Acrylic question. What is this??

[kcress]

This is at the top, (left rear corner), of a 72"x24"x36H" tank. The acrylic is 3/4" thick.

The tank is now several years old and was purchased used.
What caused this? And, do I have to worry about it?

http://www.box.net/shared/static/kzsldgz1c2.jpg




Second question:

There is a hole in the bottom for a feed-thru that's about 2" in diameter. It's too close to the corner where a large steel tube is providing support to the tank.

Can I plug it from the inside with a piece of 1/4"?
If I can, do I use Weld-On 16 or the standard water thin solvent?

[widmer]

Looks like the effects of what my local arrogant plastics manufacturer described would happen if I would have prepped the surfaces with rubbing alcohol before weldoning. He said using alcohol can start extremely slow cracking...

[Skeptic_07]

crazing

[Mel-E-Mel]

Same thing happened to my old 55 gallon tank. I'm thinking its the effect of warming and cooling from our tank lights, or just the tank is pretty old. Either way, I'd be looking to replace it soon.

[troylee]

That's crazing..Stress cracks... Most likely someone tried to repair a seam and the glue ran down it causing this... Once a tank has seen water for a short time this will happen if you try to glue it... As for the patch ya it will work fine but be prepared for more of what you see...

[Acrylics]

Definitely crazing, but an odd placement and pattern to occur "naturally" - more pics from different angles might be more useful in determining cause.

Widmer, soaking acrylic in alcohol can cause crazing, but a brief wipe on virgin material will not have this effect, not today, not in 20 years.
Now using alcohol to continually clean a fabricated product certainly can have this effect - esp if the product was flame polished and stressed, like this tank.

James

[kcress]

Thanks all. I'm about to base a full build on this tank and certainly am not thrilled about a $2k replacement.

I'll get some more pics.

[kcress]

Here's more pics.

This first is looking down from the top with an angle that maximizes what's happening on the outer face that shows the cracks.

http://www.box.net/shared/static/c7c1x14dz4.jpg



This pic is shot EXACTLY down the center of the last view showing the penetration depth of the cracks.

http://www.box.net/shared/static/ktydsp7uy7.jpg




This is a close up of the affected surface.

http://www.box.net/shared/static/j4ux87ppka.jpg

It looks like something wet was applied that caused it all. Notice the wipe marks on the edge.


Should I worry about it?
Should I do anything about it?

[noobtothereef]

that looks like heat related crazing, its just like a candle, take a candle and put it under really cold water and it will crack like that, if it were stress crazing it would look a little different and have more directional cracking, and heat crazing usually happens at the top of the tank at or above the water line like seen here, once it starts to craze the hole panel is in jeopardy , like mentioned earlier it might be from rubbing alcohol also, take a piece of acrylic and dip it in alcohol and it will crack just like that

[noobtothereef]

it almost looks like somebody tried to fill all the small cracks ith some weldon solvent by the looks of the wipe marks and white discoloring around the edges of the cracks

[azreefer]

It's hard to tell what angle the first picture is but if that's in the seam then it's starting to rip apart. If any of the seams are turning white like that I wouldn't fill it with water.

[noobtothereef]

or its from moving the tank around and banging into stuff...... you said its been sitting around for a long time....

[Acrylics]

In the last pic it looks as though someone tried to glue a patch on, saw what was going on and stopped, but no solvent marks and the joint doesn't appear to need any patchwork - so I'd guess an alcohol or similar solvent on the flame polished edge is the likely culprit. How it got there is anyone's guess, if that is indeed the case.

It doesn't look too deep, doesn't appear to be growing, and isn't in a high stress area. If there are no other issues, it's more than likely okay but do keep an eye on it and maybe print out some of these pics and place them near the area for reference. If it starts growing, you may wish to look to alternatives.

James

[kcress]

That was my feeling too since the cracks only penetrate about 1/16" max, and this, at the top of the tank.

Thanks A.