Design of hangers for oil tanks

[maneesha0702]

I am designing fire prevention system for oil tank. The fire prevention system has 10" & 6" lines at 3rd level i.e. 24ft above grade and 24" from top. (Ht of tank is 48' and dia is 220'). The hangers need to be attached to the shell. The shell is designed for hoop tension and the thickness(0.66 in) is sufficient for 26000 psi stress as against allowable 28000 psi. How can install these pipes without increasing the stress on the shell.

 

[JStephen]

Check some of the pressure vessel handbooks for various methods of calculating local stresses in shells. Main problem is that the t/R ratio is smaller than the ranges covered in many cases.

Note that local stresses at an attachment are evaluated differently from general hoop stress- you're not just limited to using that extra 2,000 psi left over from your allowable stress.

 

[paddingtongreen]

You cannot unless you have sky hooks. It may be possible to avoid increasing the hoop stress, or minimally increasing it. you cannot avoid increasing the vertical compressive stress unless you include a complete system within and independent of the tank

You could hang them from the roof, or from brackets attached to a vertical piece that is fixed to the wall. If the moment couple of the vertical piece on the wall pushes the hoop tension too high, make it longer to reduce the outward/inward forces.

If you make it an independent system, the distribution piping itself could provide the structural support as well as serving the sprinkler or deluge heads.

Michael.
"Science adjusts its views based on what's observed. Faith is the denial of observation so that belief can be preserved." ~ Tim Minchin

 

[dhengr]

Maneesha0702:
Could you stand 46' high legs (a W6x? or some such) outside the tank shell, and attach this to the shell for stability purposes only. Otherwise, this leg carries most of the weight and any eccentricity of the 10" and 6" lines to the foundation ring.

 

[JStephen]

If this is piping running around the shell, I would expect the supports to take the form of knee-braces attached to the shell, possibly with reinforcing pads at the attachment points.
If this is vertical riser pipes, support the vertical load at the shell/pipe interface and design the supports for horizontal loads only.
Vertical stress on a tank like that will be low, both before and after the piping is supported. Local bending is the main issue.
I assume these pipes are on the outside, so hanging them off the roof would be awkward, more so if it's a floating roof.

 

[Bagman2524]

Agree with paddintongreen & dhengr. No way to avoid adding stresses in the tank without supporting the piping from ground or another structure.

Faith is taking the first step even when you can't see the whole staircase. -MLK