advice on paint removal for re-welding.

Here is the situation, I just finished a set of intercooler pipes for my car. For those of you that are not familiar with the term, it means it needs to be completely air tight and carry pressurized air from the turbo to the engine.

I have a MIG running co2 argon mix. Cheaper model only 4 power levels.

and I just find out my welds are leaking air all over the place. Due to low heat, lumpy welds, my newbie skills (or lack off).

I did some experiment on a scrap pipe and it seems if I do a 2nd pass over it with higher heat, it should seal everything up very well. This heat level was not suitable for my initial welding because it would end up blowing holes on the edges too easily for my skill level.

The main problem now is I already painted the pipes, the welds are sort of lumpy and some of the paint are in there good. The paint is the "engine enamel" sold at auto stores. Something like brake cleaner would wipe it off quickly, but I need to know how to clean up the paint in the welds. I am not sure bringing it to sandblasting shop will work? Steel wire brush? What happens when I weld over some of the residue?

P.S. I don't have a big chemical tank to dip it in or anything like that.

*newbie welder in shame*.. how i found out was that, I try to weld a piece of pipe to a sheet metal like how I usually would do it, pour water and it start seeping out, so my mistakes is not doing a 2nd pass.

Thanks in advance.

Reply to
jj3000
Loading thread data ...

Sand blast or just use a wire wheel on a hand drill. You will have to work hard to get into the small cracks...Might have to grind some of the welds to open the cracks enough for the wire wheel to get to. Paint stripper might work too, or a combination of all of the above.

Reply to
Bruce

Reply to
Jamie Arnold (W)

may I suggest lacquer thinner dip with high presure air directly after the dip.

Reply to
Mr. Bill

The instructor in the class I am taking told us that MIG tends to produce porous welds -- not in the sense of lacking strength, but non-air-tight welds. (Thus, pipe welding is either stick or TIG.) Those of you who are experienced welders -- is this true?

Reply to
Andy Wakefield

MIG can do perfectly air-tight welds if done properly. The problem is that the begining of a MIG weld is often "cold". A cold start gives you a bead that is not fully fused to both pieces being welded. That is where you will get a leak assuming the rest of the weld is sound. You instructor may be a bit off-base here. A sound MIG weld is by no means "porous". Porosity is considered to be a defect.

I don't do a lot of pipe, but I would bet this would work: Run your bead all the way around the pipe joint and when you get to the start of the weld, keep going, making sure to melt the first bead fully into a puddle (much like you want to fully remelt a tack weld when you weld over it.) You only need to keep going a few centimeters.

John T. McCracken is one of the resident pipe weldors so maybe he will comment.

Ernie could probably comment, too. I remember in class some folks welded up a cube with an air fitting in it. They then pressurized the cube to see whose held more pressure before leaking. Some of the better ones loked more like balls when they were finished. Don't try this at home though...

Jeff Dantzler Seattle, WA

Reply to
Jeff Dantzler

You are right, this is exactly my problem, I was focused to make it pretty, in a pipe usually I have to do many pass as I stop and rotate the pipe.

Worse scenario is trying to start a weld where the last one ended, very poor penetration on initial and if I moved on it's hard to realize a leak visually.

What I did was went with a higher heat (part of the problem was cold weld) and weld over the first pass real good, and WIDE. Everytime I start I make sure I make a puddle before I moved on and zig zaged everything up. It doesn't leak this time as all the leaks before have been melted up and covered.

Not pretty tho!

For reference I used M.E.K and it took all the basic paint off just by wiping.

Reply to
jj3000

. .

There is no reason MIG welds shouldn't be pressure tight if properly done. We have several MIG and fluxcore procedures (preaccepted standard AWS procedures acceptd by ASME) for boiler work at my shop.Cleanliness is of the essence, both on the material and the wire, and proper technique and setup are critical.

The porosity went away when I learned to hold gun position so as not to venturi in air (straight into the joint) and began using a screen from breezes--inside, the fume extractor will create enough to cause problems in some positions.

The starts were helped by starting off of the start point, either on the end of the previuos bead, if there is one, or a little into the weld and backing up to build heat, then running over the start while it is still hot-- this is a fairly quick motion at start so as not to put too much metal in while getting some heat in, then run back over at normal speed to fill and get penetration. Starting on the previous bead is preferable, but may require extra grinding, and may require extra metal on the previuous bead where you will start so the start can be completely ground out.

Don't be afraid to grind. It gets rid of all of the contamination. You CAN'T be too clean. Angle grinder with hard wheels and tiger wheels, die grinders with stones, flap wheels, and burr points, are all real handy. If your previous job is rough, grinding a smooth, even groove will make the job a lot easier to contorl as well as providing a clean base.

