Condition based maintenance (CBM) for engines
Until the steam age, every piece of equipment on ships was powered by manual labour. The only data collected was navigational taken from sextant and compass readings, speed measured with a log line and in shallow water the depth read from a lead line. Once steam engines appeared, records of when they were use, boiler pressure, revolutions, coal and lubricating oil consumption began to be made. If a ship was time chartered, consumption figures were important as was the need to estimate quantity needed between bunkering. Record keeping was mostly at the discretion of the shipowner and perhaps the insurers.
At some point in time, the record keeping was formalised and some is now mandatory although engine room logs are not needed to be kept for as long a period as the ship’s main log book. Depending upon the shipping company concerned, the extent of what records are required can be extensive. As a ship ages and passes into the hands of less diligent owners, the quality and extent of record keeping inevitably diminishes.
Recording what goes on in the engine
Until the advent of the computer age, engine record keeping was limited to reading the dials and gauges indicating pressure, temperature and rpm at various locations on the engine, turbocharger, exhaust and cooling systems of main and auxiliary engines. In addition there were other records connected with manually crankshaft deflections, lube and fuel consumption and tank ullages, maintenance and repairs. Readings would normally be taken and recorded at the end of each four-hour watch period.
On a modern ship, the readings are still displayed at the various locations on the engine or a control panel but are much more likely to be digital displays rather than analogue and they are also duplicated in the main engine control room where they can be stored electronically.
The data on a modern ship is generated from sensors mounted inside the engine or equipment and as well as temperature and pressure, vibration is also closely monitored as it is the best way to identify wear and time to failure.
Both manual and electronic methods allow for trends to be detected but with a manual system that has to be done by way of laboriously produced plotted graphs whereas an electronic system can display or print them at the touch of a button. Exactly what use is made of the data collected is mostly for the shipowner to decide. In the event of an incident, official investigators, the insurer or average adjuster will be keen to have access to data to carry out investigations.
Making use of the data collected
Collecting information is one thing but even on the most sophisticated engines it is only recently that using it for maintenance purposes has become common. On poorly run vessels maintenance as with record keeping is haphazard and more repairs than maintenance is the norm.
On the vast majority of ships in the world fleet, maintenance is carried out as planned or preventive in accordance with OEM recommendations based on running hours. This has served well for decades but is time consuming and can be expensive when perfectly serviceable parts are replaced with new. Furthermore, it is not unknown for replacement parts to be installed incorrectly leading to early failure or worse.
Around the turn of the century, the two leading engine makers Wärtsilä and MAN B&W began talking of remote diagnostic services for their products. This was an extension of the services offered to shore-based customers such as power generators where it was not unusual for the engine maker to take full responsibility for running, maintaining and repairing the engine including providing on site personnel. Today most engine makers offer similar services.
The advent of electronic engines has made this possible with for example MAN Diesel and Turbo having delivered all engines from 2000 onwards with an integrated data interface. The interface can be upgraded to complete local systems for engine monitoring, called CoCoS EDS. If online access is facilitated via this data interface, all engine and turbocharger operating data can be made available to MAN’s specialists for analysis. Exactly how many marine engines are monitored is open to question as none of the makers will reveal the information. Wärtsilä does say that some 24GW of power is covered by around 600 contracts but this also includes shore-based engines.
However it is carried out, diagnostics permit the move to condition-based maintenance (CBM) in place of the previous preventive method. Instead of servicing according to hours run, the data from the sensors (and lube oils analysis) is used to determine the condition of the engine and key components. It therefore allows consumable spares such as rings and bearings to be used until their condition deteriorates beyond a certain point.
The advantages of condition based maintenance
The benefits of CBM have been well publicised and few could argue that fewer openings of the engine to replace components that are still serviceable is not a good thing. The older method was designed to protect the engine from sudden failure but assumptions about wear were always based on worse case scenarios. An engine that has been run hard for all of the allotted hours would likely be in a worse condition than one treated more gently.
The added advantage of CBM is that predictions about component wear or failure can be based on using data from the whole set of engines of the same type. Furthermore, if the monitoring and diagnostics is being done by the OEM or a third party, the pool of engines from which data is gathered can be much larger than from just the fleet of a single owner.
There are however caveats to consider in the field of two-stroke engines which are most usually made under licence. The licensees can and do introduce changes to original specifications so that apparently identical engines are built to different specifications and with components sourced from differing manufacturers.
A key element of successful CBM is that there must be engineers on board or ashore who can interpret the reports generated. For trend analysis there must be a period of data gathering needed before any patterns can be identified.
By analysing the data accumulated over time and from many engines, it may be possible to identify a unique set of parameters that almost always occurs before a specific problem has been experienced. Developing algorithms that automatically recognise that when data from a monitored engine is analysed can allow the owner to be alerted instantly and to take appropriate action. What that may be will depend upon circumstances. It may involve running at less than full load, taking a cylinder offline or even diverting for immediate repairs. The initial action in each case will however be to check that the data being reported is accurate. A sudden change in temperature or pressure or increased vibration may be due to nothing more serious than a failing sensor. On the other hand, every component in an engine could be subject to sudden failure regardless of the quality of maintenance and contaminated fuel or lubes can also cause problems as can using a lube of the wrong specification.
Although it is a natural extension of the engine installation, diagnostic and remote monitoring services are not limited to engine makers alone. Specialists such as Kongsberg and ABB along with many smaller third-party service providers are active in this area. Some of these will produce their own sensors and measuring equipment as well as complete onboard engine management systems, others are more involved in providing the equipment for others to make use of.
The types of service agreements available may all be referred to as remote but in some the data collected may not be constantly monitored. The more usual arrangement is for a daily transmission of data that may only about to half a megabyte sent to the OEM. This is perfectly adequate for CBM purposes as there is a usually gradual loss of performance over time rather than a sudden catastrophic failure. If something of that type is likely, the engine’s own alarm systems should alert the crew in time to shut down the engine.
As the novelty of engine monitoring service agreements has worn off, engine makers have come up with new variations. For example, Wärtsilä now offers what it calls Lifecycle Solutions aimed at optimising the efficiency and performance of marine and offshore customers’ assets. There are three levels and at the top end, the Guaranteed asset performance goes a step beyond maintenance. Under the agreement, performance targets are determined based on measured data, and Wärtsilä can guarantee that these targets are reached and maintained. Measurable indicators can include, for example, availability, reliability and fuel consumption.