Turbo Machinery: Seven risks on the turbine floor
The process of using steam turbines to generate electrical energy is complex and has many parameters. Maintaining these systems therefore requires (extensive) knowledge and experience; not only to identify and solve failures, but also to recognize distinct details that relate to the way machines interact and influence each other.
Our Stork specialists have this knowledge embedded in their genes through experience. They know, see, hear, feel and even smell when something isn't right. A look inside the minds of our inspection staff:
1. Stay vigilant
Safety always comes first in everything we do, which means Lock Out, Tag Out (LOTO) for various maintenance operations. In most cases, this involves disconnecting all cables to ensure the entire installation is de-energized. Whether the earthing should also be disconnected is another matter. After all, the earthing connection is an intrinsic safety feature that allows any accumulated or stored energy to flow out in case of an electrical issue.
It's a logical train of thought to say that if the voltage is disconnected, you don't need earthing because the electricity has to come from somewhere. But don't forget that certain mechanical work, such as turning the machine by hand, can lead to a build-up of static energy that cannot be dissipated without an earthing connection. Discharge then occurs when the maintenance technician touches the machine and becomes the conductor of that energy, with potentially serious effects.
2. Check, check, and double check – the piping
Maintenance work on turbines and all corresponding equipment is often carried out by different parties. The focus is primarily on one's own specialist area to safeguard that particular share of the equipment. If none of those parties are made responsible for the system as a whole, there is a potential risk that the parties will unintentionally get in each other's way.
Let's assume for a moment that Party A has put the pipe hangers out of service as part of their LOTO procedure. The next party then has to check whether the blockage has been resolved before commencing their own work. If they don't, the system can be damaged when the turbine is serviced. Blocked pipe hangers prevent proper thermal expansion of turbine components, which can lead to (high) mechanical stresses and ultimately to an increased risk of leaks and misalignment.
3. All fixed doesn't always mean all good
Comprehensive knowledge of the installations is needed to be able to distinguish each component's functionality. For major maintenance, you need to dismantle the installation completely. When preparing the installation for reassembly, it's important to know which connections need to be tightened securely and which ones to leave looser to create space. Every turbine, for example, has two clamping bolts that are specifically intended to give components room to expand when heat develops inside. If these bolts are tightened with too much torque – simply because all bolts have to be nice and tight – that room no longer exists. This can lead to uneven expansion, high mechanical stresses, and ultimately to failure or damage. Individual inspection of these bolts is paramount.
4. Old-fashioned greasing of contact surfaces
The days when the “newbie” had the task of greasing the system are long gone. Research and years of experience prove that thorough lubrication maintenance can extend the service life, reduce the number of failures and increase efficiency. Looking specifically at maintaining steam turbines, we use grease or graphite powder to lubricate the sliding surfaces. This reduces friction, so that less energy is lost, and less heat is generated in areas where it isn't needed.
Lubricating parts and surfaces isn't simply a matter of choosing the right lubricant, but also doing so at the right intervals, with the right methods and the right quantities. ‘The more the better’ doesn't apply to lubrication. In fact, the opposite is true.
5. Take care of your tools
Foreign objects in a turbine can cause severe damage and machinery failure. Tools that are left behind, for example. This can be prevented by having a solid Foreign Material Exclusion (FME) procedure in place that includes a register for FME equipment, a drop-log and well-defined zoning around the turbine with associated rules of conduct.
Examples are having an ‘empty bag’ policy, a tool registration form and a system where only staff who actually need to be there have access. In addition, an obligatory toolbox check when leaving the zone can be very helpful to ensure no tools are left behind in the turbine.
6. Wrap it up nice and warm
We can be brief about this: with renewable energy on the rise, steam turbines are stopped and restarted more often than they were originally developed for. This has an effect on the insulation. Based on the assumption that the turbines are continuously in operation and are heated homogeneously, they are insulated on all sides. With shorter runs and more stops and restarts, that insulation hypothesis needs to be reassessed. Underneath the turbine requires particular attention because gravity plays a negative role in this area.
7. The base rule against corrosion
A medium's acidity depends largely on the temperature. That's why the water for steam turbines is pre-leached (pH value is raised). The water is then a base substance at room temperature, while in the steam phase it is neutral enough not to affect the materials of the turbine. Due to the previously mentioned growth of renewable energy and the consequential higher number of starts and stops, the steam condenses more frequently in the turbine and causes this highly corrosive water to accumulate. At this pH level, the medium is extremely corrosive and the turbine will corrode.
Steam installations these days have drains against water accumulation, which operational staff unfortunately sometimes see and use as steps. Such improper use can cause the drain to deform in such a way that condensate “is left behind”, leading to corrosion problems in those places over time.
These are just a few of many risks we run into – and solutions we find – in daily practice. One thing is clear though: having knowledge and experience of the different types of turbo machinery is crucial to optimize maintenance and thus increase the uptime of TM.