1. Causes and
Control of
Fastener Better
Failures Buildings
from
Better
Fasteners
Gregg Melvin – Senior Applications Engineer
Elco Construction Products
© 2012 Elco Construction Products

2. AIA Credits: Elco Construction Products an Infastech company is
Registered Provider with American Institute of Architects
Continuing Education Systems. Credit earned on completion of this
program will be reported to CES Records for AIA members.
Certificates of Completion for non-AIA members available on
request.
This program is registered with the AIA/CES for continuing
professional education. As such, it does not include content that
may be deemed or construed to be an approval or endorsement by
the AIA of any material of construction or any method or manner of
handling, using, distributing, or dealing in any material or product.
Questions related to specific materials, methods, and services will
be addressed at the conclusion of this presentation.

3. Copyright Materials
This presentation is protected by US and
International copyright laws.
Reproduction, distribution, display, and
use of the presentation without written
permission of the speaker is prohibited.
© Elco® Construction Products 2012

4. Learning Objectives
Identify where A/E must specify fasteners
instead of leaving product selection to contractor or
supplier.
Learn techniques for reducing fastener rust and
galvanic corrosion damage.
Be able to explain causes of hydrogen
embrittlement and HASCC.
Be able to specify high-performance, HASCC-
resistant fasteners.
Explain role of fasteners in building sustainability.

5. PART ONE
SPECIFYING FASTENERS
Risks and Responsibilities

6. For want of a fastener…
“For want of a nail,
the shoe was lost.
For want of a shoe,
the horse was lost.
For want of a horse,
the rider was lost.”
“God is in the details.”
Mies van der Rohe - 20th Century Architect

7. Your reputation hangs on
specifying the right fasteners.
Fastener specification are
critical to project success.
Standard types and grades of
fasteners are sufficient in many
construction applications. In these
instances, fastener selection can
usually be based upon industry
standards, building code
requirements, and design loads.
It may even be acceptable in some
cases to leave fastener selection to the
The Petronas Towers in Kuala discretion of contractors or building
Lumpur, the world’s tallest building
when constructed, required careful product fabricators, allowing them to
engineering to assure that the
millions of fasteners used to install
select fasteners based on cost,
cladding would not be the convenience, and trade practices.
installation’s weakest link.

8. Your reputation hangs on
specifying the right fasteners.
Fastener specification are
critical to project success.
At other times, however,
fastener selection can be one of
the most crucial aspects of
building design.
Professional judgment is required
to specify fasteners that:
Perform as intended
Are dependable and economical
The Petronas Towers in Kuala
Lumpur, the world’s tallest building
when constructed, required careful Last the life of the building
engineering to assure that the
millions of fasteners used to install
cladding would not be the
installation’s weakest link.

9. A big job for such a small part
Structural capacity:
Static and dynamic load.
Pull-out and pull-over.
Shear on fastener and attached materials.
Corrosion resistance.
Seal against liquid or gas.
Constructability, practicality, and inspectability.
Design intent and aesthetics.
Removability and other special requirements.
Service life exceeds that of attached materials.
Specifying fasteners is part of designing safe, durable,
and practical connections between components.

10. HASCC
Another Threat to Fasteners
HASCC = Hydrogen-Assisted Stress
Corrosion Cracking.
HASCC has only been identified as a
fastener failure mechanism within the
past few decades.
“Best Industry Practices” now require
consideration of HASCC when specifying
fasteners.

11. PART TWO
VISIBLE CORROSION
Rust and Galvanic Action
Before considering HASCC, let’s review
some basics of ordinary fastener corrosion:
Oxidation (Rusting)
Galvanic Corrosion

12. Must it Rust?
Most architectural fasteners are made from grades or alloys of steel that will
react with oxygen to create ferrous oxide, commonly know as rust. Rust is a
type of corrosion that weakens and deteriorates steel. Rusting is
accelerated when steel is also exposed to moisture, especially if the
moisture contains chlorides (salts), a condition that is common in marine,
industrial, and urban atmospheres.
When designing steel-to-steel connections,
both the fasteners and the items being
joined must be protected against rusting.
Steel building panels, for example, can be
protected by using zinc galvanizing and a
high-performance coating.
As a general guideline, fasteners should
have greater corrosion resistance than Once rust starts, it can
items being joined so that fasteners do not spread rapidly to adjacent
become weakest link in connection. exposed steel surfaces.

