repair of crack in steel pipe that conttains oil.

[nauticalmike]

I was once told by someone that I now feel lacks much credibility that when you are welding on a pipe that has any oil in it, that when yoou attempt to weld up the crack that any oil in the pipe will be drawn too and will contaminate the weld. this is wrong, isn't it? Won't the oil actually be pushed away bfrom the weld until after the weld has been cooling down for some time. Then after cooling for awhile the oil will be drawn to the weld. The oil will in no way contaminate your weld though, right? You can just inert the pipe and weld it, right?

 

[Carburize]

You are both correct!! The heat of the welding does tend to drive the oil away from the area of the weld but welding anything which has been contaminated with oil presents difficulties. My own experience is with gearbox housings. It is impossible to clean the cracked area sufficiently well to remove all the oil and the weld is generally of poor quality ( lots of porosity) however if the first weld bead is ground out and then the part rewelded the second weld is usually much better and if the process is repeated several times, welding/grinding, welding/grinding etc. a reasonable weld can be produced.

 

[jeffita]

If it is possible to tig it thats what i would i would try.

I repair thin wall tubing quite frequently that has had oil,
Alcohol and Nitromethane in it and have had no problems by slowly preheating the start zone before adding filler rod.

This works on mat. up to .125

Jeff

 

[nauticalmike]

Carberize,
I appreciate your help, hoowever I ddon't really feel that gearbox housings have the same characteristics as steel pipe. I would guess that your gearbox housings are either cast aluminum, cast iron, or cast steel. The emphasis of course being on the "cast." Although I may be mistaken, I would expect a gearbox housing crack would contain many more fissures and inclusions so any oil would be very difficult to remove. If you aare dealing with cast iron, it almost seems to absorb oil like a sponge, whicch I guess is why oil makes it much harder once oiled it becomes considerably more difficult to machine. If your housing is aluminum... we already know that aluminum needs to be immaculately clean to weld. Cast steel is somthing that I've had little experience with, but I still wouldn't expect it to have as clean a crack as steel pipe. If I am wrong please do not hesitate to correct me, Becaause most of my statements came from within rather than a text book, and I'm not a mettallurgist, see I can't even spell it correctly.

 

[Carburize]

I have had similar experience with cast iron housings and those fabricated from welded steel plate. As I said in my earlier post - it is possible to get a decent weld but it sometimes takes several reworks to get there

 

[rmp319]

We have repaired steel tanks holding oil and diesel and found great success with pre-heating the area around the repair prior to welding. This tends to bake out any contaminates and at least in our applications, eliminated porosity and defective welds.