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ML00127 - May.2018

Hydrogen Cracks of Cadmium Plated Studs

Low magnification micrographic image of the stud thread, in the longitudinal section, showing the segregation lines of the steel cut at the thread indicating it was machined.

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Low magnification micrographic image of the stud thread, in the , showing the segregation lines of the cut at the thread indicating it was machined.
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Material

Low Alloy Medium Carbon QT
  • ASME B18.3
  • AISI 4140
  • UNS G41400
Ds

Description

During assembling of external parts in gate , several allen studs have fractured in a brittle way. The studs were specified as 18.3, 39HRc-45HRc, cadmium plated, chromate treated. The analysis showed a mixture of intergranular, and quasicleavage micromechanisms, indicating that during electrolytic plating the stud has cracked and during torque the stud fractured with localized ductile . This specification is not compatible with charging conditions.

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Chemistry (% in weight)

Stud Analysis

0.38C; 0.26Si; 0.91Mn; 0.007P; 0.007S; 0.93Cr; 0.16Ni; 0.16Mo.

Associated Images
Fractographic analysis by scanning electron microscopy of the stud fracture surface after opening the cracks. Brittle intergranular morphology with dimples and quasecleavage micromechanisms indicate that the internal cracks, intergranular, occurred by a hydrogen embrittlement effect during electroplating, and the ductile aspects are probably associated to overloading during torque.
517
VIEW
ML00127 / May.2018
Hydrogen Cracks of Cadmium Plated Studs
M - Low Alloy Medium Carbon QTP - Allen StudAp - Oil and GasCd - Hydrogen Embrittlement
Cm - Fractography by SEMDf - Fracture
Allen stud, 1/2" nominal diameter, cadmium plated and chromate treated, cracked during assembling external parts in a gate valve.
63
VIEW
ML00127 / May.2018
Hydrogen Cracks of Cadmium Plated Studs
M - Low Alloy Medium Carbon QTP - Allen StudAp - Oil and GasCd - Hydrogen Embrittlement
Cm - Aspect Before AnalysisDf - General View
Macrography of a longitudinal section of the stud, showing the flat fracture of brittle aspect.
46
VIEW
ML00127 / May.2018
Hydrogen Cracks of Cadmium Plated Studs
M - Low Alloy Medium Carbon QTP - Allen StudAp - Oil and GasCd - Hydrogen Embrittlement
Cm - NItal Etched MacroDf - Longitudinal Section
Allen stud, 1/2" nominal diameter, cadmium plated and chromate treated, cracked during assembling external parts in a gate valve.
40
VIEW
ML00127 / May.2018
Hydrogen Cracks of Cadmium Plated Studs
M - Low Alloy Medium Carbon QTP - Allen StudAp - Oil and GasCd - Hydrogen Embrittlement
Cm - Aspect Before AnalysisDf - Fracture
Allen stud, cadmium plated and chromate treated. The fracture appearance is brittle.
38
VIEW
ML00127 / May.2018
Hydrogen Cracks of Cadmium Plated Studs
M - Low Alloy Medium Carbon QTP - Allen StudAp - Oil and GasCd - Hydrogen Embrittlement
Cm - Aspect Before AnalysisDf - Fracture
Fractographic analysis by scanning electron microscopy of the stud fracture surface after opening the cracks. Brittle intergranular morphology with dimples and quasecleavage micromechanisms indicate that the internal cracks, intergranuar, occurred by a hydrogen embrittlement effect during electroplating, and the ductile aspects are probably associated to overloading during torque.
37
VIEW
ML00127 / May.2018
Hydrogen Cracks of Cadmium Plated Studs
