Galvanisation En

7/29/2019 Galvanisation En

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Corrosion protectionof rolled steel sections using hot-dip galvanization

Long Carbon EuropeSections and Merchant Bars

ArchitectsClaudeVasconi&JeanPetit-ChamberofCommerceLuxembourg


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Contents

1

Foreword 3

1. Risk o corrosion and protection period 5

2. Corrosion protection methods 8

3. Hot-dip galvanizing 10

4. Characteristics o hot-dip galvanizing o steel structures 17

5. Requirements or materials 21

6. Requirements o structures suitable or hot-dip galvanizing 25

7. Requirements or the abrication o steel structures 31

8. Requirements or hot-dip galvanizing 33

9. Duplex systems 35

10. Cost eectiveness 37

Reerences 39

Technical advisory & fnishing 42

Your partners 43


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Dren Car Park, Germany

CourtesyofVollackManagementGmbH,Germany


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Foreword

When it comes to choosing materials, steel,

because o its exceptional physical and

mechanical characteristics, is the most popularamongst designers. It can be used to rapidly

build economical, durable, and sae structures.

The steel used to make hot-rolled sections,

which can themselves be indenitely recycled,

is made rom recycled scrap. It is particularly

suitable or machining and shaping. However, it

tends to react with agents in the atmosphere

to orm stable thermodynamic bonds errous

oxides and/or salts.

The ability o steel to revert to its natural or

original state is called corrosion.

In laymans terms: steel rusts!

The primary quality o steel i.e. its ability to

retain its physical and mechanical strength, or

in the case o a steel structure, its load bearing

capacity, is generally long-lasting and is only

compromised when corrosion reduces its cross

section to such a degree that saety is adversely

aected.

The service lie o a structure depends on

the rate o reaction between the steel and itsenvironment. These reactions depend on the

nature and concentration o the corrosive agents

present.

Corrosion protection o structures must

thereore be considered as intervening in this

process in order to prevent the reaction or

greatly reduce the rate.

Large numbers o steel structures, some

o them a hundred years old, which have

beneted rom the combination o a suitablecorrosion protection treatment and regular

maintenance, show impressively the potential

o steel. However, these types o structures,

requiring high maintenance costs, are no longer

acceptable today.

New requirements govern the design o the

steel structures o the twenty-rst century:

l Environmental protection policies enorced

at both the national and international level

have lead to a considerable reduction in the

amount o corrosive load in the atmosphere

over the last twenty years. This has

resulted in a noticeable drop in the average

corrosion rate o steel and zinc as well as

improved resistance o coating systems.

l The design o steel structures is substantially

improved through the eectiveness o

welding procedures and the vast range o

rolled sections available thus contributing

positively to ensure that corrosion protection

systems have long service lives. Maintenance

and renovation costs continue to all becausethe amount o exposed surace area has

been greatly reduced and ease o access

improved. The ability o new coatings to

resist the stresses in their surroundings

has been increased considerably. New

inexpensive coating methods are employed in

abrication shops and on construction sites.

l Zinc baths have suicient capacity and

are large enough to allow widespread

hot-dip galvanization o steel structuresinvolving large components.

l Combining the hot-dip galvanization

technique with adapted paint systems or

zinc coatings - so called duplex systems

renders maintenance unnecessary with,

in most cases, the corrosion protection

not requiring any attention or the

entire service lie o the structure.

l Corrosion protection is becoming

an integral part o the abrication

process or steel structures.


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Erco high rack warehouse, Ldenscheid, Germany

ArchitectsSchneid

er+Schumacher


7/4655

1. Risk of corrosion and protection period

1. Risk of corrosion

The risk o corrosion o steel structuresemanates rom the surrounding atmospheric

conditions.

The nature and extent o any corrosion is linked

to the amount o time that metal suraces are

exposed to moisture and to the amount o air

pollution.

The exposure time to moisture, which is the

amount o time that the relative humidity o the

air is > 80% at an ambient temperature of >0C,

is the main determinant as regards atmosphericcorrosion and corrosion rate o metals.

The absence o moisture considerably slows

down the corrosion rate o steel and zinc even in

the presence o high concentrations o gaseous

(SO2, NOx etc) or solid polluters (dust containing

aggressive particles).

Over the last ew years, the complex inluence

o atmospheric polluters on the corrosion rate o

unprotected structural steel and zinc has beenanalysed as part o several European research

programmes [1].

The result o this work has led to the drating

o the standard ISO 9223 Corrosion o metals

and alloys Corrosivity o atmospheres

Classiication. The basic inormation containing

the classiications or the corrosivity o

atmospheres and the corrosion rates o plain

carbon steel, zinc, copper, and aluminium,

determined as a unction o the corrosive load,

is suiciently accurate to allow the protection

period o paints and zinc coatings to be

calculated in a practical ashion.

This standard was also used as the basis or

the classiication o the corrosivity o ambient

atmospheric conditions in EN ISO 12994-2.

EN ISO 12944 characterises atmospheric

conditions in the orm o corrosivity categories

based on igures o the loss o mass or thicknessper unit surace area o steel or zinc during the

irst year o exposure to dierent atmospheric

conditions (Table 1).

Examples o characteristic ambient conditions

help to assign the appropriate corrosivity

category to the structures and acilitate

the determination o the required corrosion

protection, by emphasising the protection

period.

Apart rom unusual circumstances, this method

allows a suiciently reliable assessment to be

made o the corrosive load or the majority o

steel structures.

Corrosion riskcategory

Loss o thickness o zinc

in the

frst year (m)*

Examples o typical environments

External Internal

C 1 Very low Less than 0.1 Isolated building. Relative humidity o air:

less than 60%

C 2 Low 0.1 0 .7Slightly polluted atmosphere,

dry climate e.g. rural areas

Non-isolated building with temporary water

condensation e.g. warehouses, sports halls

C 3 medium 0.7 2.1

Urban or industrial atmosphere with low

level o SO2 pollution or coastal areas with

low salinity

Premises characterised by high relative

humidity o the air and impurities, e.g.

breweries, laundries, diaries

C 4 high 2.1 4.2Industrial or coastal atmosphere with low

salinitySwimming pools, chemical actories

C 5 Very high I 4.2 8.4Industrial atmosphere with considerable

humidity and aggressive atmospheresBuildings or areas with almost

continuous water condensation and high

levels o pollutionC 5 Very high M 4.2 8.4 Coastal area with high salinity

* can also be expressed in loss o mass (g/m2)

Table 1 Risk o corrosion - Classiication o ambient conditions according to EN ISO 12994-2.


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The levels o airborne SO2 are measured at numerous locations in Europe.

European research has also allowed the relationship between the corrosion

rate o zinc, the levels o airborne SO2 and the wetting time / amount orainall, to be analysed [2].

The loss o zinc as a unction o the concentration o airborne SO2 has

been plotted on a graph on the basis o this research (Figure 1). This

shows a simpliied, but perectly useable version or determining the

corrosivity category according to EN ISO 129442, on the basis o the

igures available or SO2 concentrations [g/m3] at various locations.

However, it should be emphasised that the corrosivity category

determined in this way characterises the corrosive load at the

macroclimatic level. Particular microclimatic eatures, perhaps deriving

rom emission sources in the vicinity o the steel structures, or the use o

an unsuitable design or ensuring corrosion protection, are not included

and must be speciied by the owner, or example, in the case o structures

built or the chemical industry.

