Charpy impact on failed piping piece
Charpy impact on failed piping piece
(OP)
Hello Friends, We had a failure (fish mouth) in our piping (106 Gr.B) due to freezing . There are theories that it might have failed due to local overpressure because of water trapped between two ice plugs or the pipe froze 100% and burst. One of the suggestions was to do Charpy Impact on the failed piece to determine if the failure was actually due to brittle fracture.
(1)A 106 Gr.B is typically rated upto -29C. Conducting charpy on A106 Gr.B above -29C is not going to fail the material by brittle fracture though it had failed by brittle fracture during service. is this true?
(2)The brittle fracture is best assessed by fracture surface rather than Charpy impact. is this right?
(3)Is there a value in doing post charpy impact testing on a failed piece above -29C?
(4)I believe, if we know the failure mode is brittle, we can do a post testing at temperatures lower than
-29C to determine the possible ductile - brittle transition temperature for that particular heat of material. We can only estimate that at the time of failure what might have been the possible temperature.Is this right?
Thanks.
(1)A 106 Gr.B is typically rated upto -29C. Conducting charpy on A106 Gr.B above -29C is not going to fail the material by brittle fracture though it had failed by brittle fracture during service. is this true?
(2)The brittle fracture is best assessed by fracture surface rather than Charpy impact. is this right?
(3)Is there a value in doing post charpy impact testing on a failed piece above -29C?
(4)I believe, if we know the failure mode is brittle, we can do a post testing at temperatures lower than
-29C to determine the possible ductile - brittle transition temperature for that particular heat of material. We can only estimate that at the time of failure what might have been the possible temperature.Is this right?
Thanks.





RE: Charpy impact on failed piping piece
RE: Charpy impact on failed piping piece
An examination will tell you how ductile the fracture is.
I have seen pipe a lot stronger and tougher than this split by freezing water.
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P.E. Metallurgy, Plymouth Tube
RE: Charpy impact on failed piping piece
I had an experience where a hardness test indicated the strength of the pipe was outside the specification.
RE: Charpy impact on failed piping piece
RE: Charpy impact on failed piping piece
Weldstan, my initial impression with fishmouth appearance is that the failure ductile in nature. That is why i specifically mentioned in my thread.
RE: Charpy impact on failed piping piece
Granted, the conditions were "right at" the transition temperatures, but a single casting (?) properties can vary between one end and the other (cool rate, crystal structure, surface flaws, inclusions, holes, stress risers, etc) so the results of a impact test on one end might not show what failed at the other end under the higher stresses there. So, the break happened at one location at one temperature, and another part that looks identical "may not" break at exactly the same temperature. A little higher or a little lower.
And you may get a brittle failure "Start" at a flaw, then that failure reduces the area until ductile failure splits the rest of the part. Or vice versa.
How accurate do you know actual temperatures at the location of the break? They can vary also across the single piece.
If the Charpy test is done on a sample piece after the examination, remember to do the test at the lowest temperature that was possible at the day in question. Again, small temperature changes will matter there.
RE: Charpy impact on failed piping piece
At best, that would determine that it "could have been" due to brittle fracture, but you won't even get that far.
What is the minimum value for absorbed energy would mean it could have been a brittle fracture? There is no real answer, it's a waste of time and effort. Even if you had a value that was determined reasonably, you still can't quantify the force from the ice well enough to draw any conclusions.
Did the charpy suggestion come from someone who "knows just enough to be dangerous" and is probably proud to make that claim? It's not just a catch phrase, there is some truth to it.
RE: Charpy impact on failed piping piece