08tramp,

Appendix S is a discussion on preloading flange bolting after the flange has been designed. The allowable stress for bolts to be used in the design of Appendix 2 flanges is as defined in Appendix 2; the appropriate maximum allowable stress from Section II, Part D, Table 3. In addition to Appendix S, I recommend you review PCC-1, "Guidelines for Pressure Boundary Bolted Flange Joint Assembly". PCC-1 is available from ASME Order Department.

Don Kurle PE
Codeware Technical Support

I have looked into COMPANION GUIDE TO ASME CODE, an interpretation of various changes or inclusions brought about in the code, and have seen nothing but recommendation or apprehension that actual bolt stress may exceed allowable. Thus bolt stress be taken as much as 45000/d. According to my understanding this bolt stress shall be employed while calculating Wm1 and Wm2 which shall yield the required bolt area etc. From there onward once the worked out stress, per Appendix S recommendation, will be used in verifying Crushing width of Gasket, secondly it will be employed in calculating Mg moment. This moment will be used in calculating various kinds of stresses, like Sh, St etc. and then they will be compared with 0.9 times of yield of the Flange Material because the said appendix suggests that fears leakage are high during hydrostatic testing of the flange.

I would like to welcome your opinion.

regards,

Muhammad Imran Mirza

Bolt stresses are not used in the calculaton of Wm1 and Wm2.  Bolt allowable stress is used in the calculation of W for gasket seating.  If you use the higher stresses you are suggesting, then the required bolt area, Am, will be incorrect and smaller than if calculated using the allowable from Sec II, Part D, Table 3.  Depending on the value you use for Sa in the calculation of W, you could have a design that would not be adequate for the design condition.  

Don Kurle PE
Codeware Technical Support

Yes you are right. I must have approached it wrongly because Am is, actually, the larger of Wm1/Sb or Wm2/Sa; of course it would suggested that required bolt area will be smaller than that what have been in case of Sa-Sb's values taken from II Part D. However if W, if worked out employing Sa value as taught by Appendix S recommended formula, will be greater than that, determined by using usual code value. The greater value of W will later on result in higher SH or ST stresses.

Or we can only comply Appendix S thereby using Sa value, determined as 45000/d, the Gasket Crushout width; you see, it will be increased if Sa is increased and resultantly it will influence other Flange Loads as well.

You referred to the formula in Appendix S, S = 45,000 / sqrt(d), as indicating the allowable stress in the bolt.

But the Appendix describes the formula as "The probable bolt stress developed manually, when using standard wrenches". So they are describing the probable actual stress resulting in a bolt that is manually tightened; there is no mention that this is the allowable stress.

The next paragraph states "it can be seen that smaller bolts will have excessive stress unless judgment is exercised..." Thus the point made is that smaller bolts may easily be overstressed by tightening without special procedures, whereas larger bolts may be insufficiently tightened.



   "Although this forum is monitored by Codeware it is not intended as a venue for technical support and should not be used as the primary means of technical support."

  Tom Barsh
  Codeware Technical Support
  www.codeware.com
   

Mr. Tom if you look into "COMANION GUIDE TO THE ASME BOILER AND PRESSURE VESSEL CODE" it will be otherwise and wouldnt be true as you have interpreted.

S=45000/d
S= Nominal bolt stress, psi
d=the nominal bolt diameter.

I would like you to read it as well and I hope your opinion will be different.

Regards,

Mirza

We will have to agree to disagree on this matter.


 

   "Although this forum is monitored by Codeware it is not intended as a venue for technical support and should not be used as the primary means of technical support."

  Tom Barsh
  Codeware Technical Support
  www.codeware.com
   

As the luck would have it.