Post on 23-Jul-2022
Famous Failures: Hydrogen Embrittlement -
Potential Failure Cause on Plated Parts
Moderator
Melissa Gorris
Host
Rebecca Stawovy
Metallurgist
Host
Ben Schmidt
Metallurgist
FAMOUS FAILURES
FAMOUS FAILURES
Failure Analysis
Bell Helicopter Failure
Hydrogen Embrittlement
Contributing Conditions
How Does Failure Occur?
Prevention
NSL Failed Washer Analysis
What we’ll talk about today…
About NSL Analytical
NSL provides independent laboratory testing services to a diverse array of customers within
regulated end-markets, where testing speed, accuracy and consistency are mission
critical to operations.
Our teams of chemists, engineers and metallurgists provide scientific expertise in
materials testing with a focus on metals, alloys and technical ceramics that are utilized
in critical end market applications.
Spectroscopy Thermal AnalysisMetallurgical /
Failure Analysis
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Testing
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Spectrometry
Particle Sizing &
CharacterizationMicroscopy
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Failure Analysis
• Get background information
• Do non-destructive testing
• Do destructive testing
• Draw conclusions
• Provide documentation
From ASM International, Metals Handbook, Desk Edition, Second Edition, J.R. Davis, Editor, p.1203
© 2021 NSL Analytical Services, Inc. All rights reserved
Why is Hydrogen Embrittlement Important?
• Attributed to sudden, catastrophic failure
• Well below expected load capacity
• Delayed fracture
• Little macroscopic yielding – microplasticity only
• Difficult to detect and prevent
• Still an active area of research
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Famous Failure:
Case Studies –
Bell Helicopter Failure
What Happened?
• June 2, 2010
• Midlothian, Texas
• Bell Helicopter BELL 222 N515MK
• Helicopter had been in service for
several years, and had undergone
repairs
Photo taken from:
https://www.ntsb.gov/_layouts/NTSB/OpenDocument.aspx?Document_DataId=40353991&FileName=Photo 1 - Photo
Showing First Responders on-scene (Midlothian Fire Department Photo)-Master.PDF
© 2021 NSL Analytical Services, Inc. All rights reserved
What Happened (cont.)
• Fractures in several locations
around the rotor head/rotor
control system
• A side drive pin was not
attributed as overload alone.
2. NTSB Report No. 11-013
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What Happened (cont.)
• View of some of the
rotor components
• Drive pins inside
swashplate assembly
2. NTSB Report No. 11-013© 2021 NSL Analytical Services, Inc. All rights reserved
What Happened (cont.)
• The A side pin fractured where
the head met the shank
• NTSB investigation of failure
• Failure likely due in part to
hydrogen embrittlement
Intact B Side Pin
Recovered head of
fractured A Side Pin2. NTSB Report No. 11-013
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NTSB Investigation
• Did not fail due to overload alone
• Determined to be Cd plated part by
EDS, chemistry checked between
pins using handheld XRF
• Several cracks observed
• Hardness was approximately 51
HRC
2. NTSB Report No. 11-013
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NTSB Investigation (cont.)
• Magnified view of
radial cracking
• Area where pin contacted
the outer ring visible
– Cd plating partially worn
2. NTSB Report No. 11-013
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NTSB Investigation (cont.)
• Small areas of dimpled
fracture surface
• Significantly higher
hydrogen content in pin
2. NTSB Report No. 11-013
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NTSB Investigation (cont.)
• Torque test of the material’s
susceptibility
• Plating stripped, reheat treated,
aged, pickled, and plated
• Similar fracture surface: brittle,
small areas of dimples
2. NTSB Report No. 11-013
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NTSB Investigation Takeaways
• Conditions were right for internal reversible hydrogen embrittlement to occur
• Typical indicators of hydrogen embrittlement were present
• Drive pin was shown to be susceptible to embrittlement when improperly processed
Photo taken from:
https://www.ntsb.gov/_layouts/NTSB/OpenDocument.aspx?Document_DataId=40353990&FileName=Photo 2 -
Main Wreckage (FAA Photo)-Master.PDF
© 2021 NSL Analytical Services, Inc. All rights reserved
Hydrogen Embrittlement
Hydrogen Damage
• Hydrogen Induced blistering
• Internal Hydrogen Precipitation
• Hydrogen Attack
• Hydride Formation
• Hydrogen Embrittlement
ASM Handbook, Volume 13B, Corrosion: Materials, Stephen D Cramer
and Bernard S Covino, Jr editors, 2005.
