Buying Pre-cut Coupons from the Local Steel Yard

[erikmannie]

Next week I will be calling the local steel yard to order a lot of .120” thick, 3” X 4” mild steel pre-cut coupons. They will sell me the sheet & cut it on their behemoth press brake.

I have been going to this place for 20+ years, & they are pretty reasonable for material & labor costs.

I will post here what I ended up paying by the pound for these pre-cut coupons, but here are some questions:

(1) What size coupon would *you* choose? I use these for joint & position practice for MIG, TIG, stick & gas welding. Right now I am working on 1F (i.e. flat horizontal). I do butt, lap, corner, edge, & T-joints. No bevel on .120”, obviously.

(2) Is this a good plan to order from the steel yard? They sell nice pickled & oiled coupons online (see screenshot), but they are very expensive.

(3) How would *you* prep these coupons? I *always* remove all the mill scale. I have been using a flap disk on a 4-1/2” angle grinder, but I am going to try to use a milling machine. I will process them in bulk.

(4) I will sell some to interested forum members at my cost. You remove the mill scale. Local pickup is best, but I will ship to US addresses.

(5) Any cost effective ideas on re-using these after I weld them? Pipe welding coupons easily lend themselves to re-use if you don’t mind filler material in your coupon. I could use the scrap for torch cutting practice & then take to a scrapper to be recycled.

 

[stupoty]

Have you tried "strip and clean" discs for angle grinder , absolutely leave the metal unscratched (might polish it a bit) but cut through mill scale and rust and paint like it's not there.

Basically there the hard scouring pad with glued abrasive. If you press to hard you can heat them up and make little melty plastic marks with them, apart from that they are a total dream.

Stu

Strip Discs Stripping Wheel for Angle Grinders Clean and Remove Paint, Rust Weld | eBay

Not suitable for stripper paint or drilling rigs. [Scope of application]-The peeling and cleaning disc is suitable for grinding interface grinding, oil pipe deburring, ceramic bottom polishing, surface paint removal, etc.

www.ebay.co.uk

 

[benmychree]

Bead blasting would be another option, Just blast the area that is to be welded upon.

 

[benmychree]

I worked at a steel fabricating plant (Kaiser Steel) we did a lot of processing of mostly large coupons for welder qualification tests, and vever noticed any scale removal preparation of the coupons, for the most part they were about 3/4 - 1" thick with a machine burnt angular edge, tack welded to a piece of flat bar for backing and separated from each other so that the weld was of full penetration, after the welding was done, the backing strip was machined off and the plates were sawn into strips 90 degrees to the axis of the weld and surface ground on the sides. All production welding done there was also without scale removal, so far as I saw.

 

[aliva]

Check with your state welding qualification board and see what they require. Here in Canada the CBW ( Canadian Welding Bureau) doesn't require that the mill scale be removed but all welders do it them selves to lessen any contamination that might show up in an x-ray or bend test . The scale is removed just from the weld area no more. I wouldn't remove the scale it just adds to your labour, if the buyer wants it removed they can easily do it themselves.

 

[erikmannie]

I used to work as a bench hand for a guy that MIG welded about 97% of his stuff, almost always structural steel. I never saw him remove mill scale. He has made a living doing steel fab for decades.

Funny story, his workshop was in a mountainous, rural area so his building had a huge amount of dust in it (and mud in the winter). One day he was MIG welding/fabricating a gate. He had a huge gap in the joint. He rectified this by *looking down on the floor* for a rod approximately the diameter and length that he needed to fill the gap. His floor had so much stuff on it that he didn’t even have to walk anywhere. He picked up a dusty piece of scrap rod, didn’t even clean it off, put it in the gap, & kept welding. Of course, this doesn’t matter because it was just a gate for a ranch. Ya gotta fill the gap somehow!

At the welding schools I went to, the students would MIG, gas & stick weld the mild steel sheet coupons without removing mill scale.

 

[General Zod]

Stick practice - I wouldn't bother removing millscale. Again, for practice. For projects I do clean the edges.
MIG short-circuit w/ C25 gas - clean the millscale off the edges as much as possible to minimize undercut. Hard grinding disc is fastest, coarse flap disc or silicon carbide "quick strip" disc is almost as fast. 3M abrasive bristle brushes are really good I'm told. Anything else is a waste of time.
TIG - remove all millscale and all foreign material/substances at all costs.

Depending on your own preferences and practices, you can just dunk all the practice coupons (or a lot anyways) in a large tub filled with muriatic acid from the hardware store. It's about 50% hydrochloric acid by concentration and produces nasty fumes when reacting with the millscale on the steel, so proper respirator is necessary but in about 1 hour all your coupons could be 100% rust and millscale free. You obviously just have to do it outdoors so the fumes don't rust nearby clean steel/tools, and neutralize the acid before properly disposing of it. I've been doing this more and more lately. I just keep a neutralizing solution in the tub next to it, clean off the pieces right away, and then pat them dry on an old towel and just leave them there. Very minimal rust formation and whatever light surface rust does appear, I get rid of it very easily with a 3M Scotch Brite Clean and strip wheel 07470 on a low-RPM straight air drill I got from Grizzly.

 

[erikmannie]

Stick practice - I wouldn't bother removing millscale. Again, for practice. For projects I do clean the edges.
MIG short-circuit w/ C25 gas - clean the millscale off the edges as much as possible to minimize undercut. Hard grinding disc is fastest, coarse flap disc or silicon carbide "quick strip" disc is almost as fast. 3M abrasive bristle brushes are really good I'm told. Anything else is a waste of time.
TIG - remove all millscale and all foreign material/substances at all costs.

Depending on your own preferences and practices, you can just dunk all the practice coupons (or a lot anyways) in a large tub filled with muriatic acid from the hardware store. It's about 50% hydrochloric acid by concentration and produces nasty fumes when reacting with the millscale on the steel, so proper respirator is necessary but in about 1 hour all your coupons could be 100% rust and millscale free. You obviously just have to do it outdoors so the fumes don't rust nearby clean steel/tools, and neutralize the acid before properly disposing of it. I've been doing this more and more lately. I just keep a neutralizing solution in the tub next to it, clean off the pieces right away, and then pat them dry on an old towel and just leave them there. Very minimal rust formation and whatever light surface rust does appear, I get rid of it very easily with a 3M Scotch Brite Clean and strip wheel 07470 on a low-RPM straight air drill I got from Grizzly really helpful.

That was really helpful. How do you neutralize the muriatic acid afterwards?

Also, if I may ask, how do you get rid of the neutralized liquid?

 

[General Zod]

That was really helpful. How do you neutralize the muriatic acid afterwards?

Also, if I may ask, how do you get rid of the neutralized liquid?

baking soda neutralizes it. It becomes salt water when properly neutralized. The leftover sludge I can take to my local hazardous waste drop off.

 

[erikmannie]

@General Zod

What thickness & dimensions would you choose for MIG, TIG, stick & gas welding practice?

I will be on 1F for awhile.