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Heat Soak Testing

Heat Soak Testing

Toughened glass is a hugely popular product and SGP supply it in all forms, flat, toughened and laminated and it is used for many applications including Balustrade, canopies and partitioning.

On rare occasions toughened glass can break spontaneously, without any applied load, due to small Nickel Sulphide inclusions that may be present in all float glasses. These breakages can occur months or even years after installation.

When Nickel sulphide inclusions (NiS) are present, the standard toughening process changes the state of the inclusion and due to the fast cooling it cannot return back to its original form.  Over time, NiS may slowly convert to its pre-toughened form but with an increase in volume.  That increase in size can cause breakage.

Due to the impossibility of finding such very small inclusions, no float glass manufacturer can guarantee the complete absence of NiS inclusions in glass. As such, any breakages are not warrantied and therefore SGP recommend Heat Soak testing to BSEN 14179.

Heat Soaking is a destructive process where toughened glass is placed inside an oven and heated to 295°-300° and it remains at this temperature for 4hrs, this is to accelerate the expansion of any inclusions and cause breakage within the oven therefore reducing the risk of breakage when on site at a later date.

Here at Specialist Glass we currently have 2 Heat Soaking ovens to service our customers’ requirements. We can Heat Soak any thickness of glass in curved or flat form.

For more information please do not hesitate to contact one of our sales team.


  • David / 27 September 2017 10:26

    Wonderful article! Very informative. I never knew the reasons for unexpected breakage in glass (which is Nickel Sulphide) but thanks to this article I’ve learnt something new today. I’m glad there are methods to help test against this issue instead of leaving it up to the unknown. Keep up the great work! :)

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