Large openings in steel tanks
Large openings in steel tanks
(OP)
Hi,
I would like to detail a 6' wide by 7' high opening at the base of a liquid storage tank (65' diameter by 45' high). I found guidelines in API 650 for the design of manhole with diameters of 36" and less. Where could I find guidelines for larger openings?
Thanks,
I would like to detail a 6' wide by 7' high opening at the base of a liquid storage tank (65' diameter by 45' high). I found guidelines in API 650 for the design of manhole with diameters of 36" and less. Where could I find guidelines for larger openings?
Thanks,






RE: Large openings in steel tanks
RE: Large openings in steel tanks
From a code standpoint API makes no accomodations for openings/nozzles over 36" diameter other than "door sheets" which are covered under API 650. As aggman said you'll have to address the vertical compression and hoop tension, but you may have to also consider out-of-plane bending if whatever you're attaching to the tank shell has an eccentric center of gravity (use WRC 107 for that - ht
As far as reinforcement, you'd probably want to use the "full area replacement" method that is common to this issue. It basically indicates that you must replace the total removed cross-sectional wall area at the vertical level of max calculated stress with an equal or greater cross-sectional area of reinforcement.
RE: Large openings in steel tanks
From an engineering standpoint, it's just a bad idea all the way around. The main structural component of the tank is the shell, acting in hoop tension. You're proposing to cut out an entire course of shell plate, then try to reinforce what's left to handle the load. While it can be done to some extent, you're on your own as to how you figure the stresses and reinforcement required, and the required details and welding to make a suitable tank. Unlike a normal API-650 tank, you can't rely on past history of similar tanks to show that your product is going to be adequate.
Suppose you build a suspension bridge, and then decide that the cable needs to be cut at some point and offset to go around an obstacle. That is the situation you have here, on a smaller scale.
It is much better, if necessary, to put large openings in the roof.
On the reference to WRC-107 up there, I don't think it covers the thickness ranges you'd need, even if otherwise applicable.
RE: Large openings in steel tanks
Aggman has his finger on it.
RE: Large openings in steel tanks
RE: Large openings in steel tanks
I'm not saying it can't be done- I've actually done such a door, only somewhat smaller- but am saying it's just not a good idea and should be avoided in the first place. At some point, you have to decide whether to adapt the tank design to suit the operational requirements, or to adjust the operational requirements to suit the tank design.
Note that large doors are not uncommon in elevated tank pedestals- but that's mainly compression loading. And some of the silos will be governed by compression rather than hoop tension as well.