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Crevice Corrosion in a Subsea System — Aspect Before Analysis

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The location of the threaded fitting started leaking after less than five years in service. Although the corrosion rate was not high, the localized material loss in the threaded surface of the carbon steel flange allowed the connection leakage.
769
VIEW
ML00184 / Apr.2023
Dissimilar Steels in a Threaded Connection
M - Low Carbon SteelP - ForgingAp - OffshoreCd - Localized Dissolution
Cm - Aspect Before AnalysisDf - General View
The titanium rotor blade of a flowmeter broke after two years in service in an acid environment, containing H2S.
339
VIEW
ML00176 / Nov.2021
Hydride Formation in a Titanium Blade
M - Unalloyed TitaniumP - BladeAp - Oil and GasCd - Hydride Formation
Cm - Aspect Before AnalysisDf - General View
Aspect of the wire rope, 1 1/2" diameter, presenting regions of flattened areas at the surface of the outer wires. It is a 6 x 19 Seale construction, right regular lay.
552
VIEW
ML00175 / Aug.2021
Localized External Wear of a Wire Rope
M - High Carbon SteelP - Wire RopeAp - Oil and GasCd - Wear
Cm - Aspect Before AnalysisDf - General View
Aspect of the broken spring. The wire is 36 mm diameter and the ourter diameter of the spirals is 320 mm. It was broken in different locations.
434
VIEW
ML00172 / Mar.2021
Brittle Fracture of a LAS Valve Spring
M - Low Alloy Medium Carbon QTP - SpringAp - Oil and GasCd - Brittle Fracture
Cm - Aspect Before AnalysisDf - General View
Aspect "as received" of the seamless tube at the curved position, showing the longitudinal crack and corrosion products at the tube surface.
836
VIEW
ML00165 / Jul.2020
SCC of Aluminum Bronze Heating Coil
M - Aluminum BronzeP - Seamless tubeAp - Oil and GasCd - Stress Corrosion
Cm - Aspect Before AnalysisDf - General View
General view of the broken socket. The failure occurred during service, when the tool was tightening 3 3/4" bolts at 75% of the torque capacity. The fracture occurred associated to the smaller section of the socket, thickness of 13 mm, at the corner of the radio, that is a stress concentration raiser.
602
VIEW
ML00161 / Mar.2020
Brittle Fracture of a High Strength Socket
M - Medium Carbon Tool SteelP - ToolAp - Oil and GasCd - Brittle Fracture
Cm - Aspect Before AnalysisDf - General View
Optical micrography of a longitudinal section of the fractured bolt, at the thread. The material is austenitic, free from carbides, and the threads were almost removed by the stress corrosion cracks.
756
VIEW
ML00157 / Feb.2020
Bolts Under Chloride SCC Conditions
M - Austenitic Stainless SteelP - BoltAp - Oil and GasCd - Stress Corrosion
Cm - Oxalic Acid Electrolytic EtchDf - Stress Corrosion Cracks
The shaft was removed from service without a failure. It was 4' long and the diameters varied from 2 1/2" to 4 1/2". It was analyzed to be specified for purchasing a new one but properties evidenced bad ductility and brittle behavior even at ambient temperature, associated to a microestruture "as hot rolled".
1238
VIEW
ML00152 / Dec.2018
Low Alloy Steel Pump Shaft
M - High Strength Low AlloyP - ShaftAp - Oil and GasCd - Removed From Service
Cm - Aspect Before AnalysisDf - General View