13. Corrosion-Resistant Plating
How they work:
1. Barrier against air and moisture.
2. Sacrificial, galvanic protection.
Available Types:
Hot-dipped galvanizing: Thick zinc clogs
threads.
Plating is not Electroplated Zinc: Insufficient protection for
acceptable protection exterior or high performance fasteners.
for high performance
fasteners. Cadmium and Hexavalent Chromates:
Greater protection, but environmental
concerns.
Plating is contraindicated for case-
hardened fasteners.

14. Corrosion-Resistant Coatings
Better protection for high-
performance fasteners.
Base Coat: Baked-on, zinc-
rich, cross-linked polymer.
Top-Coat: Baked-on,
aluminum-rich, cross-linked
polymer. Pigments optional.
Colors provide product Eco-friendly: Minimize or
identification and
aesthetics. eliminate heavy metals.
Lubricate threads: Eases
installations

15. Corrosion-Resistant Stainless Steel
300-series stainless steel provides greater corrosion
resistance.
Use for critical structural connections, exposed
exteriors, and in locations with corrosive environments.
Can require coating for protection against galvanic
corrosion of materials they are attaching.

16. Galvanic Corrosion
Occurs when dissimilar metals are in presence of an
electrolyte (an electrically conductive medium) and form a
galvanic cell.
Like an electric battery, except two pieces of metal form a
circuit. H+
H+ H+
(electrolyte)

17. Galvanic Series
Metals conduct electricity because they have a tendency to give
up electrons easily. Some metals give up electrons more easily
than others. They can be listed in order of their potential to yield
electrons, in a table known as a Galvanic Series.
Cathode (Least Active)
More “noble” Gold
(protected and Silver
less corroded) Aluminum is more active
Stainless Steel
Bronze
(anodic) than steel or
Copper stainless steel. Where
Brass aluminum and steel form a
Nickel galvanic cell, aluminum
Lead
will corrode, sacrificing
Steel & Iron
Less “noble”
Aluminum
electrons that will deposit
(sacrificial
and more Zinc onto and protect the steel.
corroded) Magnesium
Anode (Most Active)

18. Galvanic Corrosion
This aluminum plate received two screws made from 300-series stainless steel,
a grade that is highly resistant to oxidation and rusting. It was then exposed to
1000 hours of salt-water spray that acted as an electrolyte to form a galvanic
cell between the aluminum plate and stainless steel fasteners. The screws
were them removed to allow examination of the plate.
Stainless Steel Stainless Steel Screw
Screw: The With Anti-Corrosion
aluminum sacrificed Coating: The coating
electrons to the prevent formation of a
steel. The surface galvanic cell and
of the aluminum is prevented corrosion of
visibly deteriorated. the aluminum plate.
Using ordinary steel fasteners in architectural aluminum elements (such as
windows, curtain walls, or wall cladding) can also create galvanic corrosion of the
aluminum, weakening the connection until it fails at well below design loads.
Avoid this problem by specifying fasteners with high-quality anti-corrosive
coatings.

19. Galvanic Corrosion
Dissimilar metal combinations are
common in construction. For example:
Aluminum framed glazing units and
cladding get attached to structural steel
framing using steel, self-drilling, self-
tapping screws.
Aluminum parts are often attached to
concrete or masonry with self-tapping
screws made of steel.
Even steel-to-steel connections can
involve dissimilar metals, if either of the
steel parts, or the fasteners joining
them, has been coated with zinc.
Thin veneers can be
attached with self-drilling
fasteners in the support
structure.

20. Galvanic Corrosion
It is difficult to prevent electrolytes from contact with fasteners.
Moisture can enter construction due to:
Rain or dew during Construction
Condensation inside a wall or roof
Leaks in building envelope
Water from building maintenance or operations
Plumbing failures
Flooding and spills
Perspiration from workers who installed the part
Air pollutants can make atmospheric moisture more conductive
If dissimilar metals are in contact, assume that an
electrolyte will also be in contact with the fasteners.
Specifying fasteners with adequate corrosion resistance protects
against catastrophic failure, loss of use, injury, death, and liability.

21. PART THREE
HASCC
“The Invisible Corrosion”
A secondary effect of the galvanic reaction can
also lead to fastener failures. Hydrogen, a by-
product of galvanic corrosion, can weaken
standard, hardened fasteners and cause them to
fail. It produces a type of corrosion that is not
readily apparent…until it is too late.

