Condition monitoring challenges
15 Aug 2007
Condition monitoring of decanter centrifuges highlights the need for joined-up strategies that link conventional and technology-based maintenance regimes. Patrick Raleigh reports
Engineers increasingly rely on predictive maintenance tools, such as vibration monitoring, to check the condition of components instead of the more traditional — and costly and time-consuming — process of dismantling machines.
For instance, with decanter centrifuges the options are to completely strip the machine every 12 months, check bearings, ports and flights and replace if necessary; or to check the machine with an endoscope every three months and strip down only if a problem is detected.
Among the companies active in this field, Centriquip believes that only by stripping these machines during major servicing and inspecting these critical components can you be sure that the equipment is safe to operate.
Decanter separator machines are expensive pieces of equipment, typically weighing several tonnes, with the bowl rotating at speeds up to 3,000rpm. And, as a Centriquip engineer said: "If one of those goes out of balance due to a mechanical failure, you don't want to be anywhere near it. The problem is that vibration monitors and endoscopes cannot check the condition of flight tips or for cracking in the bowl. By the time something comes to light, it might be too late."
Centriquip, therefore, quotes on the basis of stripping machines during major servicing to establish the condition of all the critical components — bearings, bowl, scroll, flight tips, ports, etc — of these machines. Its maintenance programme is designed to keep the equipment running at maximum efficiency, but also to ensure its safety between service schedules.
Jim Trueman, Alfa Laval's key account contracts manager, parts and service, takes a slightly different view. He believes that predictive monitoring is safe, reliable and appropriate in these applications — if employed appropriately.
Alfa Laval has been offering predictive maintenance for decanter centrifuges for over six years as part of its planned preventative maintenance programmes. For decanter centrifuges, the company uses predictive maintenance to examine and identify wear on crucial components such as bearings, centrifuge bowl, scroll, flight tips and ports.
According to Trueman, the success of predictive maintenance in such applications hinges on three key elements:
1 The proven accuracy and reliability of the equipment being used to measure key parameters;
2 The experience and expertise that is available to interpret these findings;
3 A genuinely open and honest partnership between the supplier and the customer, with full agreement on the objectives and timing and regular communications to keep everything on track.
"In six years of using these techniques, we have never experienced a breakdown or catastrophic failure because either the measurements or the interpretation were incorrect," said Trueman. "In a large majority of cases, we have improved productivity significantly. So I think we can safely say that we have been successful on all three counts."
According to the Alfa Laval engineer, predictive maintenance is preferable to conventional service and maintenance practices. For instance, he said, the technology can check all of the parameters listed above in just three hours, compared with around two or three days to strip a decanter and re-build it manually.
"As importantly, the use of predictive maintenance puts the customer firmly in control of maintenance schedules," continued Trueman. "Instead of being tied to pre-set service or maintenance intervals, they can schedule the work to fit in with production cycles to maximise productivity and throughput."
Looking at the bigger picture, Ian Taylor of Corus Northern Engineering Service (CNES) believes it can be a challenge to achieve a good balance between condition monitoring and routine maintenance regimes. There is a wide variation of standards in this area, said Taylor, noting that he has seen some "frightening practices" in the process industry.
"Whether you are producing chewing gum or steel or chemicals there are tremendous pressures to meet targets. And sometimes, with the skills gap that is happening, we need to be sharper to make sure we have everything covered," asserted Taylor.
Under-pressure engineers should not rely purely and simply on routine maintenance or on condition monitoring, continued Taylor . "They should find a happy medium between the two, but both must run together."
At Corus, "We used to take motors off every two years because we had no idea what the condition was," explained Taylor. "Now, through condition monitoring, we don't have to as we know if the motor is going to last until the next shutdown. That's how maintenance and condition monitoring work together."
According to the CNES engineer, the pharmaceuticals and mining & quarrying industries are a bit behind in this regards whereas chemical companies are well ahead in terms of fitting condition monitoring and maintenance together.
For most companies, maintenance has four different areas: breakdown, maintenance, lubrication and condition monitoring, noted Taylor. "If there's a breakdown everyone runs to the plant to fix it and concentrate on the breakdown.
