Flange joint - mixed type of flanges

[mech8790]

Hello!

I am wondering if this is OK to mix up in a flange joint a slip on flange with welding neck flange in accordance with B16.5 and B31.3? The joint is made between pressure vessel's nozzle end (slip on) and manifold end (welding neck). The pressure rating, material, bolting, gasket etc all the same.

Also, replacing a slip on flange with a welding neck flange or a piece of pipe with an elbow in a nozzle configuration do any changes to the overall design of the nozzle? Again, all materials are the same, pipe schedule etc.

Thanks!

 

[Dhurjati Sen]

This slip on flange would be a part of the pressure vessel, so you need to adhere to ASME Sec VIII.

Possibly its ok although never seen a slip on flange on a pressure vessel.

Replacing a slip on flange with a weld neck one makes the joint stronger (fillet vs butt).


DHURJATI SEN
Kolkata, India

 

[LittleInch]

First part - Yes, the joint is the same regardless of how the flange is connected to the pipe, providing of course they are the same size, type (RF) and class rating.

Replacing a SO flange for a WN flange - no problem. It's a better connection but see below.

Piece of pipe with an elbow for a nozzle? don't fully understand - add a drawing /sketch.

All depends on where the limits of the Pressure vessel are. If PV side of the weld, can't see an issue, but if it's part of the PV design then you need to pass it through the PV design.

So long as they are listed components to B 16.9 there shouldn't be an issue, but not if the vessel has been tested and included this component.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[mech8790]

Hi guys!

Thank you for your quick messages. I have got an approved PV design with a straight pipe coming out from the shell with slip on flange at the end. The only thing I want to do is replace this pipe and slip on flange with a long radius elbow and a welding flange at the end. All design boundaries are remaining the same. The elbow wall thickness same SCH as per pipe that is being replaced so nozzle minimum wall thickness calculations should be still valid for the elbow. The way how the elbow is attached to the shell same as per pipe scenario. Size of the elbow and the pipe same same. This is an alternation to the existing approved PV design and nothing has been tested yet. I think a joint made of slip on flange and a welding neck flange is quite odd and the welding neck flanges are much better for high pressure units and spiral wound gaskets.

I use elbows that comply with ASME B16.9.

 

[LittleInch]

Well we're so busy commuting these days.....

The only Issue I see is possible stress issues with a 90 degree elbow vs a straight pipe, but should be within the PV design.

While the surface area of the raised portion of a SO flange is slightly smaller than a WN flange, it's clearly OK as far as B 16.5 is concerned as there are no de-rating issues noted.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[XL83NL]

Possibly its ok although never seen a slip on flange on a pressure vessel.

Ive seen dozens of SORF's on various vessels, and under the right circumstances, they're a good, cost effective solution. Not sure why they couldnt be ..

Huub

 

[r6155]

SO and WN flange both have the same strong, as you can see in ASME B16.5 for pressure-temperature rating and class.
Another thing is the type of welding (fillet or butt weld) which depends of service conditions
When Radiographic test is required use welding neck.
For low temperature use welding neck
For general service use slip-on
Slip-on is widely used.
Many specifications require WN for process nozzles and SO for manway

Regards