Why is 95/5 solder not recommended for brass?

[Mliu]

I just happened to read a product review for solder that said 95% tin/5% antimony solder is not recommended for soldering brass and should not be used for copper plumbing in general. I've never heard this before and thought that 95/5 was a common lead-free solder used for plumbing. I just checked on the Harris Products website and, on their 95/5 solder page is the following note:

Typical Application: Not recommended for use on brass or HVAC connections.​

Well crap. If this stuff is not recommended for plumbing, not recommended for brass, and not recommended for HVAC, what the hell is it used for?

I've been using an old spool of Oatey Safe-Flo solder that I think is labeled as 95/5 (I'll check when I go to the shop later today). If it is, I'm very disappointed because I recently soldered up a nice water filtration manifold (complete with brass ball valves and brass sweat/union couplings for a PRV).

So what exactly are the problems with using antimony with brass?

 

[Reach4]

http://what-when-how.com/materialsparts-and-finishes/solder-alloys/ is old, but has an interesting relevant section:

Tin-antimony-lead. These may normally be used for the same applications as tin-lead alloys with the following exceptions: aluminum, zinc, or galvanized iron. In the presence of zinc, these solders form a brittle intermetallic compound of zinc and antimony.​

Brass is copper+zinc.

https://en.wikipedia.org/wiki/Intermetallic says "Inter-metallic compounds are generally brittle and have high melting points."

https://en.wikipedia.org/wiki/Solder#Intermetallics_in_solders says "Antimony is added to increase strength without affecting wettability. Prevents tin pest. Should be avoided on zinc, cadmium, or galvanized metals as the resulting joint is brittle."

 

[Sponsor]

 

[Mliu]

In the presence of zinc, these solders form a brittle intermetallic compound of zinc and antimony.

Brass is copper+zinc.

I knew about the composition of brass. I didn't know about the "brittle intermetallic compound of zinc and antimony."

Btw, reading the Harris spec sheet for their 95/5 solder, they state that it's used for general plumbing. So the guy who wrote the product review (and who said it should not be used for plumbing and that it's typically used for HVAC) must have gotten his facts reversed.

In any case, if manufacturers are going to sell a plumbing solder that is incompatible with brass, you bloody-well would think they'd put a warning on the packaging. I mean it's not like brass fittings with sweat connections are common in plumbing or anything.</sarcasm> Perhaps if they weren't required to repeat everything in Spanish, they'd have room on their labels for such pertinent information.

So I wonder if I have to worry about my three 3/4" brass ball valves and PRV sweat unions now.

 

[Reach4]

So I wonder if I have to worry about my three 3/4" brass ball valves and PRV sweat unions now.

Brittle would be a problem with flexing, and I doubt those are subject to flexing.

 

[Mliu]

Brittle would be a problem with flexing, and I doubt those are subject to flexing.

They are on the cold water supply, so I think you're right.

Actually, I just remembered that the PRV union couplings were 3/4" FNPT (connected to the pipes with soldered copper male adapters). I do have a tempering valve that does have brass sweat union couplings and I have a number of brass sweat x PEX connectors, but fortunately, I haven't soldered those yet.

So I only have to worry about the 3 brass ball valves. They're very rigidly supported by the filter manifold so I probably don't have to worry.

I still need to check that old spool of Safe-Flo.

 

[Kreemoweet]

There's no antimony in Oatey Safe-Flow solder.

 

[hj]

HVAC joints are usually brazed, not soldered.

 

[Mliu]

There's no antimony in Oatey Safe-Flow solder.

I know that there's no antimony in the Oatey Safe-Flo solder that's currently sold. However, the spool I was using is probably around 20 years old and I seem to recall it being labeled 95/5. I haven't had a chance to stop by the shop yet to check. I hope I'm wrong.

 

[Mliu]

HVAC joints are usually brazed, not soldered.

I am aware of this, having brazed copper AC lines myself. But solder is used in the trade (albeit, mostly for copper drain lines, which are really no different than DWV plumbing connections).

 

[Mliu]

Well, I stopped by the shop this evening and took a look at my remaining 1 lbs spool of Safe-Flo. There is no chemical composition printed on the spool, so hopefully I was mistaken about thinking it was 95/5. I'll call Oatey tomorrow and ask them if Safe-Flo has always been free of antimony.

 

[hj]

condensate lines are not considered when referring to hvac lines. so the original statement stands.

 

[Mliu]

condensate lines are not considered when referring to hvac lines. so the original statement stands.

You said "usually"; I said "mostly." The point is, both of us allow that soldering is appropriately used in HVAC lines (besides condensate lines). So let's just agree to agree.

 

[Mliu]

I did contact Oatey and, according to their chemistry department, their Safe-Flo branded solder has never been formulated with antimony. Disaster averted!