22. Construction Scene Investigation
20 years after installation, self-drilling screws began
snapping for no apparent reason.
Screws complied with code requirements and industry
standards.
They had been exposed to weather due to roof damage,
but were not visibly corroded.
Scanning electron micrographs
revealed fractured fastener
surfaces and separated grain
boundaries in steel.
Screws had also lost ductility.
The Verdict: HASCC

23. Hydrogen & Embrittlement
HASCC starts with hydrogen.
Hydrogen embrittlement is associated
with galvanic action. However, steel
fasteners are not necessarily weakened
by galvanic corrosion itself. Rather,
hydrogen generated by galvanic
action attacks the steel.
Even if steel is protected from galvanic
corrosion, hydrogen can attack it rapidly.
Screws attacked by
hydrogen lose ductility Specialized fasteners have been
and become embrittled developed to avoid this risk.
They typically show no
visible corrosion.

24. Source of Hydrogen
Galvanic action creates electrical current.
Water in electrolyte separates into oxygen
and hydrogen.
Oxygen bonds with anode and oxidizes
metal. Since oxides have little structural
strength, anode weakens and corrodes.
Hydrogen is attracted to cathode and
penetrates into metal.
Process is similar to laboratory procedure for separating
water into hydrogen and oxygen by passing electrical current
through it, a process called electrolysis.

25. Hydrogen Diffuses into Steel
Hydrogen, the smallest atom,
penetrates voids in steel’s crystal
structure.
Hydrogen atoms are unstable and
bond with other hydrogen atoms.
The larger H2 molecules put
pressure on the surrounding
steel structure.
Internal tension in steel enlarges
grain boundaries and reduces
ductility. Scanning electron
microscope image of steel
Steel can no longer bear design
shows enlarged grain
load, and the fastener can fail.
boundaries indicative of
hydrogen embrittlement.

26. The Role of Case Hardening
Hydrogen has little effect on
Case
Rockwell
“mild” (soft) steel.
Hardness Many building fasteners are
HRC 52 min. case hardened,
In case hardening, low-
carbon steel is heated in a
high-carbon environment to
Core infuse extra carbon into
Rockwell
Hardness
metal’s surface.
HRC 32-40 This hardens “case,” but
makes it brittle.
HASCC affects steel of Rockwell
hardness ≥ HRC 35. The harder the
Case hardened self-drilling
steel, the more susceptible is it to and self-tapping screws
HASCC. are hard enough to cut into
structural steel or concrete.

27. Hydrogen Embrittlement & Stress
In case-hardened fasteners, the hard outer layer is most
vulnerable to HASCC.
Cross-section of failed
case-hardened fastener:
• HASCC Failure Mode
• Strength loss due to
Ductile and Embrittlement
Mode
• Ductile failure due to
reduced cross-section
of fastener.

28. Stress Concentration
Stress increases steel’s susceptibility to embrittlement.
Stress concentration occurs at screw heads for 3 reasons:
1. MANUFACTURE
Deformations
required to form
steel rod into screw
heads induces
stress into metal.

29. Stress Concentration
2. CLAMPING FORCES
When screws are tightened, their
heads bear on the surface of the
object being attached.
This places the area of the shank
immediately under the head into
tension, inducing stress.

30. Stress Concentration
3. OUT OF ALIGNMENT
Screws are rarely perfectly
perpendicular to surfaces
they are attaching.
When tightened, uneven
pressure is put on head by
oblique angle at which it is
A test for resistance to hydrogen
installed. embrittlement closely mimics this real-world
situation. The fastener is screwed through
This puts additional stress on two plates of dissimilar metals. A shim is
placed under one edge of the top plate,
one side of fastener at creating an angle between the two plates and
placing the screw at an oblique angle with
juncture of head and shank. respect to one of them.

31. Stress Cracking
Galvanically generated
hydrogen at stress points
leads to microscopic
cracking.
Micro-cracks further
concentrates stress points.
Once propagated, cracks
can spread quickly through
hardened steel.
Metallurgists call this
cracking “Hydrogen Assisted
Stress Corrosion Cracking”
(HASCC).

32. Plating and Hydrogen Embrittlement
Case hardened fasteners must still be protected against rust
and galvanic corrosion.
Standard plating of case hardened fasteners generates
hydrogen that could contribute to “Hydrogen Embrittlement”.
This is unlikely, because platers bake hydrogen out of
fasteners @ 400+ for several hours after treatment.
But you cannot bake-out Hydrogen from continuous Galvanic
reactions on the job.
In low stress, completely dry areas, zinc or other plated, case
hardened fasteners, may work well, or, if exposed to moisture
it can pose a risk for delayed failures.
Case hardened fasteners can be protected with high-
performance anti-corrosion coating. But it does not stop
hydrogen diffusion into hardened steel.
However, new innovations – described in next section – will.

