Clinical performance

Condition monitoring technologies can check the health of your equipment and pave the way for a proactive maintenance strategy.
By Administrator
Wed 01 Aug 2007 12:00 AM

Ensuring your plant's equipment is in good condition is now more essential than ever before. This applies, in particular, to critical equipment in the power or oil and gas industry, where an unpredicted or sudden breakdown can prove to be very costly, even if the machine is down for only an hour.

It is important to detect faults at an early stage to avoid such breakdowns - and there are essentially five technologies used to determine the condition of equipment: vibration measurement and analysis, infrared thermography, oil analysis, ultrasonics, and motor current analysis. Condition monitoring, when carried out correctly, is the key to a good predictive maintenance programme in any plant.

The techniques can be compared to the checks a medical doctor might make on the human body. A vibration reading can be viewed in the form of a signature, or graph, like an electrocardiogram; thermography analyses temperatures; ultrasonics primarily checks for steam and vacuum leakage; oil analysis is like a blood test, enabling early detection of emerging mechanical problems, and motor-current analysis monitors the input electrical signal, much like a pulse.

The term ‘condition monitoring' has been around for the last 50-60 years, but up until the 1980s plant workers would simply walk around their plant, take the readings and record them on pieces of paper. In today's computerised age, condition monitoring is software-driven and can be a plant-wide system if required. Through software and network capabilities, everyone in the plant, from top to bottom, can see the data being measured.

Beating heart

Vibration measurement is a primary method for monitoring equipment. "Each and every machine in a continuously-running plant vibrates," says Ernst Woecker, regional manager of Provibtech, a company providing vibration monitoring solutions, for Europe, Middle East and Africa. "Vibration is the heartbeat of machines - if there is any change in temperature, pressure or load, it is reflected in the form of vibration.

"If this changes from the recommended value, it can harm the machine," explains Woecker. "As time passes, machines deteriorate from their original state and simultaneously vibration increases, which can severely harm any machine. Keeping an eye on vibration measurement is a must in the utility sector."

But what sort of faults will vibration measurement be able to detect on, say, a pump, turbine or compressor? "There is very little about the machine which you cannot detect using vibration, from a rotordynamics perspective," says Sary Diab, marketing director for optimisation and control for Africa, India & Middle East at GE Energy.

GE acquired the well known Bently Nevada condition monitoring line in 2002.

"You can check the condition of the rotor itself and all the supporting components around it. In the rotor you can detect imbalance or misalignment. Any disturbances which take place get picked up with vibration. In the supporting elements, the bearings and the bearing houses, you can detect any looseness. Any misalignment between coupled equipment gets picked up by vibration signatures."

Critical issue

There are two ways vibration can be monitored: on a portable basis, where a data collector is taken to measure vibration at intervals, or online, i.e. around the clock.

Woecker says any plant should use both portable and online vibration monitoring, pointing out that online monitoring is able to provide protection more efficiently for critical machines, whereas portable monitoring is fine for periodical check-ups.

Critical components, such as turbines and compressors, should be monitored 24 hours per day, 365 days per year, and have built-in alarm and trip functions to automatically shut down and protect a machine if the vibration goes beyond certain levels. For less critical machines, portable instruments are used, where a person goes once per week or fortnight to take all the data and download it to the software and the DCS (Distributed Control System).

The investment in vibration monitoring equipment is not great, relative to the cost of the plant assets themselves, so the return investment comes in preventing serious outages with the potential to cost an operator a very large sum.

"Investment in vibration monitoring systems is not through direct but indirect profit to the company. If there is an unplanned shutdown due to a fault, the company will have to bear a loss of millions of dollars in a day. Whereas the cost of maintenance is lower, the cost of production is very high," says Woecker.

"Companies must install a good and reliable vibration monitoring system, with a protection and safety system, to increase their profitability. There are many examples of machines running without a vibration system and the plant suddenly stopping. Nowadays, there are compulsory norms, whereby an ISO vibration system is a must on each machine, so that each plant ensures its safety."

Thermal thinking

Another prevalent fault-finding technology is infrared thermography. Infrared can detect any problem that generates heat and reveal temperature differences on the surface. With a user-friendly infrared camera, you can see where the hot spot is and whether the temperature differences are too great, which would indicate some sort of problem, such as overheating because of a loose or corroded connection, fuse or switch. Cameras can generally operate from temperatures of -20 up to 2 000 º C, and store in the region of 2 000 - 3 000 images on memory cards.

"There are two main advantages to infrared thermography," says S.M. Ameen, sales manager of the power and industrial projects division at the Kanoo Group, which is a long-term partner of thermal imaging solutions provider FLIR systems on the UAE market. "The first is that you are doing it on-load - you are not switching off anything to take any measurements. The second thing is that you are doing it non-contact. You are not touching any equipment. You are at a safe distance and can do a power plant in a couple of days, which is not possible with any other application."

