Fixing welding occlusions and porosity

[JohnRobHolmes]

I have some mild steel welds that have an issue with porosity. Best guess, it is from contaminants on the inside of the tubing. I cleaned everything just fine, but in spots where I overheated the weld it started getting bubbly and porous. I assume the molten puddle broke through the inside of the tube and gobbled up something nasty. Using a Tig with argon and mild steel filler.

1. How can I best fix these? Grind em out and reweld?

2. How can I avoid this in the future? I can't always get into the middle of the tube to clean it out, but I assume that cleaning the inside may be very important. If I can't clean it, maybe I should use a mig with flux core so I can get some slag in there to help bring the impurities out?


many thanks for any help you can give.

[4wd4ws]

1.Yes.
2.Backing gas.(insert a tube with holes in the pipe)

[Sydwaiz]

I grind it out. If you are breaking through then I think you have the power to high but Im sure you realized that. Also make sure your nozzle is clean. I know when my nozzle gets cruddy, I have problems. The cruddy nozzle keeps the argon from making a nice uniform shield. (it basically disrupts the gas flow out the tip)

[thumper68]

1st make sure that nozzle is clean and you have good argon flow. 2nd make sure that you are not welding in a drafty area. If you don't have a good cloud of shielding gas you will get a poor weld.

to clean up and reweld, I use a dremel with a carbide bur to clean up small areas for big spots use a grinding stone.

tig welding is just like rock crawling, low and slow, turn your heat down and take your time.

[Fastball]

It is hard to say what happened to your weld, could have been overheating, insufficent gas, or contamination. It could also have been contamination on the filler rod. You should make sure that you wipe down that base metal inside and out, and the filler rod. Make sure that you do not use brake cleaner for this as many people do. When you weld it it produces some very nasty chemicals that are quite bad for you. These chemicals are produced even after it is dry. Use alcohol or acetone. On the subject of filler rod, I recommend using stainless rod unless you are trying to preseve the strength of a specific base metal alloy. You will have better results and no copper coating that is also bad to breathe. There are also tube metals that just plain tig poorly. I find this to be the case often times with hardware store quality tube.

Fastball

[Benzbuildr]

What size tube? If big tube you will have to drill a release hole in the tube to let the argon escape, or you will continue to get porosity no matter how well or many times you clean it, the build up of pressure will continue to cause you problems.

If your tube is open on one end then you could have impurities in your steel, the only way to remedy that is to cut it out.

[Grizzly4x4]

When I was TIG welding SS flow meters it was necessary to purge the area behind the weld with Argon to prevent contamination. You need to grind out all the porosity then drill two holes in the tube. One to pump Argon into the tube and purge out the air and one to let the Argon and gas pressure escape once the weld seals up.

[ultimate_monkey]

what sort of joint are you doing?.

yes the best and about the only way to fix this is like mentioned befor is grind it all out and start over

for the future nice tight joints! in my experiance TIG welding definaty dislikes trying to fill any sort of gap, (small ones are ok but no where near what mig / arc will do) running a backing sheild gas is a big help on some forms of tube joints but cant be used in all applications. say for a "T" stile joint in tube , make sure u have a nice tight fit then beval the edges to allow for nice penitration but make sure theres no gaps. on say a end to end but joint on tube, backing gas is deffinatly a good technique to use

[bastard]

What are you welding? little more info would be good.

[Jwelder24]

Many good ideas of what could be causing it. (pics may help)

what size tube you welding?

grind it out re weld.

should not get porosity from being too hot.

maybe if weld contaminated by improper shielding gas (what flow rate you at) may be too high causing it to draw contaminated air into weld.

is your tungsten nice and sharp and clean? it may still weld decent with contaminated tungsten.
could be if you are doing a weld that would seal up the tube it is building pressure.

[bastard]

Originally Posted by Jwelder24

could be if you are doing a weld that would seal up the tube it is building pressure.

That is what my thought was.

[JohnRobHolmes]

The offending joint is a t joint on two 2" tubes. One is sch 40 and the other is thinner. Can't grab a pic now, I'm out of state. More info per your requests-

The item is a headtube on a 50cc bike of mine. I mAde it a big wheel and the headtube angle got too raked out. I just used an angle grinder for the fishmouthing, but it is pretty tight. No gaps more than a few mm.

The headtube is china steel, the top tube is American steel. Hi-ten for both.

Both tubes are vented.
Flow rate is 20cfpm, new #6 nozzle so I can get in there easy.
2% thoriated tip, all I had. Fresh grind, clean grinder.
I didn't wipe the surfaces or filler off, I'll do that on the repair.

I noticed a strange arc when I passes over the wire fed tacks. Maybe another source of impurities? I cleaned the slag with a rotary paint stripper and wire brush.

Also, if I can't get a tool inside the tube to knock off pAint, how can I get to it? Torch it, brush it, wipe it?

Many thanks for the help. I will back purge on the next one. I want to get my shit right before building a chromo frame from scratch.

[ultimate_monkey]

yeah it almost sounds like you need to back purge if your gaps are a few mm. or atleast i would.

how far do you have your tip sticking past the cup?

did you use smaw or flux core for the tacks? both leave some form or contamination, obviously flux core will leave slag, but smaw will leave glass, for tack it usually sits right in the center or right tight on the corner of where the tack meets the base metal.

as far as the paint thing goes, you will never be able to tig over it, tig is the most picky form of welding, arc and mig can usually just burn off impurities but tig wont. so idealy sanding it all off would be best, torching wont remove it all.

where do you store your filler rods? if they are in a dusty / dirty area they could be what was contaminated and cuaseing you greif as well. also did u check all ur hose / torch fittings were tight? even with the flow rate up if there is a leak it wont be doing dick all

[the DMG]

herer ya go !! - CHINA STEEL , its crap !!
U never know whats in it ?
ive experenced the same thing with bad mixed steel.

[ultimate_monkey]

http://www.gottrikes.com/PDFs/Bender.../tubemiter.exe


this will help you get nice tight notches as well so ur fitment is damn near perfect

[DUDE]

Originally Posted by JohnRobHolmes

Also, if I can't get a tool inside the tube to knock off pAint, how can I get to it? Torch it, brush it, wipe it?

If there was paint inside, that is what caused the problem. gases from the burning paint inside back pressured on you and basically blocked your argon sheilding gas from doing it's job.