# DOM versus Seamless drawn

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#### PTAirco

Given that a piece of 3/4" x 0.035" 4130 steel tube now costs $7.50 a foot, I have been looking at other options. DOM tubing is starting to look attractive for certain application. It is already used for a wide variety of structures (race cars and motorcycles for example) and in an application such a a steel tube fuselage frame I can't really see much objection to it. Most tubes are sized for buckling loads for which the lower ultimate strength doesn't really matter, since the modulus of elasticity is the same for both types of tubing. (Or close enough.) Trying to find reliable property values for these tubes is a little difficult; some suppliers are decidedly optimistic with their values, but even if considered an average mild steel (say 60kpsi ultimate, 40kpsi yield) it would be a useful material. For bending applications, I'd still go for 4130. #### Hot Wings ##### Grumpy Cynic Supporting Member If only EMT came in EMT-thin wall.............. Pretty easy to remove the zinc where welding is needed and it's generally 1018 Had a source of ERW DOM 1026 in aircraft gauges, but it cost more then AS+S 4130. Price might be competitive today, but the source has dried up. #### dog ##### Well-Known Member you are giving the online retail price try an order of 250' from a supplyer and get a frieght account that delivers to a business adress #### TFF ##### Well-Known Member I haven’t seen it cheaper than chrome moly. If you found some it’s a bubble. It depends on what you want to build. Legal Eagle I say maybe. Something like a Bearhawk, I probably say no. #### GeeZee ##### Well-Known Member Well I just tried to buy 5/8 x .035 4130 tube at AED Motorsports and they had no stock. They still had some Docol in that size so i decided to give it a try.$3.69/ft. Docol tube is a seamed alloy that’s about 10% stronger than 4130 yet more ductile. The only downside is that it can’t be Oxy welded. TIG or MiG only.
a Long long time ago I bought some unplated thin wall seamed tube, essentially unplated conduit at AED. Not sure if they have anything like that now.

#### wsimpso1

##### Super Moderator
Staff member
Well I just tried to buy 5/8 x .035 4130 tube at AED Motorsports and they had no stock. They still had some Docol in that size so i decided to give it a try. \$3.69/ft. Docol tube is a seamed alloy that’s about 10% stronger than 4130 yet more ductile. The only downside is that it can’t be Oxy welded. TIG or MiG only.
a Long long time ago I bought some unplated thin wall seamed tube, essentially unplated conduit at AED. Not sure if they have anything like that now.
Why can it not be gas welded?

#### TFF

##### Well-Known Member
I think it’s like HSS steel used on car bodies today .

#### Dan Thomas

##### Well-Known Member
DOM has no seam at all. A solid rod is heated and pulled over a mandrel to form the tube. Like pulling a sock over your foot. All othe tubing including most seamless, has a welded seam

#### mcrae0104

##### Well-Known Member
Supporting Member
I think it’s like HSS steel used on car bodies today .
Could you please clarify? To some, HSS means hollow structural section (e.g. HSS 4x2x0.25). Sounds like you’re talking about something different; would be good to learn what you have in mind.

#### Hot Wings

##### Grumpy Cynic
Supporting Member
Why can it not be gas welded?
Per their web site it is a dual phase HSLA similar to what autos switched to back in the 80s.
All the body shops back then had to upgrade from gas to MIG (or better yet spot welding) - presumably because the HAZ zone needs to remain very small.

The Docol tube is apparently an ERW product with high quality post treatment of the weld. The cold working seems to be an important part of their process.

#### BBerson

##### Light Plane Philosopher
Supporting Member
DOM has no seam at all. A solid rod is heated and pulled over a mandrel to form the tube. Like pulling a sock over your foot. All othe tubing including most seamless, has a welded seam
Drawn over mandrel is welded seam. Drawn Over Mandrel Tubing - DOM Round Steel Tubing | Industrial Tube and Steel Corporation
Cold worked tubing is strong, but welding will remove the hardening. 4130 is air hardened so after weld strength isn’t impaired.
The problem is finding a small amount of these tubes. These companies sell truckloads to other companies.

#### Dana

##### Super Moderator
Staff member
Prewar Taylorcraft fuselages were made of 1025 tubing, postwar used 4130. I suspect economics was a large part of the switch, as so much aircraft grade material became available cheap after the war.

