PET carboys with strange discoloration (pictures)

[feartheroo]

Hey everyone,

First time poster here. I am on my third and fourth brew (using the same PET 6 gallon primarys as last brew) and I noticed a strange discoloration after cleaning AND what looks like a melted part near the opening of one bottle? I cleaned them with standard brew wash thoroughly and the only thing I can possibly think is the water from my bathtub was too hot?

The slight morphing near the mouth on the one does not worry me as much as the strange blue tinge in the plastic. I did not see it in the daylight only when the lights were on at night time.

These are not BB brand, but my local ubrew says he uses them all the time without problems (years per bottle).

Has anyone seen anything like this before? I really hope I didn't ruin my strawberry cider I worked on this one all day.

 

[Bensiff]

One of mine has a small area where it got bent in that has that discoloration. So, my guess is that you, or someone, shoved down really hard on the neck pushing in the entire shoulder causing a stress mark...like stretch marks for carboys.

 

[Ike]

"stress-induced crystallization," as described in the link below, was the first thing that came to the long-dormant, decade-forgotten materials engineer in me. Again, it's been a while, so I'm going to let them do the talking.

The next guy in the thread mentions crazing. For me, it's a "continuum" thing, keep stressing the plastic and it will go from crystillization to failure as in the crystalline state it can't handle as much deformation (IIRC).

OR, I may be totally wrong. Again, it's been a while. So much information has been crammed into my head on top of all that materials engineering info, that a lot of it has leaked out into my feet, I think.

EITHER WAY: your example looks pretty mild. Sure, if there may be microfractures that could allow oxidation. BUT, again, your example is really mild... if you don't start to notice off flavors specifically related to these carboys, "keep rocking" is my vote!

http://www.reddit.com/r/askscience/comments/1fyf6y/why_does_plastic_turn_white_when_you_bend_it/

 

[Harry482]

I have a BB that has a white ring like that. It was caused by using too strong of a bleach solution to sanitize.