MemberJanuary 6, 2021 at 1:31 pm
Had a problem occur earlier today where the heat exchanger in my convotherm 4 unit split, actually broke apart right after the burner housing where it transitions into a smaller tubular diameter.
I contacted convotherm to get their opinion on it but figured I’d ask here as well, any idea why this happened?
We had another heat exchanger on the shelf since this bottom one has been replaced once before due to a small crack where the burner sits.
MemberJanuary 6, 2021 at 1:36 pm
MemberJanuary 6, 2021 at 2:26 pm
Boy you get into some different things.
No, your pictures are blocked out like everyone’s lately.
Heat exchangers have to go through a lot of temperature change and grow with heat. Common causes of cracking are ;
1 Rapid temperature change. Internal stress.
2 Overheat , like flame impingement or lack of heat removal for the BTU’s of input.
3 Stress from to ridged mounting or vibration.
4 Age out. They do not have a infinite life.
5 Manufacturing or design defect. Even with the best of quality controls, sometimes there is a alloying failure in stainless manufacturing. They can’t do like the military does in the aircraft or Nuclear industries due to cost. Nobody is going to pay $100,000 for a oven.
Where the burner necks down you have a substantial reduction in circumference. So you also have stress from the amount the metal grows. Your looking at a growth of about .080 per ft as the burner gets near a dull red. I no longer have my pattern scales,
MemberJanuary 6, 2021 at 2:36 pm
Haha true, I’m lucky that way I guess.
It’s odd, if I click on the second post with photos I can see them but otherwise I can’t, not like it used to be, anyways.
It’s a pretty severe break, I’ve never seen anything like it, must’ve just worn out, can’t imagine it being anything else, I checked the oven recently and it’s burners were happy, the unit hasn’t had any significant work done to it for some time since the last time something severe happened.
If any of the 2 fan motors stop, it triggers error codes. So I doubt it’s a lack of heat transfer causing it to simply blow apart as the metal inched closer and closer to molten, if it can even heat it to that point.
I guess well see what happens with the new one and what convotherm has to say about it, so far no response.
It’s a flange mounted heat exchanger with 8 studs if I remember correctly, but even then where it broke is not where it mounts.
MemberJanuary 6, 2021 at 2:37 pm
That looks like a weld break. Straight across and 90 degrees from the flow.
MemberJanuary 6, 2021 at 2:38 pm
Just what I noticed in a different picture, it’s the HAZ ( heat affected zone) of the weld which is an area that is weakened when welded.
Manufacturer flaw I can only imagine, perhaps the weld was overheated
MemberJanuary 7, 2021 at 3:58 pm
Once a weld goes thru a burn cycle it shouldn’t have much stress in the HAZ area. But often the weld will be thinner at the edge where it ends..
MemberJanuary 8, 2021 at 11:59 am
Good point, but regardless the haz is a weakened area even if not stressed per say.
MemberJanuary 8, 2021 at 6:36 pm
Perhaps it spent a bit to long in the nitric acid.
MemberJanuary 8, 2021 at 6:46 pm
could be, we’ll see what Convotherm says.
MemberJanuary 12, 2021 at 1:40 pm
Some more photos.
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