Transcript Process Survey from Hot-Dip Galvanizing Plants 2003

HYDROGEN
EMBRITTLEMENT OF HIGH
STRENGTH BOLTS
American Galvanizers Association
Tom Langill
October 3rd, 2012
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Hydrogen Embrittlement
• Chemical Processes generate hydrogen
• Hydrogen goes into the atmosphere or diffuses
into the steel
• Issue is trapped hydrogen – Hydrogen does
not release at high temperatures
• Trapped hydrogen starts moving at later date
when part is under external stress
• Movement of hydrogen causes micro-cracking
which expands under stress – failure
• Dissimilar metal interactions can generate
hydrogen and cause embrittlement
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Hydrogen in the Hot-Dip
Galvanizing Process
• Main source of hydrogen is the pickling
operation
• Fluxing can also generate some hydrogen
• Temperature of the galvanizing bath
drives out most hydrogen
• Previous work showed only steels with
over 150 KSI strength trapped hydrogen
• Hydrogen embrittlement does not occur
immediately after galvanizing
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ASTM A490 Bolts
• High Strength Bolts – UTS 150 KSI to 173 KSI
• Rockwell “C” Hardness - 33 to 39
• Practical limit is determined by Wedge Tensile
Test of Bolts
• Failure mode in Wedge Tensile Test is
separation of bolt head from shaft
• Qualification of corrosion protection systems is
per Industrial Fastener Institute (IFI)
Specification 144
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IFI 144 REQUIREMENTS
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Rotational Capacity
Salt Spray
Cyclic Testing
Hydrogen Embrittlement
Adhesion Test
Paintability
Coating Thickness
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ROTATIONAL CAPACITY
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Full size bolts tested with lubricant
Tighten greater than 110% of Proof Load
Skidmore-Wilhelm Tension Calibrator
¾” and 1” bolts tested
Apply 35 Kips then add 5 degrees rotation
Measured Torque on ¾” – 417 Ft-lbs (547
Ft-lbs maximum)
• Measured Tension on ¾” – 44 Kips (40 Kips
minimum)
• ¾” bolts passed the test
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ROTATIONAL CAPACITY
• Apply 64 Kips then add 5 degrees rotation
• Measured Torque for 1” – 966 Ft-lbs (1333
Ft-lbs maximum)
• Measured Tension for 1” – 79 Kips ( 74 Kips
minimum)
• 1” bolts passed test
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SALT SPRAY TESTING
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ASTM B117 Test Procedure
1000 Hours test duration
ASTM D1654 Inspection after Testing
Measure % of red rust on bolts
% converted to rating number
Ratings from 0 to 10
Higher number is better performer
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SALT SPRAY TESTING
bolts of each size – ¾”
and 1” tested per B117
• 10
•Head and Body inspected
separately per D1654
•For 1” Bolts - Head
Rating Average = 6.3; Body
Rating = 5.9
•For ¾” Bolts – Head Rating
Average = 7.1; Body Rating
Average = 7.3
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CYCLIC TESTING
• GM
9540P Test Procedure
•80 cycles duration – each cycle 24 hours
•Parts inspected every 8 cycles for red rust
•5 bolts of each size tested under load
•Then 5 bolts of each size tested under no load
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CYCLIC TESTING
• Head and Body
inspected separately
per D1654
• For 1” Bolts - Head
Rating Average = 9.0;
Body Rating = 9.0
• For ¾” Bolts – Head
Rating Average = 9.0;
Body Rating Average =
9.0
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HYDROGEN EMBRITTLEMENT
• Bolts harden through heat treatment to
maximum allowed by A490 specification
• Two tests were performed to evaluate
embrittlement potential – ASTM F606 and
ASTM F1624
• Tests were performed on actual galvanized
A490 bolts
• Bolts were mechanically cleaned and flash
pickled before galvanizing
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HYDROGEN EMBRITTLEMENT
• ASTM F606 Test Conditions
– 4 degree wedge under bolt head
– Tightening torque giving tensile load of 37,575
lbs for ¾” bolts = 75% UTS minimum
– Tightening torque giving tensile load of 68,175
lbs for 1” bolts = 75% UTS minimum
– Load applied for 48 hours
– 20x scope used to examine bolt after testing
• Examination found no signs of cracking
• Samples met the specification requirements
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HYDROGEN EMBRITTLEMENT
• ASTM F1624 Test Conditions
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Rising Step Stress
Bolts machined to hemisphere cross section
Coated to electrically isolate galvanized steel
Internal Hydrogen Embrittlement (IHE) – air
Environmental Hydrogen Embrittlement (EHE) – Immersed
in salt water with imposed potential of -1.15 V
• Perform Fast Fracture Test – No Step Stress
• Determine Step Rate Through Series of
Tests under Rising Steps
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HYDROGEN EMBRITTLEMENT
• Rising Step Stress Tests used to determine
optimum test conditions
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Length of Step
Time of Step
Overall Test Time
Step Stress Increase
• Optimum Condition Reached When No
Further Change to Stress Value for Initiation
of Cracking
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HYDROGEN EMBRITTLEMENT
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HYDROGEN EMBRITTLEMENT
• Evaluation of Hydrogen Embrittlement
Potential is Stress at Cracking Divided by
Fast Fracture Load
• For Hot-Dip Galvanized 1” Bolts the
Average Stress at Cracking was 449 lbs.
• The Fast Fracture Load of 1” Bolts was
603 lbs.
• The Ratio of Cracking Stress to Fast
Fracture Strength is 65%
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HYDROGEN EMBRITTLEMENT
• Acceptance Criteria in Accordance with
ASTM F519 – Minimum 60% FFS
• Hot-Dip Galvanized Bolts Tested at 65% of
FFS in Step Stress Testing
• Bolts of 1” Diameter or Less are Not
Susceptible to Hydrogen Embrittlement
• Test Performed with Scribe Mark in
Coating to Simulate Coating Defect
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ADHESION TESTS
• Test Conducted in Accordance with ASTM
B571
• ASTM A153 is also Referenced in
Adhesion Test
• Tests using the Stout Knife Test in
Accordance with A153 were Performed by
RMMP Labs
• Bolts of 1” and ¾” were Tested and
Passed All Requirements
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PAINTABILITY
• Test were Conducted in Accordance with
IFI 144
• 10 Bolts of Each Size (1” and ¾”) were
Painted
• Spray Paint was Approximately 12” from
the Bolts
• Three Layers of Paint were Applied
• Paint Layers Dried in 1 Hour Exceeding
the 48 Hour Minimum
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COATING THICKNESS
• Test were Conducted in Accordance with
ASTM E376
• Ten Bolts of Each Size (1” and ¾”) were
measured with Oxford Instruments
CMI200
• 21 Measurements were Taken on Each
Bolt to Insure Reproducible Results
• All Measurements Exceeded the
Specification Minimum of 2.1 mils.
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ACTION PLAN
• ASTM Just Approved a Version of IFI 144
• New Specification is ASTM F2660
• Compare Results to Requirements of
F2660
• Publish Paper of Results in ASTM
Materials and Characterization Journal
• Request Change to ASTM A490
Specification – Allow Hot-Dip Galvanizing
of A490 Bolts
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