"We are working to turn this 180° around, so that we have monitoring at the top, followed by lubrication, followed by maintenance, followed by breakdown."
Taylor went on to express surprise that the Health & Safety Executive and the insurance companies were not providing more guidance in this area given the potential contribution that condition monitoring can make to plant safety — indeed the HSE failed to provide a spokesperson to reply to Process Engineering's enquiries on this subject.
Meanwhile, Steve Lacey, engineering manager at Schaeffler UK, — the Schaeffler Group includes the FAG Industrial Services maintenance and condition monitoring business — believes that process operators should adopt "a more holistic approach to plant maintenance."
There is, he said, a need for education in this area, particularly in the boardroom where senior managers often do not understand the benefits of condition monitoring, or how it can enhance their existing maintenance regimes.
Lacey highlights how modern, intelligent, online, monitoring systems can automatically measure, record, analyse and issue alerts on vibration data from rotating plant such as electric motors, drives, bearing arrangements, gearboxes, pumps, generators and fans.
The latest modular systems, added Lacey, can be readily integrated into a company's existing control and automation environment and cater for the different maintenance and condition monitoring strategies of specific industry sectors.
Back at CNES, however, Taylor, identifies further potential for misunderstanding with certain types of condition monitoring, for instance when it comes to checking the condition of machinery used in slow-speed, fluctuating load applications.
Vibration monitoring is fine for high speed motors, fans and pumps, but much less so where components or machines rotate at less than 80rpm and operate under fluctuating load conditions, or only move through a part revolution, according to the Corus engineering expert.
In these applications, he emphasised, acoustic emission monitoring equipment has a high sensitivity to machine faults, but is also immune to audible noise and low frequency background vibration.
Acoustic emissions are the high frequency stress waves generated by the rapid release of strain energy that occurs within a material during crack growth, plastic deformation or phase transformation. Acoustic emission monitoring systems use surface-mounted transducers to detect these stress waves, which lie within the 25kHz to 1MHz frequency range.
"Many engineers are not fully aware of how acoustic emission monitoring systems can help them reduce plant maintenance costs and improve machine availability," warns Taylor. "Also, many companies simply do not possess the necessary skills in-house to interpret the data from acoustics emissions monitoring, so they continue to use vibration monitoring or other devices."
For instance, with decanter centrifuges the options are to completely strip the machine every 12 months, check bearings, ports and flights and replace if necessary; or to check the machine with an endoscope every three months and strip down only if a problem is detected.
Among the companies active in this field, Centriquip believes that only by stripping these machines during major servicing and inspecting these critical components can you be sure that the equipment is safe to operate.
Decanter separator machines are expensive pieces of equipment, typically weighing several tonnes, with the bowl rotating at speeds up to 3,000rpm. And, as a Centriquip engineer said: "If one of those goes out of balance due to a mechanical failure, you don't want to be anywhere near it. The problem is that vibration monitors and endoscopes cannot check the condition of flight tips or for cracking in the bowl. By the time something comes to light, it might be too late."
Centriquip, therefore, quotes on the basis of stripping machines during major servicing to establish the condition of all the critical components — bearings, bowl, scroll, flight tips, ports, etc — of these machines. Its maintenance programme is designed to keep the equipment running at maximum efficiency, but also to ensure its safety between service schedules.
Jim Trueman, Alfa Laval's key account contracts manager, parts and service, takes a slightly different view. He believes that predictive monitoring is safe, reliable and appropriate in these applications — if employed appropriately.
Alfa Laval has been offering predictive maintenance for decanter centrifuges for over six years as part of its planned preventative maintenance programmes. For decanter centrifuges, the company uses predictive maintenance to examine and identify wear on crucial components such as bearings, centrifuge bowl, scroll, flight tips and ports.
According to Trueman, the success of predictive maintenance in such applications hinges on three key elements:
1 The proven accuracy and reliability of the equipment being used to measure key parameters;
2 The experience and expertise that is available to interpret these findings;
3 A genuinely open and honest partnership between the supplier and the customer, with full agreement on the objectives and timing and regular communications to keep everything on track.
