Technical Note Cold-Formed Steel
Technical Note Cold-Formed Steel
Technical Note Cold-Formed Steel
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Washington, DC 20005
(202) 785-2022
2.0 GALVANIZING
2.1 Definition
Galvanizing is a process whereby steel is immersed into a
bath of molten zinc (865F/460C) to form a metallurgically
bonded zinc coating. This same hot dip immersion process
is also used to produce aluminum-zinc alloy coatings.
Most cold-formed steel is galvanized by unwinding coils
of cold rolled steel and feeding the sheet continuously
through a molten zinc bath at speeds up to 600 feet per
minute (200 meters/minute). As the steel exits the molten
zinc bath, air knives blow off the excess coating from the
steel sheet and control the coating thickness to the
specification requirement. The coated sheet steel is
chemically treated (passivated) to protect against storage
Cold-Formed Steel Engineers Institute
September 2007
Table 2.1
Zinc Coating Weights (Mass) / Thickness
Coating Designation
Minimum Requirement
Total Both Sides
Thickness
Nominal per Side
(oz/ft2)
(g/m2)
(mils)
(microns)
0.40
0.60
0.90
120
180
275
0.34
0.51
0.77
8.5
12.7
19.4
0.50
150
0.80
20.0
Zinc (Galvanized)
G40/Z120
G60/Z180
G90/Z275
55% Aluminum-Zinc
AZ50/AZM150
Table 2.2
Minimum Coating Weight Requirements
Framing Member
Designation
Zinc (Galvanized)
55% Aluminum-Zinc
Structural
G60/Z180
AZ50/AZM150
Non-Structural
G40/Z120
AZ50/AZM150
September 2007
Additionally, a survey was performed in May 1995 on a 20year old steel-framed house in Stoney Creek, Ontario11. The
inspection revealed no visible signs of corrosion of the
zinc coating or the steel studs. Coating thickness measurements taken on exterior and interior studs showed no
measurable loss in coating thickness.
The corrosion rate of zinc coatings in an indoor atmosphere of a buildings structure is generally low. According to a three-year British Steel study9, the corrosion of
zinc is lower than 0.1 m (microns) per 3-year period in
houses located in different rural, urban, marine and
industrial atmospheres (Figure 3.1). This indicates that
under similar conditions a 10-m (microns) zinc coating
should last for more than 300 years.
Corrosion loss of galvanized steel, exposed in the loft of 15 residential houses located in three different
geographical areas in England, UK, as a function of exposure time (John, 1991). The data points are the mean
values of 6 samples for each house; the equation in the figure is the best fit from linear regression analysis.
Figure 3.1
Cold-Formed Steel Engineers Institute
September 2007
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Coupled Alloy
Mild Steel
Stainless Steel
Brass
Copper
Lead
Nickel
Aluminum
High
Low
High
High
Medium
Medium
Low
Table 4.2
12,13
September 2007
5.4 Fasteners
6.0 CONCLUSIONS
Zinc and zinc alloy hot dip galvanized coatings are
economical and recommended methods of providing
long-term corrosion protection of steel framing members.
The galvanizing process produces a tough metallic
coating that can withstand the physical demands
created during fabrication, distribution, site storage and
installation of the steel-framing members.
5.3 Welding
Galvanized steel can be joined by spot or continuous
welding. Welding may be an economical joining method
when shop fabricating wall or roof assemblies. Although both welding operations volatilize the zinc
coating at the weld site, spot welding is a much more
localized process.
Spot welds and continuous welds will remove the
zinc coating. Damaged areas should be repaired
using zinc rich touch-up paint or by zinc metallizing
in accordance with ASTM A780 15. Zinc metallizing is
a thermal process that propels molten zinc particles
onto the steel substrate producing a continuous
metallic zinc coating.
Cold-Formed Steel Engineers Institute
September 2007
CONTRIBUTORS
This publication was developed by the Corrosion and
Durability Task Group, a joint effort of the Committee on
Framing Standards of the American Iron and Steel Institute
and the Cold-Formed Steel Engineers Institute, a Council
of the Steel Framing Alliance. This publication is intended
to provide designers with guidance in selecting coated
steels and enhancing durability in buildings that utilize
cold-formed steel framing members.