M - Low Alloy Medium Carbon QTP - Allen StudAp - Oil and GasCd - Hydrogen Embrittlement
Cm - Fractography by SEMDf - Intergranular Cracking
Micrography of the longitudinal section of the stud presenting a tempered martensite structure, slightly banded. Hardness 45 HRc.
33
VIEW
ML00127 / May.2018
Hydrogen Cracks of Cadmium Plated Studs
M - Low Alloy Medium Carbon QTP - Allen StudAp - Oil and GasCd - Hydrogen Embrittlement
Cm - Nital Etched Micrography by OMDf - Martensite
Micrography of the longitudinal section of the stud presenting a tempered martensite structure in the center of the thickness.
32
VIEW
ML00127 / May.2018
Hydrogen Cracks of Cadmium Plated Studs
M - Low Alloy Medium Carbon QTP - Allen StudAp - Oil and GasCd - Hydrogen Embrittlement
Cm - Nital Etched Micrography by OMDf - Martensite
Low magnification micrographic image of the stud thread, in the longitudinal section, showing the segregation lines of the steel cut at the thread indicating it was machined.
30
VIEW
ML00127 / May.2018
Hydrogen Cracks of Cadmium Plated Studs
M - Low Alloy Medium Carbon QTP - Allen StudAp - Oil and GasCd - Hydrogen Embrittlement
Cm - Nital Etched Micrography by OMDf - Machined Thread
Micrographic detail of the stud at the thread bottom.
26
VIEW
ML00127 / May.2018
Hydrogen Cracks of Cadmium Plated Studs
M - Low Alloy Medium Carbon QTP - Allen StudAp - Oil and GasCd - Hydrogen Embrittlement
Cm - Nital Etched Micrography by OMDf - Machined Thread
Micrographic detail of the thread top, showing that the thread was machined.
29
VIEW
ML00127 / May.2018
Hydrogen Cracks of Cadmium Plated Studs
M - Low Alloy Medium Carbon QTP - Allen StudAp - Oil and GasCd - Hydrogen Embrittlement
Cm - Nital Etched Micrography by OMDf - Machined Thread
Micrography of the longitudinal section of the stud showing internal cracks, secondary (not the cracks that opened the fracture). It is evident that the cracking from the thread fillet, of a ductile aspect, presented a different aspect than the internal cracks, of a brittle aspect.
31
VIEW
ML00127 / May.2018
Hydrogen Cracks of Cadmium Plated Studs
M - Low Alloy Medium Carbon QTP - Allen StudAp - Oil and GasCd - Hydrogen Embrittlement
Cm - As polished micrographyDf - Cracks
Micrography of the longitudinal section of the stud showing a crack from the thread fillet, of a ductile aspect, opened during torque.
30
VIEW
ML00127 / May.2018
Hydrogen Cracks of Cadmium Plated Studs
M - Low Alloy Medium Carbon QTP - Allen StudAp - Oil and GasCd - Hydrogen Embrittlement
Cm - Nital Etched Micrography by OMDf - Fracture
Micrography of the longitudinal section of the stud at the fracture (top of the figure) of a brittle aspect.
29
VIEW
ML00127 / May.2018
Hydrogen Cracks of Cadmium Plated Studs
M - Low Alloy Medium Carbon QTP - Allen StudAp - Oil and GasCd - Hydrogen Embrittlement
Cm - Nital Etched Micrography by OMDf - Fracture
Micrography of the longitudinal section of the stud at the fracture (top of the figure) of a brittle intergranular aspect.
25
VIEW
ML00127 / May.2018
Hydrogen Cracks of Cadmium Plated Studs
M - Low Alloy Medium Carbon QTP - Allen StudAp - Oil and GasCd - Hydrogen Embrittlement
Cm - Nital Etched Micrography by OMDf - Intergranular Fracture
Micrography of the longitudinal section of the stud at the fracture (top of the figure) of a brittle intergranular aspect.
24
VIEW
ML00127 / May.2018
Hydrogen Cracks of Cadmium Plated Studs
M - Low Alloy Medium Carbon QTP - Allen StudAp - Oil and GasCd - Hydrogen Embrittlement
Cm - Nital Etched Micrography by OMDf - Intergranular Cracking