ATEG - Hot Dip Galvanizing fundamentals (steel industry)

Hot Dip Galvanizing fundamentals

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Hot-Dip Galvanizing fundamentals:
an approach
ATEG

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ATEG
–The Spanish Galvanizing Technical Association (ATEG) is a non-profit
industrial association dedicated to serving the needs of after-
fabrication galvanizers, fabricators, architects, specifiers and
engineers
–The ATEG provides technical support on today's innovative
applications and state-of-the-art technological developments in hot-
dip galvanizing for corrosion control

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THE CORROSION PROBLEM
Bridge in Denver (USA)

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THE CORROSION PROBLEM
Corroded Trolley

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THE CORROSION PROBLEM
Blistering, peeling and rusting

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Corroded Pier
THE CORROSION PROBLEM

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Williamsburg Bridge - New York City (USA)
THE CORROSION PROBLEM

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CORROSION COSTS
•NACE, CC Technologies, & FHWA jointly produced a report in
2001 detailing the costs of corrosion: $297 billion USD annually.
3.1% of US GDP (1998)
•In Spain, updated estimations from the painting industry place
this number in 2,2% of Spanish GDP (circa 20.000 MEUR)

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The Solution: The Solution:
Hot-Dip GalvanizingHot-Dip Galvanizing

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Weathered Guardrail
BARRIER PROTECTION

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ZINC - Anode
STEEL - Cathode
This arrangement of metals
determines what metal will
be the anode and cathode
when the two are put in a
electrolytic cell
(arrangement dependent on
salt water as electrolyte).
CATHODIC PROTECTION: GALVANIC SERIES

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With a cathodically protective coating, such as galvanized
steel, damaged areas will be protected by the surrounding
zinc
Zinc Coating
Bare Steel
Exposed Steel
is Protected
CATHODIC PROTECTION

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Steel is dipped in a series of tanks including solutions that
remove impurities from the steel surface. The galvanizing
reaction only occurs on perfectly clean steel.
The steel is inspected after galvanizing to ensure
conformance to the appropriate specifications.
HDG PROCESS

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Barrier
Cathodic
Zinc Patina
(corrosion
byproducts)
Zinc Patina Cathodic
Barrier
Long-lasting
Protection
LONG-LASTING ZINC PROTECTION

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Zinc-iron metallurgical bond
only occurs on clean steel
Degreasing
•Removes dirt, oils, organic
residue
Pickling
•Removes mill scale and oxides
Fluxing
•Mild cleaning, provides
protective layer
Caustic cleaning
HDG PROCESS: SURFACE PREP

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Steel articles are immersed
in a bath of molten zinc (≈
450
0
C)
> 98,5% pure zinc, minor
elements added for coating
properties (Al, Bi, Ni)
Zinc reacts with iron in the
steel to form galvanized
coating.
Zinc bath removal
HDG PROCESS: GALVANIZING

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Steel articles are inspected
after galvanizing to verify
conformance to appropriate
specs.
Surface defects easily identified
through visual inspection.
Coating thickness verified
through magnetic thickness
gauge readings.
HDG PROCESS: INSPECTION

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Hot-Dip Galvanized Hot-Dip Galvanized
Coating PropertiesCoating Properties

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METALLURGICAL BOND

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Micrograph of galvanized edge
Same thickness at corner
EDGE PROTECTION

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Complete Coverage
ADDITIONAL BENEFITS OF HDG

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Variety of sizes
and shapes
ADDITIONAL BENEFITS OF HDG

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Zinc is 100% recyclable as is the steel
•Properties of zinc do not degrade w/
reprocessing
•Zinc is a natural element in the Earth’s crust
The longevity of galvanizing means no
additional energy exerted or waste created
maintaining galvanized structures
HDG IS GREEN

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ESTIMATED SERVICE LIFE OF HDG

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Hot-Dip Galvanized Hot-Dip Galvanized
Coating PropertiesCoating Properties

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Shop or in-field application
Suitable for very large pieces
Coating Properties:
•Thick coating
•Mechanical bond
•Less dense than HDG zinc layers
•No interior coverage
Metallizing Appliation
METALLIZING

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Metallic zinc dust
•Inorganic
•Organic
Barrier protection
Cathodic protection
•Limited
•Dependent on % Zn
Use salt spray data to make
performance claims
Zinc Rich Paint Application
ZINC RICH PAINT

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Produced by a continuous in-
line hot-dip process
•Coil-to-coil process
•400-500 FPM
•“Air knives” remove excess zinc
•Pure zinc with little alloy layer
•Galvannealed (Zn-Fe)
•Galvalume (55% Al)
Sheet Steel of Continuous
CONTINUOUS GALVANIZING

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Strip, sheet, or small parts
•Smooth finish
•Slightly more expensive than
sheet galvanized
Good formability
Paintable
Electroplating Application
ELECTROPLATING

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Similar to electroplating
•used for fasteners and small
parts
Parts are tumbled in drum
with zinc powder and glass
beads
•mechanically bonded zinc
Mechanical Plating Application
ZINC (MECHANICAL) PLATING

