Any Engineers here? Steel Stand Help Needed

[HTXReefer]

So I built a steel frame stand for my new 6x2x2 180 gallon tank. The stand is built out of 1-1/2”x3”x0.125” and supported by 5 1-1/2”x0.125 square tube legs. The material is A36 carbon steel and all joints are full penetration GTAW welded.
I started my initial leak test last night and onleaks but took off the front wood panel and noticed about 1/16” gap between the 3/4” plywood and top of stand in the center of my unsupported run.

 

[HTXReefer]

 

[HTXReefer]

I put a 4ft straight edge under the long span and noticed about 1/16” gap. So I put a floor jack under the center span to see if there was any movement and all it did was lift the front of the stand off of the ground without closing the gap. I immediately drained all of the water and the gap has grown to about 1/8”. I then out the straight edge under the 3/4 plywood and it is clearly bowed up in the center.
Is it possible the tank bottom is bowed up? Is it possible the wood is bowed enough to support the tank without complete contact across the entire span? Any ideas? Should I add an additional brace in the front?

 

[GK3]

Take the plywood off and put a level across the steel bar. Is there a gap? You need to see if it’s the steel that is bent or the plywood.

 

[K7BMG]

Yes you need to use a level to see if its the steel rails or warps in the plywood.
The top rail could very well be curved due to many factors
Poor handling is most likly the culprit.

In anycase you need to confirm the stand is straight and true.

 

[r20crazy]

any weld boogers the plywood is sitting on? if not check the center brace for flatness, then all others. Box tube stock is very rarely straight (like lumber) and you gotta put the parts together for the best match. welding also causes the metal to move around.

 

[HTXReefer]

Thank you for all of the responses. I am waiting for a few friends to come by so we can lift the tank off of the stand. When I fabricated the top section I tack welded it down to a 1” thick steel fan table in dimension and welded the 3 sides I could get to at each joint. The cut the tracks flipped it over and made the last weld. There are definitely no weld spatter or caps left n place, I blended all of them smooth with a flapper wheel.

I am leaning more that the wood is warped. There is a slight bow on the back side right above a vertical leg support. The plywood was a little difficult to put down after I finished coating the stand. I did glue and screw guides on all 4 sides to keep the plywood frommoving while we were putting the tank on.

as soon as I get the tank off I’ll respond back to the thread

 

[HTXReefer]

Ok new update. The tank has a slight bow up in the center on the frame but the glass is straight. The plywood is slightly bowed to the contour of the tank. The stand rails have a slight bow down in the center. Each one is somewhere around 1/32” to 1/16”. Which makes sense because I have around 1/8” gap. I think I’m going to do some testing to see if there is any movement in the stand by placing some shims in the gap and tying some braided fishing line from the top rail to the bottom and fill the tank back up. Hopefully this will tell me where the movement is occurring. Sound like a bad idea?

 

[K7BMG]

IMO you need to make the foundation (stand) as flat as humanly possible.

The plywood having some flexibility will conform to the foundation and be fine. You need to water seal the plywood with several coats of Thompsons or Olympic water sealer. Three coats on the edges, this will prevent the plywood from dry rott.

The tank itself is another situation all on its own.

 

[HTXReefer]

IMO you need to make the foundation (stand) as flat as humanly possible.

The plywood having some flexibility will conform to the foundation and be fine. You need to water seal the plywood with several coats of Thompsons or Olympic water sealer. Three coats on the edges, this will prevent the plywood from dry rott.

The tank itself is another situation all on its own.

I agree trying to figure out how to do that without cutting it apart. If it was a fit up issue I have no problem cutting that joint and re-welding. But it’s a slight sag and I’m afraid I’ll do more damage than good trying to get it straight. I do have two coats of flex seal on the top and bottom of the plywood but the edges could definitley use more.

 

[K7BMG]

Obviously you are good with metalworking.
Can you put a 1/4 inch plate on the top of the stand.
And using gussetts make it flat and true?

I know its a lot of work and extra weight but in the long run the pay off will be well worth it.

 

[HTXReefer]

Obviously you are good with metalworking.
Can you put a 1/4 inch plate on the top of the stand.
And using gussetts make it flat and true?

I know its a lot of work and extra weight but in the long run the pay off will be well worth it.

I thought about that or trying to weld build up the low areas and grind or machine them back flat

 

[K7BMG]

I built my own wood stand twice as it was not right the first time round.

I actually had to mill my wood.
I know another person here was saying how wood vs steel is straight.
I would differ on that. I used the best kiln dried wood I could find and every piece had a camber to it. So I made a jig for my table saw and cut the material to make it straight and true. I remember when good kiln dried wood was flawless, not anymore.

 

[HTXReefer]

I built my own wood stand twice as it was not right the first time round.

I actually had to mill my wood.
I know another person here was saying how wood vs steel is straight.
I would differ on that. I used the best kiln dried wood I could find and every piece had a camber to it. So I made a jig for my table saw and cut the material to make it straight and true. I remember when good kiln dried wood was flawless, not anymore.

I hear you on that. I spent a good amount of time and money picking out straight boards at the lumber yard only to have the Houston humidity bow them over night. I did something similar with my tablesaw but that is definitley a tool I need to spend some more money on a better one if I’m going to do any serious wood work

 

[LeftyReefer]

Technically, that tubing is either A500 or A513 steel, not A36, but for all intents and purposes, they are the same when it comes to welding. But A500/A513 is used for tubing and pipe while A36 is used in flat bars, plates, channels, and angles, etc... A500 and A36 are very very similar, but not quite identical. But for welding purposes, both are the same.

If there is a small gap/dip in the frame, I'd just fill it with a weld and grind it down flush/smooth. Of you could add a thin shim plate to fill the gap, tack it down, grind it smooth, repaint, gap gone.

I think as long as your frame is flat/level, your tank will be OK.

nice work, btw!

 

[HTXReefer]

Technically, that tubing is either A500 or A513 steel, not A36, but for all intents and purposes, they are the same when it comes to welding. But A500/A513 is used for tubing and pipe while A36 is used in flat bars, plates, channels, and angles, etc... A500 and A36 are very very similar, but not quite identical. But for welding purposes, both are the same.

If there is a small gap/dip in the frame, I'd just fill it with a weld and grind it down flush/smooth. Of you could add a thin shim plate to fill the gap, tack it down, grind it smooth, repaint, gap gone.

I think as long as your frame is flat/level, your tank will be OK.

nice work, btw!

Thank you. You are absolutely correct about the material type it is A500. I have a R&D project in the shop right now on some thick A36 with a weird joint geometry we are designing an inspection system for so I got them crossed.
The frame is level and square from the corners and all legs are plumb. So I am breaking the tank down now and will be doing a weld build overlay with ER70S-6 GMAW and grinding smooth. I did hook up some dial indicators and filled the tank up and over 48 hours haven’t had any movement in the span of concern so I am confident it was naturally bowed from the mill and not because of stress from the weight of the tank.

 

[cmoore806]

is the floor it is on perfectly flat?

 

[HTXReefer]

is the floor it is on perfectly flat?

The floor isn’t perfectly flat it’s about a 1/4” drop across 24” front to back of the stand. I have heavy duty adjustable feet on all legs that I leveled the stand with before placing the tank on it and verified the top of the tank was level prior to adding water.

 

[EeyoreIsMySpiritAnimal]

Any update? How did the stand turn out?