Cracked glass and when to retire a vessel

Glass gives notice. A star in the base, a chip on the rim, or a graduation that has gone cloudy is the notice. This selection guide states the damage that should take a vessel out of service, and the words to use when you specify the replacement. Intact choices among beakers, flasks and volumetric ware are laid out in choosing laboratory glassware.

Criteria for retirement

Retire a vessel that shows a crack, including a star crack in the base or a hairline running from a chip. The piece has already spent its safety margin. The next stress it sees does not need to be dramatic. A hot plate, an autoclave, a slight vacuum, or the knock of a drawer is enough. "Using it carefully" is how careful people get cut.

Retire a chipped rim, a chipped spout, or a chipped joint. The missing flake is sharp, and the remaining edge is the origin of a longer crack. A ground joint with a chip will not seal and may lock or split when clamped. A bottle neck with a chip will not take a cap reliably and will cut the person who finds out.

Retire volumetric ware when the line, the numbering, or the neck surface is etched enough that two readers can disagree, or when the base is starred even if the line still looks fine. The volume claim is a metrological claim. NIST calibration practice assumes an intact vessel. A frost from alkali is permanent. It is not a film you can rinse past.

Retire glass that has been through a thermal shock you heard or saw: a tick, a new star, a wet path on a hot bench that now has a cracked base. Borosilicate 3.3, the low-expansion type distinguished in ASTM E438, resists shock better than soda-lime and still retires once it is cracked. Soda-lime retires for the same visible damage, and it should not have been on the hot plate in the first place if it was unmarked.

What can stay, with a narrower job

A beaker with a worn but uncracked graduation can stay as a handling vessel if the method never reads that graduation as data. Say so. A flask with a discoloured but smooth surface from a stubborn sample may be chemically contaminated rather than cracked. The test is whether the mark washes off under the laboratory's cleaning method. Stain that is only a stain can stay if the chemistry of the next method allows it. Stain that is etch cannot.

Scratches on a stir-bar path are a judgement. Deep scoring that catches a glove, or any crack branching from a scratch, is retirement. Light wear on a thick borosilicate beaker used only to hold a probe is a different object from scored volumetric glass. When you are unsure, retire it from heat, vacuum and calibrated work.

Do not repair laboratory volumetric glass with a file, a flame you are not trained to use, or a glue. A glassblower can sometimes rework ordinary apparatus. A volumetric neck is a calibrated surface. Assume a repaired volumetric flask needs a new calibration or retirement. This page is not a glassblowing procedure.

Causes to write into the replacement decision

Thermal stress causes stars in bases: cold liquid into a hot thick bottom, a hot flask onto a wet bench, or an autoclave load cooled in a draught. If you are replacing several pieces at once, the specification is not only "more beakers". It is borosilicate 3.3, plus a cooling habit, plus inspection.

Autoclave cycles cause cap and shoulder damage when bottles are sealed full, and they reveal cracks that were already there. Replace with the same thread class and a cap policy that loosens ordinary caps. Do not replace a cracked soda-lime jar with another soda-lime jar for steam duty.

Etched graduations come from alkali storage and from harsh washer chemistry used on volumetric ware for years. The replacement flask should not live in a sink of sodium hydroxide. A plastic container the resin chart allows may be the better store for that base. The flask returns to the job of making up a volume and then being emptied.

After retirement

Empty the vessel by the chemical or biological waste rule before it goes into a sharps or broken-glass stream. A starred flask that still holds solvent is a chemical incident, not a glassware incident. Biological glass follows the WHO laboratory biosafety manual only as background to your local rule, and the CDC BMBL the same way. Do not autoclave a cracked sealed bottle to settle your nerves.

Remove the twin of a matched stopper from service with the flask, or you will grind the stopper into the next neck. Record which calibrated pieces left the set so a certificate is not orphaned onto a replacement that has not been checked. A new Class A flask is not the old flask's certificate.

Hearing a tick is already the decision

A tick as a hot beaker meets a wet bench is the sound of a crack finishing, even if you cannot yet see the star. Set that piece aside until it is cool enough to inspect in a good light. If you find the star, retire it. If you do not find a mark, still keep it out of vacuum and out of the next heating cycle until someone else has looked. Two pairs of eyes on a thick base catch stars that one hurried look misses. The replacement specification does not wait on a debate about whether the tick "might have been the bench".

Warm benches and cold rinses

The local version of this damage is a hot wash or a hot autoclave unload meeting a cold rinse or a stone bench that sweats in humid weather. Specify borosilicate for anything that will see that cycle, and specify inspection after the cycle. A power cut that stops a drying oven does not crack glass by itself. Unloading a half-cooled oven onto a wet rack can. Build the cooling surface into the room, then buy the replacement glass against the damage you actually see.

What the enquiry needs

The vessel form, capacity, glass type, class if volumetric, joint size or cap thread if it has one, and the quantity of replacements. Mention that the order replaces retired damaged ware so nobody "helpfully" sends a soda-lime jar. Use the laboratory glassware catalogue and, for marked volumes, the volumetric glassware catalogue. Send the line through the quote request.