Mill Scale inside of smoker

[Gaddywb]

I just disc it off, but phosphoric acid may work as well. Ace hardware carries a product called ospho which works for converting rust and also for etching bare metal to accept paint. It isn't caustic like muriatic acid is. You can put it in a spray bottle and spray the sheets down a time or three and flap disc.

That is worth some investigation. Vinegar works well, but it’s like a 12 hour set and wait. I get what you are saying because the mill scale comes right off of the square tube I’m using, no problem at all. Just doesn’t work on the plate. Here’s a picture of where I’m at! This is the base.

 

[Fueling Around]

Sorry, I'm traveling and don't have more than a few hours late at night to read stuff on the forum and I don't have email to find replies.

ANY acid is the key to converting the scale.
If you're not up to using the best (Muriatic Acid), then phosphoric acid is a better choice. Vinegar (acetic acid) is a g.. not I won't call it good, only a choice as 5% is too weak to work in a reasonable time. If you can get pure acetic acid that is a better choice.

Working with any acids does require using PPE. Personal Protection Equipment.
Gloves and eye protection is the minimum.

Thanks DougE for mentioning the phosphoric.
After acid treatment and descale, rinse with baking soda water, dry and oil coat or it will start another oxidation called rust.

I once read another of the HUGE amonts of internet stupidity.
A person recommended using window cleaner to neutralize the acid wash. The person never replied back to my comment of BAD idea, because they may have killed themself in the process. Most window cleaner (while also basic as baking soda) is ammonia based. Contact with anything acid releases a very toxic chlorine gas.

AS far as removing scale from tubing or plate/sheet. Surface area is your enemy.

 

[LanceR]

Thicker hot rolled steel takes longer to cool than thinner steel and develops a thicker, harder scale than thinner sections do so the examples of cleaning thin wall tubing shown are not the same as you have to deal with. What you have is going to be thicker and harder and you have a lot larger surface area to contend with.

Yes, either a flap wheel or sanding disc will leave scratches and they will be glaringly obvious under an oil finish. Like woodworking, the only way to remove them will be to work through progressively finer grit abrasives to remove the scratches.

There are any number of direct-to-metal paints (usually called "DTM paint") that can be successfully applied over mill scale. As an industrial contractor I've used them for over 30 years. Go to your local Sherwin-Williams store (or similar store that deals in professional/industrial paint) and they can advise you. With DTM paint it's usually it's a simple as de-greasing the steel and painting it. If you were painting your smoker a "high build" primer or paint would help hide the scratches and save a lot of work.

If having clean blemish free steel is important for future projects I'd suggest asking your steel supplier for pickled and oiled steel (often referred to as "P&O") which is hot rolled steel that has had the mill scale removed in a caustic bath and was then dried and oiled. My supplier, Race City Steel in Denver, NC gets about a 35 to 40% premium for P&O 1/4" plate but I balance that against not needing to grind mill scale off around every weld and not having to sandblast the project and gladly pay the difference.

With that said, I have 2-2/3 sheets of 4x8' hot rolled 1/4" steel on my stock cart so I'll be sandblasting the next few smokers before painting them.

I don't know how much steel you want to clean or what your budget is but a "surface conditioning tool" can be a great addition you your tool arsenal. Harbor freight makes an inexpensive one that I have no personal knowledge of and Eastwood has one that at least two guys I know have spoken well of. Used properly, they can leave a ready-to-finish surface. You'll find plenty of videos on Youtube.

9 Amp Surface Conditioning Tool

Amazing deals on this 9A Surface Conditioning Tool at Harbor Freight. Quality tools & low prices.

www.harborfreight.com

Eastwood CONTOUR SCT® - Surface Conditioning Tool

Multiple Tools In One! Removes Rust, Paint, Body Fillers Conditions Metal so it is Ready to Paint Buff Metal to a Mirror Finish Professional Grade Backed by a 3 Year Warranty US Patent #D814,261

www.eastwood.com

If you add your general location to our profile you may find that you're near enough to one of us that we can offer to help you out or maybe even lend you a tool or two.

