Design of steel ring flanges

[BarryEng]

Standard steel-ring flanges

Tables 5 and 6 of AWWA C207-01 for NPS 48” provide dimensions as below:

Class Bolt (number X dia) Thickness of flange

E (275psi) 44 X 1.5” 3.5”

F (300psi) 40 X 2.0” 4.5”

Although I have not made any calculations for the two cases above, on the surface, the increase in flange thickness and bolt force for the 9% increase in pressure does not appear to be based on stress limitations.

Ideally I would like a design approach to establish steel-ring and blind flange thicknesses and bolting requirements for NPS 84” with a design pressure of 305psi (2.1MPa).

Does anyone have any suggestions on this?

 

[codeeng]

You could use ASME Section VIII Div 1 App. 2.5

 

[rconner]

For perhaps reference purposes the thickness of 84" Class E ring flanges (275 psi) per AWWA C207, Steel Pipe Flanges for Waterworks Service..." is 4.75". This standard also says, "The pressure ratings for the flange should be based on the design of the maximum operating pressure plus the anticipated surge pressure. Test pressures should not exceed 125 percent of the ratings..." With regard to very large (e.g. 84") and high pressure steel blind flanges, many folks nowadays where they can be used opt instead for suitably designed hemispherical or ellisoidal heads (where there is adequate axial space etc.), as same are generally lighter and make more efficient use of steel fabrication material (if the application is for water/sewer etc. a large steel pipe vendor e.g. American SpiralWeld at

http://www.acipco.com/aswp/

can be helpful in the design and procurement of such heads).

 

[BarryEng]

"Thanks for the responses. Flange is for water service. Calculations to ASME VIII indicate a flange thickness of about 7.7" using AS36 material. This is higher than what might be extrapolated from AWWA C207. Presumably AWWA equations are somewhat different to the ASME ones."

BarryEng

 

[JStephen]

If I'm not mistaken, doesn't ASME give a design for raised-face flanges, and say you're on your own for flat-faced? And of course, the AWWA flanges are flat faced.

In the C207 standard, blind flange thickness is in a separate table- don't confuse the flange thickness with blind flange thickness.

 

[JStephen]

Perhaps the jump in thickness is more related to the size and number of bolts or flange OD than to the nominally different pressure?