Nozzle Connection - Section VIII, Div.1 - UW-16

[johnnymist2003]

Hi all,

I have a vertical reboiler with fixed tubesheets. The tubesheets are required to be fittied with vent and drain connections(NPS 1/2).The nozzles will be attached to the tubesheet rim,sticking out radially so that the vent and drain holes run between the bolt holes.The nozzles will be set-on, with a full penetration weld through the nozzle wall thickness [similar to Fig.UW-16.1(a)].My question is, do the nozzles need to have fillet welds of throat thickness "tc" as shown in Fig UW-16.1(a) and calculated to UW-16? If anyone knows of a Code Case / interpretation which deals with this, please advise the reference.The reason for the question is that if the fillet weld is required, then the tubesheet overall thickness needs to be increased to accomodate the vent/drain nozzle.Thanks in advance.

 

[deanc]

Don't know why you would have to make the tubesheet thicker.
See the definition of t min. Also see UG-45.

 

[johnnymist2003]

Hi deanc,

the tubesheet tickness need to be increased because of the addition of the fillet welds.
Say for NPS 1/2 300# LWN without fillet, then the rim (bolting extension) could be say 40 mm thick (38 mm OD nozzle neck).
For the same nozzle, tc = 6 mm or 0.7tmin (lesser), where tmin would be 12.7 mm, thus tc = 6 mm.
Thus the fillet weld leg size is say 8.5 mm (min).
Thus, the tubesheet rim (bolting extension) thickness would have to be 38 + 2*8.5 = 55 mm (min).
I hope this clarifies what I'm getting at.
John

 

[deanc]

Now I understand-but you must sit up late at night for this. Sounds like you may be borderline on the tubesheet thickness after you drill the drain hole. With what you have described there may not be an out. But,some ideas.
1.Thin the nozzle wall down.
2.Use a smaller drain size.
3.Thread it or thread a pup and butt weld it to the neck.
4.Clad weld or pad the area required on the tubesheet to accommodate the fillets.

 

[johnnymist2003]

Hi DeanC,

from what you say, I guess that you agree with my view that we must provide a fillet weld.I've had similar ideas to yours to solve the problem, but I can't do your proposals because :
1) Client wants a LWN (won't even accept a sockolet, etc).
2) Client has specified the drain/vent diameter.
3) Client will not accept this arrangement.
4) Tubesheet bolts onto a girth flange, so cannot fit a pad onto the thickness without providing a cut-out in the girth flange to clear the pad.This would mean increasing the girth flange thickness to accomodate the cut-out for the pad.

Anybody else out there have a view on this ?
John

 

[GenB]

Are you implying that there is no space for part of the fillet? or is the problem just not sufficient t on the tubesheet?

ER

 

[GenB]

There is not any code case for that.
If it is not problem with loadings, the AI may accept the variance with partial fillets.
The customer has to redesign the requirements, it looks to me that the designer made a mistake.
It happens all the time and some times I make money out of it and some times is the other way around, I like the first!

ER

 

[GenB]

johnnymist2003, where are you?
you may be home free... (this keyboard...),
Tc is the smaller of .25" ot of .7 tm
so the most weld you have to put is .356" or .25 x 1.41
or .25 sin 45 deg
I hope you have sufficient room for that...Regards,
ER

 

[ijzer]

You could press the LFWN a little bit flat(oval) and than you have just enough space for your fillet , which is required.

 

[unclesyd]

johnnymist2003
There is a style weldneck flange that has an extended area back from the bevel that we used to short couple with socket welds. We cut straight pipe threads on this section and then it only takes a very small seal weld to do the job. Sorry I don't have the manufacturer and figure number, will try to get. This makes up kinda short so you might want to use the second one.

We have also accomplished the same thing with a "Flanged Pipet" where we cut of the end and used straight threads and small seal weld.

Both procedures are used at 900#-1500# PSIG system at 600°F

Is you client requiring the 1/2" pipe bore for the entire length of the vent?

ijzer,
What you are suggesting is called making a "boat". We uncovered some piping onetime that actually had 1" pipe boated into 1/2" pipe. I wanted to keep a sample but was prevented by supervision.

 

[ijzer]

What I mean is make the pipe slightly flat at the weld end only. So in the circumferential tube sheet direction it is larger , but there you have enough space for the welds. In the tubesheet thickness direction it is smaller .
We do this for nozzles on a square header box of aircoolers in order to keep the depth of the box small.

 

[GenB]

I think johnny was fired, he desapear,
the soap opera was interesting!!!