Designation: A 384/A 384M – 07

Standard Practice for

Safeguarding Against Warpage and Distortion During Hot-
Dip Galvanizing of Steel Assemblies1
This standard is issued under the fixed designation A 384/A 384M; the number immediately following the designation indicates the year
of original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval.
A superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
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1. Scope 850°F (438 to 454°C), the stress can be slightly relieved but the
1.1 Steel assemblies and subassemblies fabricated by weld- constraint of the framing does not allow the stresses to be
ing, such as composite structural members, sash, weldments, completely relieved. The stress relief is minimal and, thus, the
etc., that are to be hot-dip galvanized after fabrication, are internal stress level of the sheet or plate compounds because of
subject to warpage and distortion of the material due to the the addition of the contraction forces. When the fabrication
heating and cooling integral to the galvanizing operation, cools after galvanizing, the framing also restricts the contrac-
particularly when it is necessary for the assembly to be dipped tion of the sheet or plate further increasing internal stresses. If
more than once to coat the entire surface. the warpage or distortion is minimal, the fabrication may be
1.2 This specification is applicable in either inch pounds or acceptable but, if the distortion is significant, the fabrication
SI units. Inch pounds and SI units are not necessarily exact may need to be reworked with the sheet or plate attached to the
equivalents. Within the text of this specification and where frame after hot-dip galvanizing.
appropriate, SI units are shown in parentheses. 3.2 Warpage is accentuated by the use of nonsymmetrical
sections such as channels. Regardless of size, channels that are
2. Referenced Documents galvanized by themselves often require straightening after
2.1 ASTM Standards: 2 galvanizing. This is not true of an I-beam, pipe, H-column, or
A 143/A 143M Practice for Safeguarding Against Em- any other section that is symmetrical about both its major axes.
brittlement of Hot-Dip Galvanized Structural Steel Prod- Channels and other nonsymmetrical sections should be avoided
ucts and Procedure for Detecting Embrittlement for the framework of a sheet metal assembly that is to be
A 385 Practice for Providing High-Quality Zinc Coatings hot-dip galvanized whenever it is possible to use symmetrical
(Hot-Dip) shapes or sections as framing pieces.
A 780 Practice for Repair of Damaged and Uncoated Areas 3.2.1 Checkered plate may also warp or distort during
of Hot-Dip Galvanized Coatings galvanizing due to the asymmetry of the plate design. Since all
of the deformations are on one side of the plate, the residual
3. Factors in Warpage and Distortion stress from fabricating the checkered plate may cause warpage
3.1 One of the most commonly distorted and warped mem- or distortion. This may be accentuated by attaching checkered
bers of assemblies is that of sheets or plates from No. 20 gage plate to a frame before hot-dip galvanizing.
[0.812 mm] to 1⁄4 in. [6.35 mm] in thickness which are 3.3 The use of wide radii bends in corners is recommended.
assembled by welding or riveting to bar-size shapes, angles, In the case of sheet metal, the product that has a right-angle
channels, tees, etc. The sheets or plates have residual stress bend in the sheet metal itself will remain flatter and be freer
from the welding or riveting as well as stress from rolling from distortion if the radius of the bend is as large as practical.
operations to bring the sheet or plate to its final thickness. As For extremely tight bends that are integral to the fabrication,
the sheet or plate is heated to galvanizing temperature, 820 to stress relieving in accordance with the section on Cold Work-
ing and Thermal Treatment of Practice A 143/A 143M is
recommended to avoid warpage or distortion.
1
This practice is under the jurisdiction of ASTM Committee A05 on Metallic- 3.4 Certain welding practices, weld sizes and configura-
Coated Iron and Steel Products and is the direct responsibility of Subcommittee
tions, and thickness differences between welded components
A05.13 on Structural Shapes and Hardware Specifications.
Current edition approved May 1, 2007. Published June 2007. Originally can introduce imbalanced stresses into the weldments. If these
approved in 1955. Last previous edition approved in 2002 as A 384/A 384M - 02. stresses are combined with other stresses during hot-dip
This practice is based upon the work of the Technical Services Committee of the galvanizing, the stress relieving effect of galvanizing may
American Galvanizers Association.
2
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
permit distortion to occur.
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM NOTE 1—One example of this situation is the bracing of two large
Standards volume information, refer to the standard’s Document Summary page on
pieces in a fabrication by a smaller piece. The smaller piece is welded at
the ASTM website.

