In every sector, performance levels and safety standards are being closely scrutinised to develop new methods of improving efficiency. Moreover, traditional operating practices, such as In every sector, performance levels and safety standards are being closely scrutinised to develop new methods of improving efficiency. routines, are being revised to cope with the more stringent economic climate. Maritime industries in the UK are no exception.
Performance monitoring is receiving unprecedented levels of attention due to this reassessment process brought about by the changing commercial environment. Condition monitoring, and in particular vibration monitoring, provides an effective method of improving maintenance planning while reducing operating and servicing costs and encouraging greater environmental-friendly initiatives.
Today’s commercial ocean-going vessels incorporate a myriad of technologically-advanced equipment that requires periodic maintenance to ensure sustained operation at optimum levels. The traditional approach to maintenance has been to follow a schedule or running-hours system that provides a pattern of regular ship servicing.
This approach is, however, deeply flawed and presents companies with inflated servicing bills and unnecessary dry-dock time. For example, perfectly sound turbines are often dismantled during routine services even if mechanical failures are not subsequently identified. The man hours and equipment costs involved in this ‘scheduled’ repair has severe implications for companies already overstretched by economic slowdown. Component damage and human error during servicing can also compound the situation and result in costly servicing bills that could so easily be avoided.
At the other end of the scale, extended intervals between services can result in complete mechanical failure leading to a major engineering overhaul or ‘mission-critical’ component replacement. Both of these traditional approaches incur unnecessary costs and avoidable dry-dock time.
Unsurprisingly, numerous maritime companies have adopted proactive condition monitoring techniques in a variety of vessel types to provide accurate machine or component performance surveillance – while vessels are still at sea. This benefits the ship’s operator by ensuring that maintenance is performed in a timely and planned manner, allowing the vessel to remain operational for as long as possible.
Condition monitoring equipment has two main derivatives – those which supply continuous, permanent monitoring; and those which are hand-held and mobile. Both typically rely on piezoelectric accelerometers, which are the foundation for vibration analysis of rotating machinery and propulsion systems.
Available in a variety of designs, piezoelectric accelerometers are ideal for a number of maritime applications because they can operate in the harshest environments. The solid-state design also means piezoelectric sensors are not only unaffected by dirt, oil and most chemical agents but can also perform within a large temperature range.
Typically, a vibration sensor’s piezoelectric element is constructed from either synthetic piezoelectric ceramics or quartz - both developed specifically for sensor applications. The sensor produces a signal that is directly proportional to acceleration and can be amplified for acceleration measurements, or electronically integrated within the sensor into a velocity or displacement signal.
Characterised by wide frequency and dynamic ranges that help engineers predict maintenance shutdowns that will have the least operational impact, piezoelectric accelerometers are both versatile and durable.
Although a number of manufacturers, including Monitran, supply both fixed and portable vibration monitoring devices, the most effective sensors are those which are permanently mounted. These devices also offer the highest levels of monitoring accuracy by providing continuous monitoring. Safety levels in hazardous areas can be further improved by hardwiring the permanently mounted sensors back to switch boxes located in easily accessible and safe locations.
The Oil Companies International Marine Forum (OCIMF), a voluntary organisation of oil companies involved in shipping crude oil and oil products, indicated the importance of vibration analysis in their information paper on pump room safety. The Forum stated: “Routine vibration monitoring and analysis should be considered as a means for providing early detection of component wear.”
The OCIMF used pump room ventilation fans – extraction systems that draw gases and vapour through blades – as an example of a suitable application for vibration monitoring. If the blades come into contact with the fan’s casing, or if the fan’s bearings or seals become overheated, the gas could ignite. A suitable vibration monitoring system will detect performance discrepancies that could eventually lead to an explosion.
Condition monitoring, and in particular vibration sensors, offers a viable route to improved ship safety, shorter dry-dock time and reduced servicing expenditure. The impact of these benefits could be crucial in riding out the economic storm ahead.
