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Bolt Elongation Formula and Calculator per. ASME PCC-1

Pressure Vessel Design Formula and Calculators Resources
Fastener and Screw / Bolt Design, Formula & Calculations

Bolt Elongation Formula and Calculator per. ASME PCC-1

When bolt elongation (bolt stretch) measurement is selected as the load-control technique to be used, the required bolt elongation is computed according to the following equation (assumes the bolt is threaded full length):

Equation 1
ΔL = [ ( Sb · Leff ) / E ] · ( Ar / Ats )

Equation 2 (Metric Threads)
Ats = ( π / 4 ) ( D - 1.3 · P ) / 2

Equation 3 (ANSI Inch Threads)
Ats = ( π / 4 ) ( D - 1.3 / n ) / 2


Ar = root area (minor diameter), mm2 (in.2)
Ats = tensile stress area, mm2 (in.2).
n = threads per inch
P = thread pitch
E = modulus of elasticity, MPa (ksi)
Leff = effective stretching length, mm (in.). The conventional assumption is that the effective stretching length in a through-bolted joint system is the distance between mid-thickness of the nuts, where the nominal thickness of a heavy hex series nut is one nominal bolt diameter. By the same standard, the effective length of the portion of a bolt that is studded into a tapped hole is one-half of a nominal bolt diameter.
Sb = Target Bolt Stress (root area), MPa (ksi). It is noted that bolt stresses computed in accordance with Mandatory Appendix 2 of Section VIII, Division 1 of the ASME Boiler and Pressure Vessel Code are based on root area. If Target Bolt Stress (tensile stress area) is used, drop the Ar / Ats term from the ΔL computation.
ΔL = bolt elongation (bolt stretch), mm (in.). Select a tolerance on this computed value and include it in the joint assembly procedure.



Guidelines for Pressure Boundary Bolted Flange Joint Assembly
ASME PCC-1-2010