I have a question that pertains to a variety of projects. When using tubing, how do you prevent rust from the inside out? It's nearly impossible to coat the inside of the tubing and be sure that it's been 100 percent coated I would think. Are their any tricks or something to prevent this? I've had people on a do-it-yourself forum tell me to weld each side closed, but this won't make a difference if moisture or rust has already started inside. Another person said drill drain holes, while yet another said drain holes would just make the problem worse.
What do you guys think? Is there a remedy to this problem, or do you just take it in account on your design and use solid material if you need it to be rust free?
Mathius
By -
Date 12-10-2003 07:11
The aircraft industry employs an oil that is put into the tubing prior to closing the final weld. Sorry, that's the limit of my experience and I can't provide you with information on the oil itself.
Is it feasable to put drain holes in it and hot dip galvanize the tubing?(After fabrication)
John Wright
If you choose to hot dip galvanize, please put vent holes in the lowest point and in the highest point. Dipping without proper vent holes will destroy your part and possibly hurt someone when it comes apart. Steam is very powerful and will build pressure until it relieves itself. The zinc bath is about 850F and it will coat your part inside and out, try to put the vent holes where it won't cause a problem, like trapping mud or snow.
Or posssibly use another material that won't be effected by the elements?
John Wright
Rust is an organic bacteria thats breathes oxygen.
If you weld up both ends of a tube, air tight, and have no other holes in the tube, then rust cannot live in the tube.
Rather, it will only live as long as the trapped oxygen lasts.
That is why oil coated steel doesn't rust, because the oil blocks out the oxygen.
The same goes for paint.
I used to work in a shop that made oil rigs for offshore use in which corrosion was a very big concern for us. Whenever we wound up with a tight inside corner that could not be sand blasted and painted properly, we would "box it in". This means that we would weld in pieces of plate that were cut to fit and would seal up the inside corner air tight. Then we wouldn't have to worry about it rusting out.
Tim
Hot linseed oil, heated to approximately 180 degrees F, is pumped into the tubing through a small tapped hole at the forward end and finally reaches the small tapped drain opening at the lower end. Once the tubing structure and all of its weld joints have been pressurized one or two pounds (checking for leaks) the oil is drained away and the tapped hole plugs are replaced. The oil coats the inside walls of the tubing.
I don't know if a petroleum based oil would be better than linseed oil. Maybe someone knows the viscosity and properties of the different oils.
The only ways I know of to deal with rust inside of tubing are:
1) Seal off all openings to prevent oxygen and water (electrolyte) from getting inside. There will be a small amount of rusting until the oxygen is used up, but not enough to cause problems.
2) Use stainless steel, aluminum, or other non-rusting material. Or use a weathering steel that will rust up to form a durable and protective patina.
3) Hot dip galvanize. This requires proper venting but all surfaces, inside and out, will be covered with a protective coating. (Usually cheaper to have done than painting would be)
4) Leave everything open, allow for drainage so water can't accumulate, and don't worry about it. Many times we make a bigger deal about rust than we need to. As long as the interior stays dry there won't be enough rusting to be a concern in our children's lifetime.
There are exceptions, of course, where you have corrosive environments or unusual corrosion cell situations. You didn't list any specific situations so I'm being generic here. Many things are possible but there is always a cost involved. How much will rust prevention cost compared to service life of the product, replacement costs, and safety concerns. However nearly everyone has seen handrails that have had no special treatment other that paint on the exterior (sometimes not even that), that lasted for many, many years. Be careful but also be realistic.
Chet Guilford
I don't understand Mathius' concern. Back in my days of erector engineer, I installed hundreds of tons of piping in oil refineries, power plants, chemical industries, oil and gas pipelines, water works etc. The pipes are received from the manufacturer with a priming on the outside and, true, show some degree of rusting on the inside.
What is it done then? You should clean a region of, say, one inch adjacent to the welding ends, both inside and outside, and make the weld.
What about the rust and other foreign matter existing on the inside pipe wall? Well, that's why the piping systems are purged before putting them into service: to remove rust and foreign matter. For example, steam lines are blown out with steam, compressed air lines are blown out with compressed air, other lines are washed with water or some kind of solvent, lube oil lines are pickled and passivated with chemical products etc.
