Fastener Strength given Pressure 1

[modo78]

Hello. I am trying to calculate the stress on a given thread within a pressure assembly. The knowns are the thread size and material, the working pressure, and the number of threads currently engaged. Can anyone help...I'm rusty on the calculations.

 

[Metalguy]

If your application is similar to a blind flange on a pipe, the added stress from pressure with be very small. The vast majority of the tensile stress in a fastener had better be from the preload.

"You see, wire telegraph is like a very long cat. You pull his tail in New York and his head is meowing in Los Angeles. Do you understand this? Radio operates the same way: You send signals here, they receive them there. The only difference is there is no cat." A. Einstein

 

[Tmoose]

And, the clamping force from all the bolts' preload needs to be greater than the force trying to hoist the cover off the flange, or there will oil all over the place.

 

[boo1]

Controlling the load (fastener torque) is essential to ensuring the gasketed joint will seal properly. Several codes cover gasketed joint elements: ASME Boiler and Pressure Vessel Code, ASME B31.3, Process Piping Code, ASME B16.5, Bolted Flange Connections (BFC) EN 1591-1 and ENV 1591-2 and API 6A flange are a few. ASME PCC-1, Guidelines for Pressure Boundary Bolted Flange Joint Assembly Torque calculations are based on the simplified formula.

T= (k?f?d)/12 (U.S. Customary Units)

The fastener load has to compress the gasket so it conforms to the flange surfaces, and to "seat" the gasket into the flange. The combined force needs to:

1. Overcome the hydrostatic forces generated by the internal fluid pressure trying to push the flanges apart
2. Compress the gasket enough to hold it in place when the internal pressure is trying to penetrate through the gasket and/or gasket/flange sealing surfaces
3. Maintain some residual load on the gasket after the hydrostatic load has unloaded the gasket, which involves the gasket factor m.

The hydrostatic end load on the flanged joint and a residual gasket load:
Wm1 = ((?•G2 • P)/4) + (2 •b•? •G • m • P)

Minimum seating load on the gasket:
Wm2 = (?•b•G)y

The greater of the two values-Wm1 or Wm2-will is the minimum required design bolt load. Minimum required fastener load divided by the number of fasteners in the joint will determine the minimum force.

or try:

http://engineersedge.com/general_engineering/gasket_cover_compression.htm

http://www.engineersedge.com/calculators/machine-design/bolt-preload/bolt-preload-calculation.htm