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ML00168 - Aug.2020

SCC of Austenitic SS Flange Stub End

Aspect of the stub end, that is used in combination with a lap joint flange. In this case it was prepared from a seam welded pipe, longitudinal, also with circunferential weld to the stub face (which means it was not flared). The cracking is circunferential in the non painted region, not associated to any welded area.

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Aspect of the stub end, that is in combination with a joint . In this case it was prepared from a welded , longitudinal, also with circunferential weld to the stub face (which means it was not flared). The is circunferential in the non painted region, not associated to any welded area.
M

Material

Austenitic Stainless Steel
  • AISI 304
  • UNS S30400
Ds

Description

The stub end , welded, was operating in a chemical plant, at a gas discharge line in temperatures between 50°C and 90°C, and suffered a through wall from the external side of the line, where it was exposed to an industrial atmosphere rich in HCl and Cl2 vapours, combustion gases and salt emissions. The line was externally painted several months after the installation, and the appeared in the confined region under the flange, not painted.

C

Chemistry (% in weight)

Stub end

0.045C; 0.47Si; 1.04Mn; 0.038P; 0.010S; 18.2Cr; 9.0Ni; 0.07Mo; 0.16Cu.

Associated Images
Aspect of the stub end, that is used in combination with a lap joint flange. In this case it was prepared from a seam welded pipe, longitudinal, also with circunferential weld to the stub face (which means it was not flared). The cracking is circunferential in the non painted region, not associated to any welded area.
435
VIEW
ML00168 / Aug.2020
SCC of Austenitic SS Flange Stub End
M - Austenitic Stainless SteelP - Stub EndAp - Chemical IndustryCd - Stress Corrosion
Cm - Aspect Before AnalysisDf - General View
Detail of the external side of the stub end showing that the cracking is circunferential, located in a corroded surface, that corresponds to the confined region under the flange.
85
VIEW
ML00168 / Aug.2020
SCC of Austenitic SS Flange Stub End
M - Austenitic Stainless SteelP - Stub EndAp - Chemical IndustryCd - Stress Corrosion
Cm - Aspect Before AnalysisDf - Cracking
The stub end was manufactured from a plate and the microstructure in a longitudial section shows a refined granular austenitic structure.
62
VIEW
ML00168 / Aug.2020
SCC of Austenitic SS Flange Stub End
M - Austenitic Stainless SteelP - Stub EndAp - Chemical IndustryCd - Stress Corrosion
Cm - Oxalic Acid Electrolytic EtchDf - Longitudinal Section
Micrography of a longitudinal section of the stub end showing a refined austenitic structure.
57
VIEW
ML00168 / Aug.2020
SCC of Austenitic SS Flange Stub End
M - Austenitic Stainless SteelP - Stub EndAp - Chemical IndustryCd - Stress Corrosion
Cm - Oxalic Acid Electrolytic EtchDf - Austenite
Micrographic detail of the austenitic structure. Free from grain boundaries carbide precipitation.
53
VIEW
ML00168 / Aug.2020
SCC of Austenitic SS Flange Stub End
M - Austenitic Stainless SteelP - Stub EndAp - Chemical IndustryCd - Stress Corrosion
Cm - Oxalic Acid Electrolytic EtchDf - Austenite
Macrographic detail of the longitudinal section of the stub end, showing the external side to the top and the internal side to the bottom. There are multiple cracks starting from the external side.
54
VIEW
ML00168 / Aug.2020
SCC of Austenitic SS Flange Stub End
M - Austenitic Stainless SteelP - Stub EndAp - Chemical IndustryCd - Stress Corrosion
Cm - Longitudinal Section AspectDf - Multiple cracks
Micrography of the stub end, external side to the top, presenting multiple cracks propagating throught wall.
48
VIEW
ML00168 / Aug.2020
SCC of Austenitic SS Flange Stub End
M - Austenitic Stainless SteelP - Stub EndAp - Chemical IndustryCd - Stress Corrosion
Cm - As polished micrographyDf - Close to the External Surface
Micrography of the stub end longitudinal section, presenting multiple cracks, branched.
40
VIEW
ML00168 / Aug.2020
SCC of Austenitic SS Flange Stub End
M - Austenitic Stainless SteelP - Stub EndAp - Chemical IndustryCd - Stress Corrosion
Cm - As polished micrographyDf - Multiple cracks
Aspect of the stub end. The cracking is circunferential in the middle of the non-painted region, not associated to any welded area.
36
VIEW
ML00168 / Aug.2020
SCC of Austenitic SS Flange Stub End
M - Austenitic Stainless SteelP - Stub EndAp - Chemical IndustryCd - Stress Corrosion
Cm - Aspect Before AnalysisDf - General View
Macrography of the longitudinal section of the stub end, showing the external side to the top and the internal side to the bottom. The stub end was manufactured by welding, longitudinal seam (not evidenced in this image) and circunferential weld of tube to disc (partial penetration). The cracks starts from the external side of the stub end.
31
VIEW
ML00168 / Aug.2020
SCC of Austenitic SS Flange Stub End
M - Austenitic Stainless SteelP - Stub EndAp - Chemical IndustryCd - Stress Corrosion
Cm - Macro Oxalic Acid Electrolytic EtchedDf - Longitudinal Section
Micrography of the stub end close to the external surface, outer diameter in the top of the image, presenting multiple cracks starting fro the surface and propagating into the thickness, through wall.
32
VIEW
ML00168 / Aug.2020
SCC of Austenitic SS Flange Stub End
M - Austenitic Stainless SteelP - Stub EndAp - Chemical IndustryCd - Stress Corrosion
Cm - Oxalic Acid Electrolytic EtchDf - Close to the External Surface
Micrography of the stub end in the middle of the thickness, outer diameter to the top of the image, presenting multiple branched cracks.
27
VIEW
ML00168 / Aug.2020
SCC of Austenitic SS Flange Stub End
M - Austenitic Stainless SteelP - Stub EndAp - Chemical IndustryCd - Stress Corrosion
Cm - Oxalic Acid Electrolytic EtchDf - In the Center of the Thickness
Micrography of the stub end longitudinal section, showing multiple branched transgranular cracks.
25
VIEW
ML00168 / Aug.2020
SCC of Austenitic SS Flange Stub End
M - Austenitic Stainless SteelP - Stub EndAp - Chemical IndustryCd - Stress Corrosion
Cm - Oxalic Acid Electrolytic EtchDf - Transgranular Cracking
Micrography of the stub end longitudinal section, showing multiple branched transgranular cracks, typical of a Chloride Stress Corrosion Cracking mechanism.
34
VIEW
ML00168 / Aug.2020
SCC of Austenitic SS Flange Stub End
M - Austenitic Stainless SteelP - Stub EndAp - Chemical IndustryCd - Stress Corrosion
Cm - Oxalic Acid Electrolytic EtchDf - Corrosion Cracking
Micrographic details of the Chloride Stress Corrosion Cracks, transgranular and branched.
33
VIEW
ML00168 / Aug.2020
SCC of Austenitic SS Flange Stub End
M - Austenitic Stainless SteelP - Stub EndAp - Chemical IndustryCd - Stress Corrosion
Cm - Oxalic Acid Electrolytic EtchDf - Corrosion Cracking
SCC of Austenitic SS Flange Stub End
1
VIEW
ML00168 / Aug.2020
SCC of Austenitic SS Flange Stub End
M - Austenitic Stainless SteelP - Stub EndAp - Chemical IndustryCd - Stress Corrosion
Cm - Transverse Section AspectDf - Cracks