[Ermin]

I build a 24" tall DIY kalk reactor several weeks ago with 4" extruded acrylic tube. Reactor was fed by peristaltic pump and mixing done by a magnetic stirrer. After using it for about 3 weeks, the tube wall cracked. The tube was cut clean and glued with Weld-On #3 without any visible problem initially. Not until after several weeks did the tube started to crack starting at the bottom.

I then remove the entire setup and drained the reactor to prepare for more Weld-On to seal the crack. However, after two days, I found the crack to extend even further up the tube. This is with no liquid in the tube. It was just sitting there.

If the initial crack was caused by vibration or pressure build up in the reactor, I assume taking it apart will have already stopped it from cracking further. What is cause the tube to crack more?

I want to know so I can prevent it from happening again in the next reactor. I know cast acrylic is supposed to be stronger. But I assume it would only matter in the initial cutting (ie. less likely to chip in cutting).

[kevinpo]

Cast acrylic is much stronger but I suspect that is not the problem in your case. Are you are recessing the tube into the flange at each end or are you flush mounting the ends? If you recess the ends and they fit tight into the grooves they can crack over time due to the differing expansion rates of the flanges and the tube. Over time this causes stress creep in the tube. The best way to prevent this is to cut the groove the tube fits into slightly oversized so there is clearance on both the ID and OD of the tube.

HTH,
Kevin