ACC Fan Blade cracks

[Joshua Rinkes]

All,

Looking for some support regarding ACC Fan blade cracks our site is experiencing. These are Italian made blades (Cofimco), and can get the model number if required for a better answer. Basically there is a metal plate that appears to be added to the blade for additional support. All of the cracks we have are originating from this point ( metal plate). There is no pattern of what fans are having these cracks in regards to location on the ACC.

Looking for some help on this issue. Any criteria for blade crack repairs? who they used for repairs, if possible to be repaired. Any upgrades to prevent in the future. Also if this has occurred at other sites, what was the runtime on the fans before seeing this issue. Ours currently have around 20k on them.

thanks

[gmirsky@galebreaker.com]

Hello Joshua,
Cracks in fan blades has historically been an issue on A framed ACCs through many years. It is a forced draft arrangement and on the windward side of the ACC the air flowing into the fans is turbulent creating almost a cavitation effect. At high ambient wind speeds there can be a downdraft on the windward side and a updraft on the leeward side. So as the fan blades rotate inside of the fan bell the blades are being stressed which over time can fatigue the fiberglass laminate and result in blade cracking. Galebreaker offers perimeter mounted wind screens which causes the airflow on the wind ward side to be more uniform , thus resulting in less stress on the fan blades. We are installing this concept on 4 ACCs starting this week which had blade stress issues. Sorry to hear about your problem and you can discuss further with me at gmirsky@galebreaker.com

[John Brushwood]

The fact that the cracks are originating from the metal support plate leads me to believe there is something suspicious about the stress distribution design in this region of the blade. Unless there were issues with the manufacturing of the laminates (i.e., contamination between layers, poor curing temperature control, nonuniform heat press, etc.), consider performing a FEA on the blade composite structure and verify no cyclic stress limits are exceeded, especially at the metal-fiberglass junction.

[powerplantdocs]

Joshua,

As a former Commissioning Manager for SPG (SPX) Dry Cooling and B&W SPIG Dry Cooling for over 10 years I have had experience with what you are currently experiencing. If you want you can e-mail me at mcyr@powerplantdocs.com or mcyr01@outlook.com and I can provide you with some info and possibly direct you to the folks who can help you.

[powerplantdocs]

Joshua,

At your earliest opportunity check the torque of these bolts. Have experienced loosening of the bolted joint due to compression of the fiberglass over time. The plates are installed to increase the clamping surface area and to minimize compression of the fiberglass material. Last project where I witnessed issues with Cofimco blades the bolts started to snap, fiberglass cracked as you are experiencing, bolts fell out, etc. Had to replace/rebuild the affected fan blades and retorque others. Cofimco increased the bolt torque value for this particular unit.

[Desmond de Haan]

Hi Joshua,

Can you email me the specific case at: rene.bunskoek@howden.com

I will bring you in contact with my colleague David Kuehl, he is very knowledgable on the Cofimco product.

We at Howden would also like to examine your case and see if we could assist.

Looking forward to your reply.

Rene Bunskoek

[Adam Dawe]

Hello Joshua,

Just to confirm, are these cracks on the fiberglass shaft or the blade portion? We are currently replacing all of our Cofimco blades after less than 6 months operation, after it was discovered that the clamp blocks that hold the shaft at the hub were installed upside down, resulting in incorrect blade angle from the hub and increased stress on the shafts right at the edge of the metal reinforcement. We had numerous cracked shafts and no confidence in the reliability of the existing blade shafts, even after correcting the position of blades with no visible cracking.You can contact me at adawe@saskpower.com if you would like to discuss further.

Adam Dawe

[Author]

Posts