In Europe, the considerable reduction in the amount o airborne SO2 has

resulted in a substantial decrease in the corrosive load. The average annual

corrosion rate o zinc or 1992/1993 was 8 g/m2 or 1.1m [3]. These

igures are still valid today.

Figure 1 Loss o zinc as a unction o SO2 pollution (according to Knotkova/Porter)

Loss o zinc/year [m]

Average annual igure o sulphur dioxide [g/m3]

0

100 20 30 40 50 60

0,5

1

1,5

2

2,5

3

ArchitectsHelmutJahn-PhotoK.Idelberger


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2. Protection period

The protection period o coatings is deined in EN ISO 12944-1 as theexpected service lie up until the moment where the system needs

attention or the irst time.

EN ISO 14713 deines the protection period up until attention is irst

needed o zinc coatings as being the time between the application o the

irst coating and the moment when it irst needs maintenance in order to

ensure the protection o the base material.

The protection period is a vital actor when selecting and deining

corrosion protection systems. This technical concept helps the owner o

the structure to speciy his maintenance schedule.

The protection period is not a guarantee period. Generally, the guarantee

period, a legal concept, is shorter than the protection period. There is no

link between these two concepts.

Nowadays, it is possible to imagine corrosion protection not requiring any

or hardly no attention or the entire service lie o hot-dip galvanized steel

structures, even i exposed to poor weather conditions.

The protection period o a zinc coating depends mainly, or a given

corrosive load, on the thickness o the applied coat. Figure 4 uses the

igures or loss o thickness o zinc indicated in Table 1 to show the

relationship between the protection period / the thickness o the zinc

coat and the corrosive load. It can be generally assumed that there is auniorm loss o zinc across the entire coated surace. I we consider the

macroclimatic corrosive charge o category C3, currently valid in Europe,

and characterised by a zinc loss o between 0.7 and 2.1 m during the

irst year, we obtain a protection period o at least 40 years or a minimum

zinc coat thickness o 85 m, as speciied in EN ISO 1461 (Table 3) or

steel product thicknesses o >6 mm.

Protection period (years)

Thickness o the zinc coating [m]

We have to once again state that the protection period determined in

accordance with the method above is only valid or the corrosive loads

considered at the macroclimatic level.

Special microclimatic eatures and higher loads particular to the structure,

such as an accumulation o dust with a prolonged exposure to moisture

can considerably reduce the protection period.

It is now possible, as a result of the clear definition of ambient atmospheric

conditions - corrosivity categories - and access to measurements used as

the basis or calculating the protection period, to properly design suitable

corrosion protection systems in accordance with EN ISO 12944-5 and

EN ISO 1461.

Figure 2 Protection period o zinc coatings as a unction o the thickness o the coatand the corrosive load

200 40 60 80 100 120 140

C5

100

80

60

40

20

0

C4

C3

C2

C1

Santiago-Bernabeu Stadium, Madrid, Spain


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2. Corrosion protection methods

ArchitectsEstudio

Lamela-PhotoEstudioLamela,FranciscoPabloLaso


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When considering the corrosion protection o

steel structures, a distinction is made between

active and passive measures.

Active corrosion protection aims at preventing

corrosion or reducing the rate o the corrosion

reaction by:

l interering in the corrosion process,

e.g. reducing air pollution

l choosing a suitable material, e.g. using

corrosion resistant materials

l using detailing appropriate or

corrosion protection

The goal o passive corrosion protection is

to shield the steel surace rom corrosive

substances.

Due to their broad range o application

possibilities and their eiciency, the ollowing

methods dominate the corrosion protection osteel structures:

l coatings based on liquid or powder coatings

l metallic coatings (zinc, aluminum or

zinc-/aluminum alloys) applied by hot-

dip galvanization or thermal spraying

l combination o metallic coatings

and paint systems

Optimal corrosion protection is achieved

by combining active and passive corrosion

protection methods, based on the appropriatedetailing prior to the application o the passive

corrosion protection.

In the ollowing, the most eicient passive

corrosion protection method or steel structures,

namely hot-dip galvanizing, will be presented

together with material-, design- and process-

related requirements.

Santiago-Bernabeu Stadium, Madrid, Spain

Cognac-Jay Foundation, Rueil-Malmaison, France

ArchitectsJeanNouvel&DidierBrault-PhotoPhilippeRuault


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3. Hot-dip galvanizing


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1. Method

Hot-dip galvanization is the application o zincor iron/zinc alloy coatings by immersing the

prepared steel in molten zinc.

A distinction must be made between:

l the continuous method (or sheets, wire

rod, etc.),

l the discontinuous method (or sections,

structural elements, and small parts).

Only the discontinuous method in accordancewith EN ISO 1461 may be used or steel

structures.

It is essential or hot-dip galvanizing, namely

the iron-zinc reaction, that the steel surace to

be galvanized shall be metallically clean, i.e. ree

rom grease, rust and scale.

This high level o surace preparation level Be

according to EN ISO 12944-4 is achieved by

irst conditioning the material to be galvanizedin acid or alkali degreasing baths, then pickling

in diluted hydrochloric acid, ollowed by luxing.

When the part to be galvanized is immersed in

the zinc bath (between 440 and 460C), the

lux, which is usually a mixture o zinc chloride

and ammonium chloride, protects the metallic

surace and improves its wettability as regards

the molten zinc.

Zinc is the main component o the zinc bath,

and the total amount o additional elements

(with the exception o iron and tin) shall not

exceed the sum o 1.5%.

The cleansed and luxed part can be dried prior

to galvanization in an oven at temperatures

between 80 and 100C.

During immersion in the zinc bath, layers o

iron-zinc alloys build up on the surace o the

steel element which are generally covered with

a coat o pure zinc upon removal rom the bath.

Figure 3 Principle o the discontinuous galvanization process

The speed o the iron-zinc reaction depends on

the galvanizing parameters and the chemical

composition o the steel, particularly its siliconand phosphorus content. Reactive steels

build up thick layers o iron-zinc alloys and the

residual heat in the galvanized material can even

transorm the pure zinc coat into a coat o iron-

zinc alloy.

This reaction can be interrupted or slowed down

considerably by an immediate quenching o the

galvanized part in a water bath.

Figure 3 schematically represents the principle of

the discontinuous galvanization process.

Degreasing bath Pickling bathRinsing bath Flux bath Drying oven Zinc bath Water bathRinsing bath


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2. The iron-zinc reaction

Nowadays, the usual structural steels arebasically all suitable or hot-dip galvanizing.

However, they possess individual characteristics

which inluence the result o the galvanizing

process.

Hot-dip galvanizing is a reaction between the

surace o steel and molten zinc which results in

a zinc coating whose thickness and appearance

are basically determined by the chemical

composition o the steel and the galvanization

parameters (zinc bath temperature, immersiontime). The surace condition o the steel element

may also inluence the result o galvanization.

The behaviour o steels during galvanization can

be divided into our groups on the basis o their

Si and P contents (Table 2).

The steels o the ArcelorMittal long products are

o the Sebisty type and have typically a silicon

content o between 0.15% and 0.25%, and a

phosphorous content o less than 0.040%.

There are overlaps between the groups,inluenced by the temperature o the zinc bath.

The iron-zinc reaction also depends on the

topography o the steels surace, especially

when using steels in the transition range

between the ones with a low Si and P content

and the ones rom the Sandelin group,. This may

result in local or widespread variations in the

thickness and appearance o the zinc coat.

