Fasteners - hdgasa

Contribution from South America
Bob’s BANTER:
What readers have
to say...
Hello Bob,
I wrote to you last year re using
your “Cleaner Fish” article in the
GALVANIZING magazine. I have
spoken to Terry Smith, the editor.
He is delighted to hear we read
his magazine! He said I may send
it on to others. Obviously with
your email details.
Coincidentally our sons were
friends at school and still
maintain contact.
Please send me a copy.
Thanks a lot.
George Savage
Picasso Digital Graphics
Hi Bob
After 15 years’ of retirement I find
that the pure scientific articles are
getting less interesting, or is it
understandable. Your Bob’s Banter,
with its often philosophic slant, is
however always great reading. I
especially enjoyed your latest one
based on Darwin’s evolution
theory. Thanks. Best wishes for a
lovely 2012 and many more to
come.
Regards
Wim Skinner
Hi Bob,
Just read your article “Bob’s
Banter” in HD Galvanizing Today
no. 47 – what an inspirational way
to start my day.
Hope to see more of your
writings in the magazine in the
future.
tx
Conrad Hubbe
for STATIC Structural Engineers
cc (In association with Geni
Consulting Engineers cc)
Motivation and methodology
of hot dip galvanizing steel
railway sleepers for Vale Do
Rio Doce, Brazil
Introduction
Due to thermodynamic laws, steel
when left unprotected will in time
return to its natural state of iron ore.
This means that insufficient corrosion
protection, will result in premature
corrosion, ultimately reducing the
mechanical properties and strength of
the steel.
Table 1 shows the corrosion rates of
steel and zinc for five environments or
corrosivity categories outlined in the
Brazilian standard ABNT NBR 14643
(For ease of reproducibility Table 5, which is
similar, taken from ISO 9223, was used
below).
If we compare the maximum corrosion
rates on the environment "C5"
(exterior: industrial with high humidity
or high coastal salinity), which is the
environ-ment of Port of Vale in
Victoria, the corrosion rate of steel is
twenty times higher than the rate of
zinc, therefore, 200 microns of steel
per year compared to 8.4 microns of
zinc per year.
This corrosion rate of steel can be
catastrophic and can lead to untold
costs.
Hot dip galvanizing is an effective way
to protect steel from corrosion. As
seen in Table 1, zinc has a lower
corrosion rate than steel in any
environment. The corrosion rates
defined in the standard, allows it to
extrapolate the life of the metallic
coating, an effect that cannot be
replicated by other conventional
methods of protection.
The corrosion protection criteria of hot
dip galvanizing and therefore its
service life is based on three pillars:
Galvanic Protection, Atomic Diffusion,
Full Coverage.
In addition to these three pillars, hot
dip galvanizing also provides excellent
adhesion of the coating (metallurgical
bond), a differentiated hardness (of
iron/zinc alloy layers) that helps to
resist impact caused by normal
handling, transportation and
installation. Both these properties
continued on page 28...
1 2 3 4
Corrosion Description of environment Corrosion rate Corrosion rate
category (ave. loss of (ave. loss of
steel in µm/yr.) steel in µm/yr.)
C1 Interior: dry ≤1.3 ≤0.1
Interior: occasional condensation
C2 Exterior: exposed rural inland >1.3 to 25 0.1 to 0.7
Interior: high humidity, some air pollution
C3 Exterior: urban inland or mild coastal >25 to 50 0.7 to 2.1
Interior: swimming pools, chemical plant etc.
C4 Exterior: industrial inland or urban coastal >50 to 80 2.1 to 4.2
C5-I or
C5-M
Exterior: industrial with high humidity or high
salinity coastal
>80 to 200 4.2 to 8.4
Table 1: Standard ABNT NBR 14643 (Similar to the table above extracted from Table 5 in ISO
9223, (Corrosivity of steel and zinc).
Volume 9 Issue 1 2012 Hot Dip Galvanizing Today 27