Pharma glass defects - 35. Scratch

Welcome to Part 35 of my “Pharma glass defects” series in which we consider visual defects that may be observed in pharma glass vials.  Today’s quick post is a natural follow up to last week’s discussion on Scuff marks.  A Scratch defect is defined by PDA TR 43 as “a shallow surface abrasion or damage on a glass surface in a form of a line” (refer to an example illustration in Figure 1).  In other words, a Scratch consists of a single abrasion mark while a Scuff is a collection of (typically smaller) marks.  Just like a Scuff, a Scratch defect is created by handling-related damage to the glass vial surface at any point along the supply chain.  With that said, I would typically assume a Scratch to be caused by point contact and a Scuff to be caused by more of a surface interaction – i.e., the likely root cause for the two related defects can be different.

Classifying the criticality of a Scratch defect requires sizing with an appropriately calibrated measurement tool (e.g., an optical microscope or eye loupe with a graduated scale, calipers, etc.).  A Scratch is considered a Minor defect if it is ≥0.2 mm in width AND ≥1/3 of the vial body height OR ≥0.2 mm in width AND its length circumscribes ≥90° of the vial body.  A Scratch is an Acceptable Imperfection if it falls below these dimensional thresholds.  I previously noted in my Scuff post that classification requires a relative measurement – i.e., the size of the Scuff mark relative to the body surface area.  The same is true for a Scratch, which is measured relative to the vial body height and the body circumference.  Body height (also referred to as dimension h ₂ in the ISO 8362-1 standard for converted tubular glass vials) is the distance from the footprint to the beginning of the shoulder region as shown in Figure 1.  Combining the dimensions for body height and outer diameter from ISO 8362-1 with the previously described dimensional thresholds can be used to calculate the minimum length in the vertical and horizontal directions for a Scratch to be classified as a Minor defect (see Table 1).  A key feature of converted tubular glass vials is that the same tubing can be used to make multiple formats.  For example, 16 mm OD tubing is used to make 2R, 3R, and 4R vials.  This means that the minimum Scratch length in the vertical direction increases in going from 2R to 3R to 4R (i.e., increasing body height) while the length in the horizontal direction remains constant.

Also like a Scuff, the Scratch defect is an aesthetic nuisance given its potential impact on the visual inspection process.  It can also act a strength-limiting defect that increases the likelihood of container cracking or breakage.

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

About the Author

Matthew Hall is Technical Affairs Director for Corning Pharmaceutical Technologies, a manufacturer of primary glass packaging for parenteral drug products.  Based in upstate New York, Dr. Hall serves as a technical expert supporting business operations, sales, and marketing and educating customers on pharmaceutical glass packaging.  He is a member of the Parenteral Drug Association and the International Society of Pharmaceutical Engineering.