What is the trick to making leak free welds?

[Bison]

I use a oxy/acy welding tip to weld or braze hydr tubing,never had them leak yet.
Sometimes if there was room i cut the bad section out and used a compression union.

 

[Renze]

I like to preheat with the propane torch... burns off the oil from the crack, and the paint nearby... contamination is the biggest cause for welding pinholes and a torch cleans them best.

Also what the other guy said, make sure its open before you weld. If some fluid inside the system evaporates it will build up pressure, which will push through your weld before the melting bath is solidified.

 

[ak9]

I might add ... to pay attention to arc blow/ ground placement and how the +/- flows for ya

 

[jenkinsph]

I might add ... to pay attention to arc blow/ ground placement and how the +/- flows for ya

Your dog is way cool.