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ML00094 - Sep.2017

MIC of a Subsea Hydraulic Line

Aspect of the fitting welded to a tubing, ND 5/8" in a hydraulic line. The through wall cracking is longitudinal in the fitting side.

1

1031
Aspect of the welded to a , 5/8" in a hydraulic line. The is longitudinal in the side.
M

Material

Super Duplex Stainless Steel
  • ALLOY 2507
  • UNS S32750
Ds

Description

The through wall longitudinal of this in a hydraulic line was detected after 6 years in operation. The cracks started from the internal side of the line, far from the , in a region where the surface was and presenting high roughness due to machining effects. The cracking morphology suggests a stress mechanism, probably related to , since the hydraulic fluid could be stagnated in the fitting.

C

Chemistry (% in weight)

Fitting Analysis

0.04C; 0.46Si; 0.86Mn; 0.035P; 0.015S; 25.48Cr; 7Ni; 3.79Mo; 1.00Cu.

Associated Images
Aspect of the fitting welded to a tubing, ND 5/8" in a hydraulic line. The through wall cracking is longitudinal in the fitting side.
1031
VIEW
ML00094 / Sep.2017
MIC of a Subsea Hydraulic Line
M - Super Duplex Stainless SteelP - Fabrication WeldAp - SubseaCd - Brittle Behavior
Cm - Aspect Before AnalysisDf - General View
Detail of the longitudinal through wall cracking in the fitting welded to a tubing, ND 5/8" in a hydraulic line.
87
VIEW
ML00094 / Sep.2017
MIC of a Subsea Hydraulic Line
M - Super Duplex Stainless SteelP - Fabrication WeldAp - SubseaCd - Brittle Behavior
Cm - Aspect Before AnalysisDf - External Surface
Macrography of a longitudinal section of the fitting to tubing weld, with the longitudinal cracking at the tubular fitting position.
69
VIEW
ML00094 / Sep.2017
MIC of a Subsea Hydraulic Line
M - Super Duplex Stainless SteelP - Fabrication WeldAp - SubseaCd - Brittle Behavior
Cm - Kalling Etched MacroDf - Longitudinal Section
Aspect of the internal side of the fitting to tubing welded joint, after longitudinal cut. It is possible to see that the cracking (still filled with corrosion products) is located in the fitting side (left side) far from the welded joint to the tubing (right side).
58
VIEW
ML00094 / Sep.2017
MIC of a Subsea Hydraulic Line
M - Super Duplex Stainless SteelP - Fabrication WeldAp - SubseaCd - Brittle Behavior
Cm - Aspect Before AnalysisDf - Internal Surface
Aspect of the internal side of the fitting, at the cracked position with corrosion products and several surface microcracks adjacent to the main crack.
52
VIEW
ML00094 / Sep.2017
MIC of a Subsea Hydraulic Line
M - Super Duplex Stainless SteelP - Fabrication WeldAp - SubseaCd - Brittle Behavior
Cm - Surface AspectDf - Internal Surface
Aspect by scanning electron microscopy of the cracking at the external surface of the fitting.
47
VIEW
ML00094 / Sep.2017
MIC of a Subsea Hydraulic Line
M - Super Duplex Stainless SteelP - Fabrication WeldAp - SubseaCd - Brittle Behavior
Cm - Surface Aspect by SEMDf - External Surface
Aspect by scanning electron microscopy of the cracking at the external surface of the fitting. Interesting to observe that the cracks are deformed.
39
VIEW
ML00094 / Sep.2017
MIC of a Subsea Hydraulic Line
M - Super Duplex Stainless SteelP - Fabrication WeldAp - SubseaCd - Brittle Behavior
Cm - Surface Aspect by SEMDf - External Surface
Aspect by scanning electron microscopy of the cracking at the internal surface of the fitting.
36
VIEW
ML00094 / Sep.2017
MIC of a Subsea Hydraulic Line
M - Super Duplex Stainless SteelP - Fabrication WeldAp - SubseaCd - Brittle Behavior
Cm - Surface Aspect by SEMDf - Internal Surface
Aspect by scanning electron microscopy of the cracking at the internal surface of the fitting. Interesting to observe multiple cracks with brittle characteristic.
