Failure of Carbon Steel Pipe 1

[pipewelder1999]

I have question about failure of welds and surrounding pipe.

If

1) a weld failed in a brittle fracture mode and
2) the piping was above the minimum design metal temp and
3) the piping was verified to meet the original mechanical specification

Would the surrounding un welded pipe many feet from the original failure, show evidence of brittle failure or would it show some deformation prior to failure?

Tanks

Gerald Austin
Iuka, Mississippi

http://www.weldinginspectionsvcs.com

 

[CoryPad]

It could be either. Why did the weld fail in a brittle manner? Perhaps the entire pipe has impurities that led to brittle failure, or perhaps the welds had segregation/residual stress/etc. that caused brittle failure. You will need more information to answer this question.

 

[pipewelder1999]

I dont know what failed first. I just thought it would be odd for piping to fail as shown in the pictures at

http://www.weldinginspectionsvcs.com/CSPipeFailurePics.htm

just because of a weld failure.

I was just wondering if piping would fracture like this just due to another failure.

Thanks for your time Gerald Austin
Iuka, Mississippi

http://www.weldinginspectionsvcs.com

 

[Carburize]

The images all appear to show brittle behaviour in both the weld area and the material away from the immediate area of the weld. Its difficult to tell from the images where the fracture initiated, frequently on brittle fracture surfaces there are chevron markings which point back to the origin, are there any such indications on your samples?
If the fracture initiated in the weld area it is entirely possible for the pipe material to show a brittle behaviour even though the original specification properties were met. If the crack initiated suddenly at the weld while the pipe was under pressure the remaining material, even though meeting specified properties and appearing to be ductile in for example a tensile test, would be subjected to a fast moving sharp crack. Under these conditions the base material could also behave in a brittle manner.
A great deal of work on this type of failure was carried-out in the 1960s and 70s by API in the USA and what was then called British Gas in the UK on gas transmission pipelines.

 

[pipewelder1999]

I saw no pieces with any chevron markings. I would imagine that those pieces had been picked up already.

I haven't seen a report on anything but you anwered my question regarding the failure.

Thanks Gerald Austin
Iuka, Mississippi

http://www.weldinginspectionsvcs.com

 

[Metalguy]

That's a lot of brittle fracture! I'd run some impact tests on the base metal and verify the temp. at the time of failure. Makes me wonder if a bomb/explosives were involved here.

 

[pipewelder1999]

Preliminary hardness tests were performed and found the hardness to be within the requirements for A-53. Impact tests have not been completed.

The operating pressure was around 200 PSI nitrogen. I'm not sure what the metal temp. was but the ambient temp was around 5 deg f. I suspect this was the cause but everyone seems to think its the welds (Which had been in service for many years).

I lean toward going below min metal temp. but I wanted some opinions based only on what I observed. Some of the welds exhibit conditions not acceptable per B31.3 and this may have been a contributing factor but I am only guessing. Gerald Austin
Iuka, Mississippi

http://www.weldinginspectionsvcs.com

 

[Metalguy]

A-53 and 5 deg?! You have an unkilled steel. I wouldn't stand around stressed A-53 when it's that cold!

 

[pipewelder1999]

I don't stand anywhere when its 5 deg !

G Austin Gerald Austin
Iuka, Mississippi

http://www.weldinginspectionsvcs.com

 

[desertfox]

Hi pipewelder1999

I am know expert in this field but looking at the pictures you have provided I would agree that this is a brittle fracture.
Further though looking at the third picture where the pipe has failed and it looks as though it has failed at an angle of roughly 45 degrees to the pipe cross section.
If this is the case then the pipe has failed along the lines
normal to the maximum tensile stress, this type of failure is common in materials that are weaker in tension than in shear and is relevant also to brittle materials, as you inform us that the pipe was possibly at 5 degrees F or lower
then the above is relevant.
A practical observation of this type of failure can be achieved by holding a piece of schoolboard chalk in both hands and twisting it till it snaps, if you do this you will observe a fracture surface like the pipe in the third picture.What is also interesting is that if the pipe failed by fatigue over a period of time it would also show a fracture surface like the above mentioned picture, because fatigue cracks can only grow under tensile stress.
In a nutshell what I am saying is that the pipe could have failed as a result of repeated torsional loads ie fatigue or as a result of say static tensile loading in which the steel was weaker in tension than shear due to possibly the extreme cold temperature it was exposed to.
Hope this helps

regards Desertfox