Design for Galvanizing

V&S Galvanizing Locations

Designing for Hot-Dip Galvanizing

The AGA has met the standards and requirements of the Registered

Continuing Education Providers Program. Credit earned upon completion

of this program will be reported to RCEP at RCEP.net. A certificate of

completion will be issued to each participant. As such, it does not include

content that may be deemed or construed to be an approval

or endorsement by RCEP.

AIA/CES Policy on Endorsement -The following program is registered with

AIA/CES and does not include content that may be deemed or construed to

be an approval, sponsorship or endorsement of any material of

construction or any method or manner of handling, using, distributing or

dealing in any material or product.

The AGA is a provider of Green Building Certification Institute (GBCI)

approved courses for continuing education. This course has met GBCI

requirements and is designated an approved course.

Continuing Education

The purpose of this seminar is to educate

architects, engineers and

other specifiers about

successful specification,

design, inspection, and

coating (paint/powder)

hot-dip galvanized steel.

Purpose of the Seminar

Upon seminar completion, you will be able to:

Understand the need for communication throughout the

design process

Identify best design practices for products to be

galvanized based on ASTM specification guidelines

Conduct proper inspection and testing methods to hot-

dip galvanized steel

Recognize the importance of proper surface preparation

to the overall success of a duplex system

Learning Objectives

American Galvanizers Association

Non-profit trade association established in 1933

Dedicated to serving as a unified voice and

expertise in the after fabrication hot-dip

galvanizing industry

Provides technical support on innovative

application and technological developments in

hot-dip galvanizing for corrosion protection

Free assistance for North American specifiers

Resource for our members

Why Specify Hot-Dip Galvanizing

Corrosion Protection

Durability

Longevity

Availability/Versatility

Aesthetics

Sustainability

Environmental

Economical

Tour of Projects

Knox County Bridge Rehab

Date Galvanized

2010

Components Galvanized

structural parts, bolts,

diaphragms, floor sections

Environment

Rural

Location

Knox County, OH

Liberty Place Parking GarageDate Galvanized

2012

Components Galvanized

Castellated beams,

columns, steps, stringers,

rail risers, handrail, angles

Environment

Urban

Location

Columbus, OH

Ohio State Central Chiller PlantDate Galvanized: 2012

Components Galvanized: All

Structural Steel

Environment Urban/Campus

Location: Columbus, OH

Hot-Dip Galvanizing

Hot-Dip Galvanizing Process

Surface Preparation

Thorough cleaning is

necessary as zinc will

only adhere to clean

steel

Degreasing – removes

dirt, oils, organic residue

Pickling – removes mill

scale and oxides

Fluxing – Mild cleaning,

provides protective layer

Galvanizing

Steel immersed in bath

of molten zinc (~830 F)

>98% pure zinc, up to

2% additives (Al, Bi,

Ni)

Zinc reacts with iron in

the steel to form

coating

Reaction is complete

when steel reaches

bath temperature

Inspection

Steel is inspected after

galvanizing to verify

conformance to specs

Visual inspection to

identify any surface

defects

Magnetic thickness gauge

to check coating thickness

Downloadable Inspection

App offers a clear visual

guide to surface

conditions

galvanizeit.org/mobile

HDG Specifications

ASTM SpecificationsASTM A123 – iron and

steel products (general)

Minimum coating

thickness

Finish

Adherence

ASTM A153 – hardware

Centrifuged/spun

after galvanizing

Minimum coating

thickness

Finish & Adherence

ASTM A767 – rebar

Finish – no bare spots,

free from sharp

spikes/tears

Bend diameters

Minimum coating

thickness

Supporting SpecificationsPre-galvanizing specs

related to design

ASTM A143 –

Safeguarding against

embrittlement

ASTM A384 – Minimizing

distortion

ASTM A385 – Practices

for high-quality coatings

ASTM A1068 – Life-cycle

cost analysis of steel

corrosion protection

Post-galvanizing specs

ASTM A780 – Touch-up

and repair of galvanized

products

ASTM D6386 – Surface

preparation for painting

over galvanizing

ASTM D7803 – Surface

preparation for powder

coating over galvanizing

Other Galvanizing StandardsInternational Standards

Organization (ISO)

1461

Canadian Standards

Organization (CSA)

G164

American Association

of State Highway and

Transportation Officials

(AASHTO) M111 &

M232

Design & Fabrication

Communication is KeySteel Chemistry &

Surface Condition

Size & Shape

Process Temperature/Heat

Venting & Drainage

Welding

Threaded

Parts/Connections

Post Galvanizing

Design/Use

Design Data Detail Software

SDS/2 has incorporated

galvanizing details

Automated vent/drain

locations and sizes

Designate at set up or as

each member is designed

Checks for kettle size fit,

dissimilar materials,

vents/drains, welds

Defaults to AISC

Standards

Visit sds2.com for details

Steel Chemistry & Surface Condition

Suitable MaterialsFerrous Metals

Carbon steel

Weathering steel

Stainless steel

Fasteners

Centrifuged after to

remove excess zinc

Castings

Special

cleaning/design is

important

Steel Chemistry

Surface Conditions

Varying surface conditions lead to varied appearance

Old/New steel

Combining materials Different chemistries

Rusted/pitted steels vs. new/machined surfaces

Fabrication Methods

Process requirements/time

Size & Shape

Lane Avenue Bridge, Columbus, OH

Size & Shape

Variety of sizes/shapes

Average kettle is 40 feet

V&S 56’ long kettle

Design large structures

in modules or sub-units

Connect after

galvanizing

Progressive dipping

Oversized pieces

Material Handling

Hoists and cranes

used to move the steel

Chains, wires, racking

systems, or perforated

baskets hold the

material

Weight is also an

important factor

Process Temperature

Cold-Working

Severe cold-working

increases possibility of

strain-age embrittlement

Heat of HDG can

accelerate the affects

Keep bend radii as large

as possible

At least 3x the section

thickness

ASTM A143

Heating/Cooling Rates

Heat of process can

relieve stresses

Can lead to distortion

and warping of parts

Tips for Minimizing

Symmetrical designs

Equal or near equal

thickness in assemblies

Maximize bend radii

Continuously weld

joints

Use temporary bracing

Thin-walled items

Asymmetrical designs

Venting & Drainage

Gusset Plates

Cropped Corners

(preferred) Holes Close to

Corners

(alternatively)

