Fabricated Tee Design

[pingmi]

Hello,

We need to review designs of fabricated Equal Tees (Sizes- 52" NB Tee & 36" NB Tee) as per ASME B31.3 for low pressure applications. As far as I know, ASME B31.3 won't allow welded branch where branch & run pipe sizes are same. Hence it would be safer approach to analyze these branch connections as per ASME Sec VIII Div II at design & hydro test conditions and verify the pipe thickness.

Is this a correct approach?

Kindly advise.

Thanks in advance.

 

[C2it]

Equal size welded branch connections are allowed by B31.3 but there are limits imposed regarding Dh / Th > 100 (para 304.2.1) and where pipe is cold expanded (para 304.3.5).

 

[pingmi]

Thanks C2it for your reply.
Actually the pipe will be made out of plates by forming and welding the longitudinal joint. I suppose this will need considerations as per para 304.3.5.
Kindly comment.

 

[C2it]

Pipe is commonly rolled from plate then formed into a tee. You need to check the requirements of all the relevant para's in B31.3.

 

[11echo]

You're are actually going to take flat steel plate and roll it to form a tee!?? ...Not construct a fabricated tee out of pipe?

 

[pingmi]

11echo,

The pipes would be made out of plates by rolling and welding a longitudinal joint. These pipes would be further used to fabricate Tee by welding.
Hope this clarifies the manufacturing process.

 

[11echo]

pingmi ...That sounds ALOT more expensive then fabricating your tees from pipe! I've been in this business alot of years and I've seen a fair amount of fabricated fittings, but never have I seen them fabricated from rolled plate! Now I'm not saying they don't have that capablity, and "if" you need something from a "special steel" then your locked in, but "IF" you can find some normal pipe steels that can accomplish the job I'd suggest going that way ....just for the cost savings! ...My $0.02!!!

 

[saplanti]

11echo,

1. Are you using the same wall thickness what the run pipe has to fabricate the tee?

2. If your answer is "Yes", do the users know what they are buying?

3. If your answer is "No" and you use thicker pipe, how do you match the internal diameters? And do the user know they are buying a tee with a reduced internal diameter?

4. Do you use a reinforcement at the branch connections? Or does the branch directly welded onto the run pipe as it is?

5. Does anyone check the stress intensification factors on the tees that you have been manufacturing?

I guess these questions will create some questions on your mind, and you may be asking more question to clearify.

Kind regards,

Ibrahim Demir

 

[pingmi]

saplanti,

Just to clarify further, branch pipe diameter is same as that of run pipe. Hence branch reinforcement is not possible. Also the ratio of branch to run pipe size exceeds limit mentioned in ASME Section VIII Div I.

That is the reason why I would like to take a safer approach to analyze these branch connections as per ASME Sec VIII Div II at design & hydro test conditions and verify the pipe thickness.

Please comment.

 

[stanier]

Branch reinforcement is possible if designing per AWWA M11. The reinforcement is not by use of a pad but by external wings. I have seen this in refineries & chemical plants so expect that the code does allow such designs.

"Sharing knowledge is the way to immortality"
His Holiness the Dalai Lama.

http://waterhammer.hopout.com.au/

 

[davefitz]

Similar large dia tees and wyes are fabricated for hydropower penstocks- search google for latestest designs Also unusual reinforcement designs now rationalized based on ubiquitous finite element models. However those reinforcement plates can only be used for modertate temperature applications ( near room temperature +- 50F)to aovid thermnal stress issues.

 

[waterpipe]

Just to clarify further, branch pipe diameter is same as that of run pipe. Hence branch reinforcement is not possible.

As stanier mentioned, branch reinforcement is possible. It is called crotch-plate or wye-branch and AWWA M11 (for water work) allows the design of the same diameter branches (there's a photo of a three-way, same diameter, 90 degrees wye with two crotch plates and one back plate in M11.

please note that AWWA has treated this type of branch different than the "normal" branch connection explained under ASME B31.3 para 304.3. So your concern is valid.