Bolt Lengths 1

[DGrayPPD]

Good morning all,

Do bolt lengths change for flat faced flanges? Or do they stay the same length as raised face flanges per ASME 16.5?

 

[XL83NL]

Hypothetically, not a real world issue ... worst case, you have a 7 mm raised face (one for each flange), and a compressed gasket thickness of 3-4 mm (kammprofile). Keeping everything the same and changing to flat face, and assuming 1.5-2 mm (compressed) gasket thickness, you 'lose' some 15 mm.

The B16.5 bolt length is, for most cases, a bit too short if you need 2 - 3 threads after the nut. Nevertheless, I believe the length meets Code requirements for most, if not all, cases. So changing from a facing with metallic gasket to flat face will not impact Code requirement. If you, on the other hand, still have sufficient threads after the nut, is a different matter, although it's less important for flat face gaskets I presume, due to their low gasket seating stresses and therefore, bolt stresses.

 

[Krausen]

It is good to have a few threads visible on each end of the stud after final torquing. To achieve this, one must often add 1/4" or 1/2" to the stud bolt lengths calculated under B16.5.

Tolerance is the virtue of the man without convictions -GK Chesterton

 

[curtis2004]

CPPD,

As XL83NL mentioned, this isn't real world issue. Although in FF flange you loose 1/16"-1/8" thickness. However, your FF cast iron flange a bit thicker (1/16"-1/8") than RF cast steel one. So it will even out in the end.

Regards,
Curtis

 

[pennpiper]

Remember Stud Bolts are cheaper if you stick to the "Standard Lengths" that are available off the shelf. Go here to see the standard Chart for "Bolt and Stud Dimensions" - ASME B16.5 Flanges:

http://www.texasflange.com/index.php/flange-dims-weights/flange-bolting-chart

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The wise thing to do is not try to customize the bolt length for each and ever Flange joint. To do that would create a nightmare in; ordering, marking for point of use, replacing damaged Studs and warehousing spare parts.

Sometimes its possible to do all the right things and still get bad results

 

[XL83NL]

@ pennpiper; I dont (fully) agree. We have calculated bolt lengths for all B16.5 (and EN 1092-1) studs. We use these lengths for all our (piping) projects, and buy studs at our 'own' lengths. Sometimes they match the B16.5 length, sometimes they dont. We dont have (had) issues with ordering, marking, pricing, etc.
The lengths we demand do not challenge our suppliers with added cost or increased delivery time. Not sure how that would hold for a large industrial plant, as the sizes of our jobs are reasonably small compared to industrial plants (a large job for us would require about 8000 bolts).

 

[dhanasekaranrenga]

Dear Friends
I am using the attached table for stud bolt length. Hope it will be helpful for someone who is in need of it.

http://files.engineering.com/getfil...1d942586&file=stud_bolt_length_for_upload.pdf