Best regards to all,

 

[Gaddywb]

Thicker hot rolled steel takes longer to cool than thinner steel and develops a thicker, harder scale than thinner sections do so the examples of cleaning thin wall tubing shown are not the same as you have to deal with. What you have is going to be thicker and harder and you have a lot larger surface area to contend with.

Yes, either a flap wheel or sanding disc will leave scratches and they will be glaringly obvious under an oil finish. Like woodworking, the only way to remove them will be to work through progressively finer grit abrasives to remove the scratches.

There are any number of direct-to-metal paints (usually called "DTM paint") that can be successfully applied over mill scale. As an industrial contractor I've used them for over 30 years. Go to your local Sherwin-Williams store (or similar store that deals in professional/industrial paint) and they can advise you. With DTM paint it's usually it's a simple as de-greasing the steel and painting it. If you were painting your smoker a "high build" primer or paint would help hide the scratches and save a lot of work.

If having clean blemish free steel is important for future projects I'd suggest asking your steel supplier for pickled and oiled steel (often referred to as "P&O") which is hot rolled steel that has had the mill scale removed in a caustic bath and was then dried and oiled. My supplier, Race City Steel in Denver, NC gets about a 35 to 40% premium for P&O 1/4" plate but I balance that against not needing to grind mill scale off around every weld and not having to sandblast the project and gladly pay the difference.

With that said, I have 2-2/3 sheets of 4x8' hot rolled 1/4" steel on my stock cart so I'll be sandblasting the next few smokers before painting them.

I don't know how much steel you want to clean or what your budget is but a "surface conditioning tool" can be a great addition you your tool arsenal. Harbor freight makes an inexpensive one that I have no personal knowledge of and Eastwood has one that at least two guys I know have spoken well of. Used properly, they can leave a ready-to-finish surface. You'll find plenty of videos on Youtube.

9 Amp Surface Conditioning Tool

Amazing deals on this 9A Surface Conditioning Tool at Harbor Freight. Quality tools & low prices.

www.harborfreight.com

Eastwood CONTOUR SCT® - Surface Conditioning Tool

Multiple Tools In One! Removes Rust, Paint, Body Fillers Conditions Metal so it is Ready to Paint Buff Metal to a Mirror Finish Professional Grade Backed by a 3 Year Warranty US Patent #D814,261

www.eastwood.com

If you add your general location to our profile you may find that you're near enough to one of us that we can offer to help you out or maybe even lend you a tool or two.

Best regards to all,

Thanks. I’ve updated my location, I’m probably not too far away from one of your supplier locations. I haven’t heard of that place and I wasn’t able to find P&O Steel. I found 4x8 3/16” for around $330 for a 2 hour drive. Locally the same piece was $500. But I’m going to finish out with what I have. I wasn’t planning on painting, I wanted the dark metal look. But like you said, that’s a lot of surface to prep and would leave a lot of imperfection if not done right. I’m thinking I’ll give everything a really good cleaning, burn in, and then clean again before seasoning with boiled linseed oil. I messaged a guy on YouTube who does a lot of build videos and he recommended just applying the oil directly on the mill scale and it would give it a nice look and save a lot of time.

 

[LanceR]

Thanks. I’ve updated my location, I’m probably not too far away from one of your supplier locations. I haven’t heard of that place and I wasn’t able to find P&O Steel.

First, I confess that for some reason I missed the word "inside" in your thread title and was thinking of the outside of your smoker when I commented on scratches. If my brain cell hadn't spaced out on the word "inside" my advice would have been the same as his; oil the mill scale and forget about it.

Did you get that price from Race City's website or somewhere else? Regardless, if you haven't talked to them give them a call. Unless steel prices have changed drastically in the last few months without me knowing it they will likely beat that price by a good bit. They have locations in Denver and High Point, NC (a new location) and in Spartanburg, SC.

