Back to Low Alloy Medium Carbon QT
ML00162 - Apr.2020

Valve Body Crack Growth from Weld Defects

Macrography of the longitudinal section of the valve body, at the cracked position, a little far from the actuator hole. The valve body is 40 mm thick at this position and it is possible to see that at this position only one region is welded in repair, close to the outer surface (top), and there is a crack, transverse to the thickness, that is difficult to see with this magnification and that is clearly the propagation in fatigue.

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of the of the body, at the cracked position, a little far from the actuator hole. The body is 40 mm thick at this position and it is possible to see that at this position only one region is welded in repair, close to the outer surface (top), and there is a , transverse to the thickness, that is difficult to see with this magnification and that is clearly the propagation in .
M

Material

Low Alloy Medium Carbon QT
  • AISI 4340
Ds

Description

The control flow presented after three months in operation. During pressure test to identify the leakage location it was detected a linear , transverse to the body, originated in the actuator hole. The metallurgical analysis showed that the body is a high strength , with good impact energy at -18°C, and there was a close to the actuator hole, with (hot cracks) that created a condition for propagation through wall.

C

Chemistry (% in weight)

body chemistry

0.42C; 0.27Si; 0.73Mn; 0.019P; 0.010S; 0.78Cr; 1.76Ni; 0.23Mo; 0.17Cu.

weld metal chemistry

0.21C; 0.49Si; 1.33Mn; 0.018P; 0.016S; 0.39Cr; 0.68Ni; 0.35Mo; 0.21Cu.

Associated Images
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
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
Low magnification micrography of a longitudinal section of the valve body, in the center of the thickness. As expected for this high strength steel, the microstructure is martensitic, but with segregation bands.
48
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 - Nital Etched Micrography by OMDf - Banded Structure
Micrography of a longitudinal section of the valve body presenting a martensitic microstructure. The structure is banded and the darker regions show inclusions (grey sulfides).
50
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 - Nital Etched Micrography by OMDf - Martensite
Micrographic detail of the martensitic microstructure, in the longitudinal section. The hardness of the valve body is 34 HRc (Rockwell C) all through the thickness.
47
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 - Nital Etched Micrography by OMDf - Martensite
Macrography of the longitudinal section of the valve body, at the cracked position close to the actuator hole. The valve body is 40 mm thick and at this position it is possible to see that there are two regions where the body was welded, close to the inner surface (bottom) and at the close to the outer surface (top). The through wall crack presented a branch aspect close to the repair in the ID and a straight aspect when propagating from the repair.
55
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 - NItal Etched MacroDf - Weld Repair
Macrography of the longitudinal section of the valve body, at the cracked position, a little far from the actuator hole. The valve body is 40 mm thick at this position and it is possible to see that at this position only one region is welded in repair, close to the outer surface (top), and there is a crack, transverse to the thickness, that is difficult to see with this magnification and that is clearly the propagation in fatigue.
47
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 - Nital Etched Micrography by OMDf - Fatigue Crack
Low magnification micrography at the weld repair close to the internal surface of the valve body, in a longitudinal section. Weld metal to the bottom and heat affected zone to the top.
42
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 - Nital Etched Micrography by OMDf - Weld Repair
Micrography of the weld repair at the fusion line. Weld metal to the right and heat affected zone to the left.
37
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 - Nital Etched Micrography by OMDf - Fusion Line
Micrographic detail of the fusion line.
33
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 - Nital Etched Micrography by OMDf - Fusion Line
Low magnification micrography at the weld repair close to the internal surface of the valve body, in a longitudinal section. Weld metal to the right and heat affected zone to the left.
30
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 - Nital Etched Micrography by OMDf - Weld Repair
Micrography of the weld repair at the fusion line. At this magnification it is possible to identify several voids at interdendritic positions.
26
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 - Nital Etched Micrography by OMDf - Weld Repair
Micrographic detail of the weld metal presenting hot cracks, at interdendritic positions, interconected.
28
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 - Nital Etched Micrography by OMDf - Weld Metal
Microstructure of the weld metal close to the fusion line, showing that the dilution effects created zones of higher carbon content, creating a martensitic plus retained austenite microstructure.
29
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 - Nital Etched Micrography by OMDf - Weld Metal
Macrographic detail of the cracked position close to the actuator hole. The through wall crack presented a branch aspect in the weld metal, that is the original defect created during welding, and a straight aspect when propagating from the repair.
27
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 - NItal Etched MacroDf - Hot cracking
Micrography in low magnification, as polished, of the crack in the the repair weld metal, showing the dendritic aspect of the hot cracks, formed during welding due to the high content of impurities in a high strength weld metal.
26
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 - As polished micrographyDf - Hot cracking
Micrography, as polished, of the hot cracks with rounded morphology.
27
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 - As polished micrographyDf - Hot cracking
Micrographic detail, as polished, of the hot cracks with rounded interdenritic morphology.
26
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 - As polished micrographyDf - Hot cracking
Micrography in low magnification of the cracks in the repair weld metal, showing the dendritic aspect of the hot cracks, formed during welding due to the high content of impurities in a high strength weld metal.
26
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 - Nital Etched Micrography by OMDf - Weld Metal
Micrographic detail of the weld metal presenting hot cracks, at interdendritic positions, interconected.
28
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 - Nital Etched Micrography by OMDf - Hot cracking
Macrographic detail of the longitudinal section of the valve body, at the cracked position, a little far from the actuator hole. There is a straight crack, transverse to the thickness that clearly propagated by fatigue mechanism, from the region where the welding defects were created.
27
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 - NItal Etched MacroDf - Fatigue Crack
Micrography in low magnification, as polished, of the crack in the valve thickness, showing the straight aspect of the fatigue propagation.
24
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 - As polished micrographyDf - Fatigue Crack
Micrography, as polished, of the crack in the valve thickness, showing the straight aspect of the fatigue propagation.
22
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 - As polished micrographyDf - Fatigue Crack
Micrographic detail of the straight crack that propagated by a fatigue mechanism.
18
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 - As polished micrographyDf - Fatigue Crack
Micrography in low magnification of the straight crack in the valve thickness. The crack propagates without following any microstructural aspect. Fatigue is not influenced by microstructure, but by tensile stresses.
23
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 - Nital Etched Micrography by OMDf - Fatigue Crack
Micrographic detail of the fatigue cracking, straight and without microstructural influence.
25
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 - Nital Etched Micrography by OMDf - Fatigue Crack
Valve Body Crack Growth from Weld Defects
2
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 - NItal Etched MacroDf - Crack
Valve Body Crack Growth from Weld Defects
1
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 - NItal Etched MacroDf - Fatigue Crack
Valve Body Crack Growth from Weld Defects
3
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 - Nital Etched Micrography by OMDf - Fatigue Crack
Valve Body Crack Growth from Weld Defects
2
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
Cross-sectional micrograph showing a wide, irregular crack with branching dark deposits through the polished matrix, alongside scattered small voids.
3
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 - As polished micrographyDf - Hot cracking
Cross-section showing a single jagged crack propagating through the matrix, with a small non-metallic inclusion nearby.
1
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 - As polished micrographyDf - Fatigue Crack