Welding Tips and Tricks

Here, on the island, any square tubing I get has a black substance on it that comes off on your hands but is otherwise tenacious when trying to remove it to get to silvery steel. Angle iron and flat stock has the normal mill scale.

I use a cup brush on mill scale to scratch away any surface rust and some of the scale, but since it's so tough and not greasy, I don't bother scraping away all the mill scale except for the spots to be welded. Priming and painting over the mill scale seems to work OK.

The square tubing presents a problem. It's has a greasy feel and therefore I scrub it all off with soapy water and steel wool pads, but that's an awful lot of work. There has to be a better way. Chemicals?

How are you folks getting that black gunk off of square tubing so it can be primed and painted after welding?

In general, what methods and products are folks using to clean all types of steel with priming and painting the final objective after welding.

Acetone seems to be like a decent go to. Cuts through grease and everything pretty well. Definitely wanna make sure it's all evaporated before you start welding though haha. Also probably want some gloves and eye protection at the least as well as a well ventilated area.

flapdisc on an angle grinder should make quick work of it.

I've tried Acetone, Mineral Spirits and Naptha as chemical agents and they don't work. Each takes away a bit of the gunk, but certainly not enough to weld the metal + remaining gunk even with MIG wire or TIG filler metal like ER70S-6. Priming and painter thereafter would be an issue.

It's the priming and painting that's my real concern. I can always use an angle grinder to grind away a spot to weld on but that leaves the rest of the steel not a paining candidate. Who wants a rusted welded up contraption? I have to paint.

A flap disk on thin wall tubing removes a lot of metal fast. Maybe I'll try some high grit number disks to see if they work. The 40 & 80's I have are a bit too aggressive. I think all that will happen is the disks will get clogged full of this slime.

If I had a way of using the cup brush under soapy water, that would work, I think, as the brush flings and smears the stuff but with the added soapy water, it would float away.

So far, my approach has been to cup brush each of the 4 sides as best I can. This just smears the black gunk around but does fling some of it off. Then a bucket of water and lots of dish washing liquid plus a 3M RED scrubby pad does manage to remove lot of the black stuff even better than steel wool. Boy is that a lot of manual labor! Then a rinse, sun dry (in a flash around here), and then back to the cup brush to get clean steel.

That's just too much work. I've got to find an alternative.

Not sure if it's available where you are but we use a commercial solvent sold as " Preptone " - it's a blend of more than one solvent - not sure exactly what but it wipes the protective coating off RHS easily - just be careful where you keep it & any rags used to apply it as it's very flammable.

Around here all we have is sunshine and high humidity. Everything else gets shipped in and anything exotic like TIG supplies, solvents, etc are nowhere to be found.

BTW - is there a glossary around here? What is RHS?

Sounds great - if I win Lotto remind me not to move there !

Try your LWS & ask if they can order in " preptone " or around here it is also supplied by automotive cleaning / parts companies .

RHS is the usual term for " box " section - least ways that what the steel stockists list it as here.

If acetone don't work then solvents are not the answer. If soap does work then the answer in this direction. You need a caustic solution. If my refrigeration industry we have a manufacturer called "refrigeration technologies " who manufacture a product called viperbrite. We use it to clean condensers and evaporators from all kinds of awful fouling. Squirt it on leave 10min then hose off.
Hardware stores have a product here in oz called 30 seconds outdoor cleaner. Spray on hose off as well. Either of these products will be your answer.

Rhs rolled hollow section. Sometimes called shs square hollow section.

I had some TSP (Tri Sodium Phosphate) lying around and tried it on the square tubing. It did a much better job than anything else, but its still an awful lot of work. I found a distributor for Viper Brite in Florida near my freight forwarder, so I'll try a gallon of that . Thanks for the lead.

Try a good preheat with a propane torch before you take the flap disc to it. It sounds like the same coating that comes on a lot of the pipe I work with. If you heat it up first it seams to dry it out and make it easier to grind off. Otherwise it just gums up the disc and sort of smears all over.

