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Transcript of HOT DIP GALVANIZING AND - AMEU Hope/11-1 HDG for Life A… · •Different Types of hot dip...
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HOT DIP GALVANIZING AND DUPLEX COATING SYSTEMS…
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• Different Types of hot dip galvanizing
•The general galvanizing process & Standard
•What determines ctg thickness & appearance
• Durability of HDG in the environment
• When selecting “galvanizing” specify correctly!
• Some strengths & characteristics of HDG.
• Repairs to HDG.
• Duplex coating systems.
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Ductile - smooth - attractive appearance
Coating thickness 20 microns (Z275)
Fe/Zn alloys virtually absent
SPECIFICATION - SANS 4998/3575
Ductile - smooth - attractive appearance
Coating thickness 30 microns (SANS 675)
Fe/Zn alloys < 10% of coating thickness
SPECIFICATION - SANS 675/10244/935
Ductility diminished
Coating thickness > 85 microns
Greater corrosion resistance
SPECIFICATIONS – SANS 121 (ISO 1461) /
SANS 32 (EN 10240)
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ZINC BATH
COOLING
AND
INSPECTION
CENTRIFUGING
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NOT CONTROLLED BY
GALVANIZER (BIG
EFFECT)
Steel composition (Si & P)
Steel thickness
Surface roughness
CONTROLLED BY GALVANIZER (SMALL EFFECT)
Zinc temperature
Immersion time
Withdrawal rate
Angle of exit
Efficiency of centrifuge
COATING THICKNESS
IS RELATIVELY SELF
CONTROLLING
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CA
ST
ING
SMINIMUM COATING THICKNESS ON ARTICLES THAT
ARE NOT CENTRIFUGED
SANS 121 (ISO 1461)
Category and
thickness (t)
SABS 763 (OLD)
Local
coating
thickness
µm
Mean
coating
thickness
µm
Article type
Thickness,
µm General
Application
t˃6 70 85A1,B1,D1,
E1,F185
3˃t≤6 55 70 A2,B2,F2 65
PR
OFI
LES
1.5≥t≤3 45
45
55
t1.5 35 A3, B3, F3 45, 55, 45
t6 70 80 D1 85
t6 60 70
• Coating thickness on structural
steel achieved varies from the
minimum upwards of 100%
greater.
• Life expectation predictions are
based on the minimum coating
thickness and are therefore
generally quite conservative.
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Class Description
Corrosion
rate (av. loss
for steel
µm/y)
Corrosion
rate (av.
loss for Zn
µm/y)
* Typical life
in yrs to first
maintenance )
(Z275)
** Typical life
in yrs to first
maintenance
(70µm HDG)
C1 Interior: dry ≤ 1.3 ≤ 0.1 >50 >50
C2
Interior: occasional
condensation
Exterior: exposed rural
inland
> 1.3 to 25 0.1 to 0.5 >50 >50
C3
Interior: high humidity,
some air pollution
Exterior: urban inland or
mild coastal
> 25 to 50 0.5 to 2 10 to 40 35 to >50
C4
Interior: swimming pools,
chemical plant, etc.
Exterior: industrial inland
or urban coastal
2 to 4 5 to 10 18 to 35
C5Exterior: industrial with
high humidity or high
salinity coastal
>80 to 200 4 to 8 3 to 5 9 to 18
>50 to 80
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• Nickel
• Zinc
• Carbon Steel, rolled
Ele
ctr
op
os
itiv
e
Mo
re c
ath
od
ic m
eta
ls
Ele
ctr
on
eg
ati
ve
Mo
re a
no
dic
me
tals
• Steel, low-alloyed
• Brass
• Cast Iron, unalloyed
• Cadmium
• Aluminium
• Magnesium
• Gold
• Silver
• Stainless Steel (18/8)
• Aluminium Bronze
• Copper
• Graphite
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• Milnerton Chevron
Refinery (25+25yrs)
• Waterfront (15+15)
• Newlnds Rugby Grds –
Railway Stand (32+?).
• Capricrn Prk (Muizbrg)
•(3 & 25yrs)
Somrset Wst belw Sir LP
Truscon twrs (40yrs +?)
• Mitchells Plain TI (Lite
poles 19 to 32 yrs)
• Baden Powell Drive (10
to 12 yrs)
SPECIFIC CASE HISTORIES
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SANS 3575/4998 (Z275)
SANS 121
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Surface preparation determines coating
success. An “honest coating”
Adhesion - metallurgically bonded
Process is self controlling - law of
metallurgy determines coating thickness
Complete internal & external protection
Coating solidifies immediately on
withdrawal, quicker delivery.
Ease of inspection
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60 to 80µm
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• Zinc thermal spraying
• Zinc rich paint or epoxy• SANS 121 – Individual 10cm²
• SANS 121 – Total 0,5%
• Coating thickness or DFT 100µm
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Use only as a mist coat over
appropriate repair material for
immediate aesthetical appeal.
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Duplex provides a synergistic performance,
i.e.
• Duplex life = X (zinc life + paint life)
• Aggressive Marine X = 1,5
• 1,5 (10 years + 5 years) = 23 years
• Mild rural X = 2,7
• 2,7 (30 years + 15 years) = 120 years
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Zinc has in the past been associated with lead as a heavy metal and therefore bad for the environment? The true facts:
– Zinc is not a heavy metal!
– There are 300 enzymes in ones body that that require zinc to function properly
– 48% of the worlds population are zinc deficient
– Zinc is used in ointments for combating sun burn, nappy rash, ADHD, etc.
– Used in time the throat lozenge can prevent a cold
– It is the aphrodisiac mineral, eat oysters!
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