Corrosion, Erosion or Both?
Corrosion, Erosion or Both?
(OP)
Hello All,
Problem: My fan is being eaten alive.
Fan Description: 5' Diameter Radial Blades, 465fps tip speed, carbon steel blades
Process Description: The fan is downstream of a wet scrubbing system, complete with mist a multistage mist eliminator (chevrons and mesh). The mist eliminator seems to be removing some water (about one gallon per hour) but the fan is still seeing moisture as evidenced by removing the cover after shut-down. The catch is that the pH of the mist eliminator moisture is about 2.5. As of now we are not sure if it is the high-speed/water droplets causing erosion, the low pH of the mist causing corrosion, or a combination of both that is the cause. I currently do not have a way to measure the size of the water droplets or the amount entering the fan, advice on this measurement would also be helpful.
We are looking into adding caustic to the last wet scrubber stage which should rid us of the pH issue but will also make for a low concentration salt solution. My main concern is that the blades will still see the water droplets and would still be prone to erosion problems.
I would like to know if anyone has experienced similar problems with fans/blowers located behind neutral wet scrubbing systems that released a pure water mist/droplets.
Any ideas would be much appreciated,
DB
Problem: My fan is being eaten alive.
Fan Description: 5' Diameter Radial Blades, 465fps tip speed, carbon steel blades
Process Description: The fan is downstream of a wet scrubbing system, complete with mist a multistage mist eliminator (chevrons and mesh). The mist eliminator seems to be removing some water (about one gallon per hour) but the fan is still seeing moisture as evidenced by removing the cover after shut-down. The catch is that the pH of the mist eliminator moisture is about 2.5. As of now we are not sure if it is the high-speed/water droplets causing erosion, the low pH of the mist causing corrosion, or a combination of both that is the cause. I currently do not have a way to measure the size of the water droplets or the amount entering the fan, advice on this measurement would also be helpful.
We are looking into adding caustic to the last wet scrubber stage which should rid us of the pH issue but will also make for a low concentration salt solution. My main concern is that the blades will still see the water droplets and would still be prone to erosion problems.
I would like to know if anyone has experienced similar problems with fans/blowers located behind neutral wet scrubbing systems that released a pure water mist/droplets.
Any ideas would be much appreciated,
DB





RE: Corrosion, Erosion or Both?
S
Corrosion Prevention & Corrosion Control
RE: Corrosion, Erosion or Both?
RE: Corrosion, Erosion or Both?
I know the acids will eat the heck out of carbon steel, especially in low concentration, however the blades appear to be more eroded than corroded based on the rather smooth wear and lack of discoloration.
I plan to get a lab analysis of the wear, but I have to wait until we can get another wheel fabricated.
RE: Corrosion, Erosion or Both?
Can you get plastic blades, or composite, but make sure that there is no glass fiber fill in them.
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Plymouth Tube
RE: Corrosion, Erosion or Both?
Maybe a carbon composite blade with a ceramic coating if erosion really is a problem?
RE: Corrosion, Erosion or Both?
Steve Jones
Materials & Corrosion Engineer
http://www.linkedin.com/pub/8/83b/b04
RE: Corrosion, Erosion or Both?
I would obtain a proper failure anlysis based on the various opinions offered.
RE: Corrosion, Erosion or Both?
Dik
RE: Corrosion, Erosion or Both?
Metengr- Is stellite a sprayed or welded coating? We wanted to try a paintable ceramic epoxy but the balancing issue continues to haunt us. I also spoke with our Sermatech rep about it and they told me of a similar application where ECTFE was used with success but we were holding off in hope that a cheaper solution would arise (about $50k for this option). This being a fertilizer plant we are economically limited and we are trying not to hand it over to the 'it is what it is' just yet if we can help it.
RE: Corrosion, Erosion or Both?
Thanks for the picture and this confirms to me that you indeed have a water droplet erosion problem. Stellite 6 is a weld deposit versus coating. As long as the weld overlay is applied equally across all of the carbon steel fan blades in the high erosion areas this should not result in an unbalanced condition.
RE: Corrosion, Erosion or Both?
While a Co based weld overlay is clearly the 'gold standard' for erosion resistance let me suggest an alternate.
I have run fans in acid gas service that were coated with epoxy. This was a 100% solids system with mineral fillers. And it was applied in three coats to a thickness of roughly 100 mils.
We did have some wear still at he leading edge of the blades so we used some thin (0.025") alloy 625 to make edge caps. These were put on after the first coat of epoxy so that they were well trapped in the resin.
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Plymouth Tube
RE: Corrosion, Erosion or Both?
Ed - Do you mind elaborating a bit on the epoxy? we had an epoxy on this guy to start with and as you can see it wasn't worth a nickel... I am not very experienced with epoxy options and I would like an outside opinion. Also, how did you fasten the edge caps that you described?
RE: Corrosion, Erosion or Both?
Dik
RE: Corrosion, Erosion or Both?
Try the system with the fan coated with a high build epoxy coating. It might work and save you lots of £
Best of luck.
Cleveland Corrosion Co
RE: Corrosion, Erosion or Both?
Steve Jones
Materials & Corrosion Engineer
http://www.linkedin.com/pub/8/83b/b04
RE: Corrosion, Erosion or Both?
RE: Corrosion, Erosion or Both?
The resin was loaded with ceramic filler to improve it's erosion resistance.
The leading edge strip was actually two pieces of SS. They were welded together (lengthwise, along the middles)the outer one was wider than the inner one. The inner one was formed tight to the bare blade edge and either welded or riveted down. The outer one was bent so that it was captured in the build layer of the epoxy.
All of this forming was craftsmanship, hammer and wooden block work.
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Plymouth Tube
RE: Corrosion, Erosion or Both?
Corrosionman