I miss Charlie Vogelsong.

#### TFF

##### Well-Known Member
Looking it up they are calling it AHSS. Advanced HSS. My terminology is old.

This is anecdotal. I was around 20. Learning to OA weld I go get a scrap hood and fender from a body shop and cut it into coupons. I couldn’t figure it out. When you try and get a puddle started, it completely falls apart. While my setup was not the best, sometimes I welded fine. It sets off like a sparkler and melts way earlier than what we weld. I did not figure it out for a while. Mig and TIG are much more pinpoint on heat control. Small MIG and Plasma cutters machines were developed to weld and cut these steels originally.

The cheap low amp flux welders from harbor freight are really for body panels, but they try an convince everyone it will weld 1/4 plate with ease.

#### David L. Downey

##### Well-Known Member
Supporting Member
Looking it up they are calling it AHSS. Advanced HSS. My terminology is old.

This is anecdotal. I was around 20. Learning to OA weld I go get a scrap hood and fender from a body shop and cut it into coupons. I couldn’t figure it out. When you try and get a puddle started, it completely falls apart. While my setup was not the best, sometimes I welded fine. It sets off like a sparkler and melts way earlier than what we weld. I did not figure it out for a while. Mig and TIG are much more pinpoint on heat control. Small MIG and Plasma cutters machines were developed to weld and cut these steels originally.

The cheap low amp flux welders from harbor freight are really for body panels, but they try an convince everyone it will weld 1/4 plate with ease.
Wow! The only acronym I was used to was "high speed steel".

#### David L. Downey

##### Well-Known Member
Supporting Member
Prewar Taylorcraft fuselages were made of 1025 tubing, postwar used 4130. I suspect economics was a large part of the switch, as so much aircraft grade material became available cheap after the war.

I miss Charlie Vogelsong.
Chrlie was the dictionary definition of curmudgeon...but if you needed it for building a flying machine, he had it or could get it in short order. I miss him too! I could drive out and get the stuff...

#### wsimpso1

##### Super Moderator
Staff member
We have a long and safe history designing and building in 4130 in normalized or annealed state. Weld, no heat treat, yield is normalized 63,000 psi, and most of our structural constraints in airplanes is Euler buckling and crippling. Size to prevent buckling and yield and it is usually good to go.

Change to other alloys, and we have to re-evaluate every tube. Ready to extract all forces on the welded fuselage and its bits? Then evaluate a new tube for buckling, crippling, tension, etc?

No one has yet explained what is wrong with gas welding Ducol R. I have reviewed the alloying elements, and other than a bit more manganese, it is a clean (low phosphorous and sulpher) 1015 steel that has then been heat treated. Normalized around a weld, I bet it is 40-50 kpsi yield, about 63-79% of 4130 and lower than 1020 used in many store bought tube fuselages.

Now DOM, do we have any info on its chemistry and normalized yield strength?

Bill

#### TFF

##### Well-Known Member
Part of the problem with finding information is it’s not recommended by the manufacturer. Industry isn’t going to try. Repair overview literature has heating at a low level will harden the metal. Heating at a high temperature will weaken it substantially. Heat changes the crystalline structure. With a torch a large section will be compromised in different ways.

#### PTAirco

##### Well-Known Member
. 4130 is air hardened so after weld strength isn’t impaired.
Not so. 4130 goes from about 91kpsi down to 80something kpsi in the welded area. Which is still excellent, but it does lose something.

#### PTAirco

##### Well-Known Member
you are giving the online retail price
Price at Aircraft Spruce currently. I've seen DOM tube at less than half that.

#### dog

##### Well-Known Member
When we say "aircaft tube", we mean seamless 4130 that has been cold drawn to a precision size and has been brought to an N condition vs DOM welded tube/pipe that has been cold drawn to smooth out most of the seam and may or may not have been normalised.

I still think that with a commercial shipping address it would be possible to do a lot better than the ADVERTISED RETAIL PRICE™ on an larger order that could be re sold at or near cost and come out ahead. Not thinking about pipe/welded tube.

Actually just came in from my shop, where I was separating out the utility grade stuff and dragging it out to another building, came across a bunch of hydraulic tube which is pretty much the same as aircraft tube, precision german stuff, bends so smooth, heavier wall than aircraft though.