valm coat galvtech 102804
TRANSCRIPT
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galvanize
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alvanized to exceed your expectations.
The Lead ing Galvan i zer
As a full-service coatings company, Valmont
Coatings provides quality surface finishes
that extend the service life and improve the
appearance of metal products throughout
the country. Our processes and transportation
capacities are designed to efficiently handle
steel products of all shapes and sizes, for
customers anywhere in the country.
Valmont Coatings is the market and technical leader in hot dip galvanizing.We are one of the largest custom galvanizers in North America, serving allsteel fabrication markets from coast to coast. Valmont Coatings is a membeof the American Galvanizers Association.
I ntroduct ion
The size of products that can be hot dip
galvanized is determined by the size of
the zinc kettles, the tanks in the cleaning
line, the crane capacities, or the building
structure clearances within a particular
galvanizing plant.
The most economical and highest quality
galvanizing is achieved when steel products
are sized to enable the entire product to
be totally immersed in the molten zinc in
a single dip.
When needs dictate that the product to
be galvanized must be longer or deeper
than the galvanizers kettle, it can often be
galvanized by means of the double dipping
procedure. With this method, 50% or more
of the surface of the product is immersed in
the molten zinc. When the galvanizing of that
portion is completed, the product is turned
over and the remaining uncoated portion
is lowered into the zinc and galvanized.
This section will guide the prospective
user of Valmont Coatings service to
determine common size and weight
limits for products that are single-ordouble-dipped within our plants.
We urge fabricators, engineers and
architects to consult with us if the product
under consideration is slightly larger than
the dimensions cited in this brochure.
In some situations, depending upon the
design of the product, certain special
procedures can be used to satisfy
greater requirements.
Fac i l i t i e s and Process
Valmont Coatings uses galvanizing kettles
that typically are the following sizes:
At the beginning of the process, products
are batched into bundles, trays or racks
to be handled in the most effective manner
through the cleaning line. At this stage,
each product is examined to determine the
presence of adequate details for venting
and draining of fluids during cleaning and
galvanizing, and to assure that, when
necessary, the product is provided with
holes or lugs for lifting. If additional venting
details or lifting holes/lugs are required, the
customer is notified and arrangements are
made to install them.
After batching, the products are passed
through the stages of the cleaning and
galvanizing line, illustrated in Figure 1.
This schematic applies to products whose
coating must meet the requirements of
ASTM Specification A 123.
When parts are required to have excess
zinc removed by centrifuging or brushing,
the stages shown in Figure 2 are applicable.
Products are galvanized in this manner
to conform to the requirements of ASTM
Specification A 153.
Caustic The caustic tank contains
heated water with caustic soda and
detergent additives. Oils, soil and soluble
paint markings are removed from products
during immersion at this stage.
Rinse A tank containing plain wate
used to remove residues of the caust
Pickle A bath of heated dilute sulfu
acid solution removes rust and mill sc
from the products.
Rinse Another tank containing plain
is used to remove residues from pickl
Flux Zinc ammonium chloride in sol
provides additional cleaning of the pro
being dipped. During galvanizing, the
of flux on the products improves wett
between the steel and the molten zinc
Re-fixturing Depending upon the p
uct and/or type of batching used duri
cleaning, some products are re-fixture
or re-batched, for better processing
through the molten zinc bath.
Galvanizing The fluxed, possibly re-
tured, product is taken to one of the z
kettles. Each kettle is provided with a f
black blanket of zinc ammonium chlor
flux which floats on the surface of the
ten zinc. The products are lowered thr
the flux blanket en route to the molten
below and, in so doing, receive one fin
cleaning. Products remain in the molte
until they reach the approximately +83
molten zinc temperature.
Centrifuging or Brushing (For ASTM
153 Only) When the perforated bas
containing the product is removed fro
the molten zinc, it is transferred imme
ately to the centrifuge where excess z
is spun away.