39
VIEW
ML00094 / Sep.2017
MIC of a Subsea Hydraulic Line
M - Super Duplex Stainless SteelP - Fabrication WeldAp - SubseaCd - Brittle Behavior
Cm - Surface Aspect by SEMDf - Internal Surface
Macrography of the fitting to tubing welded joint. The internal surface of the fitting (left side) is rough compared to the internal surface of the tubing (right side). The cracking is located only in the fitting and presented no association with the welded joint.
40
VIEW
ML00094 / Sep.2017
MIC of a Subsea Hydraulic Line
M - Super Duplex Stainless SteelP - Fabrication WeldAp - SubseaCd - Brittle Behavior
Cm - Kalling Etched MacroDf - Longitudinal Section
Micrography of the fitting longitudinal section, showing a coarse austenitic ferritic structure.
39
VIEW
ML00094 / Sep.2017
MIC of a Subsea Hydraulic Line
M - Super Duplex Stainless SteelP - Fabrication WeldAp - SubseaCd - Brittle Behavior
Cm - NaOH Electrolytic Etched MicroDf - Duplex structure
Micrographic detail of the fitting longitudinal section showing a coarse austenitic ferritic structure.
37
VIEW
ML00094 / Sep.2017
MIC of a Subsea Hydraulic Line
M - Super Duplex Stainless SteelP - Fabrication WeldAp - SubseaCd - Brittle Behavior
Cm - NaOH Electrolytic Etched MicroDf - Coarse Structure
Micrography of the tubing longitudinal section, showing a refined austenitic ferritic structure.
36
VIEW
ML00094 / Sep.2017
MIC of a Subsea Hydraulic Line
M - Super Duplex Stainless SteelP - Fabrication WeldAp - SubseaCd - Brittle Behavior
Cm - NaOH Electrolytic Etched MicroDf - Duplex structure
Micrographic detail of the tubing longitudinal section showing a refined austenitic ferritic structure.
43
VIEW
ML00094 / Sep.2017
MIC of a Subsea Hydraulic Line
M - Super Duplex Stainless SteelP - Fabrication WeldAp - SubseaCd - Brittle Behavior
Cm - NaOH Electrolytic Etched MicroDf - Grain refined structure
Micrography of a transverse section of the fitting, at the cracking position. Note the through wall cracking at the coarse austenitic ferritic structure.
43
VIEW
ML00094 / Sep.2017
MIC of a Subsea Hydraulic Line
M - Super Duplex Stainless SteelP - Fabrication WeldAp - SubseaCd - Brittle Behavior
Cm - NaOH Electrolytic Etched MicroDf - Transverse Section
Micrographic detail of the region where the cracking was initiated at the internal side of the fitting.
41
VIEW
ML00094 / Sep.2017
MIC of a Subsea Hydraulic Line
M - Super Duplex Stainless SteelP - Fabrication WeldAp - SubseaCd - Brittle Behavior
Cm - NaOH Electrolytic Etched MicroDf - Through Wall Cracking
Micrographic detail of the region where the cracking was initiated at the internal side of the fitting. There are evidences of strain hadening efects, probably due to internal machining of the fitting, and surface microcracks.
41
VIEW
ML00094 / Sep.2017
MIC of a Subsea Hydraulic Line
M - Super Duplex Stainless SteelP - Fabrication WeldAp - SubseaCd - Brittle Behavior
Cm - NaOH Electrolytic Etched MicroDf - Strain Hardened
The internal surface of the fitting presents multiple cracks not associated to pitting.
38
VIEW
ML00094 / Sep.2017
MIC of a Subsea Hydraulic Line
M - Super Duplex Stainless SteelP - Fabrication WeldAp - SubseaCd - Brittle Behavior
Cm - Surface Aspect by SEMDf - Internal Surface
The through wall cracking was opened by citting the two sides and the aspect was characterized by SEM. Although there was a film at the fracture surface, probably because the fitting was removed from service some time after it was leaking, the fracture micromechanism is by quasecleavage, typical of a stress corrosion cracking.
56
VIEW
ML00094 / Sep.2017
MIC of a Subsea Hydraulic Line
M - Super Duplex Stainless SteelP - Fabrication WeldAp - SubseaCd - Brittle Behavior
Cm - Fractography by SEMDf - Transgranular Fracture