Base Plates

Hollow Structures

Welding

Welding Before Galvanizing

Two items influence

the

quality/appearance of

the weld

Cleanliness

Flux and slag must be

removed by fabricator

Weld Rod Chemistry

As similar to steel

chemistry as possible

Silicon acts as catalyst

Overlapping SurfacesZinc viscosity prevents it from entering gaps less than 3/32”

Cleaning solutions penetrate smaller gaps - may weep out

Complete Seal Welding

Large overlap requires venting to prevent moisture trapping

Stitch-Welding with 3/32” gap

Threaded & Moving Parts

Threaded PartsZinc coating pick up

makes threads thickerLeads to imperfect fit

between female/male

threads

Oversizing/Overtapping

done to holes/nuts after

galvanizingZinc on male thread will

protect both components

AISC/ASTM have

guidelines

Moving Parts

Must accommodate

for zinc coating

thickness

Radial clearance of at

least 1/16” needed

Hinges – galvanized

separately and

assembled after

Adjacent edges should

be ground to give at

least 1/32” clearance

Additional Design Considerations

Masking

Treating an area of

the steel to prevent

coating growth

Threads

Areas to be welded

Studs

Not 100% effective

Add significant labor in

application and

removal

Inspection

Inspecting Galvanized Steel

Specifications have

requirements for

Coating Thickness

Adherence

Finish & Appearance

Tests are outlined for

each requirement

Magnetic gauge

Stout Knife Test

Visual – naked eye

Coating ThicknessSampling requirements are provided in the specs

At least five widely dispersed measurements per specimen

Average should not be less than one thickness grade lower than material category

Electronic gauges are easiest and most accurate

ASTM E376

AdherenceGalvanized coating is

metallurgically-bonded

to the steel at 3,600

psi

Stout knife test

Not on edges/corners

Run point of knife

along the surface

smoothly

No gouging/whittling

Coating must not flake

Finish & Appearance

Visual inspection with

naked eye

Surface imperfections

may be present

Specification details

what is acceptable

Intended use is key

Touch-up/repair

according to ASTM

A780

Finish & Appearance

Shiny

Spangled

Matte Gray

Shiny & Dull

Natural Weathering

Photo taken 12/18/02

Photo taken

03/28/03

Touch-Up & Repair

ASTM A780 identifies

acceptable forms

Zinc-based solder

Zinc-rich paint (brush

on only!)

Zinc-spray (metallizing)

Main ASTM standards

A123, A153, A767 give

restrictions on size

Proper Storage & HandlingPromote free flowing air

around parts

Stack with wood spacers

to avoid nesting

Avoid collection of

moisture

Stack at angles

Avoid stacking on the

ground where

vegetation and dew are

found

Duplex Systems

Why Coat Galvanized Steel?

Aesthetics

Branding

Architect’s preference

Identification

Safety

Hostile Environment

Repair/Extend life of

existing HDG projects

Economic benefit

Synergistic EffectPaint/Powder provides

barrier for zinc

Zinc prevents underfilm

corrosion of top

coatings

Minimizes paint peeling

Paint/Powder coating &

HDG provide 1.5x –

2.5x sum of the

systems

Extends maintenance

cycle of paint

Proper Preparation is KeySingle-Source

Responsibility

HDG goes through

passivation/weathering

cycle as patina develops

Identifying surface

condition is important

Preparation steps

based on surface

condition

ASTM D6386 – painting

ASTM D7803 – powder

Surface Condition

Painting

Newly galvanized

Partially weathered

Fully weathered

Powder Coating

Newly galvanized

Partially weathered

Free flowing air

O2

Moisture from rain (dew)

H2O

Free flowing air O2 +

CO2

Zinc Oxide ZnO

Zinc Hydroxide Zn(OH) 2

Zinc Carbonate 2ZnCO3

Preparing the SurfaceFor Paint

Clean the surface

Bumps, runs, drips

(newly and partially

weathered)

Organic compounds

(partially/fully

weathered)

Profile the surface

SSPC-SP16 Brush Blast

Paint

For Powder Coating

Clean the surface

Bumps, runs, drips

(Both)

Organic compounds

(partially weathered only)

Profile the surface (both)

Bake (both)

Powder Coat

Curing the Coating

COLORZINQ® Duplex SystemSingle Source

Responsibility

Complies with both

ASTM D6386 and

D7803

Time restraints to

begin paint

preparation

Summary

Communication amongst all parties is key

Following best design practices from the

specifications leads to best quality coatings

Inspection is simple focusing mostly on

coating appearance and thickness

Duplex systems are another area for

communication and surface preparation is

most important to success

Designing for Galvanizing

www.galvanizeit.org

AGA KnowledgeBase

galvanizeit.org/knowledgebase

AGA Project Gallery

galvanizeit.org/project-gallery

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Technical Library

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