ASME B16.47 Large Diameter Flange - Hub Thickness Vs Rating 1

[perruolo]

As per ASME B16.47, the Bore or internal diameter of WNRF flange must be specified by the purchaser.

in our case, we requested three different Hub thickness of 56" WNRF A105 Class 600 to match our pipeline wall thickness (1.012", 0.81" and 0.562")

is it right to assume that all these flanges will have a working pressure of 102.1 bar despite their thickness? (Group 1.1 - Temp -29 to 38 C)


thanks in advance for your feedback

 

[LittleInch]

No.

First off what design code?

I did a quick calc for A105 and for 102 bar you need 30mm and thats to a pipeline code.

The flange pressure is limited by the attached pipe design pressure using A105 or similar.

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[perruolo]

Littleinch Tanks for your reply

Yes. you are right. WP of the system will be limited by the lowest pressure between connected pipe and flange rating as below calculated
Hoop Stress = 2*t*S/D

Pipe Thickness---------Pipeline Calculated Hoop Stress ----------Flange Rating------------WP Limited By
1.012"............. P=2*1.012*70000/56 = 2560 psig...... .........1480 psig............... Flange rating
0.81"............... P=2*0.81*70000/56 = 2025 psig............... 1480 psig................. Flange rating
0.562"............. p=2*0.562*70000/56 = 1405 psig...... .........1480 psig............... Pipeline wall Thickness
.
My question is limited only to the flange itself. ASME B16.47 Table 3 Group 1.1 Pressure-Temperature Rating stablish a WP for a 600 Class equal to 102.1 bar (1480 psig) in the temperature range of -29 to 38 C despite any change in the Flange Hub Thickness. This table does not make any reference to flange Hub Thickness. So, I can assume that a WNRF 56" 600 class with hub thickness 1.012" will have same WP that a WNRF 56" 600 Class with hub thickness 0.562"

 

[LittleInch]

perruolo,

OK, your equation for S is the maximum allowable stress, not material SMYS, hence you forgot to apply any safety factor - typically 0.72 maximum for a pipeline.

Second, you seem to be using X70 pipe (70,000 psi). A105 SMYS is 36,000.

Now flange codes limit themselves to talking about the rating of the flanged joint itself. As there are many materials it can be made from and many design codes use them, it doesn't go into a whole set of tables about the max WP of the connection point of the flange due to a thinner hub.

For a design you have to look at the weakest part. In this case it appears to be the connection point of flange to pipe.
So for your thinnest pipe I calculate the max DP is 520 psi, much less than your flange rating.

There are two ways normally to resolve this

Either make the flange from something a lot stronger ( typically A694 F70) or make the flange a lot thicker and use a transition piece between flange and pipe made of X70 with one end your pie wall thickness and one end your much thicker flanged hub.

So, I can assume that a WNRF 56" 600 class with hub thickness 1.012" will have same WP that a WNRF 56" 600 Class with hub thickness 0.562"

NO - you can't. See also section 2.7 of ASME B 16.47 which states that pressure ratings are based on pipes of 40,000 psi. Also maximum bore sizes are listed for different classes not withstanding that whic in your case limmts it to 0.78" wt regardless of material strength

"Ratings for welding neck
flanges covered by this Standard are based upon their
hubs at the welding end having a thickness at least
equal to that calculated for pipe having a 276 MPa
(40,000 psi) specified minimum yield strength"


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