A glazing consultant has recommended that we heat soak our tempered glass to test for inclusions. Is this common procedure? Can anyone explain to me how this works and if there are any other options?
Viracon has an explanation of heat soak testing in a TechTalk on their website.
Robin: I require all glass on our projects to be heat-soaked. I’ve had only one squawk about that in the past several years, which leads me to believe that having that requirement isn’t that difficult to comply with. (adding that was recommended to me by a glazier, by the way)
We had a project many years ago that had spontaneous glass breakage with a final conclusion that it was happening because of the nickel inclusions. Viracon’s recommendation, which we have adopted, is to require glass to be heat strengthened as a base, with fully tempered only where necessary to meet building code requirements. We also include the requirements for heat soak testing in our specifications and about the only people that have questioned it are some of the developers we’ve worked with.
Robin - Heat soak is a common procedure to limit the possibility of a nickel sulfide reactions. It is always a part of any glass wall system we design.
Based on this discussion and a specific incident I know of, I’m now requiring heat soak testing in my glazing section. However, on a project we currently have out for bid, I’m getting getting some resistance from a glazing installer saying it’ll cost “thousands of dollars” and the only manufacturer that will do it is Viracon.
Does anybody know of what the relative cost increase would be, and if there are any known glass manufacturers that WILL heat soak test their glass?
Saint Gobain will heat soak.
Just as an fyi, the October 2006 issue of “Glass Magazine” has a multi-page article on glass breakage from nickel sulfide inclusions. The article is based on a presentation given in Finland so includes reference to European standards and terminology (refer to tempered glass as “toughened” glass for example).
Some insight from the glass fabricator side…
I will tell you that the reason no one (or a very rare few) heat soaks domestically is because the “inclusion” issue is so rare. The average spontaneous breakage used to be 8 per thousand, I believe it is significantly less now.
Also, at least according to Pilkington and the other primary mfg’s Nickel sulfide is more prevelant in glass that is made overseas. (though not sure if I believe that angle actually)
Regardless this issue is not a big one from the domestic side. In the last 4+ years I can count on one hand how many lites we’ve had spontaneous explode in the field- and we have the 2nd most tempering facilities in North America.
Plus as the folks that do Heat Soak like Prelco even note on their Heat Soak requirements that heat soaking does not guarantee the glass won’t spontaneously explode. That too was a reason we stayed away from that technology when we realized we probably could have the same events whether we heat soaked or not.
I know this may not be what you want to hear, and the angle of heat soaking may be what everyone wants, but I just wanted to give you some insight on why its so impossible to find anyone willing to step up and do it.
Thanks for your time-
Max Perilstein
[Max is with Arch Aluminum - Colin]