Difference between galvanized pipe and DOM
Are there any strength difference between the galvanized pipe I can get from the hardware store compaired to DOM steel tubing? I'm not sure if I could use the pipe in place of DOM and still retain the strength?
DOM (drawn over mandrel - if thats what we're talking about) steel will be somewhat stronger than galvanized pipe if the two are of the same dimensions. Gal. Pipe usually has a bigger cross section than DOM of the same size so there's more material in the pipe and so the pipe can be stronger. All depends on the dimensions of the part, then the material..
1 for the same dimensions of the material dom will be stronger.
2 thats not to say that pipe couldn't be used in place of dom but there may be some changes to the design necessary to retain the same strength.
3 generally speaking pipe from the hardware store will be of lower quality than pipe from a steel supplier or plumbing wholesaler.
4 dom (or hrew) are "structural tubing" engineered for load bearing structures, pipe, is pipe.
5 if its simply a matter of cost then you could use pipe, hrew, or dom.
6 if you are making a swingset for your ex-girlfriends neighbors nephew, then i would use pipe. if you are building a roll cage or the like, i would use hrew/dom.
7 it all comes down to what the desired use is.
8 IMPORTANT: if you are doing any welding, do not use galvanized pipe! black pipe will work as a substitute. when you weld/grind/etc. you invite a lot of heavy metal fumes into your body. this will kill you and takes less than you may think.
The galvenized part is the coating that is sprayed over the material correct? If this coating is wire wheeled off is it okay to weld on?
Galvanizing is generally a hot dipped (dip in hot molten zinc) process.
WIre brush is NOT adequate for a "certified weld". You have to sand it all off to get to parent metal as the zinc is a weld contaminant and quite poisonous.
Better yet, WHAT ARE YOU TRYING TO BUILD???. With this knowledge, we can tell you what to use PROPERLY. A swing set is one thing, a swing set that will be used to lift heavy objects (motors and trannys) is another, a roll cage is yet another thing entirely....
Regarding sanding/grinding off the zinc, REREAD POST #3, item 8. Might want to plan to say a last goodbye to your wife and kids should you choose to ignore this important caveat.
There is a difference in strength between ordinary galavanized pipe and DOM tube; for the same OD and wall thickness DOM will be considerably stronger but if you are planning on using the material for the tracks on a router or something like that this is completely unimportant.
Originally Posted by ckrantz
The important property for a router application is stiffness not strength and there is a very important distinction between these two properties of material. Strength is a measure of how much force needs to be applied to something before plastic deformation occurs; i.e. it is permanently bent and does not return to the original condition. Stiffness is how much elastic deformation occurs under a given load and when the deformation is elastic the material or structure returns exactly back to the original condition when the load is removed.
With any material under load elastic deformation occurs first followed by plastic deformation when what is called the yield strength is reached. With DOM tube a great deal more load can be applied and a great deal more elastic deformation will occur before the yield strength is reached than with galavanized pipe.
Obviously with any machine tool whether it is commercially made or a DIY effort it is essential that the loading is always within the elastic deformation region and under loads that only cause a small amount of elastic deformation there is no noticeable difference between galvanized pipe and DOM tube so either can be used for structural parts of a machine.
If the pipe or tube is being used as the tracks it could be that DOM tube is a better choice because it is much smoother than pipe and will handle the concentrated load of small bearings rolling on it with less localized distortion. However, if the pipe or tube is going to be welded in place then pipe may be a better choice because it has less internal stress; DOM tube has a lot of stress and work hardening from the manufacturing operations and the heat of welding will release the stresses unevenly and lead to much more distortion.
Also if welding is to be used black pipe rather than galvanized is preferable because it is easier to weld. Galvanizing can be ground off and it will burn off during electric welding creating a large amount of smoke. This is unpleasant but not particularly toxic.
Good Post but you are incorrect about this part. True you may not notice the effects immediately or ever if it is a small amount but this is something that should be taken very seriously.
Originally Posted by Geof
Most zinc salts irritate mucous membranes of the upper respiratory tract after inhalation.
a-Zinc chloride :
Inhalation of zinc chloride may cause :
-adult respiratory distress syndrome, death, resulting from delayed pulmonary vascular fibrosis.
Ten deaths and 25 cases of non-fatal injury occurred among 70 persons exposed to high chloride concentrations of zinc chloride released from smoke generators. Of the 10 fatalities, a few died immediately or within a few hours with pulmonary edema, whereas those who survived longer developed bronchopneumonia. On dissolution of zinc chloride, both hydrocloric acid and zinc oxychloride are formed, contributing to the corrosive action.
b-Zinc oxide : Inhalation of freshly produced zinc oxide can produce metal fume fever.