I had the same issues with A500 tubing (equivalent to 1027 mild steel tubing, but shittier to prep) at work yesterday (Thursday, still haven't gone to sleep yet) . Ours is all getting powder coated after I welded it, so they'll sand blast it. I used 60 grit sanding disc's on a die grinder to prep the ends. I wiped down with lacquer thinner/paint thinner about 3" back from where I was welded and then cleaned the end I was welding. Between prepping the tubing, and the machined end caps (which I believe they buy hand rail cap for, and then machine a flat and drill/tap a hole in, as the back side /non machined side is almost textured, in addition to having a bunch of mill scale/coating/bullshit on it) I had about 90 minutes into prepping the tube. I'd probably still be at it if I had st to prep the whole tube that way. The thinner wipe to begin with helped get rid of the oily sheen that the coating had, and it seemed to sand off with a little persuasion with no major issues. I still had a weld that was blue/gold/purple that would end up with a jet black glaze over some sections, but it was way better than the ashy gray/black welds I had on the first 11 tubes that I didn't invest as much time in.

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Yesterday, I spent 3 hours cleaning 16 1x1 tubes ranging in length from 28 to 43 inches. It took me a whole lot less time welding them up than it did to clean them. This black stuff is horrible. I'm going to soak some scrap pieces in TSP over night to see if that helps on how much time it takes to get that gunk off the metal.

When I started this thread, I was sure other people had experienced this issue and had come up with a chemical solution to this problem. Apparently, my guess was incorrect. Burning it off requires a large torch and possibly warps the metal in the process which I can't chance.
I'm curious - when purchasing square tubing in the US, does it come with this black slime all over it? I have to believe square tubing is popular for building shelving, racks, etc so how is it that no one has definitively stated what chemical process they use to clean their tubes prior to welding? The physical means of scraping it off is too much work, takes too long and in a business setting would cost too much just to get the metal clean.

Yes it does come with the same tar gunk on it here. Seams to depend on what country it's imported from. Even some of the US manufactured pipe has it at times. About the torch / preheat. You only need to warm it up to aproximaely 200 deg F. This shouldn't warp it and I think ( correct me pleases if I'm wrong) is within the recomended range of proper preheat for carbon steel.

Edit. You only need to clean an inch or two around your weld zone. In a production setting they would likely just grind the minimum they need to get a clean looking bead and then blast or chem dip in a large parts washer.

Poland308 wrote:You only need to clean an inch or two around your weld zone.

But to prime and paint it you have to clean everything and to have it stick to it, it has to be REAL clean.

Small sand blasters or soda blasters work good.

RoatanBill wrote: I'm curious - when purchasing square tubing in the US, does it come with this black slime all over it?

Does not. In a couple decades of fabrication, I have never encountered the coating you have described. Generally the square tubing is just a hot roll mill scale. For mig welding no preparation is required. I have ordered the square tubing pre-primed with a black primer paint that is designed to be mig welded through. Black Iron pipe has hot roll mill scale plus laquer coating for plumbing applications. All of these coatings are dried and sandable, not goey though.

If you have a shop nearby that do large diesel engine overhauls, enquire if they have any water soluble degreaser they use on engine components.

Thanks to all that responded. It appears my situation is a bit unique and I'll have to experiment to find something to EASILY dissolve this muck.

In general, I find I spend most of my time in metal prep and the actual welding time is almost not worth mentioning. Given the always hot and humid climate here, aggressively cleaned steel gets a thin rust coating over night. If a project takes a few days to complete, everywhere my fingers touched bare metal have a much thicker coating of rust to almost duplicate my finger prints. This constant cleaning plus the priming and painting is why I just received a TIG welder and water cooler to eventually get into aluminum.

I'm going to get flamed for this but have you tried gasoline?

Yes, I thought of trying gasoline.

I immediately also remembered my father-in-law going up in a huge flame after he washed paint off his hands with gasoline and the fumes went over to the gas hot water heater and in a flash all hell broke loose. I was on a ladder painting around the corner of the house and heard the whoosh as the flame started. I jumped off the ladder, tackled him to the dirt and smothered the flames.

He almost died of kidney failure, as that's a common side effect of a serious burn. Weeks in the hospital, skin grafts, months of tending his arms and face.

Gasoline belongs in a fuel tank, and that's it.

Some coatings I have had decent luck using the torch, but instead of heating the metal up, I hit the oxidizer lever immediately and if the coating is flammable, it usually burns up without imparting much heat to the metal. It stinks and smokes terribly, but might work for prepping the weld area at least.

As you switch to tig you will find if you just grind back a 1/4 inch or so you will be ok on thin stuff. The heat from your weld will burn off the rest. It may make the finished weld look a bit darker but it's manageable. I often use a propane / map gas torch to just warm up the material enough to start to burn off what ever that crap is. Hit it with a wire brush and then weld it.

sedanman wrote:I'm going to get flamed for this but have you tried gasoline?