Similar appearances can also be caused by local

thermal stresses at the surace o the steel,

as happens during oxygen-cutting or lamestraightening. Here, the cause is probably due to

localised changes o the chemical composition in

the heat aected zone close to the surace as a

result o the oxidation o the so-called reactive

elements in the steel (i.e. Si, P), which loose thus

their inluence on the iron-zinc reaction.

The variation in the galvanization behaviour o

welds vs. adjacent steel suraces is the result o

dierences in the chemical composition o the

welding consumables and the base material. The

zinc coating on grinded suraces o welds may

also be thicker or have a dierent appearance

with regard to adjacent areas.

Generally, blast-cleaned suraces, i.e. sand or

shot blasted prior to galvanization, react aster

on contact with molten zinc, resulting in thicker

zinc layers when compared to steel suraces that

are simply pickled.

Unevenness and imperections in the steel

surace deriving rom rolling, straightening and

other processes are usually not smoothed out

by the zinc coating, in most cases, they are evenvisually ampliied.

Galvanizers have very ew means at their

disposal or inluencing the quality o the zinc

coating, which depends mainly on the chemicalcomposition o the steel.

Theoretically, it is possible to inluence the

thickness o the zinc coat by controlling the

immersion time, the chemical composition

and the melting temperature o the zinc

bath. As shown in Figure 4, there is however

no consistent relationship between these

parameters

The thickness o the zinc coat increases

with temperature up to a Si + P content o

approximately 0.12%. Beyond this point, the

relationship is reversed up to a Si + P content o

0.27%; in case o Sebisty steels, the thickness

o the zinc coat decreases with an increase in

the bath temperature. It then increases again

with an increase in the melting temperature o

the zinc rom a Si + P content o approximately

0.27% and more.

Group silicon + phosphorous [%] Zinc coating

1 Steel with low

Si + P content< 0.03

Silvery bright, zinc spangles, thin

coat

2 Sandelin steels 0.03 < 0.13Grey, sometimes granular, very

thick coat

3 Sebisty steels0.13 < 0.28 Silvery bright to pale grey, coat o

average thickness coat

4 Steel with high

Si + P content 0.28 Pale grey, very thick coat

Table 2 Classiication o the galvanization behaviour o structural steels according to their silicon and phosphoruscontents.



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3. Adhesion capacity of zinc coatings

In accordance with EN ISO 1461, adhesionbetween the zinc coating and the substrate does

not normally need to be tested, because zinc

coatings have adequate adherence or resisting

mechanical impacts during normal handling

operations and use without spalling or laking

o.

I adhesion needs to be checked, e.g. in the case

o parts exposed to high mechanical stresses,

impact or notch tests may be perormed.

However, there is no European standard or thetesting o adhesion.

The methods routinely employed, such as

the cross-hatch test, ASTM hammer test

(ASTM A 123) and the impact tests in

accordance with DIN 50978, are restricted to a

maximum coat thickness o approximately 150

m, and provide only qualitative inormation.

Moreover, these methods mainly assess the

ductility and sensitivity to scaling o zinc

coatings rather than their adhesion capability.

The modiied test method used or organic

coatings i.e. Tear o test to assess adhesion

capability in accordance with EN ISO 26624[5] allows the adhesion o zinc coatings to be

determined with statistical reliability up to

45 MPa.

These characteristic adhesion values indicate

the tensile strength or uplit resistance o

zinc coatings, which, in conjunction with the

(adhesive or cohesive) ailure patterns, enable

the assessment o their adhesion capacity.

With the exception o Sebisty steels, measured

average values or the adhesion o zinc coatings

in accordance with EN ISO 1461 are generally

greater than 20 MPa. The values or Sebisty

steels vary rom 10 to 18 MPa.

Appropriate tests have conirmed the indication

given in EN ISO 1461 stating that undamaged

zinc coatings have suicient adhesion [6].


Erco high rack warehouse, Ldenscheid, Germany


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4. Repair of damaged zinc coatings

In accordance with EN ISO 1461, theimperections in zinc coatings may not exceed

0.5% o the total surace o the building

component. A single deect may not exceed

10 cm2 and must to be repaired in accordance

with requirements.

The internal suraces o inaccessible hollow

structures are exempted rom this requirement,

because it is difficult or impossible to inspect and

because o poor access or repair purposes.

The standard considers three repair methods:

l Thermal spraying with zinc

l Use o zinc-rich paint

l Solder with a zinc-alloy stick

The repair techniques are not ranked in any

particular order.

Unless otherwise stipulated, the repair method is

at the galvanizers discretion.

The galvanizer shall advise the building owner

or end-user o the repair method that hasbeen used. Appropriate zinc powder-based

systems are mainly used. Single component

polyurethane/zinc powder-based primers are

recommended, provided their suitability has

been certiied by the manuacturer. This repair

method is practical, eective i implemented

correctly, and reasonably priced.

The repair o imperections using thermal zinc

spraying (with or without subsequent sealing)

is admittedly the most expensive and onerousrepair method, but it does oer a protection

period comparable to that o the original intact

zinc coating. Its technical easibility must be

checked in advance, particularly with regard

to the accessibility o the suraces to be

repaired. Also, the higher costs must be agreed

beorehand.

Repair using zinc-rich paint is eective as

well, but its quality very much depends on the

preparation o the surace, the suitability o

the paint itsel, the correct application and the

thickness o the coating.

The soldering repair technique with zinc alloy

is relatively expensive and the result obtained

is usually unsatisactory. In particular soldering

with tin, which is diicult to melt, gives poor

results. This method is thereore disappearing

rom the market.

The particular characteristics o the repair

method with respect to the application

o subsequent coats must be taken into

consideration. Compatibility between therepair coating and subsequent coats must

be guaranteed. For powder coatings, stoving

temperatures up to 200C have to be

considered.

Beore applying a repair coat, the aected

surace must be cleaned and, i necessary,

descaled. A high quality surace preparation canbe obtained by manually grinding to a surace

condition o PMa or by blasting to a surace

condition o Sa 2 or (EN ISO 12944-4). The

requirements relating to surace roughness must

be considered when selecting the repair method.

The coat thickness o the repaired area shall be

at least 30 m greater than the required local

thickness o the zinc coating as given in Table 3.

According to this standard, deects in the zinc

coating resulting rom the interventions by third

parties during abrication or erection must be

repaired in the same way. Zinc coatings have

a better resistance against mechanical loads

than organic paints. It is however technically

impossible to completely avoid damages or a

reduction o coat thickness in the areas where

handling gear is applied, even i all necessary

precautions are taken.

Deects with a surace area o more than

10 cm2 may also result rom modiications made

to the galvanized structure or rom mechanical

loads generated during erection. I the deectcan be repaired without compromising the

eectiveness o the corrosion protection e.g.

by thermal spraying with zinc, there is usually

no need or the structure to be dismantled and

regalvanized. Here, an equitable solution should

be sought between the contracting parties.



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Architect

sClaudeVasconi&JeanPetit,Luxembourg

Chamber o Commerce, Luxembourg


19/46

4. Charasteristics of hot-dipgalvanizing of steel structures

1. Preliminaries

Hot-dip galvanizing is a highly eective andcost-eicient corrosion protection method or

steel structures.

