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ML00124 - Feb.2018

MIC of a Martensitic Valve Ring

Micrography of a transverse section, in the center of the ring, where the cracking was closed. The cracks are thin, not corroded, intergranular and not connected to the surface, indicating a hydrogen embrittlement effect.

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of a , in the center of the ring, where the was closed. The are thin, not corroded, intergranular and not connected to the surface, indicating a effect.
M

Material

Martensitic Stainless Steel
  • UNS S42000
  • AISI 420
Ds

Description

The ring was installed in a of a hydroelectric system that remained out of service during 6 months. When it was tested the valve leaked and the inspection detected deep associated to , suggesting that the stagnated water created a condition for microbiological adhesion and acidification, with strong dissolution and inside the pites. The material impact energy is not satisfactory but the brittle rupture occurred assisted by the environment.

C

Chemistry (% in weight)

Ring Analysis

0.19C; 0.24Si; 0.68Mn; 0.021P; 0.004S; 12.10Cr; 0.33Ni; 0.07Mo; 0.23Cu.

Associated Images
Microscopic image by scanning electron microscope (SEM) of the ring surface that presented pites under fouling deposits.
522
VIEW
ML00124 / Feb.2018
MIC of a Martensitic Valve Ring
M - Martensitic Stainless SteelP - ForgingAp - EnergyCd - Brittle Behavior
Cm - Surface Aspect by SEMDf - Pitting
Macroscopic aspect of the crack in the valve ring surface. A leakage was detected during testing after 6 months out of service and the inspection identified several transverse cracks in the forged ring. The valve was installed for one year, but it was not drained during the time it was out of service. The cracks were located in regions that were rusted and presenting a biological fouling.
51
VIEW
ML00124 / Feb.2018
MIC of a Martensitic Valve Ring
M - Martensitic Stainless SteelP - ForgingAp - EnergyCd - Brittle Behavior
Cm - Aspect Before AnalysisDf - At the Surface
Macroscopic aspect of the crack after cleaning the ring surface. Transverse cracks were identified associated to pitting corrosion.
44
VIEW
ML00124 / Feb.2018
MIC of a Martensitic Valve Ring
M - Martensitic Stainless SteelP - ForgingAp - EnergyCd - Brittle Behavior
Cm - Aspect Before AnalysisDf - Localized Corrosion
Micrography of a transverse section of the ring presenting a uniform tempered martensite structure.
43
VIEW
ML00124 / Feb.2018
MIC of a Martensitic Valve Ring
M - Martensitic Stainless SteelP - ForgingAp - EnergyCd - Brittle Behavior
Cm - Kalling Etched Micrography by OMDf - Martensite
Microscopic details of the ring surface showing the fouling at the surface and localized corrosion under the deposits.
42
VIEW
ML00124 / Feb.2018
MIC of a Martensitic Valve Ring
M - Martensitic Stainless SteelP - ForgingAp - EnergyCd - Brittle Behavior
Cm - Surface Aspect by SEMDf - Pitting
Higher magnification of the localized corrosion, showing that there are cracks at the margin of the corroded region.
39
VIEW
ML00124 / Feb.2018
MIC of a Martensitic Valve Ring
M - Martensitic Stainless SteelP - ForgingAp - EnergyCd - Brittle Behavior
Cm - Surface Aspect by SEMDf - Pitting
SEM image showing a branching surface crack extending from a region of granular corrosion deposits into the polished substrate.
32
VIEW
ML00124 / Feb.2018
MIC of a Martensitic Valve Ring
M - Martensitic Stainless SteelP - ForgingAp - EnergyCd - Brittle Behavior
Cm - Surface Aspect by SEMDf - Pitting
Intergranular morphology inside the pitting and evidences of chemical attack (dissolution).
36
VIEW
ML00124 / Feb.2018
MIC of a Martensitic Valve Ring
M - Martensitic Stainless SteelP - ForgingAp - EnergyCd - Brittle Behavior
Cm - Surface Aspect by SEMDf - Pitting
Micrography of a transverse section of the ring, at the pitting position, as polished, showing that there are intergranular cracks and the martensitic structure is corroded (chemical dissolution) inside the pitting.
33
VIEW
ML00124 / Feb.2018
MIC of a Martensitic Valve Ring
M - Martensitic Stainless SteelP - ForgingAp - EnergyCd - Brittle Behavior
Cm - As polished micrographyDf - Corrosion
Micrographic detail of a transverse section of the ring, showing the corroded martensitic structure (chemical dissolution) inside the pitting.
32
VIEW
ML00124 / Feb.2018
MIC of a Martensitic Valve Ring
M - Martensitic Stainless SteelP - ForgingAp - EnergyCd - Brittle Behavior
Cm - As polished micrographyDf - Corrosion
Micrographic detail of a transverse section of the ring, showing the corroded martensitic structure (chemical dissolution) inside the pitting.
33
VIEW
ML00124 / Feb.2018
MIC of a Martensitic Valve Ring
M - Martensitic Stainless SteelP - ForgingAp - EnergyCd - Brittle Behavior
Cm - As polished micrographyDf - Intergranular Cracking
Micrography of a transverse section of the ring at the cracking position. The cracks are intergranular and opened at the position close to the surface.
27
VIEW
ML00124 / Feb.2018
MIC of a Martensitic Valve Ring
M - Martensitic Stainless SteelP - ForgingAp - EnergyCd - Brittle Behavior
Cm - Kalling Etched Micrography by OMDf - Martensite
Micrography of a transverse section of the ring at the cracking position. The cracks are intergranular and opened at the position close to the surface. it is possible to identify dissolution of the structure adjacent to the grain boundaries,
25
VIEW
ML00124 / Feb.2018
MIC of a Martensitic Valve Ring
M - Martensitic Stainless SteelP - ForgingAp - EnergyCd - Brittle Behavior
Cm - Kalling Etched Micrography by OMDf - Crack
Micrographic detail of a transverse section of the ring at the cracking position. The cracks are intergranular and opened at the position close to the surface. it is possible to identify dissolution of the structure adjacent to the grain boundaries,
24
VIEW
ML00124 / Feb.2018
MIC of a Martensitic Valve Ring
M - Martensitic Stainless SteelP - ForgingAp - EnergyCd - Brittle Behavior
Cm - Kalling Etched Micrography by OMDf - Intergranular Cracking
Micrograph showing a fine acicular martensitic matrix with a branching crack network, more extensive near the right edge.
25
VIEW
ML00124 / Feb.2018
MIC of a Martensitic Valve Ring
M - Martensitic Stainless SteelP - ForgingAp - EnergyCd - Brittle Behavior
Cm - Kalling Etched Micrography by OMDf - Crack
Micrography of a transverse section of the ring, in the center, where the cracking was closed. The cracks are intergranular and not opened to the surface.
29
VIEW
ML00124 / Feb.2018
MIC of a Martensitic Valve Ring
M - Martensitic Stainless SteelP - ForgingAp - EnergyCd - Brittle Behavior
Cm - Kalling Etched Micrography by OMDf - Crack
Micrography of a transverse section, in the center of the ring, where the cracking was closed. The cracks are thin, not corroded, intergranular and not connected to the surface, indicating a hydrogen embrittlement effect.
25
VIEW
ML00124 / Feb.2018
MIC of a Martensitic Valve Ring
M - Martensitic Stainless SteelP - ForgingAp - EnergyCd - Brittle Behavior
Cm - Kalling Etched Micrography by OMDf - Intergranular Cracking