Punching and prying on steel tank sides 2

[Stoppie]

I have a large steel tank to which we need to install supports on its sides. The idea is to weld a triangular frame (horizontal beam with a diagonal strut) to the side of the tank. I am concerned that the moment generated by this support will dent the tank and I have no idea where to start to do some checks. Any advice or pointers?

 

[desertfox]

hi Stoppie

can you post a picture with some dimensions and thickness of tank walls? what is the tank holding inside water?

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[human909]

There is an entire forum on storage tanks:

https://www.eng-tips.com/threadminder.cfm?pid=1452

You are going to have to calculate the eccentricity and the resultant load it produces and work out the compression buckling behaviour of the tank. Of course you might need to consider the tank in all sorts of conditions depending on what the tank is being used for.

If we are talking heavy tanks then you REALLY want to keep eccentricity to a minimum.

 

[Stoppie]

Hi, desertfox. I have attached a rough sketch. The tank is about 20m high, 7.5m in diameter with an estimated 10mm thick steel wall. I am assessing the tank as if empty. The idea is to weld 10mm base plates to the side of the tank and then I-profiles onto them, knowing this would strengthen the connection area.

 

[Stoppie]

Thank you human99. Will have a look at that!

 

[desertfox]

Hi Stoppie

Are you suspending the tanks from these supports?

As the previous poster human909 stated you need the weight of the tank and it’s contents and then calculate the load eccentricity, I would treat the straight and angled legs of the supports via the tank pads as a solid frame and calculate the reactions on each pad, if the tank is suspended from those lags then the pad with the horizontal leg would be putting the tank in compression and the lower pad would be tearing off the tank, I would then stress the welds for shear failure at both pads, this would only be a ballpark calculation because the tank might be constructed to a vessel code or specification which you haven’t mentioned as yet.

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[JStephen]

Several approaches:
Bednar's pressure vessel handbook gives an approximate solution for line loads on a tank (so "clips" welded to the tank, either vertical or horizontal). The allowable loads calculated will be low, but this is the simplest method to use. And it may be cheaper to make those clips a foot longer than to prove that they can be shorter, etc.
WRC-297 and some similar documents give stress results for round or square reinforcing pads welded to a tank. Many atmospheric tanks are too thin to fall into the range of thicknesses given (it's intended for pressure vessels). These methods are incorporated into vessel design software, and fairly simple to use if you have that software.
Lastly, finite element methods.
Note with the latter two methods, the allowable stress to be used may vary, but is generally allowed to be fairly high, like 1.5 yield or so.

 

[WARose]

I've typically used some of the Pressure Vessel handbooks out there (like Bednar's) to figure stresses in these situations.

But you will likely need to get a mechanical guy involved to get allowable [stresses] and welding [to] tank requirements. That's not in most of the codes we use.

 

[Stoppie]

Hi deesertfox,

No the tank is supported at its base. Its an existing tank to which I need to install this bracket to support pipes passing at the side.

 

[LittleInch]

What sort of vertical load are you looking at?

I think it's a wholly bad idea myself.

Most tanks are designed with very little spare in terms of stress and really don't like extra loads, especially in isolated locations.

You can only design based on a full tank.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[desertfox]

Hi Stoppie

So this is just one bracket on the side of an old tank? So what vertical load will be on the bracket?

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[MotorCity]

If you did not design the original tank, be very cautious about modifying it. Tank design is very much a specialty and you may void the warranty by modifying it. As for prying, its not an issue for welded connections, only bolted