The process-related speciicities o hot-dip

galvanization (surace preparation by pickling

in acid, immersion o steel structures into a

metal bath at 450C, uneven heating during

immersion) result however in higher technical

requirements than with other corrosion

protection methods with respect to:

l

Steel quality and material characteristicsl Detailing, structural design

l Fabrication o the steel structures

All these points have to be taken into account

by the contributing parties. As a matter o act,

an unavourable combination o these aspects

can result in the ormation o cracks during hot-

dip galvanization or during the treatment o the

steel components in the aqueous solutions like

degreasing, pickling and luxing. The state-o-

the-art considers today the zinc bath as the

leading action in relation with the ormation o

issures. Consequently, special attention has tobe paid to highly reactive chemical compositions

o the zinc bath as they increase the cracking

potential.

Basically, a distinction has to be made between

the liquid metal induced embrittlement (LME)

and the hydrogen-induced cracking or expansion

o cracks (hydrogen-induced corrosion) during

the hot-dip galvanizing process.

Extensive metallographic investigations have

shown that the cracking o usual structural

steels during hot-dip galvanizing is due to LME.Hydrogen-induced cracking o structural steel

structures during hot-dip galvanizing is much

less likely to occur [7].

In order to ulil the quality requirements o zinc

coatings according to EN ISO 1461, a close

collaboration between the steel manuacturer,

the abricator and the galvanizer is absolutely

necessary, especially when dealing with steel

constructions with a high degree o welding.

2. Hydrogen-induced cracking

On principle, the absorption o hydrogen into

the metals occurs in the presence o a suicient

amount o hydrogen, e.g. during the steel

production (blast urnace process, pickling), steel

processing (welding) or during the pretreatment

o the steel surace like degreasing, pickling, etc.

According to ISO 4964, the risk o hydrogen-

induced cracking mainly exists with a local tensile

strength >1200 N/mm2, a hardness >34 HRC or

a surace hardness >340 HV. Notches, presentin the microstructure o the surace, or material

inhomogeneities increase the risk o damage.

Usual steel grades are typically not subjected

to embrittlement through hydrogen absorption

during pickling, even i hydrogen remains in the

steel. In this case, the hydrogen escapes during

the immersion process in the molten zinc.

17

ArchitectsAtlanteArchitectes

-PhotoP.RogeauxCarlier


20/46

3. Liquid metal-inducedembrittlement (LME)

Preconditions or LME to arise are:

l suicient static or dynamic tensile,

bending or torsional stresses (load

induced/ residual stresses)

l corrosive acting liquid metal

l solid metal vulnerable to LME

l critical temperature range

l mutual solubility o the involved metals

l good wettability o the solid metal by

the molten metal

l ormation o low melting intermetallic

phases/compounds.

Given the above-mentioned conditions during

the hot-dip galvanizing o steel structures, the

characteristics o steel can be unavourably

aected by wetting grain boundaries close to

the surace respectively suraces in notches orcracks with a corrosive acting liquid metal, zinc

and/or alloys o the zinc bath (or example lead

(Pb), tin (Sn) or bismuth (Bi)).

Tensile stresses in the steel can no longer be

transerred i:

l the deormation capacity (ductility)

is impaired, see also Figure 6,

l the resistance against crack

propagation is reduced.

When exceeding a critical stress level, the

development o inter-crystalline issures in

the steel, ramiied and branched out into the

material, results in the cracking o the remaining

section. The issure tips are usually illed

with zinc; in the case o alloyed zinc baths,

additional concentrations o alloying elements

may be present.

The order o magnitude o the critical stress,

above which steel is vulnerable to cracking

through LME in a zinc bath, is widely unknown

at present. On the one hand this is due to the

diiculty or deining and assessing the existing

and acting stresses in the structural element

and on the other hand it is due to the act that

stresses are generated through technological

parameters during the galvanizing process,

above all the dipping speed o the buildingcomponents and the heat transer rom the zinc

bath to the steel. Literature generally indicates

that the susceptibility to LME increases with

increasing hardness and resistance o the

structural steels. Observations in this regard

suggest that steel grades S275 and lower run a

very low LME-risk, whereas those above S460

are clearly more at risk.

Today, there is a general believe that the

potential risk o crack ormation due to LME

is substantially inluenced by the chemicalcomposition o the zinc bath, in particular the

contents o lead (Pb), tin (Sn) and bismuth (Bi).

Typical requirements on the maximum content

o these 3 elements are given in chapter 8.

4. Charasteristics of hot-dip galvanizing of steel structures


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5. Requirements for materials

19


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1. Chemical composition

The structural steels o ArcelorMittals longproducts are produced in accordance with part

2 or 4 o EN 10025:2004 and the option o

the suitability or hot-dip zinc-coating can be

agreed upon or all the steel grades up to a yield

strength o 460 MPa. It is clear here that this

option merely applies to the inluence o the

chemical composition o the steels regarding the

silicon (Si) and phosphorous (P) content on the

thickness and appearance o the zinc coating.

The perormance o the steels during hot-dip

galvanizing with regard to LME is not addressedin the European standards.

In Japan, extensive tests have been conducted

on the subject and a relation, similar to the

carbon equivalent as an indication or the

weldability, is proposed between the chemical

composition o some Japanese steels and their

LME risk potential,. [9] reports on this matter

in the context o a contribution to the current

state o knowledge regarding LME. Inquiries

about the causes o cracks in steel structures

in Europe, however, have lead to the conclusion

that optimal chemical compositions o the steelsalone according to the Japanese experience can

not prevent LME when other actors avouring

LME provoke a suiciently critical state. On a

general basis, it can nethertheless be stated that

a low carbon equivalent tends to counteract

LME.


ArchitectsClaudeVasconi&JeanPetit,Luxembourg



23/46

2. Mechanical properties of steel

The knowledge o the steel characteristicsis essential when designing the steel building

components suitable or hot-dip galvanizing.

The design or quasi-static loads is usually

based on the yield stress Re, This characteristic

is determined with the tensile strength Rm,

the Youngs modulus o elasticity E, the total

elongation at racture A, the uniorm elongation

Ag and the reduction o area Z, in a monoaxial

tensile test at ambient temperature at a gradual

loading rate.

The stress-strain diagram, obtained rom this

tensile test, shows that substantial deormation

occurs beyond the yield stress beore rupture

occurs. This means that racture o building

components is an indication that a large amount

o deormation has taken place. This ductility

has a major inluence on the assessment o

stress resistance, on the choice o the calculation

method and statical system, as well as the

application o the saety coeicients in steel

structures. In order to avoid brittle fracture, steel

needs to be suiciently ductile.

The plastic deormation also reduces stress

concentrations at notches or where residual

stresses are present. For example, residual

stresses (rom welding or rolling processes) are

either completely or partially disregarded when

designing steel structures.

Building components made rom a ductile

material may also be used or plastic design,

which means that elongation o the steel beyond

its yield stress is allowed.

Ductility however can vary considerably

between steel grades, as shown in Figure 5.

Also, it is important to note that the deormation

capacity o the steel is reduced during the hot-

dip galvanizing process (Figure 6).

Heating steel lowers its yield stress, modulus o

elasticity as well as its tensile strength.

The stress-temperature diagram in Figure 7

shows the typical reduction in yield stress or

the 3 usual steel grades S 235, HISTAR 355 /

S 355 and HISTAR 460 / S 460.

Hardness is another criterion used to assess

strength. The hardness value is used, or

example, or checking the uniormity o the

strength o semi-inished products, and can

be used or the approximate non-destructive

determination o the tensile strength.

The advantages o steel grades with high

elongation have already been mentioned.

