We want to change the flange of a manhole on several crude tanks, from API to ANSI (24", 150#). And we want to do it without emptying the thank, that is, we are going to lower the crude level below the manhole, then to cut the API and to weld the ANSI flange. So it is not a hot-tap, the inner side of the tank is not on pressure.

So we have the big problem to avoid the explosive atmosphere. The neck of the manhole is around 170-270 mm, so very short to install a globe. And we have the problem of the temperature or the weld, that we can not avoid as it affects the quality of the weld. We were thinking of a double tapper insulated with cold welding or gypsum, with an intermediate ciruclation of N2. Or to install a transition of API to ANSI (and then the valve-ball valve) further the limits of the tank to avoid the weld until the tank is empty.

Could anybody suggest us any procedure, or supplier to solve this proble, please?. We have already contected expansionseal to get a mechanical seal, but the problem was the temperature, as the seal done by rubber can not stand the temp of the HAZ.

Why are you changing the manway flange..???

I have never heard of problems with an API flange in this service ?

Do you need a 24" line for the crude?

If you can get by with a small line for the process you might be able to calculate the 24" as is and using a blind flange with as small a nozzle as you can get by with. If you have enough nozzle on the tank you might get by with this approach. 

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