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ML00167 - Aug.2020

Fatigue of a Flared Tubing Connection

Micrography of a longitudinal section of the flared tubing where the fracture occurred. The starting point of the fracture is associated to the external side of the tubing, where it was connected by a nut and there was a localized plastic deformation due to the fitting assembly.

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of a of the flared where the occurred. The starting point of the is associated to the external side of the , where it was connected by a and there was a localized due to the assembly.
M

Material

Austenitic Stainless Steel
  • AISI 316
  • UNS S31600
Ds

Description

The at the discharge line of a seal oil , cold deformed (flared at an angle of 37°) and connected using a flare slipped onto the tubing, cracked in several connections during a event at the pump suction. The surface showed striation and the failure mechanism was identified as mechanical generated in non expected stressed condition.

C

Chemistry (% in weight)

Tubing

0.048C; 0.52Si; 1.79Mn; 0.033P; 0.026S; 18.2Cr; 11.6Ni; 2.0Mo; 0.01Ti; 0.03Nb; 0.42Cu; 0.06W; 0.11V.

Associated Images
Aspect of a flared tubing, cold deformed at 37°, and the circumferential cracking.
483
VIEW
ML00167 / Aug.2020
Fatigue of a Flared Tubing Connection
M - Austenitic Stainless SteelP - TubingAp - EngineCd - Mechanical Fatigue
Cm - Aspect Before AnalysisDf - General View
Same flared tubing, with a circumferential crack, with the focus at the internal side.
65
VIEW
ML00167 / Aug.2020
Fatigue of a Flared Tubing Connection
M - Austenitic Stainless SteelP - TubingAp - EngineCd - Mechanical Fatigue
Cm - Aspect Before AnalysisDf - General View
Micrography of a longitudinal section of the tubing showing a granular structure, austenitic.
52
VIEW
ML00167 / Aug.2020
Fatigue of a Flared Tubing Connection
M - Austenitic Stainless SteelP - TubingAp - EngineCd - Mechanical Fatigue
Cm - Oxalic Acid Electrolytic EtchDf - Longitudinal Section
Micrography of a longitudinal section of the tubing, showing the austenitic structure free from strain hardening and free from grain boundary carbides.
51
VIEW
ML00167 / Aug.2020
Fatigue of a Flared Tubing Connection
M - Austenitic Stainless SteelP - TubingAp - EngineCd - Mechanical Fatigue
Cm - Oxalic Acid Electrolytic EtchDf - Austenite
Micrographic detail of the austenitic structure, free from strain hardening and free from grain boundary carbides.
54
VIEW
ML00167 / Aug.2020
Fatigue of a Flared Tubing Connection
M - Austenitic Stainless SteelP - TubingAp - EngineCd - Mechanical Fatigue
Cm - Oxalic Acid Electrolytic EtchDf - Austenite
Low magnification fractography by scanning electron microscopy, after a complete opening of the crack. At this magnification no micromechanism is evident.
51
VIEW
ML00167 / Aug.2020
Fatigue of a Flared Tubing Connection
M - Austenitic Stainless SteelP - TubingAp - EngineCd - Mechanical Fatigue
Cm - Fractography by SEMDf - Fracture
Fracture surface of the tubing, close to the outer diameter.
47
VIEW
ML00167 / Aug.2020
Fatigue of a Flared Tubing Connection
M - Austenitic Stainless SteelP - TubingAp - EngineCd - Mechanical Fatigue
Cm - Fractography by SEMDf - Close to the External Surface
Flat aspect of the fracture. The striation micromechanism is revealed.
50
VIEW
ML00167 / Aug.2020
Fatigue of a Flared Tubing Connection
M - Austenitic Stainless SteelP - TubingAp - EngineCd - Mechanical Fatigue
Cm - Fractography by SEMDf - Fatigue Fracture
The thin striation is evident in the fracture surface, suggesting a high cycle fatigue, typically identified in vibration conditions.
45
VIEW
ML00167 / Aug.2020
Fatigue of a Flared Tubing Connection
M - Austenitic Stainless SteelP - TubingAp - EngineCd - Mechanical Fatigue
Cm - Fractography by SEMDf - Fatigue Striation
Detail of the striation micromechanism.
48
VIEW
ML00167 / Aug.2020
Fatigue of a Flared Tubing Connection
M - Austenitic Stainless SteelP - TubingAp - EngineCd - Mechanical Fatigue
Cm - Fractography by SEMDf - Fatigue Striation
When the fracture propagates, the striation becomes wider and with transgranular irregular steps.
47
VIEW
ML00167 / Aug.2020
Fatigue of a Flared Tubing Connection
M - Austenitic Stainless SteelP - TubingAp - EngineCd - Mechanical Fatigue
Cm - Fractography by SEMDf - Fatigue Fracture
Micrography of a longitudinal section of the tubing where the fracture occurred. the left side is the outer diameter and the right side is the inner diameter.
37
VIEW
ML00167 / Aug.2020
Fatigue of a Flared Tubing Connection
M - Austenitic Stainless SteelP - TubingAp - EngineCd - Mechanical Fatigue
Cm - Oxalic Acid Electrolytic EtchDf - At the Surface
Micrography of a longitudinal section of the flared tubing where the fracture occurred. The starting point of the fracture is associated to the external side of the tubing, where it was connected by a nut and there was a localized plastic deformation due to the fitting assembly.
33
VIEW
ML00167 / Aug.2020
Fatigue of a Flared Tubing Connection
M - Austenitic Stainless SteelP - TubingAp - EngineCd - Mechanical Fatigue
Cm - Oxalic Acid Electrolytic EtchDf - Transgranular Fracture
Micrographic detail of the localized plastic deformation due to the fitting assembly, in the region where the fatigue has started.
30
VIEW
ML00167 / Aug.2020
Fatigue of a Flared Tubing Connection
M - Austenitic Stainless SteelP - TubingAp - EngineCd - Mechanical Fatigue
Cm - Oxalic Acid Electrolytic EtchDf - Plastic Deformation