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Discussion Starter · #1 ·
I have an opportunity to get DOM tubing pretty cheap, but it has ailed some test and is not good for pressure testing. I guess it has some flaws in the main weld. They say they are very small pin holes and the maker felt it would be fine for a roll cage...


What do you Cage Guru's think?(or anyone)

[ 09-14-2001: Message edited by: Michael Christopher Longley ]
 

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IMO....

The stuff may be just fine, BUT I would rather not trust my melon to something that is questionable...
You would ALWAYS have that thought in the back of you head, instead of the nice warm fuzy feel'n a good cage will give ya...my.02

Tin Bender
 

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Isn't DOM tubing welded like normal tubing and then Drawn-Over-Mandrel to remove the seam?
 

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Eric got it. Here is what My metal supplyer has on the page for 1020 DOM

DOM is formed from strip and electric-resistance welded, then cold drawn to size. The cold drawing process causes the weld line to virtually disappear.
 

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Find out what test it failed, often out of spec DOM is only out of dimensional spec. We got some thin wall DOM like that donated for a school project once.
 

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Originally posted by Robert L Mann:
<STRONG>Eric got it. Here is what My metal supplyer has on the page for 1020 DOM

DOM is formed from strip and electric-resistance welded, then cold drawn to size. The cold drawing process causes the weld line to virtually disappear. </STRONG>
HAHAH Yep! I got some DOM here you can see the seam on the inside of the tubing if'n ya still dont believe it <IMG SRC="smilies/wink.gif" border="0">
 

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Originally posted by mike stenson:
<STRONG>HAHAH Yep! I got some DOM here you can see the seam on the inside of the tubing if'n ya still dont believe it <IMG SRC="smilies/wink.gif" border="0"></STRONG>
yea the stuuf you get a Wal Mart is always a little strange! <IMG SRC="smilies/thefinger.gif" border="0"> <IMG SRC="smilies/thefinger.gif" border="0">
 

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I posted this before a while back, but repeating it may help you decide:

One thing I would like to comment on or clarify…all DOM is either HREW or made by some other process before being Drawn over Mandrel. This cold working (the drawing) is what makes it stronger than simple HREW or ERW tubing. It has to do with aligning the crystal lattice structure whichi shall not get into since it gets WAY into chemistry L

As a note though…there is no such thing as a “molecule” of steel…it has atoms, and grains, and crystals, and a crystal lattice structure…but no such thing as molecules!!

To add to the mix here are some clippings from some other posts I have made (edited by what I learned from Nivloc)

To clarify a misconception, you cannot compare materials by labeling one DOM and one 1018, as these two terms refer to different things.
The number 1018 is indeed a grade of mild carbon steel. The SAE designation to be precise. Designations common in automotive use include, but are not limited to:

1020. 1024, 1040, 1060, 4140, 1085, 3115, etc.

The first two numbers refer to the type or group or alloy class of the material, 10 is mild carbon steel, 41 is chromoly, etc. and the last 2 numbers refer to the carbon content. This is a rough description, there are pages of good info in "the Machinery's handbook" available from good booksellers.

DOM on the other hand is short for Drawn Over Mandrel, which is a process. The steel tubing (mechanical tubing to be correct) is hot formed (usually by HREW), and then cold worked by...you guessed it, drawing it over a mandrel, which serves to strengthen the material and make it very clean and consist ant. Note - DOM IS NOT seamless tubing...this is another product altogether, although many mistake cold working processes that remove the appearance of a seam from a product for true seamless (high pressure tubing).

Sooooo, you can in fact have DOM mechanical tubing in different grades, not just 1020. However...I expect this is what is meant in common usage....when someone says DOM they prob mean 1020 but it's not necessarily so.

And to add to the difference between pipe and tubing. Pipe is specified by a size (ID I think) and a "schedule" eg. schedule 40, and as schedule goes up, so does wall thickness. It is not designed, primarily for structural use of but can be used if the proper alloy and spec is used ( I did make a brush guard out of schedule 40) It is designed to convey fluids and gasses. Mechanical tubing, on the other hand, IS designed for structual use (assuming the correct grade is used) and is specified by an OD and a wall thicknes, as in 1.5"-.120.

The 4 digit numbers are AISI / SAE (American Iron and Steel Institue / Society of Automotive Engineers)

The UNS (unified numbering system) was developed jointly by ASTM (American Society for Testing and Materials) and SAE, and its numbers are a letter and 5 digits, and mostly resemble the SAE numbers. For example, 1020 is G10200

As to what tubing to use:

Carbon steel tubing is available as cold drawn seamless, in which case it will be drawn from SAE 1018 steel (not hot rolled or welded); Drawn Over Mandrel (DOM) which is rolled, welded and then drawn over a mandrel from SAE 1020 steel, and is probably just as strong and well finished as the cold drawn seamless, and a lot less expensive. It also comes as Electric Resistance Welded (ERW) which is produced from SAE 1020 steel unless the wall thickness is 16 gauge or lighter, in which case it will be made from SAE 1010. Hot Finished seamless tubing is made from SAE1026 but is not as strong as the cold drawn tube. It’s also more scaly.
 

