https://www.texasflange.com/index.php/blog/entry/s...
https://www.texasflange.com/index.php/flange-dims-...
I've mainly seen these on vessels, not sure why they'd show up on a storage tank. I would assume a standard flanged nozzle unless there was a good reason to use one of these.

It has been my experience that pad flanges are sometimes used on vertical pressure vessels. Only in two locations...

1) They are used on the bottom head of the vessel to save height on the installation (the center drain/discharge flange sets the overall height of the vessel) Mounting a pad flange and a valve on the bottom of a vessel prevents a dead zone from forming in the bottom outlet .... as can sometimes occur with a nozzle neck

2) They are used in the top center of the vessel where an agitator is mounted. Pad flanges welded directly into the top head are much stiffer than agitators mounted on a nozzle neck.

Agitators mounted on a flat bottomed storage tank have no need for a pad flange ....

Since you do not have either of these considerations, it seems to me that a pad flange is not necessary in your situation.

I am still advocating mandatory drug testing for all new clients ...

https://www.eng-tips.com/viewthread.cfm?qid=329525

MJCronin
Sr. Process Engineer

I'm assuming you mean one of these? http://beldingtank.thomasnet.com/item/fittings/pad...#

Must admit I've never seen one on a standard storage tank, but if you are really short of space between tank shell and some other solid body then I guess you would want to use them.

Basically it's just a way of reducing the distance from tank shell to flange face, but the amount you save looks pretty small to me.

There may be advantages in terms of maximum loading for weight or moment as the effective diameter of the connecting piece is much bigger than a nozzle or flange.

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