|SKF’s Machine Condition Indicator is a vibration sensor and indicator for monitoring non-critcal machines Credit: SKF|
Effective condition monitoring has always been key to plant reliability, but the advances of the digital age are opening up new horizons and the possibility for fleet-wide management of gas turbines and balance of plant equipment, finds David Appleyard.
Condition monitoring allows operators to switch from a preventive maintenance programme – in which key components are inspected and replaced on a regular schedule – to one based on actual physical conditions. A clear understanding of these conditions thus allows systems to be maintained more effectively, improving overall availability and reliability and reducing unplanned outages.
Furthermore, by making such a transition, owners and operators not only typically reduce both the frequency and duration of shutdowns for maintenance, but also maximise the lifespan of such machinery whilst saving money on other associated areas of the maintenance programme, for instance minimising inventory.
Principal parameters for monitoring gas turbines in on-site and combined heat and power (CHP) applications include temperature and pressure – both dynamic and static – as well as vibration. Other methods of investigation include oil analysis and thermography. Temperature and pressure readings, for example, allow operators to control combustion more precisely, enabling advanced warning of potential failure modes or unstable and potentially hazardous combustion conditions. Similarly, vibration monitoring can reveal the vast majority of machine faults which arise from shaft misalignment, imbalance or bearing and gear wear.
Indeed, the importance of effective condition monitoring in power generation and CHP assets cannot be over-emphasised. As Derek Griffiths, Sales Director, Western Europe for GE Measurement & Control’s Bently Nevada product line, explains: ‘Excessive vibration can lead to catastrophic mechanical failure and the associated environmental health and safety risk to plant personnel. Analysis of the signals obtained from a correctly selected vibration transducer can provide insight into the machinery condition and the possible cause of a malfunction. More importantly, continuous monitoring of machine vibration can provide early detection of deterioration of the machine condition and enable proactive management of the asset and its maintenance.’
And this is the crux of condition monitoring, as Griffiths notes: ‘The operating condition of a gas turbine can only be assessed by use of a comprehensive online monitoring system that provides an indication of both the mechanical integrity and thermodynamic performance of the machine’.
|Meggitt Sensing Systems’ rack-mounted VibroMeter VM600 monitoring system is designed for power plants where measurement data is accessed from a central area
Credit: Meggitt Sensing Systems
New requirements, changing demands
The need for flexible and efficient operations is central to achieving economic viability, even for captive power plants where the presence of on-site renewables is increasingly introducing an element of greater variability. As Griffths notes: ‘The current market, where machines need to operate under variable load conditions, increases the need for detailed information about machine availability and reliability. Therefore, the need for an online monitoring system that provides plant operations with a clear indication of whether it is safe to operate the machine has never been greater’.
Henry Reinmann, Vice President (Energy) for Strategy, Sales & Marketing at Meggitt Sensing Systems, echoes this theme of increasingly demanding operational requirements, saying: ‘Operational costs have to be low, emissions have to be low for SOx and NOx; it’s now also CO2. Efficiency needs to be increased and availability and flexibility of the machines needs to be high, and these are all contradictory requirements’.
Reinmann continues: ‘If you want to increase efficiency and lower emissions you have to operate the machine in a very lean manner. You have to go close to the stall limits of the machine, which is when, for example, a gas turbine starts pumping. That could potentially be dangerous and you need to monitor it to see whether, if such an event is coming up, you have to move away from that critical stage with the machine. The chemical composition of the fuel affects the combustion dynamics, so a change in the gas supply on the grid may have a significant effect. You can only do that with active monitoring’.
In late August 2013, Meggitt signed an agreement to acquire Piezotech LLC for $41.2 million, bolstering its access to high-performance piezo-ceramic technology for extreme temperature gas turbine sensors.
Adopting new approaches
Faced with growing operational complexities, asset owners and operators are increasingly turning to more sophisticated condition monitoring techniques as they attempt to maintain a competitive edge. As Griffiths says: ‘There is an increasing acceptance of condition monitoring in a range of industries, with vibration monitoring being one of the technologies used in these programmes’.