Process and Sizing Guide For Hot Dip Galvanizing
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Products that are too large to be centri-
fuged, but are still in need of removal of
excess zinc, are subjected to brushing of
the critical areas before the zinc solidifies.
Quench After galvanizing and centrifuging
or brushing (when applicable), the product
is immersed in a plain water quench to
retain as much bright zinc surface as
possible and to reduce the time required
for handling.
Inspection Products are visually checked
for coating integrity and measured to verify
that coating thickness meets or exceeds
ASTM Standards.
S ize L im i ts S ing le D i p
Lifting Capacity: 10,000 lbs.
Height
26 or 52 kettle length
Product length
26 Foot Kettle Maximum product
dimensions: 25-8 long x 4-4 wide x
6-0 high.
52 Foot Kettle Maximum product
dimensions: 51-6 long x 4-4 wide x
5-0 high.
Size L im its Double Dip
Lifting Capacity: 10,000 lbs.
1. Double dip for height
Height
Kettle length
Product length
26 Foot Kettle Maximum product
dimensions: 24-0 long x width and height,
from this table:
Width Maximum height
Up to 9 12-0
+9 to 12 11-7
+12 to 24 10-5
+24 to 52 10-4
52 Foot Kettle Maximum product
dimensions: 50-0 long x 4-4 wide x
10-0 high.
2. Double dip for length
Kettle length
Productlength
height
Maximum product dimensions: 4 x 4 wide
x length and height from table below:
Maximum
Maximum length using
length using all dip stages
Height all dip stages except caustic*
Up to 6 61-10 72-0
+6 to 12 62-9 72-0
+12 to 18 62-8 72-0
v+24 to 30 62-7 71-9
+30 to 36 62-6 67-0
+36 to 39 62-6 64-11
+39 to 42 See note 1 62-8
+42 to 48 See note 1 58-4
Note 1: Items 39 through 48 in height are
too large for caustic double dipping and
can only be processed if they are given
SP-6 Commercial Blast before supplying
to Valmont.
*Products can be galvanized to the lengths
given in this column when steel is cleaned
to SP-6 Commercial Blast before sup-plying to Valmont. Such cleaning enables
bypass of size restriction imposed at the
caustic tank.
Limited by building structure clearance.
S ize L im i ts C entr i f
Maximum product dimensions:
Rounds: 18 long x 4 diameter
Plates: 6 x 6 x 1 thick
Angles: 5 x 5 x 1/2 thick x 6 long
Consult with Valmont Coatings if the
product under consideration is slightl
larger than the dimensions given in th
brochure. In some situations, depend
on the design of the product, certain
special procedures can be used to
satisfy greater requirements.
Caustic Rinse Pickle Rinse Flux Solution Zinc Bath Quench Inspectio
Caustic Rinse Pickle Rinse Flux Solution Transfer to Basket Zinc Bath Centrifuge(or Brush)
Quench Inspectio
Figure 1: Process for ASTM A 123
FIGURE 2: Process for ASTM A 153
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Introduction and Purpose
The galvanizing of products that are made
from tube or pipe requires special attention
by the fabricator and the galvanizer. Instal-
lation of suitably sized holes in strategic
locations on the product is essential to
assure the correct galvanizing of all internal
surfaces. The holes, so placed in the prod-
uct, serve several purposes, namely to:
1. Prevent pressure build up and rupture
of the product that could result from
heating of enclosed air and moisture
during partial or full immersion in the
840 F galvanizing bath.
2. Provide for the rapid entry of cleaning
fluids and molten zinc to overcome the
natural buoyancy of hollow objects.
3. Enable air and galvanizers flux to escape
from the last remaining upper corners
of a product at the moment of total
immersion. Elimination of air pockets
allows cleaning fluids and molten zinc
to reach all surfaces to permit complete
internal cleaning and coating. Evacua-
tion of flux eliminates a potentially
corrosive internal condition.
4. Eliminate the entrapment of pockets of
zinc as the product is being withdrawn
from the galvanizing bath. Properly sized
and placed holes avoid large and costly
volumes of zinc from solidifying in
deep recesses.
