Question #148641

A steam boiler is to have a 300-mm-diameter hand hole placed on one end. If the maximum internal pressure is to be 1,3 MPa, how many 15-mm bolts will be required to keep the cover plate in position? The root diameter of a 15-mm bolt is 12 mm. The allowable tensile stress in the bolts is 100 MPa and the initial stress in the bolts when they are tightened is 60 MPa.

Expert's answer

Tightening stress + Additional stress on bolt = Allowable stress for bolt

60+ "\\frac{F}{Ab} = 100" ( here Ab = root area of bolt)

60 + "\\frac{F}{(\\pi)\/{4}\\times 12^2}" = 100

solving we get

F = 4523.89342 N

Now

F^{' }= P (A) [ pressure p active on area A]

F^{' }= 1.3"\\times \\frac{\\pi}{4}" "\\times 300^2"

F^{'} = 91891.58512 N

n = "\\frac{F'}{F}"

n= "\\frac{91891.58512}{4523.89342}"

n= 20.31250

so in whole number n=21 bolts are required

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