Sightglass Shattered!

[snoozer]

I was giving my kettle & MT a scrub and soak with hot pbw solution, I was transferrring from keg to keg playing with the pump, ball valves and disconnects getting used to how it all works. I had my kettle recirculating on itself with the flame underneath and after about 30 mins I noticed some water dripping off the elbow, I wiped it up and then noticed several horizontal cracks up to 2/3 the diameter, up the tube. The leak was getting bigger and then it snapped off in my hand as I wiped it dry
I thought polycarbonate was fairly impervious to most things? obviously not pbw at around 70c...has anything like this happened to anyone else?

 

[Goldenchild]

I was giving my kettle & MT a scrub and soak with hot pbw solution, I was transferrring from keg to keg playing with the pump, ball valves and disconnects getting used to how it all works. I had my kettle recirculating on itself with the flame underneath and after about 30 mins I noticed some water dripping off the elbow, I wiped it up and then noticed several horizontal cracks up to 2/3 the diameter, up the tube. The leak was getting bigger and then it snapped off in my hand as I wiped it dry
I thought polycarbonate was fairly impervious to most things? obviously not pbw at around 70c...has anything like this happened to anyone else?

Over on the American forum there's a ton on it seen 1 thread and the guy was doing experiments with it after going through a bunch of them. apparently there's something in pbw and it dosnt like being in confined spaces sucks the oxygen out.

 

[booargy]

plastic ain't Gunna work with boiling liquid. I learnt the hard way.

 

[snoozer]

Yeah I understand plastic not usually being ideal but I thought polycarbonate was suitable for boiling temps? Why is everyone using polycarbonate then?

 

[Wolfy]

Over on the American forum there's a ton on it seen 1 thread and the guy was doing experiments with it after going through a bunch of them. apparently there's something in pbw and it dosnt like being in confined spaces sucks the oxygen out.

I doubt very much doubt that it "sucks the oxygen out", quite likely the problem if used in confined spaces is the exact opposite.
PBW's major component is Sodium percarbonate (same stuff as in Nappisan and similar Oxy-cleaner products), when dissolved in water it produces hydrogen peroxide (which decomposes to oxygen) as can be easily seen by all the bubbles that form when using such products.
If confined this can build up pressure and is probably not good for some thin-walled-brittle-plastics, however it can be used to good effect when cleaning your kegs, simply fill them with some hot water, add some PBW/Sodium percarbonate and re-seal, after shaking it around and cleaning stuff inside, there should be enough pressure for the cleaning solution to be pushed out the dip-tube cleaning that also.

Yeah I understand plastic not usually being ideal but I thought polycarbonate was suitable for boiling temps? Why is everyone using polycarbonate then?

There are various grades of polycarbonate, with various different physical properties, and so that may depend on where you purchased yours from.
While not as clear as polycarbonate, I made my sightglass from silicon tube.

 

[snoozer]

I got the polycarbonate from a place in Acacia Ridge, other members have used the same place.
I like the idea of the little indicator (plastic ball?) so u can easily see the water level.

I guess everyone should be warned if cleaning vessels with hot PBW solution TAKE THE SIGHTGLASS OUT!

 

[pk.sax]

You didn't take a picture or few of the polycarbonate sightglass and the fracture did you?

 

[Wolfy]

I like the idea of the little indicator (plastic ball?) so u can easily see the water level.

The ball-thingy was borrowed from the kitchen-kettle.

 

[snoozer]

I'll snap a pic later on when I get a chance. Me thinks the tea kettle is gonna be put to better use!

 

[snoozer]

Took a photo tonight of the sightglass, U can see all the fractures on it. I was not aware of any problems with hot (70c) PBW, the polycarbonate lasted about 30mins before it failed...

 

[wessmith]

Had a poly carbonate sight tube on my HLT for 10 years or more. Open at the top and enclosed in a normal compression olive at the bottom. Never had a problem running at 90C. I have to wonder if over tightening the olive might be the cause??

Wes

 

[snoozer]

That is a possibility for sure, I am a notorious over-tightener! It may have then been more susceptible 'cause it was under stress?

 

[JaseH]

Hmmm that doesn't look like just an overtightened compression fitting.

This is interesting

Particularly the section titled "Hydrolysis"

Maybe you had some residual stress in the tube from the manufacturing process or prior handling, and the heated solution pushed it over the edge?

More info here

Both these suggest that cracking involves two factors, stress and a corrosive environmental liquid.

 

[snoozer]

Hmm yeah its got me.

 

[pk.sax]

It isn't crystal clear from that picture but seems like you've had had a load on that sight glass tube. Part of the fracture surface is a smooth slow fracture surface and the rest sudden failure. It may have been going on for longer than you thought.

Is your sight glass constrained (through the centre axis) at both ends? Maybe your tube was a bit oversized. causing a stress to be present that eventually cracked it.

 

[snoozer]

The sightglass just sits in the compression fitting in the elbow and is located at the top by sitting inside an eyelet bolt which it slips in neatly.
I'm just gonna remove the sightglass before A hot pbw clean in future (obviously I'll replace the sightglass with a cap so I can still fill the keg without leakage).

 

[Wolfy]

Is it possible that the when fitting it into the eyebolt it needed to be slightly bent or flexed, resulting in stress along the long axis when was attached?

 

[wessmith]

This has got me very curious - had another look at the pics posted earlier. The cracks appear to have "shattered" and do not look like typical polycarbonate to me. Are you sure the material is polycarbonate and not something like perspex? Just went and checked my HLT sight tube and even with backlighting, there is nothing remotely like stress cracking. I do recall trying a perspex tube but found the tube deformed under heat - it was just no good.

Wes

 

[wessmith]

Spoke to a colleague at the local cultural centre tonight over a Coopers or two - he operates a business that frequently machines engineering plastics - his take is that the shattered sight glass may have been subjected to (a) hydrocarbons (in a previous life?) or (B) UV.

Wes

 

[snoozer]

Ah!, mystery solved! (I think). I neglected to mention the sightglass is on my 18 gallon keg so it bows slightly to make the barrel shape .
I think I can stop wondering now. Pissed off though 'cause I just calibrated the sightglass with fancy stick-on vinyl numbers, hope I can transfer them ok.