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ML00184 — Dissimilar Steels in a Threaded ConnectionM - Low Carbon SteelP - ForgingAp - OffshoreCd - Localized Dissolution
The painting of the valve body was detaching at the vent location where the fitting was installed, not fully tighted. Three threaded fillets were outside of the body.
190
VIEW
ML00184 / Apr.2023
Dissimilar Steels in a Threaded Connection
M - Low Carbon SteelP - ForgingAp - OffshoreCd - Localized Dissolution
Cm - Aspect After CleaningDf - Painting Detachment
The austenitic stainless steel fitting was removed from the valve body and presented the sdhesion of oily deposits.
150
VIEW
ML00184 / Apr.2023
Dissimilar Steels in a Threaded Connection
M - Low Carbon SteelP - ForgingAp - OffshoreCd - Localized Dissolution
Cm - Aspect Before AnalysisDf - Surface Deposits
The cleaned fitting is sound. No corrosion, only surface stains.
121
VIEW
ML00184 / Apr.2023
Dissimilar Steels in a Threaded Connection
M - Low Carbon SteelP - ForgingAp - OffshoreCd - Localized Dissolution
Cm - Aspect After CleaningDf - General View
The threads of the carbon steel valve body is corroded. The offshore ambient is wet and chloride rich, creating an aggressive environment for the carbon steel threads.
99
VIEW
ML00184 / Apr.2023
Dissimilar Steels in a Threaded Connection
M - Low Carbon SteelP - ForgingAp - OffshoreCd - Localized Dissolution
Cm - Surface AspectDf - Corrosion
Not only the threads were corroded but all regions under the painting that was detached from the surface.
86
VIEW
ML00184 / Apr.2023
Dissimilar Steels in a Threaded Connection
M - Low Carbon SteelP - ForgingAp - OffshoreCd - Localized Dissolution
Cm - Surface AspectDf - Corrosion

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ML00176 — Hydride Formation in a Titanium BladeM - Unalloyed TitaniumP - BladeAp - Oil and GasCd - Hydride Formation
The rotor blade failed without deformation. At the rotor surface it is possible to see different colours of deposits.
53
VIEW
ML00176 / Nov.2021
Hydride Formation in a Titanium Blade
M - Unalloyed TitaniumP - BladeAp - Oil and GasCd - Hydride Formation
Cm - Aspect Before AnalysisDf - Fracture
Detail of the fracture surface, dark in the root of the blade, presenting a brittle aspect and indication that it started from this position.
39
VIEW
ML00176 / Nov.2021
Hydride Formation in a Titanium Blade
M - Unalloyed TitaniumP - BladeAp - Oil and GasCd - Hydride Formation
Cm - Aspect Before AnalysisDf - Fracture
Macroscopic aspect of the fracture surface.
37
VIEW
ML00176 / Nov.2021
Hydride Formation in a Titanium Blade
M - Unalloyed TitaniumP - BladeAp - Oil and GasCd - Hydride Formation
Cm - Fracture Surface AspectDf - Fracture
Low magnification image by scanning electron microscopy. In the bottom of the image the fracture appearance is brittle and presenting several secondary cracks. In the top of the image the fracture is fully flat, also without macroscopic plastic deformation.
33
VIEW
ML00176 / Nov.2021
Hydride Formation in a Titanium Blade
M - Unalloyed TitaniumP - BladeAp - Oil and GasCd - Hydride Formation
Cm - Fractography by SEMDf - Fracture
The position of the fracture at the starting point of the failure is brittle, transgranular, with a cleavage/quase-cleavage morphology.
24
VIEW
ML00176 / Nov.2021
Hydride Formation in a Titanium Blade
M - Unalloyed TitaniumP - BladeAp - Oil and GasCd - Hydride Formation
Cm - Fractography by SEMDf - Cleavage Facets