CFSEI acknowledges Douglas J. Rourke of the International Zinc Association and X. Gregory Zhang of Teck
Cominco Metals Ltd. as the primary authors of the first
(1996) edition of the AISI design guide on Durability of
Cold-Formed Steel Framing Members, and is grateful to
the following members of the Corrosion and Durability
Task Group who helped develop this CFSEI Technical
Note.
References
1. Townsend, H.E., Continuous Hot Dip Coatings, Metals Handbook, ASM International, Materials Park, OH, 1995.
2. ASTM A1003/A1003M, Standard Specification for Steel Sheet, Carbon, Metallic- and Nonmetallic-Coated for Cold-Formed
Framing Members, - ASTM International, West Conshohocken, PA, www.astm.org.
3. North American Standard for Cold-Formed Steel Framing - Product Data, AISI S201, American Iron and Steel Institute, Washington, DC, 2007.
4. ASTM A653/A653M, Standard Specification for Sheet Steel, Zinc Coated (Galvanized) or Zinc-Iron Alloy Coated (Galvannealed)
by the Hot Dip Process, - ASTM International, West Conshohocken, PA, www.astm.org.
5. ASTM A792/A792M, Standard Specification for Steel Sheet, 55% Aluminum-Zinc Alloy Coated by the Hot Dip Process, - ASTM
International, West Conshohocken, PA, www.astm.org.
6. ASTM C645, Standard Specification for Nonstructural Steel Framing Members, ASTM International, West Conshohocken, PA,
www.astm.org.
7. ASTM C955, Standard Specification for Load-Bearing (Transverse and Axial) Steel Studs, Runners (Tracks), and Bracing or
Bridging for Screw Application of Gypsum Board and Metal Plaster Bases, ASTM International, West Conshohocken, PA,
www.astm.org.
8. Corrosion Protection for Cold-Formed Steel Framing in Coastal Areas, Technical Note D200, Cold-Formed Steel Engineers
Institute, Washington, DC, 2007.
9. John, V., Durability of Galvanized Steel Building Components in Domestic Housing, British Steel Technical - Welsh Laboratories,
Port Talbot, UK, 1991.
10. ILZRO, ZC-4, Seven Year Report, Galvanized Steel Framing for Residential Buildings, International Lead Zinc Research
Organization, Research Triangle Park, NC, 2006.
11. DeMeo, L.D., 20 Year Inspection of LSF at DESH, unpublished report, Dofasco Inc., Hamilton, Ontario, Canada, 1995.
12. Zhang, X.G., Corrosion and Electrochemistry of Zinc, Plenum Publishing Corporation, New York, NY, 1996.
13. Zhang, X.G., Corrosion of Zinc and Its Alloys, Metals Handbook, ASM International, Materials Park, OH, 2005.
14. Pressure Treated Wood and Steel Framing, Issue Paper 4, Steel Framing Alliance, Washington, DC, 2007.
15. ASTM A780, Standard Practice for Repair of Damaged and Uncoated Areas of Hot-Dip Galvanized Coatings, ASTM International, West Conshohocken, PA., www.astm.org.
16. Corrosion Protection of Screw Fasteners, Technical Note D100, Cold-Formed Steel Engineers Institute, Washington, DC, 2007.
17. Code of Standard Practice for Cold-Formed Steel Structural Framing, American Iron and Steel Institute, Washington, DC, 2006.
This Technical Note on Cold-Formed Steel Construction is published by the Cold-Formed Steel Engineers Institute (CFSEI). The
information provided in this publication shall not constitute any representation or warranty, express or implied, on the part of CFSEI
or any individual that the information is suitable for any general or specific purpose, and should not be used without consulting with a
qualified engineer, architect, or building designer. ANY INDIVIDUAL OR ENTITY MAKING USE OF THE INFORMATION
PROVIDED IN THIS PUBLICATION ASSUMES ALL RISKS AND LIABILITIES ARISING OR RESULTING FROM SUCH
USE. CFSEI believes that the information contained within this publication is in conformance with prevailing engineering standards of
practice. However, none of the information provided in this publication is intended to represent any official position of the CFSEI or
to exclude the use and implementation of any other design or construction technique.
September 2007