The Steamboating Forum

Hi,

What grade of solder should I use on my copper runs ?

jon

I would recommend 60-40 or 50-50. Not presently legal for potable water, but used throughout housing projects for about 100 years until about 1990, for potable water. Solders and flows better than the non-lead solder, and has higher melting point than the non-lead solder.

Hi Fred,

Do you know where I can buy that grade ? Also, I assume you mean 60% lead and 40 % Silver ?

jon

classic 60-40 solder is a lead/tin alloy. Silver is used in small amounts in lead-free alloys, which you don't need.

Personally, I generally use Sil-fos 5 or 15 on copper pipe on the steamboat; it's much stronger (and higher temp).

- Bart

Be sure we are talking about temps at or below boiling here. If these are for steam runs then regular solder is likely to go soft on you. Not fun. And a leaky check valve can let steam back into water runs some times.

I would go ahead and look to a higher temp solder with much more silver. Any welding supply shop can sell you decent silver solder and the proper flux. Brazing works O.K. too especially if you happen to be using odd fittings that don't fit that well (like about half of my junk box).

High temp silver solder with a mil or so gap is very strong in all sorts of applications. I have assembled steam chests and such that way. I just use a spring loaded center punch in at least three places to raise a gap for the solder to flow in. It's great to see the solder suddenly go from solid to liquid and flow in by capillary action. Play with a test piece first. Cutting it open is educational.

Somewhere in an old steam magazine I've seen a photo of a copper pipe joint actually creeping apart when regular solder was used. I'd be inclined to use silver solder every where on the boat! Den

55% or so silver solder is really strong, and is exactly what is needed for joining dissimilar metals such as steel with copper, etc. Sil-fos 5 or 15 works well and will fill gaps and form fillets, which is handy with commercial copper pipe fittings. Refrigeration techs use this extensively; it is only for copper, brass or bronze. The phosphorous gives it a strong cleaning action, enough so it's self fluxing on copper.

- Bart

Aha! I wondered why Sil-fos worked so well on copper. I have flowed together a fairly complicated 1/12 scale locomotive boiler with that stuff and had no leaks. Pretty near set fire to myself in the process though.

I thought you were asking only about atmospheric pressure exhaust connections, and that is one of the only places where ordinary soft (lead based or tin based) solders would be acceptable. Ordinary cold water service up to 100 PSI is OK for soft solders also, but as mentioned above, valves can always leak, and if high temperatures can be encountered, better to use the high melting point "hard solders".

The Sil-fos 5 or 15 or high silver "hard solders" are the only ones acceptable for high pressures and the maximum temperatures typically found on our steam launch plants. Sil-Fos is considerably less expensive than the 45 - 56% silver solders, and perfectly acceptable for copper alloy soldering.