Fatigue

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Crevice Corrosion in a Subsea System — Aspect Before Analysis

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Fatigue Induced by a Defect 1

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General view of the cylindrical valve body, 6 5/8" nominal diameter, showing a transverse straight crack at the external surface.
406
VIEW
ML00162 / Apr.2020
Valve Body Crack Growth from Weld Defects
M - Low Alloy Medium Carbon QTP - Valve BodyAp - O&G Well DrillingCd - Fatigue Induced by a Defect
Cm - Aspect Before AnalysisDf - Crack

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ML00162 — Valve Body Crack Growth from Weld DefectsM - Low Alloy Medium Carbon QTP - Valve BodyAp - O&G Well DrillingCd - Fatigue Induced by a Defect
The valve body cylindrical diameter is 6 5/8" and the actuator hole in the body is about 2" diameter. The crack is associated to the hole edge, propagating transverse to the body.
71
VIEW
ML00162 / Apr.2020
Valve Body Crack Growth from Weld Defects
M - Low Alloy Medium Carbon QTP - Valve BodyAp - O&G Well DrillingCd - Fatigue Induced by a Defect
Cm - Aspect Before AnalysisDf - General View
The figure illustrates the position of the ball and seats, as well as the valve actuator. The crack is located at the edge of the actuator hole, transverse to the cylindrical body.
63
VIEW
ML00162 / Apr.2020
Valve Body Crack Growth from Weld Defects
M - Low Alloy Medium Carbon QTP - Valve BodyAp - O&G Well DrillingCd - Fatigue Induced by a Defect
Cm - Aspect Before AnalysisDf - Longitudinal Section
Penetrant test (dye check) image of the cracks at the surface of the actuator hole, viewed from inside of the body after the longitudinal cut. The aspect of the cracks at the hole, close to the internal side of the valve, is not the same as the aspect of the cracks at the external side (a straigth line), suggesting that the original cracks had propagated by fatigue through wall. The penetrant did not stained too much at the cracked area, indicating that the cracks are not too deep in this position, or are not fully opened to the surface.
62
VIEW
ML00162 / Apr.2020
Valve Body Crack Growth from Weld Defects
M - Low Alloy Medium Carbon QTP - Valve BodyAp - O&G Well DrillingCd - Fatigue Induced by a Defect
Cm - Aspect by NDTDf - Crack
Magnetic particle test of the same cracks at the edge of the actuator hole, viewed from inside of the body. The cracks appeared more clearly with this test than with the penetrant test, suggesting that the cracks are not fully opened to the surface.
60
VIEW
ML00162 / Apr.2020
Valve Body Crack Growth from Weld Defects
M - Low Alloy Medium Carbon QTP - Valve BodyAp - O&G Well DrillingCd - Fatigue Induced by a Defect
Cm - Aspect by NDTDf - Crack
Longitudinal section of the cylindrical body showing two pieces with the cracks, close to the position of the actuator hole. The valve body thickness is 40 mm at the location where the cracks appeared.
53
VIEW
ML00162 / Apr.2020
Valve Body Crack Growth from Weld Defects
M - Low Alloy Medium Carbon QTP - Valve BodyAp - O&G Well DrillingCd - Fatigue Induced by a Defect
Cm - Longitudinal Section AspectDf - Crack

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