Open or closed frame tubes?

[Trackstriper]

This is a bit of a spin-off question brought up by a recent discussion about sealed vs. unsealed axle tubes and interior corrosion/rust. I'll be building the frame for my near-standy, 6'x12' travel trailer soon. The primary frame components will be 2"x3" 14ga steel tube aligned vertically. I picked up the tubing the other day.

Here's the question. Does it make sense to seal the ends of the tubes with flat sheet product to keep the water out? 14ga tube is about .083 thick...thinner than the 1/8" stock that most of you use, and perhaps more sensitive to corrosion issues over time regarding strength.

I could leave the tubes open to allow for air circulation and allow any water to exit. This would be easiest. But I'm assuming that nobody preps and paints the interior of the tube, so a certain amount of rusting will happen on the inside. Perhaps by keeping the tubing open the frame will dry out quick enough so that rust is not to be worried about.

I could seal off the tubing ends and weld on small mounting tabs for the floor attachment so that the tubes would not be pierced by screws. The tubes could be purged with dry nitrogen to eliminate moisture and reduce the oxygen. More work, but is it worth it?

There's such a wealth of practical information on this forum. I'd appreciate your input and discussion.

J.B.

[G-force]

You wont be able to leave all the tubes open (the crossmembers will be closed) so I feel its better to plan ahead and design it to have all the members closed. Miter the corners and cap open end tubes (such as on an A frame tounge.) This of course requiers 100% leak free welds, which can be an effort in its self. For some boat trailers I have built, we will drill an 1/8" hole in the side members where the cross members go to vent them to the main frame, and after it is all welded up, we drill a hole and weld on an 1/8" NPT fitting on the frame so we can pressurize it and test the joints for leaks. Leaks get rewelded. Naturaly if you go through this trouble, you cannot drill or cut into the frame at all...no deck screws to hold the floor on, no holes for wiring, etc. If you do leave the members open, I would make sure the design allows for easy water drainage. If your in a high humidity or wet area, I would paint the insides. It doesnt have to be pretty, a length of PVC pipe with a round kitchen cleaning bristle brush taped to the end, dunk it in a gallon of Rustolium black pain and swab the inside of the tube untill it is coated and let the excess drain out. One more factor to deal with considering corrosion on tubing, try and design the frame so there is no overlap of members. Its easy to weld an angle to the side of the tube to bolt the floor to, but if you dont weld all around that angle, or if you dont seal the joint with a caulk, moisture will get behind it and start rusting imediatly.

Mike

[Leon]

I weld all mine closed, and where I have to attach something to the tube I use a weld-through coating on the steel before it is welded that does a pretty good job of protecting the metal yet allows a good weld.

[brian_bp]

... I use a weld-through coating on the steel before it is welded that does a pretty good job of protecting the metal yet allows a good weld.

Interesting... do you have a brand name to share with us, Leon?

[Alphacarina]

I could seal off the tubing ends and weld on small mounting tabs for the floor attachment so that the tubes would not be pierced by screws. The tubes could be purged with dry nitrogen to eliminate moisture and reduce the oxygen. More work, but is it worth it?

I would definitely seal the ends - I think it will rust 10X as fast if you leave the inside unpainted and open to thr atmosphere . . . . water will get in and not all of it will run out

If you're worried about rust in a closed tube, you could seal one end and pour a few tablespoons of oil inside before you seal the other end - The oil fumes traped inside would make a pretty good anti-rust compound. Stand it on end so you can get the oil all the way to the opposite end before you weld on the last cap

Don

[starleen2]

And something yet to keep you awake – after taking the time to coat the interior of the tubing and all that prep – work, once you weld, it will burn off any coating nearest the heat source, thus reducing the effectiveness of the coating right where it is needed the most – at the weld site. While is prepping, coating, and purging with nitrogen is all good stuff – is this REALLY necessary. I have never had trailer rust through

[Leon]

... I use a weld-through coating on the steel before it is welded that does a pretty good job of protecting the metal yet allows a good weld.

Interesting... do you have a brand name to share with us, Leon?

I use the stuff from 3M, it's available at some auto parts places, and most welding supply houses.
http://solutions.3m.com/wps/portal/3M/en_US/3MAutomotive/Aftermarket/Products/Product-Catalog/?PC_7_RJH9U5230GE3E02LECFTDQCEK3_nid=GSMX9LW15Gbe33SJ0H5T4Sgl

[Trackstriper]

Thanks for the input. If I go with open tubes I guess it is possible to drag some paint through, would have to be better than nothing. Can't see the small cargo trailer manufacturers going to that much trouble 'cause it doesn't show. Good idea. I would think a little J.B. Weld would make a great caulk. If I close the tubes there would be no reason to paint the inside of the tubing.

I'll look into that oil idea. Makes sense. I would think it would be a natural with nitrogen. Maybe way overkill though.

I'll check out that paint product, leave it to 3M to make something that actually works.

J.B.

[Trackstriper]

Opps! I must have been asleep at the switch. This topic was covered on pages 2,3 of the topic "Will it work" by Creekslick. Maybe it was rattling around in my head subconsciously so I asked the question. Thanks for the help guys.

J.B.

Additional discussion welcome.

[brian_bp]

... I use a weld-through coating on the steel before it is welded that does a pretty good job of protecting the metal yet allows a good weld.

Interesting... do you have a brand name to share with us, Leon?

I use the stuff from 3M, it's available at some auto parts places, and most welding supply houses...

Thanks!

[Trailer411]

J.B.

I have first hand experience with this issue. It has been our experience that any water that gets inside tubing is a problem. We have seen main cross members that hold water rust out extremely fast.

The only way to stop it, that we have found, is to cap the tubing, get all your welding done and then come up with a way to add some holes to undercoat the inside of your frame.

We of course have a commercial undercoat system, which we have built a long skinny wand just for this purpose. The wand is home made out of a piece of 3/8" round tubing with the end welded shut. We then drilled some holes around the circumference of the tubing to create a 360 deg spray pattern at the end.

I wonder if you could figure out a way to do this with a standard paint gun?

Just a thought.

[frank_a]

I like the idea of drilling a 1/8" hole and putting an air fitting in to test for leaks. Sometimes it's easier to fill weld leaks or obvious holes with JB Weld where it's not a structural thing. Plus you can smooth it over like body putty and sand it so it's nice and smooth looking. I love JB Weld!

Frank

[McTeardrops]

I find it easier to weld miter joints, so thats how I've built my trailers.

I built a two-rail car trailer that I had coated with catylized epoxy for protection. This trailer had to be abandoned at the U-haul yard, after renting one of theirs to finish the trip. The epoxy held up extremely well... there was just no metal left behind it.

For Benroy McFull I enlarged the vent holes, added a 1/4" pipe plug, then filled the frame with all those 7/8ths empty oil cans that accumulated on the garage shelves. I missed the step regarding the air test. After five years, 60,00 miles, I've had no problems with rust or corrosion, but I do leave an oil slick behind whenever it rains.

[vtx1029]

FYI its common practice to coat the inside of steel tubing on aircraft with boiled linseed oil to prevent corrosion

http://www.mechanicsupport.com/aircraft_tube.html

[Shadow Catcher]

Or use aluminum

If I were using steel I would be using cold galvanizing spray and having some way of periodically inspecting. For a rusting rocker panel I used a toilet brush on a pole to distribute Zero rust paint and I left a plug for inspection. Any place that does undercoating should have the fixtures/wands to get into tubing.