Pharma glass defects - 5. Chips

Hello everyone – welcome to Part 5 of an ongoing series about defects in pharma glass packaging (with an emphasis on tubular vials).? As a reminder, I’m working my way first through nonconformances that can potentially be classified as Critical defects per the newly revised PDA Technical Report 43.? The image shown above is the visual equivalent of a bad pun – this vial has a chip on its shoulder.

?A chip is defined as a small section or fragment that is broken out or missing (see Footnote 1).? It’s a technically correct description, but an accompanying picture is helpful to appreciate what’s being described.? I’m guessing a little searching at home will turn up a drinking glass with a chipped lip, such as the one shown in Figure 1. ??A typical chip is a relatively shallow defect produced when a thin flake fractures away from the original glass article.? You might consider chipping a form of breakage.? However, PDA TR 43 has a separate defect category called “Broken General” describing a container that has fully broken into two or more distinct pieces such that the container is completely unusable.?

A distinction can be made between “surface chipping” and “edge chipping”, as illustrated in Figure 2.? A localized load of contact (often sharp in nature, but not exclusively) to a glass surface creates a sub-surface region of deformation.? So-called “lateral” and “median” flaws can propagate from the bottom of this deformation zone where stress is most concentrated (see Footnote 2).? Edge chipping is more likely to occur as the contact load approaches a side wall of the glass article.? The size and shape of the chip is also dependent on the angle and magnitude of the applied load.?

How does this information apply to something like a pharmaceutical glass vial?? This is where knowledge of the fill-finish process becomes important.? For example, the needles/nozzles that “dive” into vials during the washing and filling steps are capable of exerting enough of load to cause chipping if they inadvertently strike the container.? In my experience, the flange or interior of the neck are the most commonly impacted areas.? One approach for potentially mitigating chipping is to replace stainless steel needles with plastic.? Careful inspection of the needles prior to use is also critical – needles that are bent or improperly installed often lead to strikes.? And while it doesn’t necessarily prevent the initial chipping event from occurring, it’s always important to monitor for needle strikes using alarms or visual indicators (e.g., some filling modules are designed such that needles will pop out of their manifolds to let operators know that a need strike has occurred).

Flange chipping from an accidental needle strike is an example of primary chipping.? Secondary chipping can also occur when an initial breakage event generates sharp fragments of glass.? These sharp fragments can interact amongst themselves or with other nearby objects to create chips that are unrelated to the initial root cause of fracture.

In terms of visual defect classification, a chip is considered a Critical defect if it extends ≥50% over the sealing surface of the flange or seal integrity is compromised.? It is a Major A defect if it extends <50% and >25% over the sealing surface OR exists in other locations and is ≥0.3 mm2 in size.? Chips falling outside these specifications are considered an Acceptable Imperfection.? Finally, recall that the chipping process has two parts – there is the cavity left behind (the main focus of this post) and also the fragment that is ejected from the surface.? Let’s not completely forget about that glass fragment. It has the potential to end up as particulate contamination inside of a vial – possibly the chipped vial, or possibly a different nearby vial that is otherwise intact.

Got questions?? Please them in the comments below or contact me directly.

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Footnotes

1. If you believe things you read on the Internet (and I sure hope you do given where this article is posted), you’ll find that the word “chip” is thought to come from an Old English verb “cippian” (to cut).? Early usage of the word chip referred to small fragments produced by breaking wood, cutting stone, etc.? Modern usage has expanded to other contexts such as fish and chips (fried pieces of cut up potato), gambling chips (originally made from pieces of gold, ivory, bone, wood, etc.), and computer chips (cut up pieces of a wafer substrate).? More importantly in this case, the word “chip” can also be used to describe the empty divot left behind by creation of a small fragment.

2.? The literature on this topic will frequently replace the word “flaws” with “cracks”.? As I have done in the past, I am intentionally reserving the word “cracks” to descrive a physical discontinuity produced by fracture of a glass container that permits exchange of gases and possibly microbial ingress.

3. Reference: Lawn BR (2021).? Chipping: a pervasive presence in nature, science, and technology.? Journal of Materials Science, 56: 8396-8405.