Lean Duplex Stainless Steel

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Crevice Corrosion in a Subsea System — Aspect Before Analysis

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Macroscopic aspect of the outer diameter of the flanged sleeve presenting adhered products at the surface. The flanged sleeve was manufactured by centrifugal casting in a lean duplex stainless steel and it was externally coated by thermal spray (TS) in a position of sealing. After 5 years in service the system suffered leakage.
569
VIEW
ML00147 / Aug.2018
WC Layer Detached from a Cast Lean Duplex
M - Lean Duplex Stainless SteelP - Centrifugal CastingAp - ShipCd - Lack of Sealing
Cm - Aspect Before AnalysisDf - External Surface

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ML00147 — WC Layer Detached from a Cast Lean DuplexM - Lean Duplex Stainless SteelP - Centrifugal CastingAp - ShipCd - Lack of Sealing
Detail of the external surface of the sleeve where the surface coating was detached, creating a lack of sealing condition.
67
VIEW
ML00147 / Aug.2018
WC Layer Detached from a Cast Lean Duplex
M - Lean Duplex Stainless SteelP - Centrifugal CastingAp - ShipCd - Lack of Sealing
Cm - Surface AspectDf - External Surface
General view of the 10" diameter flanged sleeve, 1/2" wall thickness, manufactured by centrifugal casting of lean duplex stainless steel (DSS), Alloy 2304 (without Mo), with an external coating applied by thermal spray (TS). The sleeve is assembled in a shaft. The internal environment is oil and a seal box is assembled in the external side that is wet with seawater.
56
VIEW
ML00147 / Aug.2018
WC Layer Detached from a Cast Lean Duplex
M - Lean Duplex Stainless SteelP - Centrifugal CastingAp - ShipCd - Lack of Sealing
Cm - Aspect Before AnalysisDf - General View
Longitudinal slice of the flanged sleeve, 180 mm long, in a macrography presenting the 1/2" tubular wall thickness where the sealing was applied. The external surface of the sleeve (seawater wet) is in the left side of the figure and the internal surface (oiled) is in the right side. The flange is to the top of the figure.
52
VIEW
ML00147 / Aug.2018
WC Layer Detached from a Cast Lean Duplex
M - Lean Duplex Stainless SteelP - Centrifugal CastingAp - ShipCd - Lack of Sealing
Cm - Longitudinal Section AspectDf - General View
Macrographic aspect of the sleeve longitudinal section where the coating was applied in the external side (top of the figure). It is possible to see that the sleeve was manufactured by centrifugal casting, with elongated grains from the external side, and equiaxial grains close to the internal side (bottom of the figure). There is a weaved interface between the sleeve and the first layer of thermal spray coating, 1 mm thick; and a second layer of thermal spray coating, 0.2mm thick (almost imperceptible at this low magnification).
49
VIEW
ML00147 / Aug.2018
WC Layer Detached from a Cast Lean Duplex
M - Lean Duplex Stainless SteelP - Centrifugal CastingAp - ShipCd - Lack of Sealing
Cm - NaOH Electrolytic Etched MacroDf - Coating Layer
Micrography of a longitudinal section of the sleeve, at the external surface where there are two layers of coating. The electrolytic etch evidenced the duplex stainless steel substrate (bottom of the figure) and the weave interface of the substrate and the first thermal spray layer, about 1 mm thick, in a stainless steel. The surface layer, of tugnsten carbide, about 0.2 mm thick, is black and not clearly visible in this figure.
50
VIEW
ML00147 / Aug.2018
WC Layer Detached from a Cast Lean Duplex
M - Lean Duplex Stainless SteelP - Centrifugal CastingAp - ShipCd - Lack of Sealing
Cm - NaOH Electrolytic Etched MicroDf - External Surface

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