A closed-end steel cylindrical pressure vessel shown in the figure is to work under 15 bar gauge pressure. The end cover is planned to fix to the vessel with 10 bolts (8.8 Grade). The weight of the cover is 55 kg. Estimate the proper bolt size for the design. (Use design factor as 4).

Note: Ignore gasket stiffness and the force occurred due to compression of gasket.

Note 2: Assume that transverse forces on the bolts occur only due to weight of the cover.

Step 1 : Write down input parameters which are defined in sample example including material properties.

INPUT PROPERTIES SUMMARY | |||

Parameter | Value | ||

Gage pressure |
p_{g} |
15 | bar |

Vessel inner diameter |
d_{i} |
250 | mm |

Design factor |
n_{d} |
4 | |

Earth gravity | g | 9.81 |
m/s^{2} |

Number of Bolts | n | 10 | |

Mass of Cover |
m_{c} |
55 | kg |

Step 2 : We need to calculate forces experinced on a single bolt. To be able to do the calculation, bar to MPa unit conversion shall be done. Go to "Unit Converter" page to convert bar to MPa. Convert 15 bar to Mpa.

ENGINEERING UNIT CONVERTER | |||

Physical Quantity | Pressure | ||

From | To | ||

atmosphere standard [atm] | megapascal [MPa] | ||

15 | atmosphere(standard) [atm] | 1.51988 | megapascal [MPa] |

Pressure inside the vessel is 1.52 Mpa.

Step 3 : Calculate the axial and transverse force per bolt.

F_{axial} = n_{d}*p_{g}*π*d_{i}^{2 }/ (4*n) = 4*1.52*π*250^{2}/(4*10) =29830 N (Note that
this force is eccentric to bolt axis. See figure.)

F_{transverse }= n_{d}*m_{c}*g / n= 4*55*9.81/(10) =216 N

Step 4 : Calculate the required bolt size by using input parameters given in Step 1 and Step 3 .

INPUT PARAMETERS | ||

Parameter | Value | |

Axial Load [F_{A}] |
29830 | N |

Transverse Load [F_{Q}] |
216 | |

Min. friction coef. between clamped parts [μ]^{+} |
0.1 | - |

Axial load type and introduction location * | Static and eccentric | |

Tightening technique | Torque wrench | |

Bolt Strength Grade | G8.8 |

Minimum friction coefficient between clamped parts is entered 0.1 which is minimum static dry friction value between steel -steel as suggested in VDI 2230 Part-1.

Since pressure is not dynamically changing, loading is static. Axial force introduction location is eccentric to bolt axis.

Bolts are assumed to be tightened with torque wrench.

RESULTS | |||

Parameter | Value | ||

Required preload |
F_{Mmax} |
100000 | N |

Required bolt size for selected grade | M20 | --- |

According to calculation results, minimally 10 bolts of M20 with 8.8 strength grade is needed to meet design requirments. As mentioned in bolted joint calculator, this calculator is just to give an initial estimate for the bolt sizing. Further calculations are needed for detailed bolt sizing.

The problem is completely solved with calculators which are summarized as follows.

Calculator | Usage |

Rough Calculation of Metric Bolt Size | To estimate size and strength grade of the bolt according to axial and transverse load. Results depend on axial load type, load introduction location, tigtening technique and friction coeffcient. |

Unit Converter | To convert from one unit type to another one. In sample problem conversion is done from bar to MPa. |

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