Pharma glass defects - Part 48. Broken ring off

Hi everyone – welcome to Part 48 of an ongoing series about visual defects in pharma glass vials.  I’m hoping to get through all of the defects for converted tubular vials listed in PDA TR 43 by the end of this year.   I only have three left to go based on my last count.

We’ll be briefly covering the “Broken Ring Off” defect in today’s post.  It may seem like a somewhat unusual name, but the additional specificity is needed to help distinguish it from two related defects –the “Broken General” and “Broken Detached Bottom” defects.  The Broken Ring Off defect is a case in which the vial fractures circumferentially around the shoulder and/or bottom regions, as illustrated in Figure 1.   The Broken Detached Bottom has a similar description – i.e., a circumferential fracture around the bottom of the vial.  However, the mechanisms leading to these breakages are different.  A Broken Detached Bottom is principally caused by the handling-related introduction of a flaw into the heel region.  This flaw is then propagated to fracture by an applied stress.  The Broken Ring Off defect traces its origins back to the initial converting process.  The heating used as part of tubular conversion results in residual stresses in the container.  These stresses are supposed to be largely removed by a high temperature annealing process.  An improperly annealed container can therefore still have residual stresses around the shoulder and bottom regions that increase the likelihood of breakage (see Footnote 1).

Classification of a Broken Ring Off defect is straightforward – it’s considered a Major A defect since the container is rendered unusable.  Perhaps the bigger challenge is correctly differentiating among a Broken Ring Off defect, a Broken Detached Bottom defect, and Broken General defect (assuming of course that the fracture occurred circumferentially around the bottom region of the vial).  All of them are Major A defects, but it’s important to properly identify the defect type for the purpose of root cause analysis.  The Broken Ring Off defect should be identifiable by observing vials with a stress polarimeter and comparing to a properly annealed vial.  The residual stresses will be apparent as bands of color in the shoulder and/or bottom regions.

Questions or comments? -- please leave them below or feel free to directly contact me.

Footnotes

1.       Lest I forgot to mention it elsewhere – what about the Broken General defect?  It’s a catch all category that is meant to cover all other situations in which a vial has broken.  Just remember that glass breaks when a sufficiently large tensile stress acts upon a sufficiently large flaw.  The Broken Ring Off defect describes a specific case where the residual (tensile) stress is important, while Broken Detached Bottom is more concerned with the introduced flaw.  Also note that the Broken General defect can be accompanied by other defects, particularly at the origin of failure.  For example, consider a case in which a bent filling needle strikes the interior neck of a vial with enough force to cause the entire flange to break off.  Assuming this was a steel filling needle, you will likely see Metal Mark defects where the needle contacted the glass vial.  However, I would still classify this as a Broken General defect.