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ML00175 — Localized External Wear of a Wire RopeM - High Carbon SteelP - Wire RopeAp - Oil and GasCd - Wear
Macrosection of the wire rope, transverse, showing 6 strands and an independent wire rope core (IWRC). Each strand presents three layers in a SEALE construction.
92
VIEW
ML00175 / Aug.2021
Localized External Wear of a Wire Rope
M - High Carbon SteelP - Wire RopeAp - Oil and GasCd - Wear
Cm - Transverse Section AspectDf - Plastic Deformation
Low magnification micrography of a strain hardened pearlitic structure, in a longitudinal section, of one 3.2mm round wire of one strand.
62
VIEW
ML00175 / Aug.2021
Localized External Wear of a Wire Rope
M - High Carbon SteelP - Wire RopeAp - Oil and GasCd - Wear
Cm - Nital Etched Micrography by OMDf - Longitudinal Section
Highly strain hardened pearlitic structure of one external wire, 3.2mm diameter, of one strand.
55
VIEW
ML00175 / Aug.2021
Localized External Wear of a Wire Rope
M - High Carbon SteelP - Wire RopeAp - Oil and GasCd - Wear
Cm - Nital Etched Micrography by OMDf - Pearlite
Micrographic detail of the strain hardened pearlitic structure, in a longitudinal section, of a 3.2mm external round wire of one strand. This structure presented a hardness level about 500 HV (1kg), measured in the center of the thickness in the metallographic section.
47
VIEW
ML00175 / Aug.2021
Localized External Wear of a Wire Rope
M - High Carbon SteelP - Wire RopeAp - Oil and GasCd - Wear
Cm - Nital Etched Micrography by OMDf - Strain Hardened
Metallographic aspect of the wire surface in one strand external wire, showing the presence of oxides.
41
VIEW
ML00175 / Aug.2021
Localized External Wear of a Wire Rope
M - High Carbon SteelP - Wire RopeAp - Oil and GasCd - Wear
Cm - Nital Etched Micrography by OMDf - At the Surface

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ML00172 — Brittle Fracture of a LAS Valve SpringM - Low Alloy Medium Carbon QTP - SpringAp - Oil and GasCd - Brittle Fracture
Aspect of the fracture of the spring. The spring surface shows shallow pits.
49
VIEW
ML00172 / Mar.2021
Brittle Fracture of a LAS Valve Spring
M - Low Alloy Medium Carbon QTP - SpringAp - Oil and GasCd - Brittle Fracture
Cm - Aspect Before AnalysisDf - Fracture
Surface to fracture interface. The spring shows corrosion and pits.
46
VIEW
ML00172 / Mar.2021
Brittle Fracture of a LAS Valve Spring
M - Low Alloy Medium Carbon QTP - SpringAp - Oil and GasCd - Brittle Fracture
Cm - Aspect Before AnalysisDf - Corrosion
Aspect of the spring surface, with a layer of corroded products, and pits.
36
VIEW
ML00172 / Mar.2021
Brittle Fracture of a LAS Valve Spring
M - Low Alloy Medium Carbon QTP - SpringAp - Oil and GasCd - Brittle Fracture
Cm - Surface Aspect by SEMDf - Corrosion
Micrography of a transverse section of the spring, at the surface showing pits full of deposits.
36
VIEW
ML00172 / Mar.2021
Brittle Fracture of a LAS Valve Spring
M - Low Alloy Medium Carbon QTP - SpringAp - Oil and GasCd - Brittle Fracture
Cm - Nital Etched Micrography by OMDf - Transverse Section
Micrographic detail of the transverse section of the spring, at the surface, showing the pits full of corrosion deposits.
31
VIEW
ML00172 / Mar.2021
Brittle Fracture of a LAS Valve Spring
M - Low Alloy Medium Carbon QTP - SpringAp - Oil and GasCd - Brittle Fracture
Cm - Nital Etched Micrography by OMDf - Surface Deposits