I'm an hour and forty five minutes from the Denver branch and to date they have delivered even small orders to my home at no additional charge (rare indeed!) although it might take a week or so for them to have a truck in my area.

I've only done business with the Denver, NC branch but as they have a new branch in High Point which is half the distance I'll likely be driving down there in the next few weeks to see what they stock.

If you ever get near Greensboro, NC check out the Alro Metals Outlet. They have a good selection of scratch and dent and unblemished sheet goods (stainless, carbon steel, aluminum, expanded metal, diamond tread plate, etc) some of which is full sheets and some of which is partial sheets. And they have both cut-off and full length tubing, rods, bar, channel and angle in carbon steel, aluminum, stainless etc.

This is where I go an browse when brainstorming a project to buy all the steel and stainless steel bits and pieces I expect to need like angle for racks, channel for rack tracks etc. They are an hour or so from home so I usually buy a bit extra while I'm there to build up my shelf stock.

They will cut material to size for an additional charge. Full lengths of stuff like angle, channel and tubing are as much as 20' long at any of these places so it is wise to bring something to cut it down if you are hauling it in an SUV or pickup. I carry a cordless angle grinder with a cut-off wheel on my foraging trips. I usually already know what the item's finished length needs to be so I cut it a bit longer and note what I cut it for on the piece with a silver Sharpie so I don't mistakenly use it for something else.

 

[Gaddywb]

First, I confess that for some reason I missed the word "inside" in your thread title and was thinking of the outside of your smoker when I commented on scratches. If my brain cell hadn't spaced out on the word "inside" my advice would have been the same as his; oil the mill scale and forget about it.

Did you get that price from Race City's website or somewhere else? Regardless, if you haven't talked to them give them a call. Unless steel prices have changed drastically in the last few months without me knowing it they will likely beat that price by a good bit. They have locations in Denver and High Point, NC (a new location) and in Spartanburg, SC.

I'm an hour and forty five minutes from the Denver branch and to date they have delivered even small orders to my home at no additional charge (rare indeed!) although it might take a week or so for them to have a truck in my area.

I've only done business with the Denver, NC branch but as they have a new branch in High Point which is half the distance I'll likely be driving down there in the next few weeks to see what they stock.

If you ever get near Greensboro, NC check out the Alro Metals Outlet. They have a good selection of scratch and dent and unblemished sheet goods (stainless, carbon steel, aluminum, expanded metal, diamond tread plate, etc) some of which is full sheets and some of which is partial sheets. And they have both cut-off and full length tubing, rods, bar, channel and angle in carbon steel, aluminum, stainless etc.

This is where I go an browse when brainstorming a project to buy all the steel and stainless steel bits and pieces I expect to need like angle for racks, channel for rack tracks etc. They are an hour or so from home so I usually buy a bit extra while I'm there to build up my shelf stock.

They will cut material to size for an additional charge. Full lengths of stuff like angle, channel and tubing are as much as 20' long at any of these places so it is wise to bring something to cut it down if you are hauling it in an SUV or pickup. I carry a cordless angle grinder with a cut-off wheel on my foraging trips. I usually already know what the item's finished length needs to be so I cut it a bit longer and note what I cut it for on the piece with a silver Sharpie so I don't mistakenly use it for something else.

Neither of those prices are from Raceway. I didn’t know about them to check at the time. The Spartanburg location is a little over 2 hours away, so it’s doable.

Yes, my original question was for the inside, but has since evolved to the outside too. I’m going to plan on seasoning on top of the mill scale on both sides after a good burnout and clean. It will avoid those scratches you mentioned, because I’ve been tearing up the metal getting the mill scale off so far. I can hide the two pieces I worked on so far so that they are never seen.

 

[LanceR]

I have been known to hide my mistakes, too. It usually involves a dark night, a secluded spot and a backhoe, though....

At two hours away, I'd see if they'll deliver it.