Back to Austenitic Stainless Steel
ML00122 - Feb.2018

Crevice Corrosion in a Subsea System

Aspect of a crevice corrosion of the flange, under the bolt head, showing evidences that the cathodic protection system was not connected to the stainless steel instrument.

1

1434
Aspect of a of the , under the head, showing evidences that the system was not connected to the instrument.
M

Material

Austenitic Stainless Steel
  • UNS S31600
Ds

Description

The instrumentation system was connected to a equipment and, after 6 months in service, it failed because seawater entered in the module and destroyed the electronic device. The metallurgical analysis showed mechanism, through wall, in the main module (a case pressurized from the external sea environment). This occurred because the module did not present its own (CP) system and its connection to the CP system of the equipment was not effective.

C

Chemistry (% in weight)

Case

0.040C; 0.33Si; 1.76Mn; 0.033P; 0.019S; 16.6Cr; 10.5Ni; 2.0Mo.

Weld Metal

0.052C; 0.92Si; 1.21Mn; 0.046P; 0.015S; 19.0Cr; 11.1Ni; 2.3Mo.

Associated Images
Aspect of a crevice corrosion of the flange, under the bolt head, showing evidences that the cathodic protection system was not connected to the stainless steel instrument.
1434
VIEW
ML00122 / Feb.2018
Crevice Corrosion in a Subsea System
M - Austenitic Stainless SteelP - CaseAp - Oil and GasCd - Crevice
Cm - Aspect Before AnalysisDf - Localized Corrosion
Flanged case, 640mm long. The photo presents a general view of the instrumentation system, destroyed after only 6 months in subsea service. The system was manufactured using only 316 stainless steel and the case was 20 mm thick.
335
VIEW
ML00122 / Feb.2018
Crevice Corrosion in a Subsea System
M - Austenitic Stainless SteelP - CaseAp - Oil and GasCd - Crevice
Cm - Aspect Before AnalysisDf - General View
Aspect of the instrument system after disassembling. The internal part of the case, where the electronic device was operating, was wet by seawater and failed to send signals to the surface.
258
VIEW
ML00122 / Feb.2018
Crevice Corrosion in a Subsea System
M - Austenitic Stainless SteelP - CaseAp - Oil and GasCd - Crevice
Cm - Aspect Before AnalysisDf - General View
Detail of the electronic device after removing the external case. It is corroded because seawater entered in the equipment that was pressurized from the external sea environment.
228
VIEW
ML00122 / Feb.2018
Crevice Corrosion in a Subsea System
M - Austenitic Stainless SteelP - CaseAp - Oil and GasCd - Crevice
Cm - Aspect Before AnalysisDf - Corrosion
After a longitudinal cut of the case it was possible to see that a localized corrosion has occurred associated to the regions where there were sealed holes, plugged, in a crevice condition, not related to any welded position.
193
VIEW
ML00122 / Feb.2018
Crevice Corrosion in a Subsea System
M - Austenitic Stainless SteelP - CaseAp - Oil and GasCd - Crevice
Cm - Transverse Section AspectDf - Corrosion
Micrography of the case, observed in the center of the thickness, showing an equiaxial granular austenitic microstructure, free from carbides. The structure is typical of a 316 SS, in a solution annealed condition.
176
VIEW
ML00122 / Feb.2018
Crevice Corrosion in a Subsea System
M - Austenitic Stainless SteelP - CaseAp - Oil and GasCd - Crevice
Cm - Micrography by OM using A262 Method ADf - Austenite
Micrographic detail of the fully austenitic granular structure of the case, in the center of the thickness.
158
VIEW
ML00122 / Feb.2018
Crevice Corrosion in a Subsea System
M - Austenitic Stainless SteelP - CaseAp - Oil and GasCd - Crevice
Cm - Micrography by OM using A262 Method ADf - Austenite
Macrography of the longitudinal section of the case, that was welded to padeyes. The corrosion occurred in a region where there were no microstructural changes, only the hole that was sealed with a plug and suffered a crevice corrosion mechanism.
145
VIEW
ML00122 / Feb.2018
Crevice Corrosion in a Subsea System
M - Austenitic Stainless SteelP - CaseAp - Oil and GasCd - Crevice
