Predicting the future of equipment maintenance

Broadly, the key to a successful process is achieving maximum profit from a minimum investment in plant and equipment. At the operational level this means increasing unit throughput, reducing maintenance costs per unit and preventing unscheduled delays. Yet although today's engineers are fully aware that machine maintenance accounts for a large proportion of plant operating costs, some still may not appreciate that a well structured condition monitoring programme can help to achieve these important objectives.

Condition monitoring uses various techniques to determine equipment condition, which in turn are used to predict and prevent potential failures.

Being aware of potential failures enables engineers to address problems before they become more serious and costly, and helps to avoid unscheduled downtime and optimise maintenance activities.

Broadly, the techniques involved include: vibration measurement and analysis; oil analysis and tribology; infra-red thermography; ultrasonics and motor current analysis.

In this article we will be examining the first two, and looking at actual results in a major installation at the Britvic bottling plant in Rugby.

Vibration analysis, which monitors the vibration of components such as motors, bearings, gearboxes (even individual gears) and the structures/mounting arrangements in order to predict functional failure, takes into account the type of component, lubrication frequency, operating temperature and cycle, as well as internal and external forces acting on the component.

Higher vibration levels, which can be induced by flow or caused by factors such as misalignment, incorrect installation, rotor imbalance or pump cavitation, can lead to much reduced life expectancy.

The condition monitoring data can therefore be used to predict the optimum time for replacement before the component fails completely.

Ideally this will provide the optimum balance between more frequent monitoring and improved equipment life for the process conditions.

Certain conditions, such as system misalignment, may require immediate action to prevent damage or failure.

Others, for example bearing or gear wear, can be trended to predict and plan the optimum time for repairs to be carried out.

Oil analysis and tribology assesses the condition of components by analysing samples of oil taken from process equipment and measuring the concentrations of different elements present in wear debris.

High concentrations of a particular element can indicate wear, and significant increases between consecutive samples may indicate impending failure.

Oil analysis is therefore especially effective in identifying particular wear characteristics in order to enable remedial action to be taken.

It can also indicate trends and/or step changes in component wear that may indicate impending failure, and monitor the physical condition of lubricants to ensure they are maintained in optimum condition to prevent unnecessary wear.

Each item of equipment will have a unique wear rate dependent on factors such as process cycle, operating environment, lubricant used etc, and will therefore need to be monitored individually.

Even the lubricating system itself, which is designed to keep friction between bearing surfaces to a minimum and help dissipate heat, should be monitored to help identify potential problems.

For example, significant changes in viscosity compared with fresh oil may be caused by overheating, contamination from hydraulic fluid or water, or use of a different grade for topping up.

High viscosity, indicated by thickening of the oil, causes overheating and restricts oil flow, and will lead eventually to equipment failure.

Low viscosity on the other hand, where oil is thinning, will cause equipment failure due to increased friction and overheating from metal-to-metal contact.

Others physical properties, such as the acidity of oil, can also be used to identify specific problems.

Effective lubrication is acknowledged as one of the most important preventative maintenance techniques, and specifying the correct lubricants, optimising and maintaining lubrication schedules and ensuring that lubrication is carried out in accordance with industry best practice, are basic requirements that will help to minimise component failures and extend equipment life.

Process industries by their very nature are highly mechanised and capital intensive operations and consequently, maintenance costs are a high percentage of their overall production costs.

In recent years significant cost reductions have been achieved by re-evaluating the traditional maintenance techniques and adopting more advanced predictive and preventative strategies.

With such a significant investment in plant and equipment most companies employ some form of condition monitoring.

However, many need to ask themselves whether it is sufficiently extensive and well structured to predict when failures are likely to occur.

In an ideal world machines would never break down, production lines would never stop and an engineer's life would be a lot easier.

But life isn't that simple, which is why industry has for years concentrated on remedying problems quickly in order to minimise lost production.

However, there is now another school of thought that says it is more efficient to prevent failures happening in the first place.