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ML00165 — SCC of Aluminum Bronze Heating CoilM - Aluminum BronzeP - Seamless tubeAp - Oil and GasCd - Stress Corrosion
Aspect of the external tube surface after cleaning. It is possible to see that the cracks are longitudinal to the tube and localized in positions where the surface is corroded.
132
VIEW
ML00165 / Jul.2020
SCC of Aluminum Bronze Heating Coil
M - Aluminum BronzeP - Seamless tubeAp - Oil and GasCd - Stress Corrosion
Cm - Surface AspectDf - External Surface
Aspect of the internal tube surface after a longitudinal cut, without cleaning. It is possible to see a clean surface inside the tube.
104
VIEW
ML00165 / Jul.2020
SCC of Aluminum Bronze Heating Coil
M - Aluminum BronzeP - Seamless tubeAp - Oil and GasCd - Stress Corrosion
Cm - Surface AspectDf - Internal Surface
Micrography of the tranverse section of the tube, in the center of the thickness. There are small grains and large grains, characterizing a dual grain size. The large grains size is about 100 microns, more than 10 times larger than the average size of the smaller grains size.
101
VIEW
ML00165 / Jul.2020
SCC of Aluminum Bronze Heating Coil
M - Aluminum BronzeP - Seamless tubeAp - Oil and GasCd - Stress Corrosion
Cm - FeCl3+HCl+H2O Etched MicroDf - Dual grain sizes
Micrographic detail of the alpha microstructure presenting dual grain sizes. Two different types of twins are presented in the structure: annealing twins and deformation twins, suggesting that the material was probably partially recristalized after cold deformation and stress relief treatment.
87
VIEW
ML00165 / Jul.2020
SCC of Aluminum Bronze Heating Coil
M - Aluminum BronzeP - Seamless tubeAp - Oil and GasCd - Stress Corrosion
Cm - FeCl3+HCl+H2O Etched MicroDf - Alpha
Micrography of a transverse section of the bent tube, external surface (OD) to the top and internal surface (ID) to the bottom of the figure. At the through wall cracking position, the external surface presented a layer of intergranular corrosion.
95
VIEW
ML00165 / Jul.2020
SCC of Aluminum Bronze Heating Coil
M - Aluminum BronzeP - Seamless tubeAp - Oil and GasCd - Stress Corrosion
Cm - As polished micrographyDf - Cracking

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ML00161 — Brittle Fracture of a High Strength SocketM - Medium Carbon Tool SteelP - ToolAp - Oil and GasCd - Brittle Fracture
General view of the broken socket. It was broken in two parts and shows no evidences of plastic deformation associated to the rupture.
93
VIEW
ML00161 / Mar.2020
Brittle Fracture of a High Strength Socket
M - Medium Carbon Tool SteelP - ToolAp - Oil and GasCd - Brittle Fracture
Cm - Aspect Before AnalysisDf - General View
General view of the broken socket, showing no plastic deformation asociated to the rupture. Looking from this side it is possible to see that the fracture followed the interface of the stem with the socket head.
80
VIEW
ML00161 / Mar.2020
Brittle Fracture of a High Strength Socket
M - Medium Carbon Tool SteelP - ToolAp - Oil and GasCd - Brittle Fracture
Cm - Aspect Before AnalysisDf - General View
Micrography of a longitudinal section of the socket at the position where the fracture occurred. Uniform tempered martensitic structure. The hardness of this microstructure is 639 HV1Kg.
74
VIEW
ML00161 / Mar.2020
Brittle Fracture of a High Strength Socket
M - Medium Carbon Tool SteelP - ToolAp - Oil and GasCd - Brittle Fracture
Cm - Nital Etched Micrography by OMDf - Martensite
Micrography of a longitudinal section presenting an uniform tempered martensitic structure.
81
VIEW
ML00161 / Mar.2020
Brittle Fracture of a High Strength Socket
M - Medium Carbon Tool SteelP - ToolAp - Oil and GasCd - Brittle Fracture
Cm - Nital Etched Micrography by OMDf - Martensite
Micrographic detail of the tempered martensitic structure.
80
VIEW
ML00161 / Mar.2020
Brittle Fracture of a High Strength Socket
M - Medium Carbon Tool SteelP - ToolAp - Oil and GasCd - Brittle Fracture
Cm - Nital Etched Micrography by OMDf - Martensite

