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Hello all,
On our plant we have cracks in our blades and we are discussing if the fan will shutdown before it breaks on vibration and if it doesn’t what would happen if a blade will break.
We would like to know so we can determine the correct mitigations.
Does anyone have experience with a blade breaking off?
Do you go out on vibration or is the fail instantaneous? Do you have pictures? -
Marcel,
If you have cracks in the fan blades that are deeper than 1/16″ then you should consider not operating the fans and plan on repairing or replacing them depending upon the extent of the cracks and where they are located. It is good practice to have one set of replacement fan blades at a minimum this way you can shutdown and replace the affected blades and then take time to properly inspect and repair the cracked blades.
If the cracking is minimal to where it just catches your finger tip and no fiberglass is exposed the fan blade may be a candidate for cleaning, prepping and recoating in-place.
As for tripping on vibration prior to breaking? Most times no. The failure is more often than not immediate and may result in additional damage to adjacent blades.
If you have additional questions, comments or concerns please do not hesitate to contact me a mcyr@powerplantdocs.com 202-486-5694. I have over 12 years of experience as a Commissioning Manager with SPG (SPX) Dry Cooling and B&W SPIG Dry Cooling and am presently a consultant to the Power Industry specializing in Air Cooled Condensers and Cooling Towers.
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Hello Marcel,
One of the more common issues on ACCs are cracks in fan blades, failures of fan blade hardware, and fan blade failure. These have been issues primarily on the windward sides of ACC. High wind and wind gusts can be the root cause. I have photos of broken fan blades and cracked fan blades. As stated by the prior respondent, a minor crack can be cosmetic and can occur in the resin rich portion of the blade. However most larger cracks can be significant and you should consider blade replacement. Some fan suppliers have blades that are matched pairs so that replacement should be done as pairs. Galebreaker has provided perimeter mounted wind screens that reduce the stress on fan blades and provides trouble free operation. Our first install was in 1998 in Belgium. Since then we have installed our screens on 50 + ACCs and they can be cofigured to reduce performance deficiencies. You can contact me at gmirsky@galebreaker.com -
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Hello All,
Thank you for the responses. We are planning on exchanging all blades but of course there is a lead time of multiple weeks and on top of that the repair time. We expect the blades will last long enough to exchange all blades, but we would like to known the impact if one would fail. Risk= likelihood x consequence.
@powerplantdocs, thank you for the response about the vibration this is very helpful.
I understand the other blades will get damaged if one would fail, is there any experience with a blade damaging the structure or the condensor tubes?-
I have no experience of blades causing damage to tube bundles but I would not rule it out if your ACC is an induced draft W style. Potential damage to the ACC structure should not be a concern. The Oh Shit! vibration trip switch should safely shutdown the motor within a few seconds of the fan blade detachment. Unlike most rotating equipment e.g. pumps and turbines the protective vibration sensors or switches typically aren’t preemptive but more so installed to shutdown upon or ater fan blade failure.
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Adding to other comments, some installations where a fan blae has broken did not trip the motor equipped with only mechanical vibration switch especially when operating below 2 Hz. This should be checked with OEM of the switch. If you do not have a good fan guard screen attached to your inlet bell, a broken blade can damage equipment below the ACC as well as being a safety hazard. Most A-framed ACC do have the fan guard but some do not.
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