Coincidentally, while re-evaluating their maintenance strategies, many companies have realised that the best results are achieved by outsourcing key functions to experts whose specialised knowledge best enables them to achieving their goals.

Once such company is Britvic Soft Drinks which, for the past five years, has used Castrol to manage lubrication and condition monitoring at its canning plant in Rugby, where many of the UK's favourite soft drinks are produced.

The plant's four existing production lines produce a staggering 720 million cans per year - almost 2 million every day - so it's no surprise that reliability is paramount for such a production-intensive operation, and tight schedules mean that lost production is difficult to recoup.

Against this background Britvic's management had identified lubrication as one of the factors most likely to have an impact on reliability, so the brief to the Castrol team was simple - 'Design a lubrication management service that will keep our machines running at all times'.

The first step was to benchmark existing practices at the plant against which the programme could be measured, and then establish key performance indicators (KPIs) that would set the targets for ongoing improvements.

The most visible difference in the working partnership is that a single Castrol engineer, based permanently on-site, has taken over the lubricating and monitoring of machines, a role that was previously filled by three Britvic engineers.

A major part of the predictive maintenance programme involves the ongoing analysis of every machine in the plant, to ensure that wear levels are accurately monitored and action taken to prevent breakdowns.

Bearing wear is tracked constantly using vibration analysis and shock pulse monitoring.

The cumulative effect of this analysis can be assessed from the 44% reduction in conveyor bearing changes within the plant - down from 114 to just 64 in the first year and now averaging just over 30 per year.

Examination of individual gearboxes and their oil consumption led to high performance lubricants being used as a replacement for the previous grades.

Since the changeover, gearbox oil levels have been maintained without topping-up, which has reduced premature unit failure and considerably extended life expectancy and reliability.

Also, oil changes at the site that had been necessary every three to six months are now required only once every four years, which provides additional savings in energy consumption and waste disposal.

Improved reliability at the Britvic plant has also been achieved through process and procedural improvements.

By improving the chain of communication for example, hydraulic oil leaks are now more easily detected and swiftly remedied, which has led to a dramatic reduction in fluid consumption.

Trials have also paved the way for the successful conversion of filler assemblies to food grade lubricants and, in response to a Britvic brief to improve waste lubricant storage, drums are now held in a safe bunded area to prevent leakage.

The on-site engineer is now responsible for maintaining the area in a safe condition, monitoring waste oil levels and arranging removal when required, which has led to reductions in the volumes/consumption of greases, oils and hydraulic fluid used by 85, 80 and 75%, respectively.

The recent addition of a second bottling line will add a further 36,000 bottles per hour to the total, making Rugby one of Europe's most productive bottling plants.

The new line, which blows, fills and packages thousands of 500ml PET bottles a day in various configurations for brands such as Tango and Pepsi, will initially produce three bottle styles with the option of others at a later date by changing the blower moulds.

Lubrication management and condition monitoring for the line (an extension of the Castrol Advantage programme already operating on the three existing canning lines and the 2-litre bottling line) will focus on the bottle blowing, labelling and palletising machines supplied by SIG Alpha, SIG Corpoplast and Simmonazzi, and filling and packaging machines supplied by KHS Kisters, all of which included Castrol food-grade greases and lubricants as first-fill on the equipment supplied to Britvic.

Assessing the impact of the new line on the condition monitoring programme, Britvic's Technical Planning Team Leader Huw Davies says that base data provided should prove invaluable in establishing the optimum operational efficiency of the new machines and the line itself.

And summing up the key benefits of predictive maintenance he points out: 'The shared expertise has allowed us to maintain world class standards of reliability throughout our plant, and improve still further the service we offer to customers'.

Leaving engineers and operators free to concentrate on core activities is the major benefit of outsourcing lubrication management and condition monitoring services.

When linked to other benefits such as optimised efficiency, ongoing cost reduction through continuous process improvements, strict budgetary control, and significant input into total productive maintenance, the service certainly delivers a real commercial advantage.