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  • #16
    Could it be that the tubes often aren't really sealed? Theory is good that they shouldn't rust from the inside as stated, but I agree with Bob and lars66--I've seen many tubes rusted from inside that appeared to be all welded closed. Not uncommon on old tail dragger airplane lower fuselage longerons (scary! inspection is important!) A single imperfect weld or two somewhere, with a small hole, moisture, temp cycles, and years to work on it yields broken tubing while the outside looks fine. I have crushed the bottom of a piece of fine looking 4130 with my fingers. Seen it on trailers too.

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    • #17
      Originally posted by lars66 View Post
      No Bob is right, have 2 piles I haven' shoveled up yet from the 7 car hauler that just left. Only way you can weld the tubing cracks near the bottom and around the bottom is cut the tubes open and clean them out. This one was an 03.

      No the AISC (and several others) are right. This was studied to death many years ago when structural tubes started coming into use by people who really couldn't afford to have bridges coming apart.
      Once the small amount of oxygen present in a sealed tube is depleted, there is no further corrosion. The science is simple.

      You don't have to believe it of course.
      Some days you eat the bear. And some days the bear eats you.

      Comment


      • #18
        Originally posted by Aeronca41 View Post
        Could it be that the tubes often aren't really sealed? Theory is good that they shouldn't rust from the inside as stated, but I agree with Bob and lars66--I've seen many tubes rusted from inside that appeared to be all welded closed. Not uncommon on old tail dragger airplane lower fuselage longerons (scary! inspection is important!) A single imperfect weld or two somewhere, with a small hole, moisture, temp cycles, and years to work on it yields broken tubing while the outside looks fine. I have crushed the bottom of a piece of fine looking 4130 with my fingers. Seen it on trailers too.
        Nail right on the head..!!!....

        while not impossible.... it is very difficult to get a hermetic seal....

        the expanding & contracting gasses moving at the end of the bead make it tough

        in many applications... a relief hole is drilled to equalize pressure while welding .... then some fogging oil sprayed inside and finally corked with twist drive rivets (sometimes called a Drive Screw)







        lot of old threads here of folks asking about severe cratering/pinholes at the ends of contained tube weds...


        And now a minor hijack... But in spirit....

        http://www.millerwelds.com/resources...light-aircraft

        Last edited by H80N; 06-17-2016, 01:44 PM.
        .

        *******************************************
        The more you know, The better you know, How little you know

        “The bitterness of poor quality remains long after the sweetness of low price is forgotten”

        Buy the best tools you can afford.. Learn to use them to the best of your ability.. and take care of them...

        My Blue Stuff:
        Dynasty 350DX Tigrunner
        Dynasty 200DX
        Millermatic 350P w/25ft Alumapro & 30A
        Millermatic 200

        TONS of Non-Blue Equip, plus CNC Mill, Lathes & a Plasmacam w/ PowerMax-1000

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        • #19
          I can agree with maybe a pin hole in the weld. When i was in the refinery all of the pipe rack supports that were put there in 1969 had rotted off most about a foot up from the ground. So i cant know how good they were welded years ago. The same with the trailers i have replaced rotted tubes in as i didn't see the welds years ago either...Bob
          Bob Wright

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          • #20
            Well the mentioned trailer will be back in here for more repair, maybe I will take the time to tap one of the main tubes for air pressure and a gauge, then open a window to clean out. only been working on them for about 40 years and all I have ever seen is rotted from the inside out same as steel house boats I used to re bottom.

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            • #21
              Like I said, you don't have to believe it. The truth is out there. If you look....you'll find it.
              There are tubular structural pieces in place since before I was born with minimal to no internal corrosion. I've cut them open on seismic retrofits. I probably have pictures.

              Keep in mind that those pieces were welded to strict codes that do not apply in cheap trailer land. Same can be said for your boats.

              Those who build buildings far, far above the ground, or bridges over water, live in a WAY different world (in the US) than your neighborhood trailer/boat builder. So take your work scope and it's weld specs into account.

              Again, You don't have to believe it. But you cannot alter the physics involved. A properly sealed tubular structural element will not suffer (even close to) structural failure due to internal corrosion. It doesn't exist.