Oh, did I mention not to be afraid to grind down to clean metal?

Chemical cleaners containing chlorine (such as trichloroethane, and many brake and electrical cleaner products) are a no-no. They will get into the surface and contaminate the weld, as well as give off toxic fumes when heated to welding temperatures. You can't get rid if the residue completely. Also note that if you are using stainless, the chlorine has other issues too.

General hints:

During fitup, gap the weld area, and bevel if the material is thick, so you can get full penetration. Any contamination on the metal MUST be removed, as must slag, before starting and between passes. For pressure work, it is a lot easier if you can use a backer, as you don't want to have slag or oxidation on the inside, which will act as a site for corrosion to grow and act as a stress riser. If you can take the intrusion on the ID or get inside to grind it off, a thin strip of a matching material can be used and left in place. This should be entirely inside and not intrude into the weld area. You may also be able to fit in a removable backer of aluminum-- it won't fuse in with proper technique.

Depending on your base metal and your filler, you may want to run a cap pass to refine the weld metal underneath (among other things to anneal it), which you then grind off flush.

(Note: I am not much of a wire welder- mostly Lo-Hy stick and TIG- so most likely some missing MIG specific details I haven't had to learn yet)

e
Reply to
e

not true at all....we build hydralic cylinders at my job -mig welded and tested at 3000 psi to check for any leaks. occasionally your going to have one that leaks but its not do to mig welding process.

Reply to
DSchledewi

What is "not true at all"? Please include the message you are replying to so we can figure out what you are talking about.

Lane

Reply to
lane

Learn to follow a thread. If your newsreader isn't threaded, get one that is.

Gary

Reply to
Gary Coffman

Yes my newsreader is threaded. But when previous parts of the thread are read, those don't show.

BTW, the standard is to include the previous message, why can't you? If your newsreader can't include the prevous message, get one that can! Lane

Reply to
lane

That's your preference, not ours. Change your settings if you want to see unread messages.

All news readers have the ability to copy and include the original message in the reply and the most popular are set to ON when installed including yours (Microsoft Outlook Express 6.00.2800.1158). I prefer to turn it off as I find it annoying to "dig" through 200 or so lines of repeated thread just to find a "yeah, me too" and prefer my replies to be as easily read as possible.

If the reply needs clarity, I just copy and paste the bit needed for understanding. It's just my style and in no way am I trying to say anyone else has to do it that way but just don't tell me how to do it to satisfy your shortcomings. A similar complaint topic is "top or bottom post" which I hope this does not become.

It is the "unusual type" like myself who tinker around with settings to discover adjustments for annoying traits of free programs to make them livable. If you want to see unread messages in OE 6.0 (hope it's the same as my 5.0) go to view, current view, and click on show all messages. I have a custom view that hides messages older than 14 days since this group is very active and that setting keeps about 350 messages in the preview pane at any one time.

This response is not meant to flame but rather to help you see the messages you're now not seeing. I seriously doubt you'll be allowed to dictate the way individuals post here.The more you try the more stubborn people will become including myself. It will make life easier if you just adjust your reader.

Reply to
Zorro

THe settings are set to delete headers after reading...

Should be keep for 20 days or so. Maybe 30 - they are headers not full text.

Martin

Reply to
Eastburn

I know trich and other cleaners with chlorine is bad news on Titainium. But did not think there was any problem on steel or stainless.

Dan

Reply to
Dan Caster

I don't recall exactly what the issues are, but the guys we have that do tanks and chemical vessels all confirm that chlorine and most stainlesses don't mix happily. I believe that it is free chlorine and aquious solutions that are the major concern. Unfortunately, most of the cleaners containing chlorine will produce free chlorine when heated to welding temperatures, and many will produce decomposition products that are very toxic. In terms of just weldability, Iv'e had to TIG mild steel that was cleaned with a chlorinated solvent inadvertantly, and there was no mistaking that there was a problem-blowholes and porosity all over. A fresh piece from the same lot, different cleaner, no prob. (that ws how we id'd that the degreaser was mismarked, in fact)

Reply to
e

What is this the standard? Got a link to a standards body? is it a RFC?

When you read through even this one group, you will find several styles - no reposting, reposting with comments on top, reposting with comments on bottom, trimmed reposting (my preference, but I'm not forcing in on anyone), or comments in the reposting.

It's called personal preference.

Rich

Reply to
Rich Jones

Reply to
Mr. Bill

PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.