Internal threads - Required wall thickness
Internal threads - Required wall thickness
(OP)
Question:
What required wall thickness is necessary to develop the full strength of internal threads for a given length?
Example: a cylinder with 3.75- 10 UNS-2B has a major dia of 3.75; now if the cylinder had an OD of 3.80 it would raise some questions as to how strong the connection would be. So what should the required wall thickness be for a given thread diameter to develop the full strength of the thread?
Is there a standard, a specification, a rule of thumb, or even a thought -
jackboot
What required wall thickness is necessary to develop the full strength of internal threads for a given length?
Example: a cylinder with 3.75- 10 UNS-2B has a major dia of 3.75; now if the cylinder had an OD of 3.80 it would raise some questions as to how strong the connection would be. So what should the required wall thickness be for a given thread diameter to develop the full strength of the thread?
Is there a standard, a specification, a rule of thumb, or even a thought -
jackboot





RE: Internal threads - Required wall thickness
C1 = [-(s/D)2 + 3.8 · (s/D) - 2.61]
for 1.4 ≤ (s/D) < 1.9
where
s = nut outer diameter
D = nut nominal diameter
The C1 factor is used to modify the nut stripping load Fstrip,nut according to:
Fstrip,nut = σn · Ashear,nut · C1 · C3 · 0.6
where
σn is the nut material ultimate tensile strength
Ashear,nut is the nut shear area
C3 is the nut thread bending factor
To insure that screw threads fracture or strip before nut threads strip, set C3 = 0.897
RE: Internal threads - Required wall thickness
RE: Internal threads - Required wall thickness
Looking the Machinist Handbook - the 1.5D rule is the standard.
jackboot
RE: Internal threads - Required wall thickness
Noting the internal minor, pitch and major diameters as 3.642/3.663, 3.685/3.697 and 3.750/3.755 inches, a mild steel tube (43 ksi yield) would only withstand around 11480 lbf loading. Depending on your seal diameter, say 3.328 inches, the wall would not take an ANSI Class 600 application and bearly an ANSI Class 300.
You need to worry about crack initiation at the root of the thread as a probably mode of failure. Depending on the design around the box threads, you have a good case for pipe swaging here.
Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada
RE: Internal threads - Required wall thickness
please could you tell me where you found that formula.
RE: Internal threads - Required wall thickness