In addition to total elongation A, uniorm

elongation Ag, and reduction o area Z, the notch

impact energy Kv is an important criterion whenassessing the toughness o a steel.

The toughness values may not be used as such

or structural design purposes, they rather

enable a qualitative comparison o various steels

with regard to their toughness. Combined with

the experience gained with steels whose stress

resistance and toughness have already been

determined, they enable an assessment o the

risk o brittle racture occurring in certain stress

conditions (i.e. plane, three-dimensional or

residual stresses, loads), at certain temperaturesor in particular loading modes (slow or ast).

Figure 5 Typical stress - strain diagram or various steels

Figure 6 Schematic stress strain diagram or structuralsteel S355 comparison o the characteristics o S355at room temperature (RT), at 460C in the air, and duringimmersion in the zinc bath at 460C

Figure 7 Typical yield stress - temperature diagram or

various steels

Yield stress [N/mm2]

Temperature [C]

HISTAR 355/S 355

S 235

HISTAR 460/S 460

0

100

200

300

400

500

0 100 200 300 400 500

Stress

Elongation

0

0

150

300

450

600

750

800

Stress [N/mm2]

HISTAR 460/S 460

HISTAR 355/S 355

S 235

6 12 18 24 3630

21

S355 RT

S355 460 C / air

S355 460 C / Zinc bath

Elongation [%]


24/46

The toughness o hot-rolled sections is

measured in longitudinal rolling direction.

Without any special measures, toughnessvalues can be lower in transverse direction and

perpendicular to the surace o the section. The

reason or this deterioration is the presence o

non-metallic deormable inclusions positioned

parallel to the surace during the rolling process.

Stresses occurring perpendicular to the surace

(mainly in welded structures) combined with

insuicient toughness can then lead to a loss

o cohesion in the material similar to lamellar

tearing. These inclusions can be modiied or even

eliminated using special steel making techniques.

Thus, Z-quality steel is characterised by

superior deormation properties in a plane

perpendicular to the surace.

The limited possibilities or using the toughness

values in the assessment o crack potential is

due to the act that the state o stress (plane or

three-dimensional, residual) and the deformation

conditions o the structure are widely unknown.

It is mainly high stress levels at the end o

a surace or internal imperections, residual

stresses rom abrication, the temperature and

the loading rate that inluence the resistance tobrittle racture.

In order to better assess, rom a quantitative

point o view, the susceptibility o a steel

to brittle racture, racture resistance is

determined on the basis o the theory o

racture mechanics and special tests made on

samples pre-notched by atigue. Their condition

is similar to the one o building components

aected by issures. A critical temperature is

thus obtained at speciied stress levels. Below

this critical temperature, a crack propagatesrapidly resulting in the sudden racture o the

entire sample.

Speciic steel production processes (e.g. the

way o killing during casting) inluence the

toughness and susceptibility to lamellar tearing;

the designation o the notch toughness shows

dierent levels (or structural steels e.g. JR, J0,

J2, M, ML, etc.).

A ine grain microstructure, such as the one o

high strength ine grained structural steels, also

enables susceptibility to brittle racture to be

reduced and weldability to be improved. The

ine microstructure o these steels increases

their yield strength without compromising their

toughness.

3. Weldability

Structural steels are typically expected topossess a good weldability, which is usually the

case. This means that the welding technique

and iller materials must be selected in such a

way that there is no deterioration in either the

strength or the toughness in the heat aected

zone and in the weld.

During the production process o the steels, the

weldability can be improved by an increase o

the purity level, through an improved control

o the alloying elements as well as speciic

processes, like the controlled thermomechanicalrolling and the quenching and sel-tempering.


Grenoble Ice Rink, France


25/46

4. Information on materials forfabricating building components

Figure 5 shows that the various steel qualities

have very high elongation capability. For design

purposes, only a small part o this potential is

used. The elongation capability o steel may

be reduced due to material embrittlement,

or generally due to local restrictions o

deormability as a result o two or three

dimensional (residual) stress states or through

the presence o micro structural impurities in

the steel. Exceeding the ductility limit obviously

results in brittle racture in the building

component. Experience shows that severalinluences can occur simultaneously.

These are very complex phenomena and

experimental results or the estimation o the

toughness. Respectively the tendency or brittle

racture are subject to very large variations.

Also, brittle racture is greatly inluenced by

the abrication processes (e.g. changes in the

microstructure in a welded area i excessively

cooled), the structural design (e.g. residual

stresses) and the way in which the structure

is used (e.g. the rate at which heavy loads are

applied).

Obviously, welded building parts may be

particularly aected by brittle racture.

The presence o hydrogen in the weld or in the

heat-aected zone, combined with residual

stresses rom welding, aects the susceptibilityo steel to hot and cold cracking. Besides hot

cracks during welding, cold cracks are to be

expected i hydrogen rom welding is present

in the weld or heat-aected zone and when

residual stresses rom shrinking take eect.

Here, hydrogen causes a reduction o the

deormation capacity.

Taking into account these considerations is

o outmost importance or the structural

design process o steel structures oreseen or

galvanization, as additional stresses during hot-

dip galvanizing and simultaneously reduced yield

stress and deormation capacities o the steels

can lead to LME or hydrogen induced crack

ormation.

This type o brittle racture during galvanizing

can occur in any type o steel. As already

indicated, susceptibility to racture is especially

inluenced by tensile stresses (mainly residual

stresses) in the building component.

5. Improving structural steels

Developments in structural steels are aimed at

increasing their yield strength and weldability

while keeping or even improving their toughness.

These improvements are achieved by eliminating

inclusions, by improving the microstructure

through the choice o alloying elements

avouring iner grains, the replacement o

ingot casting with continuous casting and the

adoption o reined rolling processes like the

thermomechanical rolling and the quenching andsel-tempering.

23


ArchitectsChemetov-

Huidobro-PhotosO.Wogenscki


26/46


27/4625

6. Requirements of structures suitablefor hot-dip galvanizing

1. General

The principles o the design o structures to begalvanized are similar to those or other steel

structures provided that the speciic demands

or the hot-dip galvanizing process are taken

into consideration.

Hot-dip galvanizing is a hot-immersion process

whose stages rom surace preparation

(degreasing, pickling, rinsing, and luxing) to

the galvanization process itsel take place in

an industrial-sized installation (e.g. tanks and

kettles) respectively in the zinc bath (440

460C). All the ollowing speciic demandso this procedure have to be taken into

consideration at the design stage:

l Technical demands associated

with the process

l Saety requirements

l Requirements imposed on the materials,

design, and fabrication of building components

to prevent deormations and cracks

Basic inormation on this subject can be ound inISO 1461 and in EN ISO 14713.

In addition, the shape o steel structures and

their design as regards corrosion protection

have a decisive inluence on the eectiveness

(protection period) and maintenance

(accessibility) o the corrosion protection.

In this respect, the basic rules or the design o

structures to be corrosion protected according

to EN ISO 12944-3 are also applicable to

galvanized structures.

2. Technical requirementsassociated with the process

2.1 Geometry o building components

The dimensions o building components that are

to be galvanized shall be chosen in such a way

that they can be immersed in a single operation.

It is thereore important or the designer to

determine in advance the maximum dimensions

o the available galvanizing tanks.

