Slipon Flange Welding 1

[TangoCleveland]

We are welding a 48" 150RF B16.47 slipon flange to a 3/8" wall pipe. For fitup adjustment, B31.3 gives minimum depth equal to pipe wall thickness for the internal weld. What's the maximum we can move the flange out? I found nothing in B31.3 for the maximum. ASME Sec VIII Div 1 and 2 show the maximum is pipe wall plus 1/4"; we need pipe wall plus 5/8". Our boilermakers say that their practice is to use 1/2 the thickness of the flange as a maximum (dimension "C" in B16.47).

In general, what's the maximum permissible projection of a slipon flange off the end of the pipe?

Larry

 

[TangoCleveland]

More details. Our fluid is 165 psig dry air at 100°F, piping materials are all carbon steel. Design Code is ASME B31.3.

Larry

 

[unclesyd]

Please give a little more information about your flange.
The dimensions make it fall under Sect VIII so the t + 1/4 is correct.
The half thickness is used all the time when you are not looking.

Does it have a Hub (Crane)?
What is the total thickness?
Is it a 16.47 A or B or an MSS.

 

[TangoCleveland]

The flange has a hub. Two weldneck flanges on the same spool are stamped "150/CL125", which I assume means 125 rating. Here are flange dimensions (from field measurement):
OD of flange (O): 59.25"
Thickness of flange (C): 3"
Length through Hub (Y): 4.25"
Diameter of hub (X): 52"
Hub is not tapered, so Hub Diam. Top (A) = 52"


Dimensions don't seem to match any 150 lb rating, neither B16.47 nor MSS SP44. It's pretty close to the Class 125 in my 1976 Taylor Forge catalog.

I'd guess that extending the flange past the Div 1 1/4" distance would effectively give a shorter hub, and increase stress at the back of the hub.


Larry

 

[TangoCleveland]

Small change to service conditions. Air pressure is 65 psig, not 165 psig.

Larry

 

[unclesyd]

I think you are OK as you have a hub. If you look at fig 8 for plate flange the addition of the bevel on the flange allows it to calculated as an integral or loose. It's the outside weld that is important. I have seen calculations that show the inside weld plays essentially no role in the actual strength of the slip-on flange connection. It would have to be a pretty bad outside weld to allow the inside weld to come into play either from axial or thermal stresses. I cannot see a condition where the inside weld would come into play unless you were try to lift the world.

I think you will be OK for your conditions with no problems. If there is any question you might slightly bevel the Hub for additional reinforcement.


Being an old hand you can remember when they didn't routinely weld the inside of slip-on flanges.
Our specification for stainless slip-ons flanges calls for the toe of the inside weld to be 1/2" from the flange face. This is to insure that heat input to gasket surface is minimized.

We have plenty of steam (175) lines that don't have the inside welded (1952). Probably all the plant air lines (90psig) were installed the same way.

 

[TangoCleveland]

Thanks for the quick answers! This actually is a 125 Class flange, slightly heavier than nominal specs. I used software (CodeCalc) to look at the normal hub, then shortened the hub to simulate the setback. I get a higher tangential stress at the hub when it's shorter.

Your opinions agree with mine, so we'll go with the 1" setback on the 3" thick flange.

Have a good day.

Larry

 

[bvi]

If this is B31.3 piping, the code requirements are clear. The only requirement with respect to depth of insertion is that the inside fillet be set back some amount from the flange face. That is what the two parallel lines at the end of the flange, with no dimension, indicates. This is to prevent damage to the flange face as a result of welding. This is no limit to this dimension back from the flange face, although some insertion is clearly necessary. Some insertion, say at least 1/2 inch or the thickness of the pipe, or to at least the height of the flange neck, is appropriate.