How to Determine Fracture Propogation in Pipe? 2

[SuperG]

Does anyone know the method of determining the fracture propogation of pipe?

I am trying to determine the resistance to fracture propogation for various grades of pipe. For example, if a pipe fractures under high pressure, what is the propensity for the fracture to continue to adjacent pipes?

Thanks for any help!

 

[Biggadike]

There is a value which should be supplied by pressure pipe manufacturers which indicates whether a pipe will fail catastrophically or by a hole which doesn't propogate.
I haven't got the data with me but it's something like the K value. Any self respecting pressure pipe supplier should be able to give you the failure mode.

That aside, you can use the Lamé equations to calculate the hoop and radial stresses in pressure pipes and determine the safety margin you are working with.

Pressure pipes are vulnerable at their joins but should suffer no shear stresses.

 

[MJCronin]

I disagree,

Piping, under high pressure loading does not "fracture" or fail in a brittle mode. Failure of the pipe looks like a "fish mouth" with the long axis of the "fish mouth" along the pipe axis.

When ASME/ASTM piping materials are purchased, they must meet minimum ductility requirements. See the ASTM A53 carbon steel piping specification, for example,for details.

I have been designing and analyzing piping systems for nearly thirty years and have never heard of this mysterious "k" factor....... where did you get it?

Can you refer me to a code, standard or website with more information ?

Concrete references not speculation and vague memories, please.......

MJC

 

[SuperG]

I have seen these "fish mouths" before. So in these cases, why did the fracture stop? I am sure it includes variables such as escape velocity (maybe), internal pressure before the burst, pipe thickness, and pipe material...but how do they combine in a way to predict whether a fracture will propogate?

 

[engrdon]

Your first stop is to a bookstore or library to find a good text on fracture mechanics. I have found "Fracture Mechanics: Fundamentals and Applications" by T.L Anderson to be quite helpful.It also has a number of good examples.


The K factor is a stress intensity factor associated with the different modes of loading that can be applied to a crack. There are two main approaches to fracture mechanics one is linear elastic fracture mechanics (LEFM). Another is elastic plastic fracture mechanics (EPFM).

I hope this helps a bit.

engrdon