Applications

Galvanized coatings are applied to iron and steel primarily to provide protection against corrosion of the base metal. Some major applications of hot dip galvanized coatings include:

• Structural steel for power generating plants, petrochemical facilities, heat exchangers, cooling coils, and electrical transmission towers and poles

• Bridge structural members, culverts, corrugated steel pipe, and arches

• Reinforcing steel for cooling towers, architectural precast concrete, and bridge decks exposed to chlorides

• Pole line hardware and railroad electrification structures

• Highway guard rails, high-rise lighting standards, and sign bridge structures

• Marine pilings and rails

• Grates, ladders, and safety cages

• Architectural applications of structural steel, lintels, beams, columns, and related building materials

• Galvanized and painted structural steel for aesthetic, color-coded or extended-life applications, including communication towers, pipe and sign bridges, railings, fencing, and agricultural equipment

• Wastewater treatment facilities, composting buildings, catwalks, gratings, railings, support steel, and related nonimmersion applications

Hot dip galvanized tower and high-strength bolts are produced and used in large quantities for service conditions where long-term integrity of bolted joints is required. In short, wherever steel is exposed to atmospheric, soil, or water corrosion, hot dip galvanized zinc coatings are a standard, effective, and economical method of protection.

The usefulness of hot dip galvanized coatings depends on:

• The relatively slow rate of corrosion of zinc as compared with that of iron (Table 2)

• The electrolytic protection provided to the basis steel when the coating is damaged

• The durability and wear resistance of the zinc coating and the intermetallic iron-zinc alloy layers (Table

• The relative ease and low cost of painting the zinc coating either initially or later, when it is necessary to further extend the life of the structure; such painting is usually done after 25 to 40 years of maintenance-free service in rural and light industrial atmospheres

Table 2 Comparative rankings of 37 locations based on steel and zinc losses

Note the relatively slow rate of corrosion for zinc as compared to steel.

Table 2 Comparative rankings of 37 locations based on steel and zinc losses

Note the relatively slow rate of corrosion for zinc as compared to steel.

Ranking of location by least amount of material lost

Location

Material lost after 2-year exposure, g

Steel:zinc loss ratio

Zinc

Steel

Zinc

Steel

1

1

Norman Wells, N.W.T., Canada

0.07

0.73

10.3

2

2

Phoenix, Ariz.

0.13

2.23

17.0

3

3

Saskatoon, Sask., Canada

0.13

2.77

21.0

4

4

Esquimalt, Vancouver Island, Canada

0.21

6.50

31.0

5

6

Fort Amidor Pier, Panama, C.Z.

0.28

7.10

25.2

6

8

Ottawa, Ontario, Canada

0.49

9.60

19.5

7

22

Miraflores, Panama, C.Z.

0.50

20.90

41.8

8

28

Cape Kennedy, ""mile from ocean

0.50

42.00

84.0

9

11

State College, Pa.

0.51

11.17

22.0

10

7

Morenci, Mich.

0.53

7.03

18.0

11

15

Middletown, Ohio

0.54

14.00

26.0

12

9

Potter County, Pa.

0.55

10.00

18.3

13

20

Bethlehem, Pa.

0.57

18.30

32.4

14

5

Detroit, Mich.

0.58

7.03

12.2

15

36

Point Reyes, Calif.

0.67

244.00

364.0

16

19

Trail, B.C., Canada

0.70

16.90

24.2

17

14

Durham, N.H.

0.70

13.30

19.0

18

13

Halifax (York Redoubt) N.S., Canada

0.70

12.97

18.5

19

18

South Bend, Pa.

0.78

16.20

20.8

20

27

East Chicago, Ind.

0.79

41.10

52.1

21

29

Brazos River, Texas

0.81

45.40

56.0

22

23

Monroeville, Pa.

0.84

23.80

28.4

23

34

Dayton Beach, Fla.

0.88

144.00

164.0

24

32

Kure Beach, N.C. (800 ft lot)

0.89

71.00

80.0

25

17

Columbus, Ohio

0.95

16.00

16.8

26

12

Montreal, Quebec, Canada

1.05

11.44

10.9

27

16

Pittsburgh, Pa.

1.14

14.90

13.1

28

10

Waterbury, Conn.

1.12

11.00

9.8

29

25

Limon Bay, Panama, C.Z.

1.17

30.30

25.9

30

21

Cleveland, Ohio

1.21

19.00

15.7

31

24

Newark, N.J.

1.63

24.70

15.1

32

33

Cape Kennedy (180 ft from ocean, 30 ft elevation)

1.77

80.20

45.5

33

35

Cape Kennedy (180 ft from ocean, ground level)

1.83

215.00

117.0

34

31

Cape Kennedy (180 ft from ocean, 60 ft elevation)

1.94

64.00

33.0

35

26

Bayonne, N.J.

