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ML00075 - Jun.2018

Hydrogen Cracking of IN 718 Subsea Fasteners

Macroscopic aspect of the stud that broke transverse to the axis, at the bottom of the thread fillet, presenting a brittle aspect.

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Macroscopic aspect of the stud that broke transverse to the axis, at the bottom of the thread fillet, presenting a brittle aspect.
M

Material

NiCrFe Alloy
  • UNS N07718
  • ALLOY 718
Ds

Description

that were in service in using two presented a transverse to the axis and longitudinal internal . The high strength alloy presenting failed by intergranular/, assisted by the generated in . It is recommended to follow subsea specifications when a high strength bolting material will be adopted in submarine environment due to its susceptibility for .

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Chemistry (% in weight)

Product Analysis

52.9Ni; 18.5Cr; 0.07Cu; 18.7Fe; 0.21Co; 3.06Mo; 4.95Nb; 0.90Ti; 0.45Al; 0.027C; 0.1Mn; 0.002S; 0.006P.

Associated Images
Transgranular brittle aspect of the stud fracture surface. Evidences of hydrogen embrittlement.
965
VIEW
ML00075 / Jun.2018
Hydrogen Cracking of IN 718 Subsea Fasteners
M - NiCrFe AlloyP - StudAp - SubseaCd - Hydrogen Embrittlement
Cm - Fractography by SEMDf - Secondary Cracks
Macroscopic aspect of the stud that broke transverse to the axis, at the bottom of the thread fillet, presenting a brittle aspect.
64
VIEW
ML00075 / Jun.2018
Hydrogen Cracking of IN 718 Subsea Fasteners
M - NiCrFe AlloyP - StudAp - SubseaCd - Hydrogen Embrittlement
Cm - Aspect Before AnalysisDf - General View
The stud presents an austenitic structure, with primary and secondary precipitates of a size that is visible in low magnification microscopy.
55
VIEW
ML00075 / Jun.2018
Hydrogen Cracking of IN 718 Subsea Fasteners
M - NiCrFe AlloyP - StudAp - SubseaCd - Hydrogen Embrittlement
Cm - Kalling Etched Micrography by OMDf - Austenite
The stud structure evidences grain boundaries precipitation of probably delta phase (an overaging of the hardening precipitate).
49
VIEW
ML00075 / Jun.2018
Hydrogen Cracking of IN 718 Subsea Fasteners
M - NiCrFe AlloyP - StudAp - SubseaCd - Hydrogen Embrittlement
Cm - Kalling Etched Micrography by OMDf - Austenite
Micrography of a longitudinal section of the stud, at the fracture surface, in the thread.
44
VIEW
ML00075 / Jun.2018
Hydrogen Cracking of IN 718 Subsea Fasteners
M - NiCrFe AlloyP - StudAp - SubseaCd - Hydrogen Embrittlement
Cm - Kalling Etched Micrography by OMDf - Fracture
Micrographic detail of a longitudinal section of the stud, at the fracture surface, in the thread. It is possible to see primary precipitates (yellow) already cracked and intergranular propagation.
37
VIEW
ML00075 / Jun.2018
Hydrogen Cracking of IN 718 Subsea Fasteners
M - NiCrFe AlloyP - StudAp - SubseaCd - Hydrogen Embrittlement
Cm - Kalling Etched Micrography by OMDf - Intergranular Cracking
Micrography of a longitudinal section of the stud, at the fracture surface in the center of the thickness, showing a long secondary cracking (vertical in the left).
35
VIEW
ML00075 / Jun.2018
Hydrogen Cracking of IN 718 Subsea Fasteners
M - NiCrFe AlloyP - StudAp - SubseaCd - Hydrogen Embrittlement
Cm - Kalling Etched Micrography by OMDf - Secondary Cracks
Micrographic detail of the longitudinal section of the stud, at the secondary cracking.
27
VIEW
ML00075 / Jun.2018
Hydrogen Cracking of IN 718 Subsea Fasteners
M - NiCrFe AlloyP - StudAp - SubseaCd - Hydrogen Embrittlement
Cm - Kalling Etched Micrography by OMDf - Brittle Cracks
The secondary cracks are easily observed in the fracture surface, longitudinal to the axis of the stud.
26
VIEW
ML00075 / Jun.2018
Hydrogen Cracking of IN 718 Subsea Fasteners
M - NiCrFe AlloyP - StudAp - SubseaCd - Hydrogen Embrittlement
Cm - Fractography by SEMDf - Brittle Fracture
The fracture of the stud presented both intergranular and transgranular aspects.
26
VIEW
ML00075 / Jun.2018
Hydrogen Cracking of IN 718 Subsea Fasteners
M - NiCrFe AlloyP - StudAp - SubseaCd - Hydrogen Embrittlement
Cm - Fractography by SEMDf - Brittle Fracture
The fracture of the stud presented transgranular aspects and secondary cracks that appear to be related to small broken particles.
32
VIEW
ML00075 / Jun.2018
Hydrogen Cracking of IN 718 Subsea Fasteners
M - NiCrFe AlloyP - StudAp - SubseaCd - Hydrogen Embrittlement
Cm - Fractography by SEMDf - Secondary Cracks