Thread engagement length and number of bolts of an o-ring joint
Thread engagement length and number of bolts of an o-ring joint
(OP)
want to check my calcs for thread engagment and number of bolts need for 240 bar test of pump casing
Bolt M16 A4-80 55mm long no shank
UTS = 800Mpa (not sure of)
UYS = 600Mpa (not sure of)
Shear ratio is 0.75 (not sure if it should be 0.7)
UTSh * 0.75 = 600Mpa
Stress Area of bolt = 156.67mm calculated
Tapped hole CF8M cast 30mm
UTS = 485MPa (known data)
UYS = 205MPa (known data)
Shear ratio =0 .75 (not sure about ratio)
UTS * 0.75
UTSh = 363.75Mpa
Minimum Length Of engagement = UTSh of bolt *0.8* Normal diameterof bolt/UTsh of tapped hole
= 600*0.8*16/363.75 = 21.2mm
Nasa Pull out load of thread
Pullout load = pi()*Min Minor diameter of thread *UTShtapped hole* Length of engagement/3
Min Minor diamet of thread = 13.872mm
= pi()*13.872*363.75* 21.2mm/3
Pullout load =112.03kN @ 21.2mm of thread in CF8m
Ultimate tensile load of bolt = UTS * At
800 * 156.67mm = 125Kn
Max tensile load of bolt = UYS * At
600*156.67 = 94Kn
Pressure is 240 bar= 24Mpa
Pcd Of bolts = 170 mm
diameter of hole in bolted flange = 80 mm
Therefore
Area of pressure = (Pi (Pcd+bolt diamter/2)^2 - Pi(80/2)^2)
Area of pressure = 22145mm
Force = Area of pressure x Pressure
= 22145mm * 24 Mpa
Force on flange = 531.5Kn
Min number of bolts = Force on flange / Max tensile load of bolt
= 531.5Kn/ 94Kn =5.6 bolts
Bolts with a Safety factor of 2 = Force on flange / (Max tensile load of bolt/2)
= 531.5Kn/ (94Kn/2) =11.3 bolts
Therefore I would need 12 bolts
Is the Flange is CF8m and 25mm long and the bolt is 55mm long and it an groove o-ring joint? what the stiffness factor of the joint?
My calcs say C is 0.9 but i think that is off by a large margin!!
Does any one have an worked example to calculate C for a tapped and flange or a studded assembly.
Bolt M16 A4-80 55mm long no shank
UTS = 800Mpa (not sure of)
UYS = 600Mpa (not sure of)
Shear ratio is 0.75 (not sure if it should be 0.7)
UTSh * 0.75 = 600Mpa
Stress Area of bolt = 156.67mm calculated
Tapped hole CF8M cast 30mm
UTS = 485MPa (known data)
UYS = 205MPa (known data)
Shear ratio =0 .75 (not sure about ratio)
UTS * 0.75
UTSh = 363.75Mpa
Minimum Length Of engagement = UTSh of bolt *0.8* Normal diameterof bolt/UTsh of tapped hole
= 600*0.8*16/363.75 = 21.2mm
Nasa Pull out load of thread
Pullout load = pi()*Min Minor diameter of thread *UTShtapped hole* Length of engagement/3
Min Minor diamet of thread = 13.872mm
= pi()*13.872*363.75* 21.2mm/3
Pullout load =112.03kN @ 21.2mm of thread in CF8m
Ultimate tensile load of bolt = UTS * At
800 * 156.67mm = 125Kn
Max tensile load of bolt = UYS * At
600*156.67 = 94Kn
Pressure is 240 bar= 24Mpa
Pcd Of bolts = 170 mm
diameter of hole in bolted flange = 80 mm
Therefore
Area of pressure = (Pi (Pcd+bolt diamter/2)^2 - Pi(80/2)^2)
Area of pressure = 22145mm
Force = Area of pressure x Pressure
= 22145mm * 24 Mpa
Force on flange = 531.5Kn
Min number of bolts = Force on flange / Max tensile load of bolt
= 531.5Kn/ 94Kn =5.6 bolts
Bolts with a Safety factor of 2 = Force on flange / (Max tensile load of bolt/2)
= 531.5Kn/ (94Kn/2) =11.3 bolts
Therefore I would need 12 bolts
Is the Flange is CF8m and 25mm long and the bolt is 55mm long and it an groove o-ring joint? what the stiffness factor of the joint?
My calcs say C is 0.9 but i think that is off by a large margin!!
Does any one have an worked example to calculate C for a tapped and flange or a studded assembly.





RE: Thread engagement length and number of bolts of an o-ring joint
Mike Halloran
Pembroke Pines, FL, USA
RE: Thread engagement length and number of bolts of an o-ring joint
RE: Thread engagement length and number of bolts of an o-ring joint
Mike Halloran
Pembroke Pines, FL, USA
RE: Thread engagement length and number of bolts of an o-ring joint
Trying to figure the right rule to use machinist handbook says one thing internet says another, I guess i am going to have to pony up for a standard....
RE: Thread engagement length and number of bolts of an o-ring joint
diameter of hole in bolted flange = 80 mm
Therefore
Area of pressure = (Pi (Pcd+bolt diamter/2)^2 - Pi(80/2)^2)
Why are you subtracting the central area of the flange?
RE: Thread engagement length and number of bolts of an o-ring joint
Are the bolts in the pressurized area?
(I'm guessing the pump shaft rotating centerline is below the picture somewhere)
Is there room to remove the bolts, and allow tightening them?
If the pressure will force the o-ring into a large chamfer back-up rings are required.
What style of washers are under the bolt heads?
RE: Thread engagement length and number of bolts of an o-ring joint
You're bolt material stress values appear to be correct in accordance with this site:-
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However I would have taken the shear stress ratio between 0.5 and 0.6 of the material yield stress again in accordance with:-
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and in view of no other information for both the bolt and cast material.
You're method of calculation appears to be ok assuming that the thrust due to pressure is correct and of course up to this point the you're assuming that the joint flanges are rigid, whereas in practice there not, so I think buying the correct code or standard for your area is the right decision because it will take the elasticity of the joint into account.
Regards
desertfox
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