You need to check for hairline cracks before use otherwise the materials can leach through to the steel mantle. Happened to me once where the crack was right at the top near the stirrer joint. We only noticed it after we observed glass in the product. Somewhere I have a picture of the hole that the conc. HCl made! Since then I always insist on a conductivity check to make sure the glass is still intact.He has kindly sent the picture:
with the following comment:
They are of a stirrer of a 1000L reactor. You can see the hole. The metal was so thin that you could move the bottom part of the stirrer with your hand. This was after 120 batch reactions of 800L 37% HCl at reflux. I reckon 1 more reaction and we were in trouble, as it was is cost a lot to replace the stirrer.Good heavens! For those at home, the purple material is the glass and the hole was made in the steel underneath the glass (I think.) This is what they normally look like, for comparison' sake.
Thank you, Quintus, for the picture and the comments -- you are valued here.