2.11

37.70

17.9

36

37

Kure Beach, N.C. (80 ft lot)

2.80

260.00

93.0

37

30

Halifax (Federal Building) N.S., Canada

3.27

55.30

Source: Ref 1

Table 3 Properties of alloy layers of a hot dip galvanizing coating

Layer(a)

Composition

%

Melting Temperature

°C

°F

Eta

Zn

70

0

454

850

Zeta

FeZn13

179

6

530

986

Delta

FeZn7

244

7-12

530-670

986-1238

Gamma

Fe8Zn10

21-28

670-780

1238-1436

Hot dip galvanized zinc coatings have their longest life expectancy in rural areas where sulfur dioxide and other industrial pollutant concentrations are low (Fig. 2). These coatings also give satisfactory service in most marine environments (Table 4). Although the life expectancy of hot dip galvanized coatings in more severe industrial environments is not as long as for less aggressive environments, the coatings are still used extensively in those exposures, because in general, no more effective and economical method of protection is available. In cases involving particularly severe exposure conditions, coatings slightly heavier than the standard 710 g/m2 (2.3 oz/ft2) minimum in ASTM standard specifications A 123-89 or paint over galvanized coatings (known as duplex coatings) are often selected as the preferred protective system.

Table 4 Corrosion of zinc in different types of water

Water type

Attacking substances

Passivating substances

Corrosion products

Relative corrosion rate

Solubility

Adhesion

Hard water

O2+CO2

Ca+Mg

Very low

Very good

Very low

Sea water

O2+CO2+Cl

Mg+Ca

Low

Very good

Moderate

Soft water, with free air supply

O2+CO2

High

Good

High

Soft or distilled, with poor air supply

O2

Very high

Very poor

Very high

Note: The different compositions of the corrosion products have not been included here because they are complex and depend on different compounds, salts, etc., that are present in all natural waters.

Note: The different compositions of the corrosion products have not been included here because they are complex and depend on different compounds, salts, etc., that are present in all natural waters.

76 153 229 305 382 460 532 610 688 763 837 916 (0.25) (0.50) <0.75) Í1.00) (1.25) (1.50) (1.75) (2.00) (2.25) (2,50) (2.75) (3.00)

11 21 32 43 54 65 75 86 97 108 1 IS 129 <0.4} (0.8) (13) (1.7) (2.1) (2.6) (3.0) (3.4) <3.3) (4.2) (4-7) (5.1)

Thickness of zinc, jjm (mils)

Atmosphere

Description

Heavy industrial atmospheres

These contain general industrial emissions such as sulfurous gases, corrosive mists, and fumes released from chemical plants and refineries. The most aggressive conditions are often found in places of intense industrial activity where the coating is frequently wetted by rain, snow, and other forms of condensation. In these areas, sulfur compounds can combine with atmospheric moisture to convert the normally adherent and insoluble zinc carbonates into zinc sulfite and zinc sulfate. These sulfur compounds are water soluble and adhere poorly to the zinc surface. They are removed by rain with relative ease, exposing a fresh zinc surface to additional corrosion. In general, zinc dissipates more when exposed to this type of environment than any other atmospheric environment. Still, the steel corrodes far more slowly in this type of environment when protected by zinc than when just bare steel is used.

Moderately industrial atmospheres

These environments are similar to those of heavy industrial atmospheric environments but, from the standpoint of corrosion, are not quite as aggressive. The amount of emissions in the air may be somewhat lower than that of heavy industrial environments, and/or the type of emissions may be less aggressive. Most city or urban area atmospheres are classified as moderately industrial.

Suburban atmospheres

These atmospheres are generally less corrosive than moderately industrial areas and, as the term suggests, are found in the largely residential, perimeter communities of urban or city areas.

Temperate marine

The length of service life of the galvanized coating in marine environments is influenced by proximity to the coastline and prevailing wind direction and intensity. In marine air, chlorides from sea spray can react with the

atmospheres

normally protective, initial corrosion products to form soluble zinc chlorides. When these chlorides are washed away, fresh zinc is exposed to corrosion. Nevertheless, temperate marine atmospheres are usually less corrosive than suburban atmospheres.

Tropical marine atmospheres

These environments are similar to temperate marine atmospheres except they are found in warmer climates. Possibly because many tropical areas are found relatively far removed from heavy industrial or even moderately industrial areas, tropical marine climates tend to be somewhat less corrosive than temperate marine climates.

Rural atmospheres

These are usually the least aggressive of the six atmospheric types. This is primarily due to the relatively low level of sulfur and other emissions found in such environments.

