ASME PCC-1 Tightening bolts (elongation and target bolt stress)

[FPPE]

Hi,

I need to calculate the needed elongation or torque in order to tightening N°32 3"1/4 bolts in material ASME SA 193 Gr.B16 for the flanged joint of the channel cover of an high pressure heat exchanger (channel cover thickness 291 mm and channel thickness 200 mm, diameter 1934 mm).

I was reading ASME PCC-1 par. 10.2 "Bolt Elongation (bolt stretch) determination" and I didn't understand what are the terms "Sb: Target Bolt Stress" and "Leff: effective stretching length".

From appendix H I obtained the following:

Ar=4831 mm2
Ats=4961 mm2
Leff=41.275 mm (I don't know if this is correct, I consider half of the bolt nominal diameter, 82.55 mm)

So, from the formula in par. 10.2: DELTA_L=(Sb*Leff/E_young)*(Ar/Ats), where E=200000 MPa and assuming the target bolt stress equal to 70% of yield strength (655 MPa) --> 458.5 MPa I obtained DELTA_L=0.09 mm, that sounds me a bit strange. This because I understood that is a good practice consider the targer bolt between 40% and 70% of yield.

P.S.: between cover and channel there is a sealing diaphragm gasket in ASME SB 443 UNS N06625. Here attached the flanged assembly:

Thank you for helping.

 

[SnTMan]

FPPE, think about how the bolt elongates when tightening. Surely more of the length will stretch than half the diameter. This value as referenced in PCC-1 is only the portion in the tapped hole. The other portions of the bolt need to be accounted for also.

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[FPPE]

Thank you SnTMan, so I need to consider the L_eff shown in the attached figure?

And for Target Bolt Stress did I consider in the right way?

 

[SnTMan]

FPPE, closer but not correct. Please read the definition carefully. Midpoint of tapped hole to midpoint of nut.

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[GD2]

FPPE,
Read the explanation of L_eff once again. For studded bolt you need to take it as one-half the nominal bolt diameter, which will be 82.55 mm in your case.

Bolt areas even looks wrong for the 3-1/4 in bolt.

GDD
Canada

 

[LittleInch]

FPPE,

It could be written a little bit clearer, but what it is trying to do is calculate the length of the bolt which is subject to strain.

What it says is that for a bolt or where it is studded into a piece of metal, the start point for your measurement is not the surface of the forging or the bearing surface of the nut, but actually extends 1/2 bolt diameter into the forging or the nut..

So in your case, you start with 0.5 of the bolt diameter for the studded end, add the distance between the face of the studded element and the surface of the nut, then add half the length of the nut.

In your diagram, move the left hand line to the right to a distance equal to half the bolt diameter from the surface of the block. Move the right hand line left a bit to a distance midway through the thickness of the nut.

That's Leff as far as I can tell, but I stand to be corrected.

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