33. HASCC Recap
Galvanic action between dissimilar metals generates
hydrogen.
Hydrogen penetrates hardened steel and creates internal
stresses that weaken fasteners.
This process occurs primarily in high hardness/case
hardened parts.
Stress concentrations initiate micro-cracking that can
propagate across fastener.
HASCC can occur days, months or years after fastener
installation if connection is exposed to moisture.
Failure is often sudden and without warning. No rust is
seen.

34. PART FOUR
HASCC SOLUTIONS
For Self-Drilling Screws

35. Benefits of Self Drilling Screws
Self-drilling screws require just seconds of
installation time and labor VS that required for
nuts-and-bolts, rivets, and other fasteners requiring
pre-drilled holes.
Fasteners install in single, fast operation using a
power driver.
They are much faster than two-handed bolt-and-nut
Dril-Flex.exe
installations, and more practical where the back
side is not accessible for installing a nut.
With hundreds of thousands of fasteners used in
large buildings, this represents an enormous
savings in labor.
Use to install windows, cladding, curtain wall,
framing, anchors, equipment, fixtures, and other
building components.

36. Design of Self Drilling Screws
Select head style for
easy installation,
Tip drills pilot hole. acceptable profile,
and pull-over
resistance
Lead threads tap
threads into Select
thread style
substrate, so to hold in
substrate
substrate acts as nut.
Lead threads cut
Available in threads into (tap)
substrate for pull-out
configurations to suit resistance
a wide range of Tip drills hole and
removes shavings
construction
applications.

37. The Remedy for HASCC
Self-drilling fasteners have to be case hardened in
order to drill and tap substrates – but case
hardening makes them vulnerable to failure.
Fortunately, there is a solution to fastener HASCC
hazards.

38. HASCC-Resistant Fasteners
Vir
tua
to lly Im
HA m
SC un
C e

39. A Metallurgical Marvel
There are two ways to achieve this performance:
• Selectively Hardened Fasteners
• Bi-Metal Fasteners
Hardened for Ductile for structural
drilling and performance and
tapping HASCC-resistance.

40. 1. Selectively Hardened Fasteners
Made from special, high-
carbon steel, they do not
have to be placed in a high-
DUCTILE WHERE
NEEDED
carbon environment during
Grade 5 heat treat heat treatment.
in load-bearing
area of fastener Tip of screw is passed
through electrical induction
HARDENED WHERE coil that heats and hardens
NEEDED
Selectively hardened drill-point and lead-threads
point and tapping without affecting rest of
threads HRC 52
shank.

41. 2. Bi-Metal Fasteners
Use where stainless steel is required
for increased resistance to
corrosive environments.
A high-carbon steel tip is fused
onto stainless shank. 300 Series
Stainless
High carbon tip is then selectively Steel Head
hardened using induction-coil heating. and
Shank
High-Carbon
Steel Tip,
Selectively
Hardened
Recommended
for exposed
fasteners.

42. Corrosion-Resistant Coatings
Use corrosion-resistant coatings on both selectively
hardened and bi-metal fasteners.
Coating provides galvanic protection and lubricates
threads.
Coating can be color matched as required.
Bi-Metal Fastener: Before coating, above. After coating, below.

43. PROOF
Self-drilling fasteners joining steel and aluminum plates, exposed
to salt-spray test.
Conventional fasteners fail due to stress concentration at screw
heads that accelerates embrittlement and HASCC.
Neither selectively-hardened nor bi-metal fasteners fail.
HASCC-
resistant
fasteners
are not
affected
Standard
case-hardened
fasteners failed

44. PROOF

45. PROOF
HASCC-resistant
screws were used to
secure crown at top of
building and building
envelope.
Exposed to marine and
urban atmosphere,
high winds, and
earthquakes.
Over two decades of
service.
US Bank Building/
Zero failures. Los Angeles, CA
Pei Cobb Freed Partners

46. Best Industry Practices
Where dissimilar metals will be
in contact, specify: selectively-
hardened self-drilling
fasteners to resist HASCC.
Where stainless steel is required
for protection against visible
corrosion or extreme
environments, specify: bi-metal
self-drilling fasteners with a
selectively-hardened tip to
resist HASCC.