Giovanni S. Crisi
Sao Paulo - Brazil
I know a lot of you have responded with questions about the impact rust could have on the project. First off let me say I didn't expect to get so many responses so quickly. Thanks everyone.
My big concern here was mostly in automotive related projects. I live in Ohio, where they salt the roads in the winter, and rust is our big enemy in the automotives industry.
I have contemplated many projects in automotives, from building a new bed for my ranger out of squared tubing, and then welding the body panels on to the possibility of someday (after I learn a LOT more) being able to make my own frame rails for a custom pickup truck.
Sealing off the tubing ends seems to be the most convenient solution. One thing I had thought of, that brings another question to mind....
Another possible solution might be to cut openings in the undersides of the tubing, where I were using tubing on a frame perhaps, or even in my pickup bed project. If I cut "slits" big enough to coat the insides at different intervals that could work.
My question: How do I know how far apart to cut openings, without compromising the strength of the tubing to the point where it no longer will work for my application? I don't suppose there's some kind of common formula I can apply here? Anyone an engineer?
Mathius
Hi Mathius,
Cutting slits in your tubing is going to be detrimental to the tubes inherent strength. Also, you'll be creating a cavity for salty sludge to remain trapped in, which will eventually eat through your coating.
If you're determined to coat the inside, could'nt you just temporarily cap one end of the tube, then fill with cleaning and coating materials alternatively? Then you could dump out the excess, remove the cap and let it dry.
Tim
Hi Mathius,
I'm in Edmonton, Alberta (Canada), and our dealerships often spray the bottom of our vehicles with undercoating. This is a black rubbery spray, which has a very thick viscosity. It helps protect the vehicles undercarriage from rusting, and it is a good 1/8" - 3/8" thick (depending how much you use), so also provides protection from the sand and rocks.
Just a visual inspection will do for knowing when to re-apply, but for most vehicles its around once every 5 years.
Good luck,
Vicki
Hi Matius,
Also, as for preventing rust in truck bodies... (we get about 4 months of snow here a year), and what we have found is building our truck bodies with an aluminum frame. This costs about 1/3 more - compared to steel, but is also about 1/3 lighter. If going aluminum, choose all aluminum - as steel / aluminum combination result in corrosion.
Aluminum does have some other set backs. If you wish to paint it, it requires a special primer, which costs aproximately $250 Can for a 1/2 Gallon. This cost tends to be a shock when it comes to painting the deck. To avoid the slippery aluminum surface on the floor, you have other options a bit cheaper.
you can use a box liner (usually around $400 Can). Or grab a rubber mat, and bolt it down. These options aren't recommended with a steel deck, as the water will collect underneath, and rust it out. With aluminum, you need not worry about this.
To justify for the cost up front - you end up with a body that will outlast the steel (by aproximately 2 times). That is stats coming from a location that lives in snow though. Good luck
Better get back to my igloo, lol!!
Vicki
Vicki,
Your post on aluminum frames interests me greatly. I did not think aluminum was strong enough for a truck frame. I had contemplated building a bedframe (for a bed in your home, not a truck bed) out of aluminum, and a lot of people told me they didn't feel it would be strong enough. I am encouraged, and intrigued by your post. Where can I learn how to properly brace my framing projects to utilize aluminum properly? Is this something that can be easily learned, or do I need to take some engineering classes?
I had thought of stainless as an option, which is supposed to be stronger than steel and of course won't rust easily (or at all?) but the cost of course is much greater.
Thanks,
Mathius
Mathius,
As Vicki said, aluminum will be 1/3 the weight, but at a cost of 1/3 the strength. Aluminum is also weird in that its weld joint typically is weaker than the base metal, unlike steel, which can be assumed to be as strong the base metal, or stronger. From personal experience, if the joints need to be able to take significant vibrations or will be exposed to some unpredictable forces, opt for steel.