              As far as "it's hard to completely seal a tube", no, it's not. Welders do it several thousand times a day on pressure pipe.
              Piping that's hydro'd to 3000 psi before going into service.
              It's done by tens of thousands of pipe/structural welders every day. This isn't rocket science it's just real world professional welding. They are tested on every job.

              And, when the oxygen is depleted, the corrosion is over/done/dead just the same as if you filled the tube with an inert gas.

              Believe it or don't.
              And I'm sure you don't : )

              Some days you eat the bear. And some days the bear eats you.

              Comment


              • #22
                Originally posted by JTMcC View Post
                Like I said, you don't have to believe it. The truth is out there. If you look....you'll find it.
                There are tubular structural pieces in place since before I was born with minimal to no internal corrosion. I've cut them open on seismic retrofits. I probably have pictures.

                Keep in mind that those pieces were welded to strict codes that do not apply in cheap trailer land. Same can be said for your boats.

                Those who build buildings far, far above the ground, or bridges over water, live in a WAY different world (in the US) than your neighborhood trailer/boat builder. So take your work scope and it's weld specs into account.

                Again, You don't have to believe it. But you cannot alter the physics involved. A properly sealed tubular structural element will not suffer (even close to) structural failure due to internal corrosion. It doesn't exist.

                As far as "it's hard to completely seal a tube", no, it's not. Welders do it several thousand times a day on pressure pipe.
                Piping that's hydro'd to 3000 psi before going into service.
                It's done by tens of thousands of pipe/structural welders every day. This isn't rocket science it's just real world professional welding. They are tested on every job.

                And, when the oxygen is depleted, the corrosion is over/done/dead just the same as if you filled the tube with an inert gas.

                Believe it or don't.
                And I'm sure you don't : )
                Don't think anybody is fighting you about a SEALED structure once depleted of oxygen suspending internal corrosion...

                Where we seem to diverge is that many times in the real world.... that seal is never made in the first place or it fails for whatever reason...

                then that cavity becomes a water trap... allowing corrosion to happily devour the steel from inside...
                .

                *******************************************
                The more you know, The better you know, How little you know

                “The bitterness of poor quality remains long after the sweetness of low price is forgotten”

                Buy the best tools you can afford.. Learn to use them to the best of your ability.. and take care of them...

                My Blue Stuff:
                Dynasty 350DX Tigrunner
                Dynasty 200DX
                Millermatic 350P w/25ft Alumapro & 30A
                Millermatic 200

                TONS of Non-Blue Equip, plus CNC Mill, Lathes & a Plasmacam w/ PowerMax-1000

                Comment


                • #23
                  EDIT-the quote function failed----

                  I believe it. But as you say, the guys welding up trailers, and even some aircraft welders, aren't making hermetically sealed tubing products. Agree that the laws of physics always apply-once a given amount of oxygen in a sealed environment is used up, corrosion will stop. Just that the average guy doesn't see 3,000 psi hydro test quality welded assemblies rolling into the shop every day, thus the apparent disconnect. And, as H80N said, imperfection in welding is why tubular structures are sometimes protected internally by putting in oil and rotating the assembly every which way to distribute the oil evenly, and using a "migrating" oil.

                  http://www.polyfiber.com/products/tu...ninhibitor.htm
                  Last edited by Aeronca41; 06-17-2016, 05:23 PM.

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                  • #24
                    A few of the multitudinous courses I took as an undergraduate was chemistry.

                    Rust is almost like a living thing. There are several chemical compounds normally referred to as rust. Wikipedia has a good discussion here. https://en.wikipedia.org/wiki/Iron_oxide The oxygen travels back and forth between types of rust as the iron changes state due to magnetism, minor electrical currents from, say, static, radio waves, even changes in direction. Keep in mind when you start to jump on this statement that this happens at the micro level, where microvolts can do this. Every once in awhile, there is enough free oxygen, even in a sealed system, to cause new rust in adjacent fresh iron. Several chemicals can be catalytic agents to oxygen rust, e.g. water, sulphur. The difference in electrical charge of some metals will cause corrosion. Different grades of steel, over long periods of time, can have such a potential, and corrode each other. All this is why engineers are so careful about specifying grades of steel, and the exact number of welding filler. It is why you see plastic washers, or a coating of something separating a bolt from a plate.