Dr Geraint Jones, Technical Manager for SKF’s Traditional Energy business, picks up on another change too. ‘Perhaps what’s slightly different now,’ he says, ‘is that the process data is incorporated within the vibration data, your analysis data and which instrument you’ve used to collect your data. That allows you, with the condition monitoring software we have now, to incorporate the process parameters that tell you how the gas turbine is operating.’ However, Jones also notes: ‘These installations are not just a gas turbine on their own. You might have something on a skid with oil pumps and other ancillary equipment, and all those extra machines are important. The task of condition monitoring is to treat the whole machine as a complete system, not just focus on the gas turbine.’
Reinmann also notes an increasingly holistic approach to condition monitoring, saying: ‘We see a combination of monitoring tasks, with vibration and combustion monitoring, for example. A trend we are seeing is that the large machines usually monitor the traditional rack-mount systems, and we now see combinations with balance of plant and the smaller machines with modular distributed systems. With distributed monitoring there is certainly an advantage of reducing cabling and installation cost and increasing flexibility.’ He adds: ‘Many machine manufacturers want to have monitoring systems on the smaller machines so they can swap out the machine, including all the monitoring around it. They take it out and put a new machine in and everything is on there already.’
Such modular ancillaries are connected to the control and monitoring system via an ethernet cable. As Rienmann notes, ‘You don’t have to worry about transporting pico coulomb signals a long distance. These signals from piezoelectric transducers are quite critical, but you cannot easily transport them over large distances.’
Mark Carrigan, Senior Vice-President of Global Operations for PAS Inc, also highlights the growing complexity of condition monitoring systems in process plants. He says: ‘For many in the oil and gas community and petrochemical industry, there has been a focus over the last couple of years on better managing operating windows. The issue that processing industries have is managing across the literally thousands of measurements and their associated operating limits. The problem is exacerbated by the fact that the storage of all those different operating windows is typically scattered across various locations, including documentation, OEM specifications and control systems.’
Carrigan continues: ‘An original equipment manufacturer, for instance, will have established reliability limits. The plant will have optimisation limits that it wants to keep within the reliability limits of the equipment. In this case, a plant that pushes production must understand the resulting long-term impact on equipment performance. This requires a co-ordinating element that is best handled through automation.’
Explaining how such a system works, Carrigan points to a hierarchy of operability limits, such as an optimisation limit, which should be lower than an alarm limit, and correspondingly should be lower than the value at which long-term reliability of the equipment is affected. ‘The main value PAS provides is bringing together all of these limits that live in many different data sources,’ he says. ‘Consolidating and normalising this data ensures that the operational limits stay in sync. It also provides additional capabilities such as varying the alarm in the distributed control system (DCS) so that the alarm always enunciates at the right time, allowing the operator to take the proper action.’
In February of this year, PAS announced a new multi-year contract with BP Downstream to help manage critical operational limits in refineries and petrochemicals assets. The product, PlantState Suite inBound, captures, analyses and alerts operators on boundary data within plant operations. Boundary data includes process alarms, safety instruments and environmental trip points, mechanical design limits, normal operating zones, and safe operating envelopes.Carrigan says: ‘Companies have realised the difficulty in managing all these systems they’ve put in place. No one plant has one control system vendor that does it all, so it’s hard to try and get these systems working together.’
He concludes: ‘Automating boundary management with software within a plant is considered an industry best practice today. Most of the majors have an initiative in place to get a handle on their operating windows.’
PAS is not alone in adopting a more holistic approach to condition monitoring, covering not just the gas turbine but also critical ancillary equipment and balance of system.
For example, in July 2014, GE’s Measurement & Control business invested in asset performance management (APM) software company Meridium, Inc to integrate Meridium’s suite of enterprise performance management and asset strategy software with GE’s System 1 condition monitoring and diagnostic solution. The new integrated solution, Production Asset Reliability (PAR), aggregates data from System 1 and other plant maintenance systems to provide plant engineers with a dashboard of reliability metrics, the company says. According to a statement, this new industrial internet offering can result in an estimated 10%–30% reduction in maintenance costs.
‘The way we do business is being dramatically altered in the era of the industrial internet. We are realising the increased productivity and efficiency gains from big data and analytics delivered in real time,’ says Art Eunson, General Manager of GE’s Bently Nevada product line.
More recently, in January Meggitt released its VibroSight software for turbines, critical machinery and balance-of-plant equipment. The company says its software suite flags critical events and monitors machinery health, enabling the use of predictive methodologies which help operators make informed decisions about asset management and maintenance.