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Metallizing
Hot-Dip Galvanized
Zinc-Rich Paint
Sheet Galvanized
Electroplated
COMPARISON AMONGST ZINC COATINGS

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Hot-Dip Galvanized Hot-Dip Galvanized
Coating PropertiesCoating Properties

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MATERIALS SUITABLE FOR HOT-DIP GALVANIZING

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Hot-dip galvanized fasteners are
recommended for joining HDG
structurals
HOT-DIP GALVANIZED FASTENERS

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STEEL REACTIVITY

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TOUGHNESS & ABRASION RESISTANCE
Hardness, HV values
50100150200250
Zn
Zn + Fe
Fe
Microsection of hot dip galvanized coating showing variations in
hardness through the coating. The zinc-iron alloys are harder than the
base steel

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Newly
Galvanized
Newly
Galvanized
Newly
Galvanized
Newly
Installed
No Spangle
Highly Spangle
Dull Coating
Shiny & Dull
Coating
COATING APPEARANCE

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COMBINING DIFFERENT MATERIALS

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Photo taken: 12/18/02
Photo taken: 03/28/03
WEATHERING OF GALVANIZED STEEL

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Different thickness
•Zinc bath temperature at
different times
Similar thickness
•Maintain original shape
DISSIMILAR THICKNESSES

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Progressive Dipping
GALVANIZING OVERSIZED PIECES

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MATERIAL HANDLING

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Drain
Vent
VENTING & DRAINAGE

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Specifications & InspectionSpecifications & Inspection

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Galvanized Products
•EN ISO 1461– General
•EN ISO 10684 – Fasteners
Supporting Specifications
•EN ISO 14713 – Zinc coatings, guidelines,
general principles of design and corrosion
resistance.
•EN ISO 12944, EN 13438 – Duplex systems
(painting over galvanising)
ISO STANDARDS FOR GALVANIZING

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Standard Specification
for Zinc (Hot-Dip
Galvanized) Coatings
on Iron and Steel
Products
•Coating Thickness – material category and steel
thickness
•Finish – continuous, smooth, uniform
•Adherence – should be tightly adherent. No tests
needed.
EN ISO 1461

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Standard Specification
for Zinc Coating (Hot-
Dip) on Iron and Steel
Hardware
•Coating Thickness – material category, steel
thickness (max. and min.), metric.
•Finish – continuous, smooth, uniform
•Adherence – should be tightly adherent through
all expected uses of article
EN ISO 10684

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Costs Less & Lasts LongerCosts Less & Lasts Longer
Hot-Dip GalvanizingHot-Dip Galvanizing

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Initial cost vs. Life-cycle
cost
QUANTITATIVE ANALYSIS

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Material
Shop cleaning labor
Shop application
Field labor
Pneumatic Bulk Trailers
INITIAL COST

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Coating System
$/ft
2
Inorganic Zinc $1.31
Inorganic Zinc/Epoxy $2.09
Hot-Dip Galvanizing $1.92
Acrylic WB Primer/Acrylic WB Intermediate/Acrylic WB
Topcoat
$2.51
Inorganic Zinc Primer/
H-B Epoxy/Acrylic Urethane
$3.07
INITIAL COST ($/FT2)

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Maintenance on a ‘practical’ (vs. ideal) cycle - unique to each
paint system, as recommended by paint manufacturers
NACE Model for NFV and NPV calculations
•4% inflation
•7% interest
Maintenance repaint at 5% rust in a moderately industrial
environment
30-Year Project Performance
LIFE CYCLE COST

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Coating System $/ft
2
Hot-Dip Galvanizing $1.92
Inorganic Zinc $3.21
Inorganic Zinc/Epoxy $4.83
Inorganic Zinc Primer/
H-B Epoxy/Acrylic Urethane
$6.43
Acrylic WB Primer/Acrylic WB Intermediate/Acrylic
WB Topcoat
$7.98
LIFE-CYCLE COST ($/FT2): 50-YEAR PROJECT PERFORMANCE

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Coating System Cost
Hot-Dip Galvanizing $19,200
Inorganic Zinc $32,099
Inorganic Zinc/Epoxy $48,261
Inorganic Zinc Primer/
H-B Epoxy/Acrylic Urethane
$64,302
Acrylic WB Primer/Acrylic WB
Intermediate/Acrylic WB Topcoat
$79,802
LIFE-CYCLE COST ($/FT2): 50-YEAR PROJECT PERFORMANCE

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Duplex Systems:Duplex Systems:
Painting & Powder Coating Painting & Powder Coating
Hot-Dip Galvanized SteelHot-Dip Galvanized Steel

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Aesthetics
•Architects decision
Identification
Hostile Environment to Zinc
Repair of Existing
Galvanized Articles
•Extended Life of the Product
Light Rail Station
WHY PAINT A PERFECTLY GOOD GALVANIZED PART?

