If its not broken why fix it?

Traditionally ship operators make use of one of two maintenance strategies – planned (or preventative) maintenance and reactive maintenance. Occasionally a mix of the two is necessary in emergencies.

by Gillian Lovering

Planned maintenance involves following the recommendations of the OEM with regards to service intervals and replacement of reconditioning of components. Reactive maintenance is to run an item of equipment until it breaks, otherwise malfunctions or is condemned by a class surveyor during routine inspections or drydocks.

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A planned maintenance programme does sometimes deviate from the OEM’s recommendations where the company superintendents and engineers determine that a longer interval can be accommodated although this is normally only done once the equipment is outside its initial warranty period.

Most classification societies and insurance policies require machinery to be regularly inspected and maintained. Sometimes the rigid schedule of inspections and maintenance can impact on commercial operations and pose logistical problems. A required maintenance may coincide with the vessel needing full use of engines to meet a charter obligation and delays in delivery of spare parts can affect the most carefully laid plans.

Reactive maintenance is normally only adopted as a strategy by operators that have very limited budgets and who plan to get the most work out of a vessel for the least expense. A sudden breakdown of equipment that has been maintained correctly under a planned maintenance regime will of course always result in emergency repairs, but breakdowns are less likely if machinery is cared for.

In recent years the concept of condition-based maintenance (CBM) has become much discussed and is being promoted by many OEMs as well as class societies and insurers. This change is as much due to new and improved monitoring techniques as it is to more robust equipment manufacture. It has been led by engine manufacturers but is not confined to engines as other equipment makers have realised its benefits.

CBM is not a new concept although it is a relative newcomer to the marine sector. Leading engine makers were promoting the concept for shore-based power production long before extending it to ships.

The benefits of CBM are that it reduces the amount of time and cost spent on unnecessary opening up of engines and replacement of components, increases efficiency and thus reduces fuel costs and emissions and, if managed correctly, can provide useful data for other engines and installations on different ships.

There is nothing magical about CBM, it is an extension of condition monitoring and is merely the collection and interpretation of data most often by the OEM but in some cases by third party contractors. On an engine for example, the data collected will relate to matters such as temperature, pressures, speed, vibration, power output and fuel use. It could also include measuring emissions and also analysis of used lubricants.

While some of this data has always been collected and recorded in engine room logs, the significance of certain combinations amongst the many possible permutations may not have been recognised as being significant. An experienced engineer may have accumulated the knowledge that would allow him to foresee a problem, and many do retain this skill, but it is not universal.

Moving from a planned maintenance regime is not an instantaneous thing as it requires the gathering of significant amounts of data. Some of the data may be drawn from existing records but there may also be a need to install new sensing and monitoring systems as well.

Under a CBM regime, the data collected is usually shared with the OEM or third party. Drawing on experience gained with many units of the same engine or machine including those on ships of different operators, the shore technicians can identify potential problems at an early stage.

Once a problem has been identified, the experts can provide advice as to appropriate measures to be taken to manage the time between the present and the expected remaining service life of components. As more and more data is gathered from across different vessels and fleets, the ability to predict problems is enhanced. Knowledge of an issue and its likely progression enables the resolution to be managed taking into account commercial and operational obligations. It also permits contractors and engineers to determine all components likely to be needed and gathered before repair takes place. This eliminates further delays caused by unforeseen circumstances.

It should not be considered that engine parameters or vibration in equipment are the only tools available to initiate a CBM system. Analysis of lubricants can also provide vital clues well in advance of a problem developing. Regular sampling of sump oil from engines or lubricants from systems such as pumps and compressors will show the presence of metals, chemicals and water that should not be present.

Before moving to identifying potential problems, there is an additional benefit of lube oil analysis in that instead of a complete oil change at specified intervals, a sample that shows the oil to be in good condition will allow it to be used for a longer period. Lubricating oil is one of the more expensive items in the maintenance budget and this can provide significant cost savings.

If any metals are present, their identification can give clues to abnormal wear of certain components. Some wear and tear is to be expected over time but the presence of excess bearing or piston ring material can highlight a looming bigger problem.

One of the main indicators of problems can actually be the presence of water in the lube oil samples. Water can cause corrosion inside the engine or machine even at very low percentages. The lube oil for a marine engine should ideally never have a water content above 0.2% for a cross head engine or 0.1% for a trunk engine. Anything above 0.5% should warrant immediate investigation of the cause which could be due to a variety of reasons. Cylinder and piston cooling systems can leak as can the lube oil cooler itself. In addition, there could be a leak in sump heating coils or condensation of water vapour inside the crankcase.

The figures quoted above are for free water or emulsions in the lube oils, but it should be noted that fresh oil has the ability to hold a certain amount of dissolved water. The maximum water amount oil can hold is called “saturation point”. Above the “saturation point” free water will fall out. The “saturation point” is influenced by temperature and other different factors like the composition of oil mineral or synthetic, formulation of additives and will change during the lifetime of the oil.

Rivertrace offers the SMART WiO sensor capable of measuring the humidity providing a key indicator of oil quality. The sensor does not measure free water or emulsion, which is detectable by regular water in oil test kits, it measures the absolute water content in oil and can indicate the presence of water before it becomes free.

The PAV (Pre Alarm Value) of the sensor is set to 50% humidity. The MAV (Main Alarm Value) is set to 90% humidity. More than 100% humidity means free water is present. From this point regular water in oil test kits can begin to measure the percentage of free water.

Normally in the field, the water in oil content is measured by a water in oil test kit. The results are mostly <0.02% (or 100.02% humidity), this value means free water content. If the WiO Sensor shows the main alarm, the value is higher than 90% humidity and damage could be caused to the engine if 100% humidity is reached.

As CBM becomes more used, new methods of predicting problems and equipment failure will doubtless become available. Their development will require the collection of more data and from different sources than is available today. Conceivably the growing use of digital twins will aid in this but it will be OEM’s and sensor and monitoring specialists that will develop the means for gathering data.

Contact our sales team here to learn more about the sensor and how it could help your maintenance system.