A further focus of development in condition monitoring has seen considerable energies expended on improving the interface between the various monitoring systems and the decision-making user.
As Carrigan explains: ‘The first thing you want to do is make it available to the operator, visualise it and see real-time data against these limits and make sure we’re operating within them. The second is that you want to provide a score card to management.’ For example, in mid-December SKF announced further investment in ‘smartifying’ its maintenance service offering, production and sales processes. As part of the investment, field maintenance engineers and others are equipped with smart devices using tailor-made software apps. ‘Integrating SKF’s condition monitoring technologies into mobile devices supports the group’s focus on asset lifecycle management. By providing access to real-time machine performance data in a user-friendly format, customers and maintenance engineers are better able to take informed decisions regarding maintenance activities and increase machine efficiency,’ a statement says.
|Metso’s wireless Maintenance Pad is a portable data collection and analysis tool that includes the Metso Machine Analyzer vibration analysis software
Building relationships with the OEMs
While condition monitoring equipment is growing in sophistication, there are nonetheless significant opportunities for further improvement. Some sensor and diagnostics companies already work with turbine and balance-of-system original equipment manufacturers in order to more effectively place or embed sensor equipment within machines during the manufacturing process, as well as enable condition monitoring systems to establish a clear performance baseline.
However, Jones argues that more could be achieved, saying: ‘Normally, in that situation, we would want to work in partnership with the client, but we would like to really get in touch with OEMs at an earlier stage and do condition monitoring at the point at which the equipment is commissioned and tested. The way we would see that working would be to encourage our clients to specify this to their OEM as a pre-requisite when ordering new equipment.’
Jones also calls for turbine manufacturers to work with such companies to design condition monitoring machines into the equipment at the outset, as well as earlier engagement with their clients on condition monitoring. He notes that owners and operators will often provide detailed specifications for the turbine, but the issue of condition monitoring will only be raised at the shipping point, when customers may belatedly realise that there is no condition monitoring equipment included in the package as specified.
‘One development we are really interested in at the moment, in terms of our varying research, is embedding the accelerometer in the bearing itself. If we could do that, we would save a lot more bearings than we currently do. The condition monitoring becomes more robust,’ says Jones. He adds: ‘Advanced processing techniques give you a better understanding of the rolling element bearing. Although those techniques are not new, they are still very useful. Simply embedding the sensor in the bearing makes them even more effective.’
There is also a continued push towards simplified modular systems. For example, SKF has launched remote wireless technology sensor systems – machine condition indicators – which include a traffic light system that activates depending on the vibration limit programmed into it. ‘This can remove some of the burden for data collection,’ says Jones.
The future of condition monitoring
A natural consequence of a more holistic and online approach to condition monitoring is the potential benefit for fleet-wide operations. As Griffths says: ‘Remote condition monitoring via the internet allows entire fleets of gas turbines to be managed from a central location. This allows fleet data to be gathered, common faults to be identified, and engineered solutions developed to improve the overall reliability of the fleet.’
This is a theme also picked up by Reinmann: ‘In the early days you had machine specialists in every power plant, and that is just not economical anymore. Large utilities concentrate resources, they have remote monitoring centres, and some of the large OEMs do that also. They want to get a central location where the specialists sit, and it can then act or react remotely, if they have a fleet of machines of the same type. If there’s an event happening on a machine, they look at the data to see if there are other machines of the same type showing similar indications – a fleet-wide approach.’
Jones also points out the development of remote diagnostic centres, saying: ‘As a condition monitoring tool, you can actually monitor your machines online and you don’t need someone walking around. As you move to an online system, you can possibly move towards remote diagnostic centres; those have been developed in the past decade.’ However, he also sounds a warning: ‘The other side of the coin is that cybersecurity is an issue. That has to be considered.’
Looking ahead, Griffiths says: ‘I believe power generation operators will continue to improve the efficiency of their operations, which will require some form of condition monitoring to provide them with an indication of where they need to focus their maintenance efforts and improve the overall availability of their plant, whilst keeping control of their operational costs. Think of this as enabling condition-based maintenance.’
And, as Reinmann says: ‘Thus, it will require more condition monitoring, data management, more knowledge and understanding of what the machine is doing, and also to be able to plan changes, upgrades etc. I think there is a long way to go for condition monitoring.’
David Appleyard is a freelance journalist specialising in the energy, technology and process sectors.