The Value of Heat Soak Testing

Heat Soak Testing (HST): Should you or should you not specify this process as a glazier, architect, consultant, or designer. The type of glass, its application and your tolerance to risk are variables that must be considered. Read on to see why HST could make sense for your needs.

Explaining HST!

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THE BENEFIT OF HST

The costs of NOT using HST can be expensive.  Once the glass is installed, the cost of repair is dramatically more than the cost of the HST process.  From additional fabrication to additional labour associated with the removal and re-installation of the problem unit, these costs will largely outweigh the small cost of HST.

Application and glass type are also important considerations.  HST makes sense if you are installing large, custom size IGUs or laminated glass which have tempered elements.  The cost of performing HST is relatively low and factors into roughly just 3% of the overall price of the unit, dependent on size and the overall volume of the order.

HST can be equated to this:

An insurance policy against spontaneous glass breakage in architectural glass. 

Like any insurance policy, the likelihood of making a claim is slim, but it is immensely helpful when things do go wrong.  Protecting yourself against this downside can be achieved through specifying HST – it is a cost-effective and sensible hedge against costly repairs and lost revenue.

In a high-value project, HST just makes sense. 

OTHER POINTS TO CONSIDER

An example of NiS breakage in a laminated unit at AGNORA.

WHY DOES SPONTANEOUS BREAKAGE OCCUR IN THE FIRST PLACE?

Spontaneous breakage of tempered glass is the result of Nickel Sulfide (NiS) expansion. NiS are small particles that are formed in the manufacturing process of glass from the sulfur of the firing agent and surrounding metallic surfaces. An estimated 1 square metre for every 10000 square metre of glass produced contain an inclusion sizable enough to cause failure.*

These inclusions undergo contraction in the tempering process resulting in an unstable, smaller structure. Overtime, the NiS inclusions will expand back to their original state, exerting immense force on the glass and eventually causing breakage.

The HST process allows NiS inclusions that may be in the tempered glass to expand back to their original size in the safety of a chamber. AGNORA uses the newest ISO 20657 standard (replacing EN14179-1:2005) which aims to react all forms (there are many) of NiS within a tempered lite.

*GCF estimation

NiS AROUND THE WORLD!

In 2016, the estimated worldwide production of glass totaled 9.2 billion square metres.* Using our 1/10000 square metre estimation, this production volume results in 1 million square metre (920 000 to be exact) of glass that potentially contains problematic NiS inclusions.

This is for one year alone. Multiply this over many years with increasing glass volume, and cumulatively, NiS is everywhere.

Granted, many lites are not tempered and NiS is NOT guaranteed to cause an issue, but this illustration is meant to show NiS pervasiveness worldwide.

*Glass Canada, 2018, Report on GPD 2018

AGNORA’s oversized HST is capable of testing glass up to 130″ x 283″