Change of API flange to ANSI on a tank on explosive atmosphere
Change of API flange to ANSI on a tank on explosive atmosphere
(OP)
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) 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.
Thnak you very much.
Best regards. Juan





RE: Change of API flange to ANSI on a tank on explosive atmosphere
Why are you changing the manway flange..???
I have never heard of problems with an API flange in this service ?
-MJC
RE: Change of API flange to ANSI on a tank on explosive atmosphere
We want to change it because we want to install a new crude (entry) line in the tank. So we want to use this manhole as nozzle for the line, but the valve (ANSI, directly connected to the tank) can not go on an API flange. So the idea was to cut it from the nozzle, then to weld a new one (ANSI) ready to be connected to the line.
Another problem is that the thickness of the API flange is valid (according to API 650) for a manhole (nothing connected to it), but not for a nozzle (with piping outside).
One way to avoid welding on this "limited" space by installing a mechanical seal (not valid, because the seal is with rubber, teflon 110ºC, and the weld temp of the HAZ is higher, so the seal for explosive atmosphere is insecure), is to connect an API flange then a piece of pipe and then an ANSI flange, till the tank planning allows to empty (and inert the tank), further in time.
Thanks for your help.
Regards.Juan
RE: Change of API flange to ANSI on a tank on explosive atmosphere
However I don't know if you can hot tap 24".
Cutting the APi and installing ANSI on the same nozzle neck seems very hard (not to say impossible) without emptying, venting and cleaning the tank.
Are you sure it is worth taking the risk?
RE: Change of API flange to ANSI on a tank on explosive atmosphere
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.
RE: Change of API flange to ANSI on a tank on explosive atmosphere
It is not possible a hot tap, it is not common in this plant, and very extrange for 24", and it has been already rejected (for security reasons). A new nozzle on the tank with a hot tap it is not possible either, because it requires PWHT (API 650, due to the thickness of the wall), so it is not possible without emptying the tank.
And it is worthwile, to empty the tank is very expensive, (not only emptying it, we also have to treat the sludge, to inspect the tank, and the time) and it affects to the normal working order of the plant. We have to wait at least 2 or 3 years to empty the tank and inert it according to the planning.
This problem is related to many tanks, so more money. We do not know if there is any way to isolate this manhole from inside (like an umbrella??) avoiding the explosive atmosphere and being enough far from the welding zone.
Thanks again for your interest.
Best regards.
RE: Change of API flange to ANSI on a tank on explosive atmosphere
http://www.hottap.com/index.html
Here is the Dylan Valve that you might be able to use. As you stated you have numerous tanks with the same problem I don't see any problem with getting two different flange faces on this valve or in fact any valve. If you could use this valve future isolation of the tank may not be a problem.
http://www.occlude.com/dylanOverview.html
RE: Change of API flange to ANSI on a tank on explosive atmosphere
RE: Change of API flange to ANSI on a tank on explosive atmosphere
But we still have to change the flange in two tanks. The solutions that you suggested might be valid for our problem in most of the cases. But in two tanks the thickness of the flange is not enough to conect piping to it.
They were, initially, designed as manways, now as we change their use we also have to change the flange, because even being API their thickness is less than the minimum fixed by API 650 for nozzle necks.
So we still have to cut them and weld new ones, with the previous problems of shortage of space and explosive atmosphere.
Thanks again. Rgds
RE: Change of API flange to ANSI on a tank on explosive atmosphere
If you were to consider an flex-line between the existing MH and the new line, the piping forces would be limited. In such cases you will find that the existing MH may be adequate. The MH neck thickness is not the issue.
Joe Tank
RE: Change of API flange to ANSI on a tank on explosive atmosphere
It would take a little calculating, but could you use a backup split flange with the existing MH flange.
RE: Change of API flange to ANSI on a tank on explosive atmosphere
The cheapest and safe way is to hire an experienced hot tap team, with their tools and equipment. They have the internal inflatable to isolate the manway from the internal atmosphere, once you lowered the level below the manway and then vent it to outside after removing the cover, no fumes or explosion. But let them do it, avoid costly mistakes. They can weld in the new 24" nozzle, safely, test and inspect as per code, the whole lot. Why risk it, reinvent the wheel?
cheers,
gr2vessels
RE: Change of API flange to ANSI on a tank on explosive atmosphere
We do not intend to do this procedure by ourselves, we are estimating its costs and then we would like to hire a team to do the proper job.
Thanks. BEST REGARDS. Juan
RE: Change of API flange to ANSI on a tank on explosive atmosphere
http://www.plidco.com/public/products/flange.php
Here is a commercial 2 piece back-up flange product.
http://www.marzolf.com/
You can make your own by using the appropriate code calculations. In my old Section VIII it is in UA-53, spit ring flange.
RE: Change of API flange to ANSI on a tank on explosive atmosphere
http://www.plidco.com/public/products/flange.php
Here is a commercial 2 piece back-up flange
product.
http://www.marzolf.com/
You can make your own by using the appropriate code calculations. In my old Section VIII it is in UA-53, spit ring flange.
RE: Change of API flange to ANSI on a tank on explosive atmosphere
gr2vessels
RE: Change of API flange to ANSI on a tank on explosive atmosphere
But the project is in Spain, so we are looking for "economic" suppliers in this area or Europe.
Nevertheless any internet information could be very useful.
I will tell you how we are going to do this process.
Thanks. Regards.
Juan