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Newly Galvanized Steel
Partially Weathered
Galvanized Steel
Fully Weathered
Galvanized Steel
Painted Bridge Rail
GALVANIZED SURFACE COATING CONDITION

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1
2
3
Time
0 – 48 hrs.
48 hrs. – 6 mo.
6 mo. – 2 yrs.
PASSIVATION CYCLE

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SWEEP BLASTING

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Fence Pole
DUPLEX SYSTEM LAYERS

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Paint Provides Barrier for
Galvanized Surface
Galvanized Coating Provides Slow
Corrosion Under Paint
Paint Peeling due to Corrosion is
Minimized
Paint & Galvanizing together have
1.5x to 2.5x Life of Individual
Lifetimes
Skaneateles Community Center
DUPLEX SYSTEM: SYNERGISTIC EFFECT

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Galvanized Steel:Galvanized Steel:
Project ApplicationsProject Applications

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Date Galvanized
1999
Location
New York (USA)
BROOKLYN BRIDGE

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FISHERMANS’ WAREHOUSES. CANGAS (SPAIN)

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CITADELLA DEL VINO, MEZZACORONA (ITALY)

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CITADELLA DEL VINO, MEZZACORONA (ITALY)

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Galvanized Sustainable SteelGalvanized Sustainable Steel

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EGGA asked Professor Tom
Woolley to examine all aspects of
our process and the contribution
galvanizing can make to
sustainable construction
Prof. Woolley is a strong advocate
of green building and well-
respected in the ‘green
architecture’ community
SUSTAINABLE CONSTRUCTION

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Decades of
maintenance-free
life have economic,
social and
environmental
benefits
DURABILITY = SUSTAINABILITY

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In ‘Social Housing’
galvanizing means
that building owners
and tenants are not
left with a
‘maintenance-
legacy’ they cannot
afford
BENEFITS ON DURABILITY

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Galvanizing industry
has invested heavily
in minimising its
environmental
footprint
Rainwater
harvesting’ means
that no water leaves
the site and mains
water use is
negligible
ENVIRONMENTALLY CLEAN

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Established using a sample of 46 EU plants
EGGA LIFE CYCLE INVENTORY DATA

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Quantifying the environmental benefits of extensive durability
LIFE CYCLE ANALYSIS
Technical University of Berlin studied a 500 tonne steel car park in (i) Galvanized and
(ii) Painted alternatives, over a 60-year service life

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Process Energy Use Energy is required to heat the hot dip galvanizing
bath and this is usually supplied by natural gas.
Although the galvanizing industry is not considered to be amongst the
most energy-intensive sectors of industry, it has made great efforts to
manage its energy use efficiently.
The galvanizing industry has set targets for energy efficiency and
encouraged improved energy management and new technology to
achieve these targets.
Examples of these advances are:
•improved burner technology for greater energy efficiency
•more efficient bath lids (used during maintenance and/or down time)
•greater use of waste heat for heating of pre-treatment tanks
Energy

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Zinc - the lowest energy profile of the major non-ferrous metals
Energy

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Emissions within the plant are carefully controlled to avoid
disturbance or problems for the surrounding neighbourhood.
Galvanizing plants are regulated under the EU Directive on Integrated
Pollution, Prevention and Control.
The industry has cooperated in the publication of a Best Practice
Reference Note (BREF) for hot dip galvanizing.
The principal requirement of the BREF is to capture the non-
hazardous particulates during dipping.
These particulates are then filtered using either scrubbers or bag
filters.
Emission control

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Pretreatment steps in the process are mainly aimed at cleaning the
steel articles.
Process consumables, such as hydrochloric acid and flux solutions all
have important recycling and/or regeneration routes.
For example:
•spent hydrochloric acid solutions are used to produce iron chloride for
use in treating municipal waste water. Many plants remove iron and zinc
and recycle regenerated acid to the re-treatment tanks
•improved monitoring and maintenance of flux tanks means that these are
rarely discarded to waste and only small volumes of sludge require
periodic disposal. Closed-loop flux recycling is used in many plants
•ambient temperature acidic and biological degreasers have been
developed
Regeneration and recycling

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Zinc recycling is
well-established,
economically viable
and environmentally
sound
HDG steel is 100%
recyclable
100% recyclable

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Galvanizing plants use relatively low volumes of water compared to
other coating technologies.
In fact, it is very rare for a galvanizing plant to discharge waste water.
Any waste water that is generated can be treated and returned to the
process, with only low volumes of stable solids sent for external
disposal.
In some cases, it has been possible for galvanizing plants to eliminate
the use of mains water by harvesting rain water falling on the site.
Rain water can be collected through gutters and stored for later use.
Water use

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Results for 500t Steel Car Park (60 year life cycle)
LCA STUDIES

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Range of values - varying steel product types and study methodologies
RANGE OF VALUES

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Hot dip galvanizing can deliver more sustainable steel structures and
reduce life-cycle environmental burdens of steel structures when
competing with concrete and other materials
LCA CONCLUSION

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Thanks for your attention