Ameen claims that the utilities are his biggest customers, pointing out that the Dubai Electricity and Water Authority (DEWA) has "five or six of our cameras", while DEWA's Abu Dhabi counterpart ADWEA also uses them. In terms of recent developments, Ameen points to the first handheld, high-definition infrared camera, FLIR's P640, which uses 640 x 480 pixels, improving on the standard 320 x 240 pixel detector. "It actually makes the pictures four times clearer - a good model for thermography professionals," says Ameen.
Again, as far as investment is concerned, the expense is insignificant compared to what could potentially be lost without thermographic monitoring. "We don't sell the cameras - we sell the application," says Ameen. "If a consultant is buying the camera to provide service, the return of the investment could occur the very first day or it could take six months. One fault could lose you billions."

Nonetheless, FLIR has developed a more budget-style infrared camera, costing in the region of US $6 200, known as the InfraCAM. "Generally, it is considered that thermography is expensive and that only people in power plants and so on use it. This is a camera which is more like a toolbox piece of equipment, which even an electrician could use to check for faults, and then re-check after he has repaired it."

Decision support

Of course, the process does not stop at fault detection. Vibration measurement and thermography, as well as the other technologies mentioned, are used to help plant operators to take decisions. To an increasing degree, software is now being used to merge equipment reliability data with process reliability data.

"One of things that is taking place now is the integration of the different platforms," says Diab. "You will see a major change in the way that different applications are now co-existing together to deliver a complete view on the health and condition of the equipment.

"With the development of more sensors and better ability to do computation, we have been able to develop more complex performance monitoring modelling, which allows customers to be able, on the spot, to detect performance changes in their equipment and use that to determine the condition of the machine."

Diab says GE Energy uses its System 1 software to integrate the Bently Nevada hardware (for vibration monitoring), performance monitoring (through its optimisation and diagnostics software), and additional predictive technologies that it can bring in.

"Hardware equipment can pick up the signals from the sensors and use it for protecting equipment in case of a fault," says Diab. "That equipment also becomes the interface between the data that you receive from the field and your System 1 service, which then picks up the data in its raw format and converts it into actionable information. The ability to generate complex alarms that come from multiple factors, e.g. a vibration signature combined with a performance measurement, could lead you to a conclusion far more accurate than if you had just the vibration signature alone."

System 1 is able to integrate to the DCS, share information with the plant historian, and is accessible from multiple locations. At the highest level of software complexity, automated decision support detects symptoms of the most common faults and then flags the operator and maintenance team to the occurrence of these well in advance via the DCS. The plant operators are then able to start planning and avoid breakdowns. Maintenance teams can focus on the problematic equipment and leave all the scanning to the software.

"A must in our experience is the integration of a condition monitoring system along with the rest of the plant processes," Diab adds. "The condition monitoring team has to have the ability to generate work orders that utilise the maintenance team so they can do work on the equipment. They have to have a channel so that they can go and talk to the operators and say ‘we found this fault'. There must be a process they can place between the different departments in order for condition monitoring to become effective."

Proactive planning

"The combination of technology and the right internal customer processes, what we call the maintenance strategy, will help the customer become more proactive," Diab continues. "Effectively, it allows the customers to be able to see in advance a fault being generated. If you apply these technologies correctly, you will be able to see that fault when it starts.

"Once you do that, you are able to assess the severity of the problem you have at hand, plan for the resolution of it, and assess the amount of damage that can take place, so that you can take an outage on that equipment before the damage propagates to additional parts of the equipment, thus minimising the impact of maintenance that you are going to go," says Diab, adding that customers with more experience tend to be able to bring out the biggest benefits.

Of course, the type of condition monitoring a company employs will depend on its size, its industry and the criticality of its assets. It might need only periodical oil analysis, or it might require a fully fledged online system.

"Companies like ourselves understood the varying levels of return on investment and we tailor-made solutions for different types of industries, so that you would always be able to get the return on your investment," explains Diab. "It doesn't make sense to apply the maximum technologies across the board - your financial return on investment becomes very difficult to justify. And that's where we have solutions that range from portable equipment, wireless solutions and sensors, small online equipment for balance of the plant all the way up to the full-time, online protection and monitoring equipment."

Conditional future

Diab does say, however, that the necessary sensors and computing elements are now becoming more affordable, in parallel to the benefits of conditioning monitoring becoming more apparent to customers.

"If a new plant gets built, you will find that they have integrated condition monitoring into the initial specifications, whereas in the past this wasn't the case. This is now a common best practice," he explains.

As the drive to reduce downtime continues, plant operators are likely to invest in integrated condition monitoring systems, which play a crucial role in helping them stay ahead of the game.

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