Cm - Macro Oxalic Acid Electrolytic EtchedDf - Corrosion
The macrography of a longitudinal section of the case shows one region where a through wall localized corrosion has occurred (in the left side of the image) and regions where the case was welded to a padeye, without any corrosion damage.
141
VIEW
ML00122 / Feb.2018
Crevice Corrosion in a Subsea System
M - Austenitic Stainless SteelP - CaseAp - Oil and GasCd - Crevice
Cm - Macro Oxalic Acid Electrolytic EtchedDf - Corrosion
Microstructure of the welded region of the padeye, at the fusion line. The weld metal is dendritic, austeno ferritic, in the left side of the figure. The heat affected zone is in the center of the figure and shows no changes in relation to the base metal. The padeye base metal is to the right side of the figure.
120
VIEW
ML00122 / Feb.2018
Crevice Corrosion in a Subsea System
M - Austenitic Stainless SteelP - CaseAp - Oil and GasCd - Crevice
Cm - Micrography by OM using A262 Method ADf - Welded Joint
Micrographic detail of the fusion line of the welded joint of the padeye. The connector where the padeye was installed was welded to the case, but presented no evidences of corrosion.
110
VIEW
ML00122 / Feb.2018
Crevice Corrosion in a Subsea System
M - Austenitic Stainless SteelP - CaseAp - Oil and GasCd - Crevice
Cm - Micrography by OM using A262 Method ADf - Welded Joint
The case where the electronic device was installed suffered a localized corrosion that allowed the seawater to wet the internal side, destroying it. The position where the leakage occurred originally presented a hole that was sealed with a plug and the corrosion occurred in a crevice condition.
166
VIEW
ML00122 / Feb.2018
Crevice Corrosion in a Subsea System
M - Austenitic Stainless SteelP - CaseAp - Oil and GasCd - Crevice
Cm - Aspect Before AnalysisDf - Localized Corrosion
Detail of the case thickness (20 mm) with the through wall localized corrosion in a crevice condition where there was a plug.
98
VIEW
ML00122 / Feb.2018
Crevice Corrosion in a Subsea System
M - Austenitic Stainless SteelP - CaseAp - Oil and GasCd - Crevice
Cm - Transverse Section AspectDf - Localized Corrosion
Micrographic detail of the crevice corrosion in the case wall, showing that the structure is not affected and is fully austenitic with equiaxial grains typical of a solution annealed condition.
85
VIEW
ML00122 / Feb.2018
Crevice Corrosion in a Subsea System
M - Austenitic Stainless SteelP - CaseAp - Oil and GasCd - Crevice
Cm - Micrography by OM using A262 Method ADf - Localized Corrosion
Micrographic detail of the crevice corrosion in the case wall, showing that the structure is not affected and is fully austenitic with equiaxial grains typical of a solution annealed condition.
72
VIEW
ML00122 / Feb.2018
Crevice Corrosion in a Subsea System
M - Austenitic Stainless SteelP - CaseAp - Oil and GasCd - Crevice
Cm - Micrography by OM using A262 Method ADf - Localized Corrosion
Micrographic detail of the crevice corrosion in the case wall, showing that the structure is not affected and is fully austenitic with equiaxial grains typical of a solution annealed condition. Even non metallic inclusions did not accelerate corrosion since the extension of the inclusions was not too long and they were not connecting to others.
76
VIEW
ML00122 / Feb.2018
Crevice Corrosion in a Subsea System
M - Austenitic Stainless SteelP - CaseAp - Oil and GasCd - Crevice
Cm - Micrography by OM using A262 Method ADf - Localized Corrosion
Micrographic detail of the crevice corrosion in the case wall, showing that the structure is not affected and is fully austenitic with equiaxial grains typical of a solution annealed condition. Even non metallic inclusions did not accelerate corrosion since the extension of the inclusions was not too long and they were not connecting to others.
81
VIEW
ML00122 / Feb.2018
Crevice Corrosion in a Subsea System
M - Austenitic Stainless SteelP - CaseAp - Oil and GasCd - Crevice
Cm - Micrography by OM using A262 Method ADf - Localized Corrosion