares with enough time in hand, then there is a good chance of being able to get them by the desired date. However, if there is a breakdown and the model is an older one, it would take a lot of effort to first find the spare, have it shipped to a workshop, checked for defects and finally sent on board. Even for models in use, there is always a delivery period after order, sometimes up to eight working weeks. WTG