Steam engine tubes soldering

[kadora]

Hello friends
I am machining my first steam engine and I would like to know
if I can soft solder engine tubes for steam distribution.
I know that boiler must be hard soldered but copper tubes on
engine ???? //I think tube joints on engine are cooler //
Thank you for your advices.

 

[Buchanan]

I have had soft soldered steam pipes come loose on an engine. It depends a lot on how hot your steam is. Does the steam line go through the flame after it comes out of the boiler? If so you are super heating it somewhat and you could have problems.

 

[kadora]

Thank you Buchanan for your quick answer.
I will solder pipes with soft silver/tin solder paste - 230 degrees Celsius melting point.
Hopefully it will not deteriorate in steam environment.

 

[Blogwitch]

It isn't the heat you have to worry about, even electronic type solder will join and hold parts together. It is vibration that is the failing point.

Soft solder doesn't penetrate into the parent metal but sort of 'sticks' on the surfaces so it is the solder itself in area between each part that fails under vibration, the more soft solder you have in/on there the more liable it is to fracture whereas silver solder actually 'bonds' to each surface and is very resilient and strong and requires only a very thin joint to make a super strong joint.

This is a test I did on a steel to copper joint, and as you can see, it stood up fairly well, in fact, the copper pipe itself would have failed before the joint gave way.

John.

 

[goldstar31]

Initially, I agree with John about the desirability of changing to silver solder for boiler making and joining bits to boilers.

Of course, silver solder 'wicks' and actually changes its melting point in the process.

What hasn't been said( so far) is that if for some reason, it is deemed necessary to use silver solder or braze, anything which was leaded will not 'take' and the possibility of the joint exploding remains high.

Norman

 

[Wizard69]

No model making experience here but have seen interesting failures in industry, in this case with steam sterilizers. You really want to us the stronger methods whenever possible, sometimes that includes brazing. As John pointed out it isn't aways the temperature but rather the mechanical failure of lead in the joint. I should point out though that temperature cycling can lead to some of those mechanical stresses. I've actually have seen cold water lines come apart under mechanical stress even if the soldered joint looked to be professionally done.

It should be noted that some of the new lead free solders may have been a factor in these failures. Often it is hard to tell what solder was used on older lines. So in a nut shell I'm distrustful of lead based solders even in mainstream usages.

 

[bazmak]

silver solder really is a must for boilers and fittings
The only time i have used lead solder is to seal a mechanical joint
ie a rivitted joint

 

[kvom]

All of the boilers I've seen at our club have bushings welded onto steel boilers. If a copper boiler than the bushings are silver soldered. All the rest of the tubing is connected via tapered pipe threads or unions, not solder.

Some joints for water and copper tubing use flare joints.

 

[kadora]

Thank you friends for your help.
By the way I read on some forum that Wilesco steam toy producer
soft solders boilers for small engines .
However when i am investing lot of time to build engine is worth to
hard solder all piping.