                    This is why it is so important to clean, clean, clean. Even if painted with a good rust inhibiting paint, if there is a rust pocket, when the sealing oil of the paint dries up, the rust will spread under the paint. No, the paint did not crack. The rust was there, biding its time, until it could spring to life, again. When you clean up rust, prior to painting, it's important to get down to bright metal. ANY dark spot is a living pocket of rust, waiting to spread.

                    Galvanizing is good, as the iron now has something to bond to. Electroplating, too. The oxygen now has to compete for something to bond to.

                    I had a 1983 25' Wellcraft walkaround. It had a trailer with tubing axles. I had to weld patches. Sold the boat. Fear for the new owner. Told him about the axles. He didn't care. What can you do?
                    ____________________________________________

                    I don't need to find myself. I'm always at my lathe.

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                    • #25
                      You told him; people choose to accept or reject advice and guidance everyday, often at their own peril. Nothing more you can do.

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                      • #26
                        Yeah, if I do weld a trailer, it will be angle. The tongue will be I-beam, with angle struts. The only place I would consider square tube is the axle. Most commercially produced trailer axles are tube, either round or square.

                        Still debating. Nice 16 hp riding lawnmower at a salvage yard. I'm sure I could get it for $150. All those parts. Then, a horror fright tools tubing bender, and lots of 1-1/4" structural tubing, either Schedule 40 or Schedule 60. The rest is there. A go-kart isn't meant to last the years. If it rusts out, patch it, or replace the tube. Or, just kick it to the curb.

                        What a choice!
                        ____________________________________________

                        I don't need to find myself. I'm always at my lathe.

                        Comment


                        • #27
                          Originally posted by buffumjr View Post
                          Then, a horror fright tools tubing bender, and lots of 1-1/4" structural tubing, either Schedule 40 or Schedule 60.

                          What a choice!


                          When or if you go to buy material, remember there is no such thing as Sch 40 or Sch 60 HSS (structural tubing).
                          It's called out by the outside dimension(s) and wall thickness such as 4X2X1/4. 4" X 2" , 1/4" wall thickness.
                          Some days you eat the bear. And some days the bear eats you.

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                          • #28
                            In manufacturing steel tube aircraft fuselages, the traditional practice was to coat the insides of the tubing with oil admitted through small drilled holes which were plugged as the last step. As McC asserts related to building bridges, aircraft builders later found that the oil was unnecessary as long as the welds were and remained air-tight. Besides saving time, omitting the oil meant that any later aircraft repair-welding was easier to do well. It would seem that the choice to extend the life of any tubing depends on welding skill and service conditions . . . either of which might call for some sort of internal protection. In the case of tubing used in trailers, from what I've seen nearly every tube is going to get holes drilled for through-bolts or runs of wiring at some point, and even if the rare owner wanted to seal all the holes, through-bolts and wires might be hard to effectively seal, long-term.

                            Has anyone built a trailer tube frame and had it dip-galvanized, and what did that cost? Do you have holes already drilled so that the galvanizing can take place inside the tubing?
                            Last edited by old jupiter; 06-24-2016, 09:46 AM.

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                            • #29
                              Originally posted by old jupiter View Post

                              Has anyone built a trailer tube frame and had it dip-galvanized, and what did that cost? Do you have holes already drilled so that the galvanizing can take place inside the tubing?
                              We have hand rails dipped where i work and have to drill 3/8" holes in all of the parts...Bob
                              Bob Wright

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                              • #30
                                105° here today. Whew.

                                I hear kids out there running their karts. In 105° heat. Ah, youth. We live on a network of dirt roads. When I'm out bicycle riding, I see where they've been drifting their karts around corners.

                                Kart or trailer. $400 or $1,000. Usable for machinery, then saleable, or absolutely no resale value, but a lot of fun. Everyone assumes a kart owner is selling the kart because there's nothing left of it.

                                I COULD cut corners on the trailer by buying a used boat trailer for a 21' to 25' boat. That's usually 5,000 lbs or so. Would yield axles and wheels, the most expensive parts. I could scrap most of the rusty steel, rehab the axles, and go from there. Hafta see what's available. If they're too proud of it, I wouldn't think of depriving them of it.

                                Meantime, I keep working on the lathe project.
                                ____________________________________________

                                I don't need to find myself. I'm always at my lathe.

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