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Originally posted by Robert L Mann:
<STRONG>yea the stuuf you get a Wal Mart is always a little strange! <IMG SRC="smilies/thefinger.gif" border="0"> <IMG SRC="smilies/thefinger.gif" border="0"></STRONG>
HAHAHAHAHA maybe I should go somewhere else than tube service of milpitas <IMG SRC="smilies/wink.gif" border="0"> it worked for tie rods though! <IMG SRC="smilies/thefinger.gif" border="0">
 

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Discussion Starter · #12 ·
Originally posted by BillaVista:
<STRONG>I posted this before a while back, but repeating it may help you decide:

One thing I would like to comment on or clarify…all DOM is either HREW or made by some other process before being Drawn over Mandrel. This cold working (the drawing) is what makes it stronger than simple HREW or ERW tubing. It has to do with aligning the crystal lattice structure whichi shall not get into since it gets WAY into chemistry L

As a note though…there is no such thing as a “molecule” of steel…it has atoms, and grains, and crystals, and a crystal lattice structure…but no such thing as molecules!!

To add to the mix here are some clippings from some other posts I have made (edited by what I learned from Nivloc)

To clarify a misconception, you cannot compare materials by labeling one DOM and one 1018, as these two terms refer to different things.
The number 1018 is indeed a grade of mild carbon steel. The SAE designation to be precise. Designations common in automotive use include, but are not limited to:

1020. 1024, 1040, 1060, 4140, 1085, 3115, etc.

The first two numbers refer to the type or group or alloy class of the material, 10 is mild carbon steel, 41 is chromoly, etc. and the last 2 numbers refer to the carbon content. This is a rough description, there are pages of good info in "the Machinery's handbook" available from good booksellers.

DOM on the other hand is short for Drawn Over Mandrel, which is a process. The steel tubing (mechanical tubing to be correct) is hot formed (usually by HREW), and then cold worked by...you guessed it, drawing it over a mandrel, which serves to strengthen the material and make it very clean and consist ant. Note - DOM IS NOT seamless tubing...this is another product altogether, although many mistake cold working processes that remove the appearance of a seam from a product for true seamless (high pressure tubing).

Sooooo, you can in fact have DOM mechanical tubing in different grades, not just 1020. However...I expect this is what is meant in common usage....when someone says DOM they prob mean 1020 but it's not necessarily so.

And to add to the difference between pipe and tubing. Pipe is specified by a size (ID I think) and a "schedule" eg. schedule 40, and as schedule goes up, so does wall thickness. It is not designed, primarily for structural use of but can be used if the proper alloy and spec is used ( I did make a brush guard out of schedule 40) It is designed to convey fluids and gasses. Mechanical tubing, on the other hand, IS designed for structual use (assuming the correct grade is used) and is specified by an OD and a wall thicknes, as in 1.5"-.120.

The 4 digit numbers are AISI / SAE (American Iron and Steel Institue / Society of Automotive Engineers)

The UNS (unified numbering system) was developed jointly by ASTM (American Society for Testing and Materials) and SAE, and its numbers are a letter and 5 digits, and mostly resemble the SAE numbers. For example, 1020 is G10200

As to what tubing to use:

Carbon steel tubing is available as cold drawn seamless, in which case it will be drawn from SAE 1018 steel (not hot rolled or welded); Drawn Over Mandrel (DOM) which is rolled, welded and then drawn over a mandrel from SAE 1020 steel, and is probably just as strong and well finished as the cold drawn seamless, and a lot less expensive. It also comes as Electric Resistance Welded (ERW) which is produced from SAE 1020 steel unless the wall thickness is 16 gauge or lighter, in which case it will be made from SAE 1010. Hot Finished seamless tubing is made from SAE1026 but is not as strong as the cold drawn tube. It’s also more scaly.</STRONG>
Bill,

This is what I was looking at(from the Mfg.):
"ASTM A-513, Type 5 Electric Resistance Weld D.O.M. (drawn-over-mandrel) tubing is preferred by most buyers of precision, cold drawn, carbon steel mechanical tubing. "


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That would certainly be suitable tubing...but it really worries me when you say the failure is in the main weld. What if it's more than pin holes? DOM tubing is pretty cheap really, even if it isn't flawed, and a roll cage is (can be) a pretty darn critical application, you might need it to save your mellon.

So, if it's my humble opinion you want, this is it.

For the safety factor, and the peace of mind, taking into account the price difference...I wouldn't personally build a cage out of tube that failed in the way this seems to have.

like Gordon said tho - if it were just a dimensional spec - that would be different.

Bill
 

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Discussion Starter · #15 ·
Originally posted by BillaVista:
<STRONG>That would certainly be suitable tubing...but it really worries me when you say the failure is in the main weld. What if it's more than pin holes? DOM tubing is pretty cheap really, even if it isn't flawed, and a roll cage is (can be) a pretty darn critical application, you might need it to save your mellon.

So, if it's my humble opinion you want, this is it.

For the safety factor, and the peace of mind, taking into account the price difference...I wouldn't personally build a cage out of tube that failed in the way this seems to have.

like Gordon said tho - if it were just a dimensional spec - that would be different.

Bill</STRONG>

I was thinking along the same lines as you. I talked to the person and they said it is flaws in the weld, and all they said was there is small pin holes in it......

I think I will hold out for "good" tubing.

Thanks!
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