When does a Piece of Pipe become a Vessel?

[byrdo]

When does a section of pipe need to be coded as a ASME Vessel? I am planning to install a “wide spot” in a line below a small tank to allow time to depressurize and refill on the run. We currently use the tank's sightglass for this, but it is not large enough for a new product I will be running. The piping is ¾” and I plan to cut it and add a section of 10” about a foot long to store ~25# of material. Does this need to be a vessel?

Thanks for any help or suggestions!

Matt

 

[TD2K]

This is always a tricky question but in this case you are fine, the volumes involved in the 10" pipe are small, way under the minimum volume in ASME 8, Div 1.

 

[unclesyd]

You didn't note the pressure but as "TD2K" states you are in the clear as to codes.
Just be careful with the 3/4" to 10" connection as you can get a pretty large stress concentration at this point.

 

[byrdo]

TD2K and Unclesyd, Thanks for the info.

Also, the system pressure ~600 PSI. I will have someone double check how we make this connection. This is not my specialty...

Regards,

 

[unclesyd]

byrdo,
The code comes into play at 1 1/2 cu ft volume and 600# psi. Your vessel is getting close to falling under the code. As it on the line your jurisdictional authority or your insurance AI should sign off on it.
This makes you connection a little more critical, so I would let some with Code experience look at the design and installation.

 

[1969grad]

The oil and gas industry quite frequently designs pig lauchers/receivers, pulsation bottles, etc. as fabricated piping assemblies per B31.8 and not the ASME BPV. Size has no restriction but you need to check the code for special provisions.

 

[unclesyd]

The difference in location determines the jurisdiction. If you are inside the battery limits of a process area/building or a chemical plant in general you usually have to play by the ASME rules.

 

[moltenmetal]

Aren't we forgetting about the 6&quot; diameter rule? Depending on jurisdiction and fluid service, they draw the line at < 6&quot; diameter AND less than 1.5 cu ft. In Canada under CSA B51, the rules for a &quot;nonlethal gas or vapour or a nonlethal liquid&quot; would put you into vessel territory.

Ultimately it matters most whether or not it looks like a vessel. Lots of 16&quot; pipe is used to connect one vessel to another and it's not designed in accordance with ASME VIII Div 1- it's designed as pipe in accordance with ASME B31.3. An expansion in a line without additional connections (vents, drains, pad ports etc.) looks like pipe, so people won't give you grief if you design it as such. Put a flanged cover or legs on it and suddenly it looks like a vessel and the inspector may treat it as such.

Agree about the stress concentration at the 3/4-10&quot; transition. Make sure it's well reinforced and you don't hang the 25# of material plus the weight of the &quot;vessel&quot; on the pipe by itself- and make sure that thermal expansion/contraction are considered if you support this &quot;vessel&quot; to the structure separately.

 

[Hookem]

ASME says if you have 6.000&quot; or higher ID, and, 15.00 psi design pressure, you must design per BPV Code. But, one way to sidestep the BPV Code is to build this item from pipe without a long seam in it. Thus, make it out of A106B Seamless Pipe, use weld cap or elliptical head closures. Several major oil/transmission companies have adopted this approach. It matters little that the item is used as a receiver/launcher, pulsation bottle, drip pot, etc.