In the case o steel structures, the economically

viable dimensions o tanks are as ollows:

l Length: 7.00 16.50 m

l Width: 1.30 2.00 m

l Depth: 2.20 3.50 m

For building components that can not be

galvanized in one operation, (Figure 8 shows

an example or double immersion), special

measures have to be taken since the dierential

heating o the building component increases

the risk o deormation and/or cracking (see

also paragraph 6.2.4). In this situation, prior

discussions should be held with the galvanizer.

First immersion

Second immersion

Figure 8 Example o double immersion

Killesberg Tower, Stuttgart, Germany

ArchitectsHansLuzundPartner


28/46

2.2 Vent holes, run-o openings,

ventilation openings

In order to ensure that the surace is correctly

pre-treated and high quality galvanization

is achieved, building components must be

designed in such a way that the pre-treatment

liquids and especially the molten zinc are in

contact with all the suraces, and that they can

reely run o when the part is removed rom

the bath.

Air pockets and air inclusions lead to uncoated

areas; constructional measures must thereore

be employed to prevent their ormation.

This does not only apply to structures made

rom hollow sections and tanks, but also to

structures comprising stieners, partition plates

and endplates, etc. in which air pockets may

orm during immersion i appropriate vent holes

are not incorporated.

The sizes o the run-o openings and vent holes

depend on the quantity o zinc that must low

through. The immersion velocity is an importantparameter or reducing the risk potential o

steel constructions with regard to LME. Further

details will be discussed in chapter 8. It has

been experimentally determined that the

susceptibility to LME decreases with an increase

in immersion velocity. An ideal immersion

velocity would be approximately 5 m/min [11].

Figure 9 shows examples o vent holes,

Figure 10 examples o run-o openings. In the

case o sections up to 300 mm high, l1 must be 20 mm, in the case o sections over 300 mm

high, l1 must be 30 mm. In order to achieve

the ideal immersion velocity or LME-critical

steel constructions, it is necessary to coordinate

the design o the vent holes with the abricator

and the galvanizer.

The run-o openings or the connection o

girders, base plates, corners o portal rames,

etc. must have a diameter between 10 mm and

approx. 35 mm. Examples can be ound in

Figure 10.

Figure 9 Examples o vent holes

Figure 10 Examples o run-o openings

l1

l1

l1

l1

Bevel cut Circular cut

6. Requirements of structures suitable for hot-dip galvanizing

D

D

D

D

Girder assembly Base plate Node o portal rame


29/4627

2.3 Saety issues associated

with the process

At the temperature o molten zinc (440

460C) the moisture contained in air pockets

(hollow parts, overlapping areas closed by

welds) generates pressurized water vapour

creating an explosion risk. Liquids rom the pre-

treatment process can also seep into overlapping

suraces i these are not perectly sealed, and

evaporate explosively when immersed in the

zinc bath.

Overlapping suraces should be avoided not

only or saety reasons, but also or corrosion

protection purposes. Table 4 provides some

suggestions, should overlapping suraces be

unavoidable.

The drilling o holes in large overlapping suraces

deinitely reduces the danger o explosion during

galvanization but it also reduces the eiciency

o the corrosion protection o the structure.

Indeed, iniltrated pre-treatment solutions do

not completely evaporate, leaving traces o salt

in gaps. In many cases, the zinc coat will not

completely cover the gaps ater evaporation

o the liquids, resulting in corrosion occurring inthese parts o the structure.

Maximum overlapping suraces Measures

Up to 100 cm2 (or product thicknesses < 12mm) Seal weld circumerence

Up to 400 cm2 (or product thicknesses 12mm) Seal weld circumerence

Table 4 Recommended maximum sizes o overlapping suraces



30/46

2.4 Inormation on detailing

suitable or galvanization

The design and detailing o steel building

components must satisy the basic principles

or the design o structures requiring corrosion

protection, and in particular, o hot-dip

galvanization. This is the only way in which

adequate corrosion protection comprising

satisactory thickness o zinc layers can be

ensured, along with the elimination o the

potential risk of structural deformation, cracks or

any other damage to the building components.

Consultation with the galvanizer must be sought

as early as possible in the design process or

galvanized steel components.

Table 5 Structural details and abrication recommendations

Potential problems during hot-dip galvanization

o steel components may be solved by

implementation o the ollowing constructionaland technological measures:

l Already at the planning stage, the abricator

must try to minimise residual stresses

generated during abrication, particularly rom

welding. Here, appropriate welding procedures

are helpul. With increasing thicknesses o

building components, the risk o three-

dimensional stresses, aster cooling rates

and hence the risk o cracking increases.

l Strict compliance with requirements as

regards the design o structures intended

or hot-dip galvanization, especially when

using high strength steels with a low notch

toughness. The amount o vent holes and

drainage holes must be minimised. Also,

inappropriate abrication will increase the

risk o cracking. It is recommended to

seek agreement with the galvanizer.

l The ratio o plate thicknesses welded directly

together should not exceed a actor o 2.5.

With increasing thicknesses o the steelparts and or elements with a high degree o

welding, the ratio should even be smaller.

l The use o highly restrained building

components susceptible o generating

internal stresses during the galvanizing

process should be avoided.

l The actual characteristics and the

chemical composition o the material to

be galvanized must be identiied prior

to galvanization. The galvanizer must be

advised about the nature o the steels

used or the sections to be galvanized.

l Multiple immersions must be avoided.

The ollowing table shows a selection o

structural details which have to be considered

as critical with regard to LME during hot-dip

galvanization.

Nr Structural detail Description

1

Welding o hal end plates induces a concentration o residual stresses in the area indicated.

Recommendation: arrange the end plate over the ull height o the section or use a bolted

connection.

2Welding o the plate induces a concentration o residual stresses in the area indicated.

Recommendation: perorm stress relie annealing in the areas indicated, and/or round o.

3Welding induces concentrations o residual stresses at the our corners o the hollow section.

Recommendation: perorm stress relie annealing in the areas indicated.



31/4629

Nr Structural detail Description

4Welding induces concentrations o residual stresses at the our corners o the connection plate.


5Welding induces concentrations o residual stresses at the ends o the plate.


6

The dierences in stiness between the section, the thick base plate, and welds induce

concentrations o residual stresses.

Recommendation: perorm stress relie annealing in the area o the welds .

7

The dierences in stiness between the section and the endplate and welds induce concen-

trations o residual straining. Hardening at the edges o the bolt holes may also occur.

Recommendations: perorm stress relie annealing in the area o the welds, careully

drill bolt holes.

8

The dierences in stiness between the section and the endplate and welds induce

residual stresses.

Recommendation: perorm stress relie annealing in the area o the welds.

9The welding o stieners between the fanges o the section induces residual stresses.

Recommendation: perorm stress relie annealing in the area o the welds.

10

The system is internally highly restrained. The inevitable dierences in temperature to which

building components are heated lead to high residual stresses.

Recommendation: bolt the diagonals to the chords ater galvanization.

11

Inappropriate execution o the rounded areas may result in hardening and the creation

o notches.

Recommendation: round-o careully, perorm stress relie annealing in the abricated areas.

12Inappropriate execution o openings may result in hardening and the creation o notches.

Recommendation: round-o careully, perorm stress relie annealing in the abricated area.



