Fighting old age
07 September 2015
Timely maintenance and protection can help to extend the useful working life of a manufacturing facility and the machines within it, explains Phil Burge, country communication manager at SKF
Just as a new car starts to depreciate the moment it is driven off the forecourt, so the ravages of time affect factories as soon as the ribbon-cutting ceremony is over.
This ageing process is inevitable: corrosion, stress cracking and erosion lay waste to steel and concrete, while fatigue, instrument drift and temperature fluctuation add to ageing effects. However, the process can be controlled, which helps to extend the life of plant assets. This is why the Health & Safety Executive (HSE) stresses that ‘ageing’ plant is not necessarily ‘old’.
"Ageing is not about how old your equipment is; it is about its condition, and how that is changing over time,” HSE says. "Ageing is the effect whereby a component suffers some form of material deterioration and damage – usually associated with time in service – with the increasing likelihood of failure over the lifetime.”
It means the effect can be counteracted – and a manufacturing plant can maintain efficiency through careful treatment.
"There are many examples of very old plant remaining fully fit-for-purpose, and of recent plant showing evidence of accelerated or early ageing,” says HSE.
Four main types of asset are subject to ageing: primary containment systems, such as tanks and pipework; process safeguards, such as pressure relief valves or overflows; electrical control and instrumentation (EC&I) systems, such as leak detection or CCTV monitoring; and structures, including safe work areas and access routes like ladders and gantries.
Most ageing mechanisms are due to physical deterioration such as metal corrosion, weathering (including expansion/contraction due to temperature changes) and stress cracking. Others, such as instrument drift and detector poisoning, relate to electrical equipment. Between them, they can cause potential failure in almost every component in the plant.
Corrosion is the most obvious example. It takes many forms and has a number of causes – through the simple action of moisture, ‘sweet’ corrosion (caused by carbon dioxide dissolved in water) or even microbial corrosion. The signs are well-known, and an obvious sign of ageing. However, a rusty surface does not indicate imminent part failure.
"Rust is merely a sign that the equipment is ageing,” says HSE. "The rate of this ageing process and its importance in risk terms are parameters the plant operator should be concerned with."
It can be prevented through measures such as coatings or cathodic protection. Susceptible components can also be monitored and controlled through four processes: identification (of components at risk); detection (locating the corrosion); quantification (how serious is the corrosion); and assessment (of implications for equipment integrity).
Inside an engineering facility, the most important assets are the machines that make the end products and generate the profit. While a leaky pipe may take time and money to fix, a faulty machine that stops the production line is far more serious.
So plant managers need to keep a close eye on machine health. Condition-based maintenance (CBM) is an effective way to do this, and fight the effects of ageing. It monitors the operation of critical systems in real time, identifying wear or faults in moving components as they develop. Service or repair intervals can then be scheduled for the most appropriate time.
Monitoring tools typically measure changes in vibration – especially on rotating shafts – or changes in operating temperatures in mechanical and electrical systems. Handheld units with either remote probes or permanently fixed sensors can be used. The advantage of permanent installation is that readings are taken continuously, and provide true preventative maintenance in real time.
For larger, more critical assets – where safety implications, production interruptions, difficult or dangerous access, and the costs of failure are significant – permanent online monitoring is more suitable and reliable. Typically, these applications include process segments such as pulp and paper, steel, mining, petrochemicals and energy supply.
Data is gathered and transmitted via permanent sensors, which can be hardwired to junction boxes or connected wirelessly. In each case, data is normally routed to a centralised computer system running an advanced management and data analysis tool.
The ageing and degradation of plant and equipment is an important challenge for industry. Plant managers can stay ahead of these detrimental effects by monitoring and controlling the processes, helping the plant to maintain maximum efficiency into old age – remembering that ‘old’ is not the same as ‘ageing’.