Catalyst damage

[pgmr]

I removed the catalyst in our Buck 80 a few weeks ago to clean it and noticed quite a bit of damage on both the upstream and downstream faces. It appears to be similar to photos of flame impingement damage, but it doesn't make sense that the outlet would have the same kind of damage, since it isn't exposed to the firebox. In fact, it seems to have more damage.

The flame shield and wire grid have always been in place and I don't burn super hot. This is after four seasons of use. Any suggestions as to the cause? Thanks.

 

[weatherguy]

I had that happen to my Princess and it was because the door gasket wasn't tight, not sure if the same would apply with a buck.

 

[Charles1981]

1) Overfire events
2) Burning wet wood - I believe you can get the stove up to proper temp but then when the bypass is closed steam from wet wood can cause significant temperature variables that can lead to cat failure
3) General Cat Failure...

There aren't any holes in that cat but it has cracked. It may still be functioning well possibly. I don't know what the manual says about cat life span for your stove. Maybe it has a few years left in it....maybe not.

 

[mellow]

I would wash it: (broken link removed to http://www.woodstovecombustors.com/Cleaning_your_combustor.html)

And then throw it back in and see how it does, you might be able to get another season out of it but I would order another one to have on hand.

Good write up on cats: http://www.woodstovecombustors.com/maintenance.html

 

[Woody Stover]

It appears to be similar to photos of flame impingement damage, but it doesn't make sense that the outlet would have the same kind of damage, since it isn't exposed to the firebox.
In fact, it seems to have more damage.

I think that the "scooping" type of damage can be the result of thermal shock as well, possibly from loading damp wood and closing the bypass again before burning the new load in a bit. It may be that both faces are subject to it, more than the middle since the middle probably stays hotter. I know that the Buck 91 I run can hit high cat temps (1800+) if I have a bunch of small stuff in there, all off-gassing at once. Do you have a new cat probe installed, and have you seen excessive cat temps very often?

 

[NHcpa]

Damp wood kills 'em. Been there, done that.

 

[pgmr]

Thanks for all the replies. I'll try to answer all the suggestions below. Btw, the cat is a Firecat from Applied Ceramics. Any opinions about them or good things to say about another mfg? There is apparently no 6"x7"x2" steel cat available.

The door gasket is fine and I've not had trouble getting the stove to run w/o visible flame.
I cleaned it using the distilled water and vinegar method. Plan to buy a replacement to have on hand if it doesn't work well.
Wood is well seasoned (2+ years) and stack tops are covered.
It's possible I've reloaded with a too hot cat or reengaged bypass too quickly.
Cat probe is same age as cat and pretty degraded. Will order new one with new cat.
The cat is not cracked, just the faces are crumbling.

The flame shield was a bit distorted when I removed it to remove the cat. I flattened it out and tack welded on a few stiffeners to hopefully keep it flat. There were two small stiffeners right under the cat, but none toward the back of the stove. Perhaps that distortion was allowing too much flame to get up to the cat. There is also a wire grid that is suspended in the cat housing that is supposed to do something to any flames that reach that point.

 

[BKVP]

The Buck 91 is a proven performer. Your cat is horizontally positioned in that unit. If the stove were to overdraft, both fore and aft surfaces will see excessive temps. More than likely the stove has run a bit high a few times and pulled the heat through the cat. You can ask the guys at Buck, I am certain they may have some observations. If high winds or drastic temps were to transpire, the stove could draft harder than normal.

 

[Ashful]

I disagree with the damp wood assessments above. Steam causes rapid cooling and thus cracking thru the cross-section of the substrate due to CTE stresses. What you have is clearly cratering, not the type of cracking that would normally result from steam due to loading wet wood.

The most common cause of cratering is indeed flame impingement, but if you're sure that wasn't the case, then we should be looking for other possible causes of cratering.

 

[MJFlores]

Depending on the age of the cat, this could be completely normal. Mine looks like that after 4 years...5 at most. I just replaced with a steel cat so we'll see how long that lasts. Ceramic cats really take a beating and are considered a consumable / replacement item. They way yours looks, if it were mine I'd flip it and try to get another year from it.