32/46

ArchitectsSRA,AnthonyBelluschi,OWP&P

Shopping Center 4 temps, Paris, France


33/4631

7. Requirements for the fabricationof steel structures

1. Residual stresses inbuilding components

Cracks rom hot-dip galvanizing o steel

constructions are oten generated in places with

high residual stresses (tensile stresses), notches

and/or hardness increases due to abrication

processes such as

l welding

l oxygen cutting

l grinding

l drilling

l punching

l

cold orming (ageing)l straightening

Residual stresses are also created in restrained

components in the zinc bath. The heat during

galvanization (450C) modiies both the

state o internal stresses and the mechanical

characteristics o the steel (reduction o yield

stress and modulus o elasticity), thereby

reducing the resistance o the building

components to elastic deormation. Stresses,

mainly localised, can decrease but also increase

and deormations may occur.

The diiculty lies, however, in determining the

magnitude o residual stresses, which in practice

can only be roughly estimated. The many

actors, inluenced by abrication and detailing,

cannot be determined with suicient accuracy

either qualitatively or quantitatively. Structural

engineers are usually unaware of the real amount

o residual stresses in the structure.

The plastic deormation capabilities o structural

steels generally allow to disregard the accurate

determination o residual stresses as they aremostly localised and tend to disappear through

plastiication when superposed with stresses

rom exterior loads. It is o course o outmost

importance here that the appropriate steel

is chosen with respect to toughness, taking

into account the dimensions o the building

component and the application temperature

(see prEN 1993-1-10). With components thatare to be hot-dip galvanized, special care must

be taken to minimise residual stresses. This is

usually achieved using constructional measures,

in order to avoid any subsequent stress relieving

beore galvanizing.

Fabrication also allows to prevent high residual

stresses and hardness increases by

l using multi-layer illet welds, which

could be welded in a single run with the

current state o welding techniques

l establishing a welding procedure

l avoiding long and thick welds

l avoiding cold deormation or reducing

the created residual stresses through

heat treatment (keeping in mind

however that not all the eects o

cold orming can be cancelled out)

l removing notches or restricting their presence

especially in thin building parts o welded

constructions and areas subject to changesin microstructure rom cold orming, welding,

oxygen cutting, drilling, punching, etc.

2. Surface condition ofrolled long products

Unless otherwise speciied in the order,

the suraces o hot rolled sections or hot-

dip galvanization shall normally conorm

to the basic requirements o EN 10163-

3:1991, class C, subsection 1.

The suraces to be galvanized must

be de-greased and any discontinuities

that could compromise the corrosion

protection properties o the zinc coat

must be removed beore galvanization.

ArchitectsMarkusOtt-PhotoAtelierKinold


34/46

Rheda Wiederbrck Car Park, Germany

CourtesyofVollackManagementGmbH,Germany


35/4633

8. Requirements for hot-dip Galvanizing

As seen in paragraph 4.3, the presence o a

corrosive acting liquid metal in contact with a

solid metal prone to liquid metal embrittlementis the precondition or crack ormation in steels

due to LME. This prerequisite is inevitably

given or hot-dip galvanizing (liquid metal =

zinc bath, solid metal = steel), as this is the

only way that the zinc coat can be produced.

Similar to the requirements or the steel

production, or the structural design and or the

abrication o steel structures (in particular or

minimising residual stresses), speciic measures

have to be taken in the hot-dip galvanizing

process to keep the risk o hydrogen-induced

cracking and LME as low as possible.

Extensive investigations [9, 12, 13] have

shown that during hot-dip galvanizing, the

temperature gradient resulting rom the

immersion o structural elements into the

zinc bath and its time-related variation during

dipping is an important process parameter in

view o LME. Here, the risk potential or LME

is small or a low temperature gradient [14].

The heat transer coeicient and the

wetting ability o zinc baths increase withhigh concentrations o alloys, especially

tin (Sn), lead (Pb) and bismuth (Bi)

thereby reducing the heating time and

consequently increasing the risk o LME.

Based on the above mentioned indings,

investigations were conducted in order to lower

the temperature gradient by modiying process

parameters o hot-dip galvanizing [11].

The temperature gradient can be reduced by

l optimizing the chemical compositiono the zinc bath, especially with

respect to Sn, Pb and Bi,

l increasing the immersion velocity

(approx. 5 m/min)

l increasing the dipping angle

l increasing the salt concentration

in the lux (approx 500 g/l)

l adjusting the drying temperature ater

luxing to 100C, to ensure a high

temperature o the building components

prior to dipping in the zinc bath

l keeping the temperature o the zinc bath as

low as possible to minimise the temperature

dierence between the building part and thezinc bath.

Recent research results deine a new sate-

o-the-art. Nowadays, it can be assumed

that contents o tin up to 0.1% and/or

bismuth up to 0.1% do not detrimentally

inluence LME. Herewith, the content

o lead should be limited to 0.8%.

It must however be noted here that both

the classical zinc bath and the one modiied

as described above can be LME-critical,

especially i the LME-critical requirements or

the quality o material, design and abrication

(see paragraphs 5 to 7) are not met.


ArchitectsClaudeVasconi&JeanPetit,Luxembourg


36/46

BavarianModelHo

usingEstate,Ingolstadt,Germany


37/4635

9. Duplex systems

Many architects use hot-dip galvanized steel

structures because o their aesthetic qualities.

In addition, the use o liquid or powder paints on

top o the zinc coat, the well-known duplex-

system, has become very popular over the last

ew years.

Duplex systems have advantages when the

ollowing aspects are important:

l long protection period

Duplex systems have a service lie 1.2 to 1.5

times higher than the combined protection

periods o the hot-dip galvanization and paintcoats (synergy eect).

l large choice o colours

l need or signalling / identiication /

camoulage

l no or reduced release o zinc into the

environment

At least the irst coat o the paint system

should be applied in the workshop, i possible

immediately ater hot-dip galvanization thereby

rendering expensive surace preparation

on the construction site unnecessary.

High quality duplex systems require

optimal compatibility between the

galvanizing coat and the paint.

The choice o suitable coating materials is o

particular importance. Only coating systems with

proven compatibility with batch galvanizationin accordance with EN ISO 1461 shall be used.

The requirements or surace preparation /

pre-treatment depend on the nature o the

coating material.

Zinc suraces designed to be powder-coated

must be sweeped, phosphated or chromated

immediately prior to coating.

In the case o liquid paints, current technology

only requires the surace o the zinc coat

to be sweeped when large amounts o zinc

corrosion products (white rust) on the surace

compromise adhesion, or in unction o the

corrosion exposure categories as per the

speciications o the coat manuacturer.

The purpose o sweep blasting is simply to clean

and rough the surace o the coats. Sweeping

exerts great mechanical stress on zinc coatings

and may, i poorly executed, damage them

(i.e. cause cracks, laking).

The optimal parameters or sweeping are [15]:

l abrasive: non-metallic slags, aluminous

abrasive, or glass beads

l particle size o the abrasive grit: 0.25 -

0.50 mm

l jet pressure at the nozzle: 2.5 3.0 bars

l jet angle :


38/46

Shopping Center 4 temps, Paris, France

ArchitectsSRA,AnthonyBelluschi,OWP&P


39/4637

10. Cost effectiveness

Hot-dip galvanization o structural steel

components exposed to atmospheric conditions

constitutes a highly eective durable corrosionprotection method. In many applications,

the corrosion protection lasts as long as the

structure itsel. Zinc coatings require no or

almost no maintenance. Hot-dip galvanizing,

in terms o lietime o the structures, including

maintenance and repair costs, is by ar the

most cost-eicient corrosion protection

system available or steel structures.

Contrary to the prevailing view that hot-dip

galvanization only becomes cost-eective over

time, it now oers substantial cost savings

when compared to other protection systems on

many types o structures, right rom the very

beginning. Studies have shown that, beyond a

speciic surace area o 15 to 20 m2/t, the initial

costs of hot-dip galvanizing are lower than those

o a three-coat paint system [17].

