stress in pipe 2

[suren12564]

what is the difference between axial stress and longitudinal stress in a pipe under internal pressure? i am always having little confuse between these two....eloborate explanation is appreciable

 

[DSB123]

No difference. The Axial direction and the longitudinal direction for a pipe are the same.

 

[suren12564]

i want to differentiate it with respect to magnitude not w.r.t direction?

 

[davefitz]

axial stress has its vector parallel to the pipe length and is imposed on circumferential butt welds. A simplified free body diagram shows that the forces are P*Pi*d^2/2 = Pi*(d+D)/2*(D-d)/2*s, where s= axial stress, P= fluid pressure, d= inside dia, D= outside dia.

circumferential stress acts on the longitudinal weld seam , and has twice the stress value of the above defined axial stress, therefore the longitudinal weld governs the life of the fabricated pipe when fluid pressure is the governing load.

"In this bright future, you can't forget your past..." Bob Marley

 

[JohnGP]

I'm with DSB123.

 

[DSB123]

davefitz,
You are not really answering his question. There is no difference between axial stress and longitudinal stress for a pipe - end of story.

 

[BigInch]

Axial stress is due to an axial load applied to the pipe and is equal to S = p/A. p is load and A is the cross-sectional area of the pipe wall. It will be either tension, or compression, corresponding to the direction of the applied load.

Stress in the Axial Direction can also be caused by internal pressure and is nominally equal to the circumferencial stress, S = P*D/2/t, * Poisson_Ratio. P = pressure, D = diameter, t = wall thickness. Poisson_Ratio for steel pipe is usually taken as 0.3
If the pipe is unrestrained, the pipe will shorten without generating stress. If the pipe is held rigidly fixed at both ends, S will result as an axial tension stress.

If the pipe has closed ends, another axial stress can be generated from internal pressure, as the pressure will act on each closed end surface to generate an end force F = pi*D^2/4 * P
If the pipe is not axially restrained, the pipe will elongate with the resulting axial stresss = F/A in tension. If the pipe is held rigidly fixed at both ends by an anchor, or is well embedded in soil, the anchor or soil will take that load and an opposite compressive axial stress, F/A, will be introduced into the pipe.

If there are changes in temperature, thermal axial stress can be generated. If the temperature is increased, a compressive axial stress can be introduced into the pipe, or if temperature is decreased, a tension stress can be introduced. Thermal stresses are only generated if the pipe is held fixed at both ends, otherwise the pipe will expand or contract, respectively, without generating any additional stress.

Bending can introduce another axial stress Sb = M * c/I , tension on one side and compression on the other. M is bending moment, c is the pipe radius, I is the moment of intertia.

Total Axial stresses is the algebraic summation of all of the above.

 

[desertfox]

hi suren12564

The post given by DSB123 is correct there is no difference between axial and longitudinal stress its the same stress just a different name.
Do you mean what the difference between axial stress and hoop stress?

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[desertfox]

read this link where it defines longitudinal stress in a thin wall pipe, it states that axial and longitudinal stress are the same.

http://www.engineersedge.com/material_science/hoop-stress.htm

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[suren12564]

thank u so much guys for clarifying my confusion

 

[saplanti]

There is a slight difference in the terminology. Axial stress effects the entire cross section, longitudinal (individual bending or resultant) stress may be variable in the cross section.

 

[saplanti]

I should improve my sentence as ; There is a slight difference in the terminology. Axial stress effects the entire cross section uniformly, longitudinal (individual bending, secondary bending or resultant) stress may be variable in the cross section.