Hydrogen Blister
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Hydrogen Embrittlement – Identification
Susceptible
Material
Hydrogen
Embrittlement
Stress
Hydrogen Source
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Hydrogen Embrittlement – Identification (cont.)
Susceptible Materials
• Steels
– High strength: 130-180 ksi minimum
– Hardness: 35-40 HRC minimum
• Stainless Steel
– Typically, cold worked or martensitic
• Nickel Alloys
• Titanium
• Refractory Metals
ASM Handbook, Volume 23, Materials for Medical Devices, Roger J
Narayan editors, 2012.
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Hydrogen Embrittlement – Identification (cont.)
Hydrogen Source
• Plating operations
• Hydrogen storage
• Welding
• Heat Treating atmosphere
• Pickling (Cleaning)
Stress
• Applied
• Residualhttp://demo.premiersteels.in/components/wp-
content/uploads/2020/04/infrastructure-1.jpg
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Hydrogen Embrittlement – Identification (cont.)
• Appears brittle at low magnifications, small isolated pockets of dimpled fracture surface
• Cracks originate internally, intergranular in high strength steels
© 2021 NSL Analytical Services, Inc. All rights reserved
Hydrogen Embrittlement – Mechanism
• Hydrogen embrittlement typically
affects high strength and heavily
cold worked steels which have a
body centered cubic structure.
API 571 Section 5.1.2.3
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Hydrogen Embrittlement – Mechanism (cont.)
H
Atomic Diameters• Hydrogen: 0.074 nm
• Carbon: 0.154 nm
• Iron: 0.252 nm
C
Fe
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Hydrogen Embrittlement – Mechanism (cont.)
© 2021 NSL Analytical Services, Inc. All rights reserved
Hydrogen Embrittlement – Mechanism (cont.)
Hydrogen induced decohesion
(HID)
• Hydrogen acts to loosen the
molecular or atomic bonds.
• Crack propagation can occur
more easily
• Also called Hydrogen Enhanced
Decohesion (HEDE)
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Hydrogen Embrittlement – Mechanism (cont.)
Hydrogen Enhanced Local
Plasticity (HELP)
• Hydrogen enhances the movement
of dislocations within grains.
• Increased localized deformation
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Hydrogen Embrittlement – Mechanism (cont.)
Hydrogen Enhanced
Strain Induced Vacancy
Formation (HESIV)
• Vacancies nucleate, grow
and link together.
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Hydrogen Embrittlement – Mechanism (cont.)
Hydrogen Induced Phase Transformation (HIPT)
• Formation of brittle hydrides at the the crack tip
• Austenite to martensitic phases in 304 Stainless
https://www.researchgate.net/figure/Schematic-diagrams-of-HE-mechanisms-a-HIPT-64-hydrogen-induced-
phase-transformation_fig5_340851994 © 2021 NSL Analytical Services, Inc. All rights reserved
Hydrogen Embrittlement – Current Research
Argonne National Labs• Using HEXD (High Energy X-Ray
Diffraction)
• 4130 Steel Samples were cyclically stressed in either air or a hydrogen environment.
• HEXD data indicated that in the sample tested in air, dislocations were evenly dispersed.
• In the sample tested in H2, dislocations had migrated to grin boundaries.