Basically what zinc does is, it causes the bodies natural defenses to go into overdrive. Thus the same as other heavy metal poisoning. This has been called in the past "Monday Morning Fever", "Brass Fever", "The Brass Shakes", "Foundry Flu", ect. . .
The flu-like symptoms do not generally cause alarm. But if you experience any flu-like symptoms after welding a plated material. "SEEK MEDICAL ATTENTION IMMEDIATELY!!" You may have been welding something that can only make you sick, or you may be dying and not even know it. Such platings can include things like cadmium. Cadmium when welded is extremely dangerous. Breathing the fumes WILL KILL YOU.
I was going to use the pipe instead of DOM for small furniture projects.. But I think I will stay away from the galvanized pipe, its just not worth even trying to wire wheel the zinc off. Thank you for the warnings.
You conflate together a lot of information and imply equivalencies that are not correct. Zinc metal is not particularly toxic and zinx oxide which is what forms when zinc burns is also not particularly toxic.
Zinc chloride on the other hand is a totally different chemical compound and yes it is very toxic. Extrapolating from the toxicity of zinc chloride to conclude that zinc oxide has similar toxicity is not valid. This is equivalent to saying that the hydride of oxygen is as toxic as the hydride of chlorine or that the chloride of sodium is as toxic as sodium metal or elemental chlorine.
You are correct when you say cadmium is highly dangerous; it is. Cadmium is a totally different element to zinc but it has a chemical reactivity that has some similarity to that of zinc. This is one of the reasons that cadmium is so dangerous; zinc is actually a trace element that is needed for a healthy diet and zinc in different states of oxidation is present in enzymes that are active in different metabolic pathways in the body. Cadmium can substitute for zinc in some of these enzymes but because its chemical reactivity is similar but not identical it interferes with the proper metabolic operation. A person with a diet that is deficient in zinc can suffer far more serious effects than one who has a well balanced diet with adequate zinc. This is often interpreted to mean that zinc has a protective effect toward cadmium poisoning which is a bass-ackward way of looking at it.
The, not particularly toxic nature of zinc, as I phrase is manifest in Metal Fume Fever; flu like symptoms that probably are a result of the immune system being knocked a bit out of kilter by excess zinc oxide absorbed through the mucous membranes of the upper respiratory tract. This is not really surprising because one of the reasons zinc is needed in a balanced diet is that it is implicated in the balanced operation of the immune system.
This is most emphatically not the same as heavy metal poisoning and it is totall inaccurate to use the phrasing "other heavy metal poisoning" because zinc is not a heavy metal in the class of the truly dangerous metals such as lead or mercury.
A short moment of reflection on the part of anyone who thinks things through should lead to the conclusion that the lack of toxicity of zinc is attested to by the fact that millions of people drink water that has been distributed through zinc coated, i.e. galvanized pipes. Similarly anyone who has used sunscreen that contains zinc oxide could come to the conclusion that zinc oxide is not particularly toxic.
I mean no offense by anything i have said and none of what has been posted is my own knowledge. i have seen threads regarding this issue on many fabrication/welding forums and i have taken it as valid. you appear to know more about the subject than myself. I just know that ever welder/ welding shop guy/ fabricator i know caution not to weld or grind on galvanized pipe unless you are properly protected, ie. respirator etc. For the average joe i would recommend staying away from all plated metals just to be safe. If you know better or know how to work with these things properly then go for it.
I can't argue with or take sides with either keebler303 or geof303 regarding their well stated comments but I can provide some first hand experience re: the subject:
I did a bunch of sheet metal welding with galvanized steel to repair a floor pan in a car one night. Was in perfect health at the time.
It was late at night and did the welding before I went to sleep. A short while later while in bed trying to sleep, I started halucinating and had some REAL scarey experiences including nausea and other issues I don't recall anymore. I learned later that YOU DON"T WELD GALVANIZED MATERIAL WITHOUT BREATHING PROTECTION.
I dunno and don't care what was in the smoke from the welding BUT I was lucky enough to survive with nothing worse or longer lasting than a real scarey annecdotal experience.
IMO, If you're lacking in zinc, take vitamin supplements or suck on a galvanized nail. Don't try to ingest it in any format via your respiratory system after vaporizing it by welding galvanized steel.
Last edited by NC Cams; 03-10-2006 at 10:14 AM.
Reason: fix typos
DOM vs pipe
Ok I got a question, What is the material difference between black pipe and DOM,I know black pipe has a laquared finish to minimize rusting, pipe is measured ID, DOM is measured OD, DOM wall thickness is .120 where as pipe is .113, ( BTW I am talking 1" DOM or 3/4 black pipe) whats the metalurgical difference. I want to use black pipe to build a motor cycle frame. I talked to a pro TIG welder and he mentioned that pipe does not weld as good as DOM? Any input.