We have a question relative to extending the expiration date on braze paste. Do you know of an industry standard that we could reference? Is there a particular rule of thumb that you would recommend about handling shelf-life/expiration dates?
There is no "industry standard" that I am aware of that you could reference that would give any guidelines about extending the expiration date on brazing pastes. Each manufacturer uses different criterion for setting their own shelf life or expiration dates for brazing filler metal (BFM) pastes. A number of manufacturers have now even stopped showing an expiration date on their paste containers but, instead, merely show a manufacturing date. They used to print an expected shelf life on the containers, but because of rejections of good BFM paste (merely because of date on the container) some manufacturers have stopped doing that.
Here are two things to do:
1. Call the manufacturer and get their specific thoughts regarding the expiration dates of their paste. Ask them what they suggest for paste that exceeds those dates. If you can, get a note in writing from them showing the maximum shelf life they would allow/guarantee for their pastes.
2. Test the "creaminess" of your BFM pastes that appear to be getting near their expiration dates. I used to do this by extruding a tiny amount of paste out of the end of the paste-cartridge, and as long as the paste was still extrudable and creamy, I would use it in our brazing shops. Obviously, for special aero-projects requiring complete traceability of all materials I would not do that since no "expired" material should ever be used no matter how good it is. With today's traceability needs, any use of BFM paste that had officially "expired" or gone beyond its printed shelf-life could cause the brazing shop to put themselves in a position where end users would have an opportunity to point their blame finger at that brazing shop should something go wrong with the brazement in service, even if there was nothing wrong with the BFM paste.
Having said that, I have had no problem using BFM paste in a variety of noncritical commercial work as long as the BFM paste is still creamy and extrudable. The filler metal in the brazing paste does not suddenly decide to go "bad" after the expiration date. In fact, even if it is older than the printed shelf life on the container, it can still be used until it is all gone. It's not like food, where expiration dates should be carefully followed for health reasons.
Here's another important point about BFM paste whether it's somewhat new or is past its so-called expiration date. Should the paste seem to be drying out – the plastic cartridge that is holding the paste does "breathe" to some extent allowing some minor amount of air-exchange (through the walls, around the end piston, etc.), which can cause paste to dry out – it can usually be reconstituted by mixing in some extra "binder" that can be purchased as a separate item from several different BFM suppliers (don't just add water).