Using an existing Vessel!??

[11echo]

I’ve got a question about using an existing vertical vessel (36” Dia. x 10’-0” S/S) …this is a 2 phase separator that deals with oil field production. We have a project that requires this vessel; it was originally built in 07, and is presently in “surplus”. Now vessel design is not my forte, but I’ve dealt with installing them for some time, I’m a Piping Designer.
I’m looking at some pictures of this thing, and I notice what I believe are a couple of issues! This vessel has a 36” Dia. skirt, about 2’-9” tall, I do NOT see any skirt vents (normally there are 4 near the top of the skirt), also there is only one access opening in the skirt, it is 10” Dia. there is a 2”-150#RF flange for a drain connection and it has a 7” projection vertically under the vessel, so the drain piping exits through the 10” access opening.
SO …it seems to me there is not large enough maintenance access to the drain flange under the vessel. AND without any skirt vents flammable or toxic gases could collection in the skirt. I’ve voiced my concerns to the project engineer, but he’s not a “bolts & nuts” type of guy …said he’s look into it. I’d like another opinion of any vessel experts so I can either agree or prepare to argue the point.
ALSO “IF” these items are required, would there be any issue retro-fitting them to the vessel without voiding the coded stamp? …THX!

 

[europipe]

When You need skirt vents(?) you can drill them into the skirt.
For draining make a spoolpiece to outside the skirt with the drainvalve and the blockvalve there.
Only my two cents.
Greetings

 

[eyec]

you can do just about anything to the skirt without impacting the Code vessel. if the skirt is not load bearing then you can do just about anything to it without re-doing load calcs.

re-route the drain piping and cut a new access entry.

just make sure you make allowances for a containment area around the vessel for spill containment.

 

[11echo]

Access is my biggest concern! "IF" the drain flange develops a leak you’re not going to be able to do any maintenance through a 10" diameter hole! And I don't believe they'll want to lift the vessel after it's been installed to fix any problems there. SO in my mind we need an 18" diameter access opening to be able to do anything. I seem to also remember, from some place, that when you cut holes in the vessel skirt and they are half the diameter of the skirt or larger they we require a re-enforcing ring. Anybody can confirm or deny that?

 

[eyec]

is the skirt load bearing or do you have seperate structural steel supports?

that will determine if you need reinforcing ring and or new calcs

 

[11echo]

No the skirt bears all the load of the vessel. I suspect that "IF" they determine anything is needed it will go back to the original fabricator (they are local) for any mod.s needed. They'd be able to "calc" anything needed.

 

[europipe]

Why do you need access to inside the skirt?
When You cut off the lower flange of the nozzle and weld a pipe with elbow to outside the skirt the problem is solved (I think)

 

[MJCronin]

echo....

Some Questions about your vessel:

- Is this an ASME Code stamped vessel ? Do you have the U-1 data report ?

- Could the vessel be designed for a low temperature and pressure and therefore there is no need for skirt vents ? If you have the U-1 datareport (or can get it from the local fabricator) then this could be determined.

- What is the new design temperature and pressure of the intended service ?

- Would it be possible to extend the flanged drain through the skirt (with a welded elbow) and therby eliminate any reason to work within the skirt ? ( I have seen this incorporated on many skirted vessel designs)

-MJC

 

[11echo]

Vessel MWP = 574 PSI, Temp = 250 deg.s F ...and Yes this is an ASME coded vessel. New operating pressures/temp.s are approx the same.
I have not seen any U-1 data, but we are just starting with this aspect of the project (coming up with a "new" vessel).
SO IF we did cut off the bottom flange and re-weld in an elbow with a penetration through the skirt, wouldn't we have to re-code the vessel? ...I'm guessing cutting in a new access to the skirt is alot cheaper!!?
…I have to ask, what does vessel temp/press have to do with whether we need skirt vents? It's still going to be operated in an area where hydro-carbons/H2S are present? ...Just asking, I don't know. Historically, what I've seen here in this area all vert. vessels with skirts have vents and duel-access.

 

[11echo]

Oops! ...This vessel has 300# flanges on it, but the piping system that'll tie into it is only rated at 150# ...so MWP is only 265 PSI. Also the drain conn on the bottom is 300#, not 150# as I had earlier stated. Temp will be alittle less too, only to 220 deg.s F.

 

[europipe]

X-ray welds from the new spool,hydrotest and put the certificates in the vesselfile.
And why not a flanged spoolpiece?

 

[11echo]

I'm sure the other oil companies have money to burn, but they are pretty tigh around here ...the cheaper the better. SO I don't think they want to re-code the vessel. AND/IF thats the way it goes, then we'll have to used a flanged spool pc. AND to bolt it up did you want to crawl thru a 10" dia. access opening?

 

[europipe]

Can't you lay down the vessel horizontally while mounting the spoolpiece?
How would you otherwise weld a spoolpiece there?
And if you want to avoid future leaking of the flange use a weldgasket.

 

[11echo]

It is normal practice here to shut down the facility once a year to do a "turn around" ...where we clean-out, up-grade, & do general maintenance. This may require disassembly of the drain system on this vessel, and I'd guess they won't want to have to uninstall this vessel, to lay it down, and "cut off" the drain connection.