Flange Rating

[Tankman650]

I think this has been asked before because I remember the question but can't recall the answer.

For SA105, 150# flanges, ASME 16.5 shows the pressure rating decressing down to 140 psig at 600 degress F.

Using App. 2 of ASME BPV Code and Section II for material stresses at 600 F, the same flange will satify App. 2 at over 200 psig.

Does anyone know of a reason why calculations per App. 2 will not satisfy the ASME BPV code???

Anyone know why the ratings per ASME 16.5 drop for SA105 material before the allowable stresses are permited to drop in Section II.?? I assume it is due to creep of the flange material at elevated temperatures.

 

[deanc]

See ASME SecVIII Div.1 UG-11a2.

 

[Raydel]

The original ratings of B16.5 flanges were formulated back in the times of yore (buried in the mists of time). There is no relationship between ASME VIII Div1 Appendix 2 and B16.5 pressure / temperature ratings. The code states that the pressure / temperature ratings of B16.5 may be used, and that the flanges need not analysed in accordance with Appendix 2, but as soon as you contemplate a custom flange, you are in for the long haul of producing the Appendix 2 calculation.

If you absolutely desparate, and do not have access to any software, I have a spreadsheet that may help you. This spreadsheet is not for general distribution, as it was developed for a special job to produce high speed results. The spreadsheet is an Excel application written in VBA with a full windows user interface. As I said, it is only for you and not a free for all - only if you are desparated.

raydel@sbcglobal.net

 

[mgp]

You should check Annex D of ASME B16.5 for explanation.

This includes the method used to establish the B16.5 ratings and a table of ceiling values (para. D3 and table D1)

You might also want to check thread378-19042 for a spreadsheet.

regards
Mogens

 

[Jsquare]

Mogens,

I have reviewed the Annex D of ASME B16.5 for explanation, but it still does not show how the pressure rating tables were generated in terms of mathematical equations (like ASME Sec VIII flange analysis). I have somewhat of reverse problem to the Tankman.

Our project is using 2" 1500# WN FLG (SCH 160, ca=.063, Matl.=A182-F347) for design condition of 2910 psig @ 325°F which pressure wise falls below the maximum pressure shown in B16.5; however, to incorporate the external piping loads from piping flexibility calc, CAESAR II flange analysis module was used for ASME Sec VIII flange.

To my (and several other colleagues) surprise, the result from ASME Sec VIII calc shows over the allowable stress with NO external loads (pressure only). COADE representative tells me that CAESAR II strictly utilizes ASME Sec VIII Appendix 2 equations and charts to calculate the flange stresses, but we do not know how B16.5 chart came about.

Could you please enlighten us?

 

[mgp]

Jsquare

Could you tell also:

Flange facing
Gasket type and material
Bolt material
Which stress is exceeded in the flange analysis?

I can then do a check to see if I also get the flange to fail

regards
Mogens

 

[Jsquare]

Sure, NP.
Flange Face: RF
Gasket Type: 347SS B16.5 Spiral Wound
Bolt Matl: ASTM A453-660
Exceeding Stress: Radial Flange Stress=21700 psi
Allowable Stress = 20000 psi
External F/M= zero
Internal Pressure = 2910 psig

B16.5 Table shows F347 to be good up to 3020 psig @ 325°F.

Please let me know what you find out.

Thanks

 

[Scipio]

Jsquare,

Can't say what went wrong with Appendix 2, but I can tell you where the pressure rating came from in B16.5.

You've got a 1500# flange, A-182 F347 steel at 325°F. Interpolating from table 2-2.5 in B16.5 gives us a pressure/temperature limit of 3020 psig @ 325°F.

Looking into Annex D, equation(2) uses this equation to calculate the pressure limitation of at a given temperature;

P_T = P_rS₁/8750

Further, the result must be less than or equal to P_c.

In your case,

P_r = 1500 psi
P_c = 3613 psi, from Table D1

To calculate S₁ it depends on the material and pressure class. In the case of a Group #2 material rated 300# or higher, S₁ is calculated according to section D2.3, and is the lesser of;

a) 70% of SMYS at 100°F
b) 70% of yield at specified temperature
c) 125% of allowable stress at specified temperature

From ASME Section II, Part D, Table 1A Section 1, and Table Y1;

SMYS at 100°F = 30000 psi
Yield at 325°F = 25275 psi
Allowable stress at 325°F = 17350 psi

Calculating;

a) 70% of 30000 = 21000 psi
b) 70% of 21000 psi = 17692.5 psi
c) 125% of 17350 psi = 21687.5 psi

Lesser of the three is 70% of yield at temperature, solving the original equation;

P_T = 1500 * 17692.5 / 8750
P_T = 3033 psi

This value is acceptable, as it's less than the ceiling pressure P_c = 3640 psi.

The value of 3033 psi @ 325°F isn't bang on the 3020 psi interpolated from the table, but I think it's reasonably close given the number of interpolations and rounding required to get there.

 

[mgp]

JSquare

The gasket is the problem.

You should really use a ring joint gasket for this flange. This will make an acceptable joint.

If you have already ordered the flanges, it will be possible to select an alternative gasket for RF flanges which are acceptable also, e.g. flat metal.
In this case try using Ceasar to experiment with different gasket types.

regards
Mogens

 

[Jsquare]

I guess the greatest mystery of all is how B16.5 came about with the equation to set the maximum allowed pressure rating.

B16.5 doesn't even include geometry. Mathematical model shown in ASME sec. VIII (shell theory) incorporates geometry/gasket values and generated different pressure stresses for differnt sizes.

Does anyone know where B16.5 equation came about?