47. HASCC Recap
• Galvanic action in dissimilar metals generates hydrogen.
• Hydrogen penetrates case hardened steel and creates
internal stresses that weaken fasteners.
• Stress concentrations initiate micro-cracking that
propagate across fastener and lead to failure.
• HASCC can occur days, months or years after fastener
installation if connection is exposed to moisture.
• Failure is often sudden and without warning.
• Failures can be avoided by using selectively-hardened or
bi-metal self-drilling screws with corrosion-resistant
coating.

48. PART FIVE
SPECIAL FASTENERS

49. Extreme Loads
Structure is subjected to brief loads far higher than
normal operating loads.
Risks include:
• Hurricane, tornado, and windblown missile impact
• Earthquake, tsunami, landslide, avalanche
• Industrial accidents and vehicular collisions
• Load redistribution due to failure of building elements
• Explosion, including boiler, natural gas leaks, attack
Located near possible targets
If there is reason to suspect a risk, design for it.
Determination Estimate Risk-Resistant
of Risk of Risk Loads Design

50. Extreme Loading of Fasteners
If a structure is designed to
withstand extreme load, load is
transferred to fasteners that
connect it to other building
QuickTime™ and a
decompressor
are needed to see this picture.
elements.
Ductile fasteners can deform to
absorb some load while
maintaining connection.
If fasteners are brittle, extreme Extreme loads can
loading may cause them to fail. affect all building
components, not just
Using ductile, HASCC-resistant
structural members.
fasteners helps assure full design
strength of fasteners can be used
to resist extreme loads.

51. Where to Specify
Blast-resistant windows
Curtain wall framing
Building equipment
Critical life safety and
communications
equipment
To assure continuous
service of essential
facilities

52. Concrete and Masonry Screws
Choice of
head styles Specifying concrete
and masonry Choice of
head
anchors also styles
requires
Grade 5
hardness for
consideration of
strength and
ductility
dissimilar metals
and corrosion
resistance. Hi-lo
thread
A variety of special taps into
masonry
Higher designs are
hardness for
tapping available to satisfy
threads
most construction
requirements.
Concrete Masonry

53. Pressure-Relief Fasteners
In buildings with potential for
interior explosions, special panels
can be designed to blow off and
relieve pressure, a built in safety
valve.
Examples include places where
highly volatile liquids are in use, or
storage for extremely fine dry,
materials subject to dust-explosion.

54. Pressure-Relief Fasteners
panel
Panels have an holes larger separates
from framing
than fastener heads. panel
member
centering
A special aluminum washer device
retains the panel in position. framing
Under explosive pressure,
washers fail and allow aluminum
washer
panels to blow off, venting pressure-
relieving
collapses
the pressure. washer
Normal Explosion
Panel is tethered to keep it
from becoming a dangerous
missile.

55. Threaded Rod Anchors
1/4-20 & 3/8-16
Threaded rods are used to support fire-sprinklers and other essential building
services. These fasteners simplify installation while protecting against potential
failures of other fastening methods that are not positively engaged in the
structural materials.

56. Sealing Washers
Special head design plus high performance washer
material help prevent leaks through building envelope.

57. SUMMARY
Manage Your Risk
Fasteners are critical components
of buildings.
A/Es must be aware of their
professional responsibility to
specify fasteners that fulfill design
intent and provide safe and
durable connections.

58. Economy
The lowest cost fastener may not be the
most economical when labor and service life
are considered.
Specialty fasteners can often save money
by providing lower installed cost.
Fasteners are typically less than .0025%
per dollar of project cost, but specifying
inadequate fasteners can cause up to 100%
of construction defect costs.

59. Sustainability
Most metal fasteners have recycled-
material content and are recyclable.
New corrosion-resistant finishes
eliminate toxic heavy metals plating.
Durability over life of structure is the
most important measure of sustainability.

60. Fasteners are critical building components
A/Es have professional responsibility to
specify fasteners that fulfill design intent and
provide safe and durable connections.
It is not safe to assume that contractors will
be aware of these issues and will select
anything other than standard fasteners.
Specify accordingly.

61. For More Information
Elco Construction Products
Dril-Flex® and Bi-Flex™
HASCC-Resistant Fasteners
www.elcoconstruction.com
Gregg Melvin
(815) 979-3249
gmelvin@infastech.com
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