Matthew Connolly1*, May Martin1, Peter Bradley1, Damian Lauria1, Andrew Slifka1, Robert Amaro2, Christopher
Looney3, and Jun-Sang Park4, “In situ high energy X-ray diffraction measurement of strain and dislocation density
ahead of crack tips grown in hydrogen,” Acta Mater. 180, 272 (2019). DOI: 10.1016/j.actamat.2019.09.020
© 2021 NSL Analytical Services, Inc. All rights reserved
Hydrogen Embrittlement – Current Research (cont.)
Imaging Methods – determining
where the hydrogen is located• Atom Probe Tomography (APT)
• Combines field ion microscope
with a mass spectrometer
• Secondary Ion Mass Spectrometry
APT Output
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Hydrogen Embrittlement – Mitigation
Hydrogen “Bake Out”
• This method involves heating
the material to an elevated
temperature for a sufficient time
to allow the hydrogen to diffuse
out of the material.
• Typical temperatures:
400°F - 800°F.
https://www.kleinplating.com/uploads/metal-heat-treatment-and-
baking-parts-klein-plating-works-chart.jpg
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Hydrogen Embrittlement – ASTM Methods
• ASTM F519 – Standard Test Method for Mechanical Hydrogen Embrittlement Evaluation
of Plating/Coating Processes and Service Environments
• ASTM F1624 – Standard Test Method for Measurement of Hydrogen Embrittlement
Threshold in Steel by the Incremental Step Loading Technique
• ASTM A143 – Standard Practice for Safeguarding Against Embrittlement of Hot Dip
Galvanized Structural Steel Products and Procedure for Detecting Embrittlement
• ASTM F1940 – Standard Test Method for Process Control Verification to Prevent Hydrogen
Embrittlement in Plated or Coated Fasteners
• ASTM F2660 – Standard Test Method for Qualifying Coatings for Use on F3125 Grade
A490 Structural Bolts relative to Environmental Hydrogen Embrittlement
© 2021 NSL Analytical Services, Inc. All rights reserved
The
Failure Analysis
Lab Experiment:
Washer Failure
Experimental – Washer Failure
• Questions to Ask:
– Is the part broken?
– Was there noticeable deformation?
– Was the part in service for over a
week?
– Was the part plated or coated with iron
or zinc phosphate?
– Was the part acid cleaned?
– Is the hardness over 40 HRC?
– Did the part break due to a sudden
impact load?
– Was the material heavily cold worked?
Taken from ASM Handbook, Volume 11, Failure Analysis and
Prevention, B. Miller, R. Shipley, R. Parrington, D. Dennies,
editors.
© 2021 NSL Analytical Services, Inc. All rights reserved
Experimental – Washer Failure
• Material: AISI 1055 steel
• Hardness: approx. 48 HRC
• Hydrogen Source:
Zinc Phosphate Plating
• Fracture Surface: mixed
intergranular/ductile failure with
grain boundary separation
© 2021 NSL Analytical Services, Inc. All rights reserved
FAMOUS FAILURES
Summary
Failure Analysis
Bell Helicopter Failure
Hydrogen Embrittlement
Contributing Conditions
How Does Failure Occur?
Prevention
FAMOUS FAILURES
References1. ASM Handbook Vol. 11: Failure Analysis and Prevention. Hydrogen Damage and
Embrittlement. Pg. 809. ASM International, 2002.
2. Materials Laboratory Factual Report. Report No. 11-013. National Transportation
Safety Board, March 14, 2011. URL:
https://www.ntsb.gov/_layouts/NTSB/OpenDocument.aspx?Document_DataId=403456
95&FileName=Materials Laboratory 15 - Factual Report 11-013-Master.PDF.
© 2021 NSL Analytical Services, Inc. All rights reserved
FAMOUS FAILURES
Q&A
Ben Schmidt
MetallurgistRebecca Stawovy
Metallurgist
Dave Kovarik
Metallurgist
Failure Analysis
Consultant
John Ratka
Director,
Metallurgical
Operations
FAMOUS FAILURES
Let’s Talk Tech!
Benjamin Schmidt
Metallurgist
bschmidt@nslanalytical.com
216-438-5201
Rebecca Stawovy
Metallurgist
rstawovy@nslanalytical.com
216-438-5235
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