Architects and designers should more than ever

be aware o this act when selecting a corrosion

protection system.

Where hot-dip galvanizing cannot meet more

stringent appearance requirements, a simpleduplex system e.g. a coat o zinc and one coat

o paint that does not need sweeping, is worth

considering.

In any case, it is useul to perorm a cost-

comparison o the various options beore

selecting the appropriate corrosion protection

system.


40/46

Bouillon Car Park, Luxembourg

ArchitectsRomainHoffmannArch

itectesetUrbanistes


41/4639

References

[7] Katzung, W. und Schulz, W. D.

On hot-dip galvanizing o steel

constructions Causes and solutionproposals reerring to cracking

[8] Pargeter, R.

Liquid metal penetration during hot-dip

galvanizing

Published: TWI Website

[9] Kinstler, Thomas J.

Current Knowledge o the Cracking o

Steels During Galvanizing

GalvaScience LLC, PO Box 501, Springville,

AL 35146

[10] Kikuchi, M.

Liquid Metal Embrittlement o Steels

during Hot Dip Galvanizing

Tetsu to Hagane, Iron and Steel, Volume

68, Number 14, 1982,

Pages 1870-1879

[11] Pankert, R., Dhaussey, D., Beguin, P., Gilles, M.

Three Years Experience with the

Galveco Alloy

Proceedings Twentieth International

Galvanizing ConerenceAmsterdam, 2003, European General

Galvanizers Association

[12] Interpretation zinc assisted cracking on

big scale steel structures and preventive

methods. 2001, reeriert in ILZRO

Project ZC 21 2.

[13] Poag, G., Zervoudis, J.

Inluence o various parameters on steel

cracking.AGA Tech Forum, Oct. 8. 2003. Kansas

City, Missouri.

[14] Pinger, T.

Avoidance o liquid metal induced

embrittlement o galvanized steel

constructions

[15] Schulz, W. D.; Schubert, P.; Katzung, W.;

Rittig, R.

Correct sweeping o hot-dip galvanized

parts according to DIN EN ISO 1461),

Der Maler- und Lackierer-meister 7/99

[16] Verbnde-Richtlinie Korrosions-schutz von

Stahlbauten Duplex-Systeme

Herausgegeben von Bundesverband

Korrosionsschutz e.V., Kln

Deutscher Stahlbauverband e. V.,

Dsseldor

Industrieverband Feuerverzinken e. V.,

Dsseldor

Verband der Lackindustrie e. V., Frankurt

[17] Dipl.-Ing. P. KleingarnCost-eective and reliable corrosion

protection using hot-dip galvanizing),

Feuer-verzinken (28 th year) n 3,

September 1999

1. Bibliography

[1] Dr.-Ing. D. KnotkovaAktuelle Erkenntnisse zum

Korrosionsverhalten von Zink und

Zinkberzgen

Vortrag 4. Deutscher Verzinkertag

1995 Kln

[2] Dr.-Ing. Knotkova und F. Porter

Longer lie o galvanized steel in the

atmosphere due to reduced SO2-pollution

in Europe

Proc. o Intergalva 1994, Paris

[3] F. von Assche

Atmospheric conditions and hot dip

galvanizing perormance

Proc. Intergalva 1997, Birmingham,

EGGA UK

[4] Katzung, W. und Mitarb.

Zum Einluss von Si und P au das

Verzinkungsverhalten von Bausthlen

Mat.-wiss. u. Werkstotech.

28, 575 587 (1997)

[5] Katzung, W. und Mitarbeiter; FuE-BerichtInstitut r Stahlbau Leipzig GmbH,

Arno-Nitzsche-Str. 45, D-04277 Leipzig

(unverentlicht)

[6] Katzung, W.; Rittig, R.; Schubert, P. und

Schulz, W. D.

Zum Einluss von Abkhlverlau und

Tauchdauer au die Hatestigkeit und das

Bruchverhalten von Zinkberzgen nach

DIN EN ISO 1461

Mat.-wiss. und Werkstotechnik 32,

483-492 (2001)


42/46

2. Standards and further reading

l EN ISO 1461 : 1999Hot-dip galvanized coatings on abricated

iron and steel articles

l Katzung, W. und Marberg, D.

Beuth-Kommentare

Korrosionsschutz durch Feuerverzinken au

Stahl augebrachte Zinkberzge

(Stckverzinken), Kommentar zu

DIN EN ISO 1461 (2002)

l EN ISO 14713: 1999

Protection against corrosion o iron andsteel in structures Zinc and aluminium

coatings - Guidelines

l EN ISO 12944-1-8 : 1998

Corrosion protection o steel structures by

protective paint systems

l DIN 267, PART 10

Mechanical assembly components -

Technical delivery conditions

Galvanized parts

l EN 10025 : 2004Hot rolled products rom structural steels

l EN 1993-1-10

Design o steel structures Selection o

materials

l DASt Guideline 009

Selection o steel grades or welded steel

structures

l Korrosionsschutz durch Feuerverzinken

(Stckverzinken)

Corrosion protection by hot-dipgalvanizing batch galvanizing

Institut Feuerverzinken GmbH,

Sohnstrae 70, D-40237 Dsseldor

l Maa, P. und Peiker, P.

Hot-dip galvanization manual

Deutscher Verlag r Grundstoindustrie

Leipzig, Stuttgart 1993

l Arbeitsbltter Feuerverzinken

Technical sheets or hot-dip galvanizing

Institut Feuerverzinken GmbH, Sohnstrae

70, D-40237 Dsseldor

References


43/46

Notes


44/46

Technicaladvisory& Finishing

Technical advisory

We are happy to provide ree technical advice to

optimise the use o our products and solutions

in your projects and to answer your questions

about the use o sections and merchant bars.

This technical advice covers the design o

structural elements, construction details, surace

protection, ire saety, metallurgy and welding.

Our specialists are ready to support yourinitiatives anywhere in the world.

To acilitate the design o your projects, we also

oer sotware and technical documentation that

you can consult or download rom our website:

www.arcelormittal.com/sections

Finishing

As a complement to the technical capacities

o our partners, we are equipped with

high-perormance inishing tools and

oer a wide range o services, such as:

l drilling

l lame cutting

l T cut-outs

l notching

l cambering

l curving

l straightening

l cold sawing to exact length

l welding and itting o studs

l shot and sand blasting

l surace treatment

Building & ConstructionSupport

At ArcelorMittal we also have a team o

multi-product proessionals specialising in

the construction market: the Building and

Construction Support (BCS) division.

A complete range o products and

solutions dedicated to construction in all

its orms: structures, aades, rooing,

etc. is available rom the website

www.constructalia.com


45/46

Your partners

ArcelorMittal

Commercial Sections

66, rue de Luxembourg

L-4221 Esch-sur-Alzette

Luxembourg

Tel: +352 5313 3014

Fax: +352 5313 3087


We operate in more than 60 countries

on all ive continents. Please have a look

at our website under About us to indour local agency in your country.

Although every care has been taken during the production o this brochure, we regret

that we cannot accept any liability in respect o any incorrect inormation it may contain

or any damages which may arise through the misinterpretation o its contents.


46/46

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66, rue de Luxembourg

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LUXEMBOURG

Tel.: + 352 5313 3014

Fax: + 352 5313 3087


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