Threaded End Plug Calculation Request

[JuryRigger]

Mr. Bob,
If you might be so kind (not too much to ask) as to run these numbers through your threaded plug spreadsheet for me-it would be greatly appreciated 

Plug 12L14 cold-drawn
Tensile Strength, Ultimate    540 MPa   78300 psi   
Tensile Strength, Yield    415 MPa   60200 psi   
(Matweb)

Threaded 5/8-18 UNF, 11 threads fully engaged, O-ring inboard to pressure (IE threads not pressurized)...

Tube 1020 DOM normalized, .75" OD-

Tensile Strength, Ultimate    440 MPa   63800 psi   
Tensile Strength, Yield    345 MPa   50000 psi   

IF I've got my little knowledge on the subject applied correctly-the tube should fail loooonngg before the threads do....
Thanks in advance,
Jesse

[JPSAXNC]

For maximum hold, the length of the thread is typically equal to the diameter.

[JuryRigger]

For maximum hold, the length of the thread is typically equal to the diameter.

Yup, that's the rule of thumb I've always heard-and why it's sitting at 11 threads (.61" engagement) now...
If I did my math right, and the formula I found is correct-the threads should have a maximum strength that was almost silly for the load-can't recall the exact figure ATM but it was several tons-and the thrust load under the maximum intended pressure is only a little over 400 pounds...

Lots of warm fuzzy feeling being designed in on this LOL... 
Jesse

[rsterne]

I didn't see a design pressure or wall thickness on the tube, but it has to be thick enough to thread, so at least 0.110" wall.... I get about 3.5:1 safety margin on the tube at 5,000 psi, and about 25:1 for the threads on the plug at the same pressure.... At 0.40" thread engagement, it is still over 10:1, so IMO you have nothing to worry about....

Bob

[JuryRigger]

I didn't see a design pressure or wall thickness on the tube, but it has to be thick enough to thread, so at least 0.110" wall.... I get about 3.5:1 safety margin on the tube at 5,000 psi, and about 25:1 for the threads on the plug at the same pressure.... At 0.40" thread engagement, it is still over 10:1, so IMO you have nothing to worry about....

Bob

Thanks Bob, the tube was/is .12" wall-that confirms my calculations/literature that I found/was going off of... Max. target working pressure is 2 KSI, but can/will nudge that up a bit to achieve the target goal if need be...

Much appreciated! 
Jesse