Carbon steel rupture without deformation

[barqueiroenmarte]

Dear all.

I am a piping engineer (so no very involved in material engineering) and I am facing a problem with the rupture of a 12" carbon steel pipe which was buried, managing gas at ambient temperature.

My question regards to the way that the pipe has broken which is strange to me: without any elongation or ductile characteristics. It seems as if somebody would have cut the pipe in two parts with scissors!!. Some of my workmates has told me that if there has been a very concentrated impact force on the pipe the rupture shape is so, that is, very similar to a brittle ruture. Is it right? A sudden and large impact shear force can make the steel pipe break into two parts without any deformation or elongation?

Best regards

 

[metengr]

It is difficult to give you a specific answer because there are many factors associated with failure of metals. In general, freeze and thaw cycles or improper backfill of a buried pipe can produce large forces that can result in similar fracture behavior (no elongation or obvious ductility). If you need to obtain an answer as to what caused the failure, you need to have it analyzed by a metallurgical laboratory.

 

[bob330]

Another strong possiblity when you see pretty highly ductile materials (like low/mild carbon steels or austentitic SS) fail in a very brittle manner without deformation is stress corrosion cracking. Cabon steel pipes have failed by SCC in bicarbonates, nitrates, ammonia, etc. This is a real possibility. Underground pipes are usually/generally:
a) warm which makes brittle failure less likekly
b) not subjected to shock or impact loading unless there is an earthquake or something.

bob