Fig. 2 Service life (time to 5% rusting of steel surface) versus thickness of zinc for selected atmospheres. Shaded area is thickness range based on minimum thicknesses for all grades, classes, etc., encompassed by ASTM A 123 and A 153. Source: Ref 2

When hot dip galvanized after-fabrication coatings are painted for protective or decorative reasons, a variety of surface preparation systems may be employed to prepare the galvanized surface for the top coat system. Table 5 shows the adhesion of paints to variously prepared galvanized surfaces. A wide range of proprietary top coat systems are available for use with materials hot dip galvanized after fabrication.

Table 5 Adhesion of air-drying paints applied to selected hot dip galvanized steel surfaces

Adhesion as determined by cross-hatch or V-cut test: E, excellent; G, good; F, fair; P, poor. See Table 9 for other characteristics of these paints.

Table 5 Adhesion of air-drying paints applied to selected hot dip galvanized steel surfaces

Adhesion as determined by cross-hatch or V-cut test: E, excellent; G, good; F, fair; P, poor. See Table 9 for other characteristics of these paints.

Type of paint (vehicle base)

Adhesion on indicated surface

Freshly galvanized(a)

Weathered galvanized(b)

Cold or hot phosphated

Sweep-blasted and galvanized

1. Alkyd-tung oil-phenolic resin combinations'"0"1

F

G

E

E

2. DCO-alkyd-calcium plumbate(d)

E

E

E

E

3. Alkyd-acrylic combinations

G

G

E

E

4. Chlorinated rubber

F-G

F-G

G

E

5. Chlorinated rubber-acrylic combinations

G

G

E

E

6. Acrylate dispersions'8"1

F-G

F-G

G

G

7. Acrylic-styrene dispersions'6"1

G

G

G

E

8. Acrylic/diisocyanate (2 compositions)

G

F

G

E

9. Vinyl copolymers

F-G

F-G

G

G

10. PVC/acrylic combinations

G

G

E

E

11. PVC-dispersions(e)

F

F-G

G

F-G

12. Epoxy resin (2 compositions)®

G

G

G

E

13. Epoxy ester®

P

F

G

G

14. Epoxy/tar (2 compositions)

P

F

F

G

15. Polyurethane (2 compositions)®

P

F

F-G

G

Note: Variations in film properties may occur with variations in formulation. Source: Ref 3

(a) Up to about 4 h after galvanizing.

(b) Weathered in an unpolluted or mildly polluted climate, for 1 to 3 months only.

(c) Precooked tung oil/alkylphenolic resin combinations, chilled with drying-oil-modified alkyd resins.

(d) Dehydrated castor oil (DCO)-modified alkyd resin, pigmented with calcium orthoplumbate (COP) as main pigment in the priming coat.

(e) Finely dispersed polymers in water.

(f) With polyamide hardener.

(g) Epoxy resin-dehydrated castor oil ester.

(h) With encapsulated diisocyanate hardener.

Galvanized steels perform well in contact with a wide variety of other materials (Table 6). Moisture conditions play an important role in the performance of galvanized steels in contact with other materials.

Table 6 Additional corrosion of zinc and galvanized steel resulting from contact with other metals

0, Either no additional corrosion, or at the most only very slight additional corrosion; usually tolerable in service. 1, Slight or moderate additional corrosion; may be tolerable in some circumstances. 2, Fairly severe additional corrosion; protective measures will usually be necessary. 3, Severe additional corrosion; contact should be avoided.

Atmospheric

Immersed

Rural

Industrial/urban

Marine

Fresh water

Sea water

Aluminum and aluminum alloys

0

0 to 1

0 to 1

1

1 to 2

Aluminum bronzes and silicon bronzes

0 to 1

1

1 to 2

1 to 2

2 to 3

Brasses, including high-tensile-strength brass (manganese bronze)

0 to 1

1

0 to 2

1 to 2

2 to 3

Cadmium

0

0

0

0

0

Cast irons

0 to 1

1

1 to 2

1 to 2

2 to 3

Cast iron (austenitic)

0 to 1

1

1 to 2

1 to 2

1 to 3

Chromium

0 to 1

1 to 2

1 to 2

1 to 2

2 to 3

Copper

0 to 1

1 to 2

1 to 2

1 to 2

2 to 3

Copper-nickels

0 to 1

0 to 1

1 to 2

1 to 2

2 to 3

Gold

(0 to 1)

(1 to 2)

(1 to 2)

(1 to 2)

(2 to 3)

Gun metals, phosphor bronzes, and tin bronzes

0 to 1

1

1 to 2

1 to 2

2 to 3

Lead

0

0 to 1

0 to 1

0 to 2

(0 to 2)

