What is the trick to making leak free welds?

[franklin2]

I thought it could not be done. I have seen people try to weld cracked steel hydraulic lines on tractors, forklifts, backhoes, etc. and they never were successful.

So, we had a skid steer with a backhoe attachment. It had steel lines running up the arm, with hoses at the flex joints. One of these metal lines cracked and fluid was going everywhere. My Dad took the line off and went to a machine shop where he thought they could make another line. When we got there the guy smiles and said "oh, I got a guy who can weld that". I thought to myself no way. A young boy came out, took the line, adjusted his mig welder a little bit, welded the line and then gave it back. $20 later we are on our way, and I looked at the line, he had run a bead right over the crack. Installed it and it worked great. I was floored, as many times as I have seen this tried, and have tried it myself, I could not believe it worked.

A couple of weeks ago I had the A/C compressor clutch fly apart on my mini van, and one of the flat springs came around and was hitting one of my steel refrigeration lines, cutting a little hole in it. Encouraged by what I saw on the hydraulic line, I got my mig out, cleaned the line really good, set the amps low, and welded it. No burn through or anything. But it had a pinhole leak. I welded it again. Pinhole leak. Frustrated, I smeared some JB weld over the welded area, and it has held ever since. But I am bummed out that I could not weld it and it be leak free.

What is the trick to welding these lines and they be leak free? I know it can be done now.

P.S. I posted this question also in the build it yourself section. Here's a link.

http://www.tractorbynet.com/forums/...-what-trick-making-leak-free.html#post3869641

 

[LD1]

I'll answer in this section.

First, everything has to be clean. And as others have said, the line has to be open. Welding heats the air inside the pipe. Builds pressure if it is a closed system. It has to vent somewhere, and the molten hot metal of the weld puddle is the softest/easiest area for the venting to happen.

Inside of the pipe also has to be clean and oil free.

Small pipe and tubing is difficult to weld just because it is small and thin material. But still doable with the right settings and starting with good clean parts. Also, trying to minimize the number of starts and stops with the mig welder will help a bunch.

 

[Stimw]

I have always Oxy-Acetylene welded or brazed steel lines that have failed. TIG is also more friendly and it is similar to gas welding. Both give you a lot better control of the puddle.
Pic is adapters that I had to make because I could not match up Chinese flat face fitting on a Jinma Hoe.
I gas welded original FF to a JIC fitting.

 

[JUBILEE1953]

Practice...

 

[Arc weld]

Wait and see if the repair lasts over time. The tiniest bit of moisture, oil or back pressure can cause a pinhole. I welded a crack on a ripper frame on a cat and while it was cooling cracked open again because of the pressure build up inside the tubing. I should have left a little hole and welded it after the bigger weld cooled and there was no pressure build up in the tubing. Usually brazing or O/A welding is best for hyd. lines as it's a slower process that heats the area hotter and causes less problems with heat affected zone cracking that you might get from arc welding with stick or MIG. TIG allows for more precise heat control so is used by people experienced with it.

 

[tnjind]

It is all about fusion, just globbing bird poop on the substrate won't do it.

 

[Mark @ Everlast]

In the case above, oil or contaminants was a likely cause...but I don't know about welding on stuff with any form of freon in it at one time. Not my cup of tea because the fumes of some of that can kill you....even a little wisp.

 

[Arc weld]

I lot of commercial air conditioning lines are silver soldered.

 

[Brad_Blazer]

I welded some hydraulic fittings a few years ago when I installed my backhoe. It seems like I tried several methods that leaked, then I stick-welded it with 6010 and no leaks.

 

[Egon]

Just think of all those welded pipeline joints that don't leak!

Course the welder has had courses, lots of practice and yearly competence checks.