QuietStove.com

Thursday, March 2, 2017

BRS-3000T – Failure #2

I recently completed a review of the BRS-3000T.  In that review, I mentioned that one of my pot supports deformed after 10 or so minutes of using the stove.

Links:
My pot, listing to the left, after one of my pot supports deformed.
Since posting that review, a couple of other people have come forward and mentioned that they've had similar experiences, including Miguel C. who kindly sent me the below photographs.
A BRS-3000T with deformed pot supports.
Photo courtesy of Miguel C.
Miguel reports the following:
Not sure how it happened.  I was just cooking rice and a cup of water.  I was using the msr [Titan] kettle and two of the stands bent a lil.   
The stove was on medium low cooked for like 15 [minutes].  It got super red.  There was no winds but it was cold.  It happened at night.

Another view of a BRS-3000T with deformed pot supports.
Photo courtesy of Miguel C.
You will note in the above photo that the pot stands are even more deformed than mine were.

Some people have criticized my use of a 1300 ml pot and 3 cups of water as "heavy."  While maybe someone could misconstrue 3 cups of water as "heavy," an MSR Titan Kettle with just one cup of water cannot.
Miguel's MSR Titan Kettle which contained only 1 cup of water and some rice.
This is not a weight issue.  This is a design and materials issue.

So, What the Heck is Happening?

Well, for one, the titanium here is not melting.  Titanium melts at about 3000 Fahrenheit (about 1700 Celsius).  The flame temperature in air of a butane-propane mix (i.e. canister gas) is about 3500 Fahrenheit/1970 Celsius, but you'd have to really focus the flame, as in a blow torch or similar, in order to get the metal that hot, and air would tend to conduct away the heat.

OK, so it's not melting.  So what is happening?  Well, metals get soft long before they melt.  Think of a blacksmith shoeing a horse.  He doesn't melt steel, pour it into a mold, and make a custom shoe.  No, he typically already has the shoe made.  He just heats it and then pounds on it until it's the right shape.  He heats it because the metal gets softer, and then it's easier to work with the metal.

The same thing is true with titanium.  Long before it melts, Titanium will become more malleable. Metals are assigned a rating called a "service" rating.  This a temperature above which the metal becomes unreliable.  The maximum service rating for titanium is 1100 Fahrenheit/600 Celsius, and that's for a really high grade alloy. The alloy used in a backpacking stove has a rating more likely around 750 Fahrenheit/400 Celsius.  Our flame temperature is 3500 Fahrenheit/1700 Celsius, more than four times the service rating of the metal of our stove.

Titanium is a poor conductor of heat.  If the heat can't be conducted away, and the small, thin pot supports of the BRS-3000T aren't going to conduct a lot of heat, the temperature can climb above the maximum service rating, and "creep deformation" can occur.  Creep deformation isn't a sudden snap or anything like that.  It's a gradual softening of the metal.   The metal slowly droops.

In the case of Miguel's stove, he had it on for a fairly long time (15 minutes) and it was a still night.  With no air currents to whisk away the heat, the temperature of the metal climbed above the maximum service rating, and... well, you can just look at the photos, above.


The Good News
Miguel reports that he just bent the pot supports back after the stove cooled and went on his way.  He continues to use the stove.  Now, how many times can you do this before the supports break?  I don't know, but I wouldn't push it.  You want to avoid getting the supports too hot.

I too just took my fingers and bent it back.  The BRS-3000T isn't exactly a beefy stove.  It's pretty easy to bend the thin little pot supports.


The Bad News
The bad news here is that Miguel's failure happened in still air (or a breeze so light as to be undetectable).  My failure occurred when the wind focused the flame on my pot support.  I was thinking that all one had to do was protect the stove from wind.  I still think it is important, vital actually, to protect the stove from wind, but one also has to worry about excessive heat build up in the right conditions.  It's a bit of a wild card here, but in general shorter burn times should be OK.

Interesting stuff.  More will be revealed.

HJ






4 comments:

  1. Good followup. As a former blacksmith I can attest that by the time your metal *starts* to glow it's lost like 60% of it's strength.

    This sounds like poor design in the pursuit of going as lightweight as possible.

    I think this qualifies as a new variant of "Stupid Light".

    That being said, what is happening with the pot supports being bendable is that the titanium has been annealed. From what little I know about titanium it's fairly plastic once annealed. In fact, I imagine that this is part of the problem- you're repeatedly annealing the Ti and it generally just gets pliable.

    I am not a metallurgist and I'm unfamiliar with titanium so I can't speak from experience, but with iron and steel repeated oxidation from a high heat can cook the alloy and make it brittle/weak. Now if you over-engineer the pot stands, you're fine since even in an annealed state you're not subjecting a lot of stress on the metal relatively speaking. But it looks like that wasn't the case here.

    One thing that may work is to find a slurry refractory coating, like ITC-100 and coat the stands. ITC-100 is a high efficiency forge insulator that would probably keep the titanium cool enough to stay strong.

    Of course, given the amounts needed and the cost of ITC-100 it's probably just cheaper to go buy a better stove.

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    1. Interesting comments.

      Yeah, my sense here is that in the quest to go light that they "under engineered" the pot supports. There just isn't a lot of metal to them. I just took out another stove, a Kovea Supalite, that has Titanium pot supports. There's a lot more metal there.

      With the thinness and overall small size of the pot supports of the BRS-3000T, there isn't much room for error. If the alloy is a little off, you get creep deformation.

      HJ

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  2. Judging from the follow up with the stress fractures and the hit and miss nature of the pot stands deforming, I think you're spot on that their alloy is not consistent. It's either a bad batch or their sourcing is inconsistent.

    Sounds like a Caveat Emptor situation to me.

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    1. It seems like a real crap shoot on this stove. You might get one that's fine; you might not. Way more hassle than I am willing to put up with. I'd rather just go with a stove with better design and QC, but each to his or her own I suppose.

      HJ

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