Magnesium and magnesium alloys

0

0

0

0

0

Nickel

0 to 1

1

1 to 2

1 to 2

2 to 3

Nickel-copper alloys

0 to 1

1

1 to 2

1 to 2

2 to 3

Nickel-chromium-iron alloys

(0 to 1)

(1)

(1 to 2)

(1 to 2)

(1 to 3)

Nickel-chromium-molybdenum alloys

(0 to 1)

(1)

(1 to 2)

(1 to 2)

(1 to 3)

Nickel silvers

0 to 1

1

1 to 2

1 to 2

1 to 3

Platinum

(0 to 1)

(1 to 2)

(1 to 2)

(1 to 2)

(2 to 3)

Rhodium

(0 to 1)

(1 to 2)

(1 to 2)

(1 to 2)

(2 to 3)

Silver

(0 to 1)

(1 to 2)

(1 to 2)

(1 to 2)

(2 to 3)

Solders, hard

0 to 1

1

1 to 2

1 to 2

2 to 3

Solders, soft

0

0

0

0

0

Stainless steel (austenitic and other grades containing approximately 18% Cr)

0 to 1

0 to 1

0 to 1

0 to 2

1 to 2

Stainless steel (martensitic grades containing approximately 13% Cr)

0 to 1

0 to 1

0 to 1

0 to 2

1 to 2

Steels (carbon and low-alloy)

0 to 1

1

1 to 2

1 to 2

1 to 2

Tin

0

0 to 1

1

1

1 to 2

Titanium and titanium alloys

(0 to 1)

(1)

(1 to 2)

(0 to 2)

(1 to 3)

Notes: Ratings in parentheses are based on very limited evidence and hence are less certain than other values shown. Values are in terms of additional corrosion, and the symbol 0 should not be taken to imply that the metals in contact need no protection under all conditions of exposure.

Source: Ref 2

Galvanized surfaces have a good tolerance to various chemicals within the range of 4 to 12.5 pH (Fig. 3). Some chemicals that have been successfully stored in galvanized containers are listed in Table 7.

Table 7 Selected chemicals that have been successfully stored in galvanized containers

Hydrocarbons

Benzene (benzole) Toluene (toluole) Xylene (xylole) Cyclohexene Petroleum ethers Heavy naphtha

Solvent naphtha

Alcohols

Methyl parafynol (methyl pentynol) Morpholinoisoprop anol Glycerol (glycerin)

Halides

Carbon tetrachloride Amyl bromide Butyl bromide Butyl chloride Cyclohexyl bromide Ethyl bromide Propyl bromide Propyl chloride

Trimethylene bromide (1, 3-dibromopropane)

Bromobenzene

Chlorobenzene

Aroclors and pyroclors (chlorobiphenyls)

Nitriles (cyanides)

Diphenylacetonitrile p-chlorobenzglycyanide

Esters

Allyl butyrate Allyl caproate Allyl formate Allyl propionate Ethyl butyrate Ethyl isobutyrate Ethyl caproate Ethyl caprylate Ethyl propionate Ethyl succinate Amyl butyrate Amyl isobutyrate Amyl caproate Amyl caprylate Methyl butyrate Methyl caproate

Methyl propionate Methyl succinate Benzyl butyrate Benzyl isobutyrate Benzyl propionate Benzyl succinate Octyl butyrate Octyl caproate Butyl butyrate Butyl isobutyrate Butyl caproate Butyl propionate Butyl succinate

Butyl titanate(a)

Propyl butyrate Propyl isobutyrate Propyl caproate Propyl formate Propyl propionate Isobutyl butyrate Isobutyl caproate Isopropyl benzoate Isopropyl caproate Isopropyl formate Isopropyl propionate Cyclohexyl butyrate

Phenols

Phenol

Cresols (methylphenols) Xylenols (dimethylphenols) Biphenol (dihydroxybiphenyl) 2,4-dichlorophenol p-chloro-o-cresol Chloroxylenols

Amines and Amine salts

Pyridine Pyrrolidine

Methylpiperazine

Dicarbethoxypiperazine

1-benzhydryl-4-methylpiperazine 2,4-diamino-5-(4-chlorphenyl-6-)ethylpyrimidine Hydroxyethylmorpholine (hydroxyethyldiethylenimide oxide) p-aminobenzenesulphonyl-guanidine Butylamine oleate

Piperazine hydrochloride monohydrate Carbethoxypiperazine hydrochloride (dry)

Amides

Formamide Dimethylformamide

Miscellaneous

Glucose (liquid) Benzilideneacetone p-chlorbenzophenone Sodium azobenzenesulphonate Melamine resin solutions Crude cascara extract Creosote

Source: Ref 2

(a) And other unspecified titanates.

0 0

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