"In six years of using these techniques, we have never experienced a breakdown or catastrophic failure because either the measurements or the interpretation were incorrect," said Trueman. "In a large majority of cases, we have improved productivity significantly. So I think we can safely say that we have been successful on all three counts."
According to the Alfa Laval engineer, predictive maintenance is preferable to conventional service and maintenance practices. For instance, he said, the technology can check all of the parameters listed above in just three hours, compared with around two or three days to strip a decanter and re-build it manually.
"As importantly, the use of predictive maintenance puts the customer firmly in control of maintenance schedules," continued Trueman. "Instead of being tied to pre-set service or maintenance intervals, they can schedule the work to fit in with production cycles to maximise productivity and throughput."
Looking at the bigger picture, Ian Taylor of Corus Northern Engineering Service (CNES) believes it can be a challenge to achieve a good balance between condition monitoring and routine maintenance regimes. There is a wide variation of standards in this area, said Taylor, noting that he has seen some "frightening practices" in the process industry.
"Whether you are producing chewing gum or steel or chemicals there are tremendous pressures to meet targets. And sometimes, with the skills gap that is happening, we need to be sharper to make sure we have everything covered," asserted Taylor.
Under-pressure engineers should not rely purely and simply on routine maintenance or on condition monitoring, continued Taylor . "They should find a happy medium between the two, but both must run together."
At Corus, "We used to take motors off every two years because we had no idea what the condition was," explained Taylor. "Now, through condition monitoring, we don't have to as we know if the motor is going to last until the next shutdown. That's how maintenance and condition monitoring work together."
According to the CNES engineer, the pharmaceuticals and mining & quarrying industries are a bit behind in this regards whereas chemical companies are well ahead in terms of fitting condition monitoring and maintenance together.
For most companies, maintenance has four different areas: breakdown, maintenance, lubrication and condition monitoring, noted Taylor. "If there's a breakdown everyone runs to the plant to fix it and concentrate on the breakdown.
"We are working to turn this 180° around, so that we have monitoring at the top, followed by lubrication, followed by maintenance, followed by breakdown."
Taylor went on to express surprise that the Health & Safety Executive and the insurance companies were not providing more guidance in this area given the potential contribution that condition monitoring can make to plant safety — indeed the HSE failed to provide a spokesperson to reply to Process Engineering's enquiries on this subject.
Meanwhile, Steve Lacey, engineering manager at Schaeffler UK, — the Schaeffler Group includes the FAG Industrial Services maintenance and condition monitoring business — believes that process operators should adopt "a more holistic approach to plant maintenance."
There is, he said, a need for education in this area, particularly in the boardroom where senior managers often do not understand the benefits of condition monitoring, or how it can enhance their existing maintenance regimes.
Lacey highlights how modern, intelligent, online, monitoring systems can automatically measure, record, analyse and issue alerts on vibration data from rotating plant such as electric motors, drives, bearing arrangements, gearboxes, pumps, generators and fans.
The latest modular systems, added Lacey, can be readily integrated into a company's existing control and automation environment and cater for the different maintenance and condition monitoring strategies of specific industry sectors.
Back at CNES, however, Taylor, identifies further potential for misunderstanding with certain types of condition monitoring, for instance when it comes to checking the condition of machinery used in slow-speed, fluctuating load applications.
Vibration monitoring is fine for high speed motors, fans and pumps, but much less so where components or machines rotate at less than 80rpm and operate under fluctuating load conditions, or only move through a part revolution, according to the Corus engineering expert.
In these applications, he emphasised, acoustic emission monitoring equipment has a high sensitivity to machine faults, but is also immune to audible noise and low frequency background vibration.
Acoustic emissions are the high frequency stress waves generated by the rapid release of strain energy that occurs within a material during crack growth, plastic deformation or phase transformation. Acoustic emission monitoring systems use surface-mounted transducers to detect these stress waves, which lie within the 25kHz to 1MHz frequency range.
"Many engineers are not fully aware of how acoustic emission monitoring systems can help them reduce plant maintenance costs and improve machine availability," warns Taylor. "Also, many companies simply do not possess the necessary skills in-house to interpret the data from acoustics emissions monitoring, so they continue to use vibration monitoring or other devices."