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ML00157 — Bolts Under Chloride SCC ConditionsM - Austenitic Stainless SteelP - BoltAp - Oil and GasCd - Stress Corrosion
Aspect of a 5/16" bolt manufactured in an AISI 316 austenitic stainless steel, that was also operating inside the pressure vessel, but was not yet damaged. It is a hexagonal head bolt, 1 1/2" long, fastened with a hexagonal nut and a lock washer.
118
VIEW
ML00157 / Feb.2020
Bolts Under Chloride SCC Conditions
M - Austenitic Stainless SteelP - BoltAp - Oil and GasCd - Stress Corrosion
Cm - Aspect Before AnalysisDf - General View
Low magnification micrography, by optical microscope, of the longitudinal section of a damaged bolt, in the center of the thickness. The microstructure is austenitic, free from carbides.
100
VIEW
ML00157 / Feb.2020
Bolts Under Chloride SCC Conditions
M - Austenitic Stainless SteelP - BoltAp - Oil and GasCd - Stress Corrosion
Cm - Oxalic Acid Electrolytic EtchDf - Austenite
Micrography, by optical microscope, of the longitudinal section of a damaged bolt, in the center of the thickness. The microstructure is austenitic, free from carbides, strain hardened. The hardness values of the material are from 200HV1 to 300HV1, that meets the class 2 of strenght (ASTM A193 B8M class 2).
79
VIEW
ML00157 / Feb.2020
Bolts Under Chloride SCC Conditions
M - Austenitic Stainless SteelP - BoltAp - Oil and GasCd - Stress Corrosion
Cm - Nital Etched Micrography by OMDf - Strain Hardened
Detail of the strain hardened austenitic microstructure. Micrography by optical microscope, of the longitudinal section of a bolt, in the center of the thickness.
76
VIEW
ML00157 / Feb.2020
Bolts Under Chloride SCC Conditions
M - Austenitic Stainless SteelP - BoltAp - Oil and GasCd - Stress Corrosion
Cm - Oxalic Acid Electrolytic EtchDf - Strain Hardened
Aspect of a broken 5/16" bolt that was operating inside the pressure vessel in a condition that exceeds the limits of use of the AISI 316 steel. The fracture is located close to the position where there was the bolt head and the threads were "removed" close to the fracture surface.
75
VIEW
ML00157 / Feb.2020
Bolts Under Chloride SCC Conditions
M - Austenitic Stainless SteelP - BoltAp - Oil and GasCd - Stress Corrosion
Cm - Aspect Before AnalysisDf - Fracture

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ML00152 — Low Alloy Steel Pump ShaftM - High Strength Low AlloyP - ShaftAp - Oil and GasCd - Removed From Service
The longitudinal section of the shaft shows a coarse structure. Only very close to the surface the structure is slightly refined.
99
VIEW
ML00152 / Dec.2018
Low Alloy Steel Pump Shaft
M - High Strength Low AlloyP - ShaftAp - Oil and GasCd - Removed From Service
Cm - NItal Etched MacroDf - Longitudinal Section
The longitudinal section of the shaft, in the center of the thickness, shows a coarse structure, and a ferritic/bainitic structure with pearlite islands.
97
VIEW
ML00152 / Dec.2018
Low Alloy Steel Pump Shaft
M - High Strength Low AlloyP - ShaftAp - Oil and GasCd - Removed From Service
Cm - Nital Etched Micrography by OMDf - Longitudinal Section
The coarse structure in the center of the shaft thickness is evidenced by free ferrite islands at the previous austenite grains. The presence of a pearlitic structure evidences the slow cool of the material.
85
VIEW
ML00152 / Dec.2018
Low Alloy Steel Pump Shaft
M - High Strength Low AlloyP - ShaftAp - Oil and GasCd - Removed From Service
Cm - Nital Etched Micrography by OMDf - Coarse Structure
Micrographic detail of the pearlitic structure in the center of the shaft thickness.
82
VIEW
ML00152 / Dec.2018
Low Alloy Steel Pump Shaft
M - High Strength Low AlloyP - ShaftAp - Oil and GasCd - Removed From Service
Cm - Nital Etched Micrography by SEMDf - Pearlite
The longitudinal section of the shaft, at the surface, also shows a coarse structure, and a ferritic/bainitic structure with pearlite islands. There is only a small refining in the previous austenite grain boundaries, indicating that the material was not heat treated.
75
VIEW
ML00152 / Dec.2018
Low Alloy Steel Pump Shaft
M - High Strength Low AlloyP - ShaftAp - Oil and GasCd - Removed From Service
Cm - Nital Etched Micrography by OMDf - Longitudinal Section

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