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 A 384/A 384M – 07
both ends and during the cool-down after galvanizing it may experience 4.5 The sheet steel should not be welded to the angle steel
significant stress as it cools more quickly than the two larger pieces. The frame prior to galvanizing if the galvanizing kettle is not of
resulting stress may cause warpage or distortion of the smaller, bracing sufficient size to permit the total immersion in one dip. If the
piece. Another example of imbalanced stresses is the welding of a
fabrication piece on one edge. When this type of fabrication is hot-dip
frame has to be dipped one half at a time, it will be better to
galvanized the welding on one edge causes all of the internal stress in the have the sheets galvanized, rolled flat after galvanizing, and
part to be concentrated at the edge of the weld and during cool down from assembled to the galvanized frame by the use of galvanized
galvanizing the contraction may cause the part to warp or distort since it rivets. These rivets can be countersunk or flat head if the
cannot move to adjust the internal stresses. protruding head of the ordinary button or round head rivet is
3.5 When two pieces of steel are seal welded in an overlap- objectionable. If the angle steel frame and sheets are punched
ping joint, the overlapping section must be properly vented per prior to galvanizing (the recommended procedure), the use of
Practice A 385. If the overlapped area is not properly vented or drift pins to bring the holes into alignment should be avoided
if it is incorrectly sealed, the pressure from the expansion of the as far as possible at the time the sheets and frame are
trapped gases in the overlapped area can distort the two pieces assembled.
of steel that are welded together and, in the worst case, can 4.6 If the galvanizing kettle is of sufficient size to permit
cause an explosion underneath the zinc bath surface destroying total immersion of the assembly in one dip, the riveting of
the parts and causing a potential safety problem at the hot-dip fabricated parts prior to galvanizing is not recommended
galvanizing facility. because contacting surfaces will not be coated and rusting will
3.6 When a fabricated assembly is too large for a particular occur due to entrapped pickling acid.
galvanizing kettle and the fabrication must be dipped, reposi- 4.7 Unequal thickness of metal should be avoided wherever
tioned, and dipped again, the thermal stresses on the fabrication possible due to the different rates of heating and cooling during
due to the temperature differences from the section inside the the galvanizing operation and the effect of unequal expansion
zinc bath to the section outside the zinc bath can create and contraction.
warpage or distortion of the fabrication. 4.8 If the fabrication is non-symmetrical and all other
3.7 Combining any of these potential causes of warpage, or attempts to minimize the warpage and distortion have failed,
distortion, or both, such as non-symmetrical design with two fabrications may be temporarily connected to make a
different thickness steel parts increases the potential for symmetrical assembly for the hot-dip galvanizing process. This
warpage and distortion to occur. can minimize the warpage and distortion during the thermal
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cycle of the hot-dip galvanizing. After galvanizing, the tempo-

4. Suggested Corrections for Panel Fabrication rary bracing to make the symmetrical assembly can be re-
4.1 The angles selected should be in as perfect alignment as moved and the areas of contact can be repaired or touched-up
it is practical to obtain. as described in Practice A 780.
4.2 The angles should be placed in position without clamp-
ing or pulling prior to welding so that the corners of abutting 5. Embrittlement
edges will lie in position without restraint. Clamps may be
5.1 Cold working before galvanizing (straightening, spring-
applied to prevent shifting or movement during the welding
ing into position, reforming, etc.) of various steel parts in
operation.
making up an assembly, or in the cold working of the
4.3 The stiffening angles should be placed in position and
individual members of an assembly, punching, cutting, etc.,
held down to prevent their being moved when in contact with
may result in embrittlement of the base metal following the hot
the electrode during the welding operation. In welding any
galvanizing operation. Necessary precautions to fabricate prop-
intermediate lengths along one side of a common member, care
erly and prepare the material for galvanizing to prevent
should be taken to prevent warpage of the common member
embrittlement are described in Practice A 143/A 143M.
due to the application of high heat on the same side at various
intervals along its length. NOTE 2—Welding, if improperly performed, may induce embrittlement.
4.4 All edges of tightly contacting surfaces should be It is recommended that welding procedures be carried out in conformance
completely sealed by welding unless the area exceeds the with the pertinent specifications of the American Welding Society.
recommended size detailed in Practice A 385. This will prevent
the rusting of the surfaces that are so connected that molten 6. Keywords
zinc cannot circulate through the crevices to galvanize the 6.1 coatings-zinc; galvanized coatings; steel products-
contacting surfaces. metallic coated; zinc coatings-steel products

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 A 384/A 384M – 07

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