Fatigue fracture surface or not?

[kissjxp]

Guys, please take a look at the attached photos and help me answer the following questions.

Was the fracture caused by fatigue? Is it possible that the fracture is caused by stress corrosion cracking?

Thanks a lot.

 

[kissjxp]

Little more background information.

It was from a carbon steel steam pipe. A crack was observed along a circumferential weld.

 

[metengr]

Based on just a visual and what I know of steam line damage mechanisms, you have a series of radial ridges along the mating fracture surfaces that emanate from the crack origin along the ID surface of the pipe. Again with little to go on, the failure could be from caustic stress corrosion cracking, thermal/mechanical fatigue or creep-fatigue along the weld heat affected zone of the carbon steel pipe.

You need to have more metallurgical lab analysis performed to pin-point the damage mechanism and root cause.

 

[kissjxp]

metengr,

Thanks for your comments. That means we can not reach a conclusion just based on the radial ridges, right? When I saw the radial ridges, I thought they may suggest fatigue related failure.

 

[metengr]

kissjxp;
At this point it is not conclusive unless further lab analysis is performed. Gunslinger metallurgy can get you into trouble, as you become older this will become more obvious.

 

[Molloy]

How long was it in service? is this an infant mortality or long term failure? If the former I'd think bad weld with hydrogen pickup. If it was TMF I'd expect a more flat, featureless surface with oxide consumed morphology. Obviously not HCF, lack of beach marks makes me think no to LCF too. I'd lean towards environmental and possible caustic as suggested by metengr.

Good luck