From what I have read on some of your posts, you sound about like me a few years back. You seem extremely interested in welding, but at the same time would like to not "just" weld, but also build. This led me to explore engineering and now I am in my fourth year as a sort of mechanical/civil/a little bit of everything else engineering student, and have found it fascinating. After finding a job as a welder here on campus, I found it satisfying to not only be able to read blueprints and physically construct fairly complex objects, but to also to be able to design that piece of machinery so that it is your own handiwork from beginning to end. Maybe that is not your proverbial cup of tea, but it wouldn't hurt to find an engineer in an area that you might be interested in, and talk to them to see what kind of projects they have done and/or are most proud of.
Good luck!
G. L.
Actually, I'm thinking of either going into autobody, or machining. You hit the nail on the head, I do like to build things. I have a billion ideas, just lack funding and in some cases engineering yes. I will take your suggestion to heart though, and mayhaps I can meet someone at my vocational school.
Mathius
Hi Mathius,
When it comes to aluminum frames, they have their benefits and disadvantages. Main advantage: no rust! Disadvantages: Impact strength.
Its not recommended to use if you will be carrying heavy loose loads, or something such as a little crane on the back. We do use aluminum with service bodies - which have drawers, and can contain most of the loose tools, and wont have any major requirements for strength (such as a crane).
The cross and long sills are that of steel, and can often use the equivelant thickness. Engineering is a benefit if you are going to have a heavy load. If it is a typical truck body, we often stick with 18" spacing between cross sills. I have seen some trucks go with 12" spacing, but this seems to be with the larger (taller) trucks, which have higher payload.
Payload is something you do want to insure you have room for. This is another advantage of aluminum. Most steel utility bodies come in to weigh about 3,500 lbs (just for the deck). Aluminum can weigh in at 2,500 - 3,000 lbs - which gives you extra weight to use on your load (such as a welding machine)!!
One other disadvantage with aluminum is if you get into an accident with it, you end up replacing the whole plate. It is not as easy to fix as a steel accident, and results in higher pricing. For this reason, we usually use steel bumpers, and insure that the steel is galvanized, as to prevent any aluminum / steel corrosion. Another reason to use steel bumper is to mount the vice. Vices have small mounting area, and form alot of stress onto the mount (whether it be held down by bolts, or by a receiver). Just something to be aware of...
As for stainless steel, we tend only to use that on our latches and handles for the boxes. Stainless steel holds up great with the cold, and tends not to expand and contract as much - making it easier to open / close. Great for moving parts, but very expensive. Stainless steel should also have rubber backing and protection when in contact with aluminum, as it can also corrode after about 5 years of contact (as we are just finding out). It is minor surface corrosion, but gives a bad time when trying to open doors and locks :(
Often with our aluminum welding decks, we will install a 1/2" steel plate on the back fold down tailgate, and to stand up to the hammering and rough activity the welders do on the back of the truck.
Good luck!
Vicki
I wouldn't make slits in the tubes. I would drill round holes but I cannot say where it would be safe to do that.
Seriously, I would either leave everything open and accessible with a hose, or completely closed.
If open, you can flush the tubes out with water when you wash the truck.
Either way, I suspect the tubes will outlast the rest of the truck.
If you absolutely have to have a rust resistant coating inside the tubes, check with the nearest galvanizer for pricing and venting requirements. You would be surprised how much cheaper that will be versus painting.
Aluminum is a nice idea, as Vicki mentioned, but it is a bit more difficult to weld than steel is. From your other posts I assume you might not have learned to do that yet.
cg
I may be reading to much in to this but I agree with Chet about the bed out lasting the the truck.
What expense are you willing to go on this and is it worth it? If it is, simply drill and tap for fittings and purge with Nitrogen. Mount a Nitrogen bottle on board with a pressure gauge to monitor the purge. The Nitrogen is the least of the expense by far.
These are few things we do with cocoons containing rotating elements of very expensive Turbines, Pumps and Compressors. Don't know if your project compares.
Do what seems to be the only truly effective way of stopping rust on vehicles. Spray it with oil every year; it has the advantage of slowing or stopping rust that has already started to eat the car away.
Drill holes, spray with oil by means of spray gun and compressed air. Tap in a plastic plug that you remove next year when you spray. You don't need a lot of holes since the oil mist travels well. You can heat the oil a bit before spraying if it is cold outside to get good travel.
My friend uses an oil sold for painting on concrete forms as a release aid. Thin and cheap.
Bill
