Repad in the form of a pipe flange
Repad in the form of a pipe flange
(OP)
Owner has received permission to cut out an overflow hole at the 19'elevation of a 73' dia. X 30' high tank so as to keep the capacity around 750,000 gallons. The current plan is to cut out 8" hole so that a 1/4" thick repad assembled with short piece of pipe and elbow can be bolted to the tank. The question now is can a 1" thick pipe flange(13 1/5" OD) be used instead of the 1/4" X 17 1/5" OD repad? I, for one thought, correctly or wrongly, that the repad thickness could not exceed the 1/4" thick shell plate. I also stated to form the repad to the tank OD which I don't believe that you could do to the flange. Owner also wants only four bolts but I believe that 8 bolts would be better for such large OD.





RE: Repad in the form of a pipe flange
RE: Repad in the form of a pipe flange
RE: Repad in the form of a pipe flange
If you don't need a riser pipe and it's just an overflow, you could cut the hole or slot, weld a hood over it similar to the overflow slots on petroleum tanks.
Generally, on a tank of that size, I would expect the shell to be flexible enough that you could bolt a flange to it. That flexibility might also make it hard to get a seal with a standard bolt pattern (or fewer bolts). Might take a thicker and/or softer gasket. Due to the flexibility, you'd want more bolts smaller and closer together. On this, page note the "nozzle flange" about halfway down, intended for bolting to bolted tanks: http://www.tankproducts.com/Flanges-Hatches.asp#
Note that a standard flange connection is intended to keep product inside the pipe and isn't necessarily watertight through bolt holes across the flange. I think they sell bolts with a rubber ring under the head to help with that.
RE: Repad in the form of a pipe flange
RE: Repad in the form of a pipe flange
On the other hand, if you are using an internal riser pipe whose opening is at the 24 foot mark, 5 feet above the shell opening then there is hoop stress and reinforcing may be needed which you can check with simple calculation and leaking in this bolted connection will be a concern which you will have to address.
I would be careful to make sure this overflow could pass the maximum liquid inflow rate with the available head pressure to help.
RE: Repad in the form of a pipe flange