5. Contribute to the safety of galvanizing
plant personnel.
Holes, placed in products to fulfill the
functions listed, are referred to as
vents and drains* in the galvanizing
industry. Size and location of such holes
are a frequent topic of conversationbetween a galvanizer and t he fabricator.
Conservative recommendations on the
size and location of openings are given
in ASTM A 385, Standard Practice for
Providing High Quality Zinc Coatings
(Hot-Dip). In order to select adequate,
yet economical details for vents and
drains, it is necessary to understand
how the product will be oriented as it
is being lowered into the baths. This is
not something that a fabricator could
reasonably know without prior guidance.
The purpose of this brochure is to
acquaint the fabricator with the principles
that Valmont uses in determining how
to position a work piece for lowering
into the baths, and how this leads to
a determination of where the vents
and drains should be located.
Some examples are given to show
how the principles are applied to
tubular products but, since the type and
configuration of products are so varied,
we are relying on these principles, coupledwith the fabricators knowledge of their
own product, to enable them to determine
where vents and drains are required.
*Holes that are used to drain as a part is
being removed from the bath have earlier
served as fillholes during the immersion
of the part. For purposes of this brochure,
use of the terms fill and drain should
be taken to describe the same hole,
depending upon how it is functioning
at a particular stage of the process.
Pr inc i p l es
1. Product Is Oriented to Maximize
Bath/Kettle Space
Bath width
Product width
Generally, products are set up for galvanizing
so that their smallest dimension parallels
the bath width. Several identical pieces
can often be galvanized side by side at the
same time, thereby utilizing most of the
width of the cleaning bath or zinc kettle.
It is with this orientation that the consider-
ation of vent and drain openings begins.
2. Initial Fill Location Is at Largest
Available End Opening
An opening at, or very near to, a lower end
location of the product is selected as the
initial entry opening to allow cleaning fluids
and molten zinc to flow i nto the interior.
When a product has an opening at each
of its two ends, and one of these openings
is larger than the other, the larger opening
will be chosen as the entry orifice, provided
that it can be situated near the bottom of
the product when suspended by a crane.
3. Final Vent Is at Position
Immersed Last
Good internal galvanizing depends on the
ability of cleaning fluids and molten zinc to
surge through the hollow product from the
entry to the exit point, without compress-
ing any air into pockets in its path. In any
hollow product, the last exit point must be
located at the place where the last portion
of the hollow component submerges into
the bath.
4. Lift Orientation Is Suited to Initial Fill,
Final Vent Locations
Vent
Fill
As the work piece is being lowered into
each of the baths, the natural tendency
of the cleaning fluid and molten zinc is
to push upward through the product.
To enhance this movement and to
encourage a flow, especially along
longitudinal components of the products,each work piece is arranged at a sli ght
angle on the hoisting equipment as shown.
5. Size, Style and Location of Open
Are Adequate
Vent
Fill
Fill
Vent
Fill
For secondary components, as for pr
members, fill holes (F) need to be loca
as close as possible to the point on th
member where the fluids first make co
during immersion. Similarly, vent holes
on secondary members need to be as
close as possible to the point where th
member is finally and completely imm
Other Valmont Coatings recommend
relating to openings are as follows:
Minimum Size of Openi
Requirements for fill and vent opening
vary according to the size of tube or p
being filled, and whether that tube or
is a primary or secondary componen
the overall product. Fill and vent open
for primary members apply when the
members have end closures of any k
The following tables provide guideline
on sizes that Valmont Coatings gene
considers to be minimum.
Pipe and Round Tube
Minimum Fill and
Vent Hole Diameter
Pipe & Tube Primary Seconda
Diameter Member Member
1-14, 1-12 5/8 3/82 7/8 1 2
4 1-5/8 7/8
6 2-3/8 1-14
8 3-14 1-5/8
10 4 2
12 4-5/8 2-3/8
14 5-14 2-5/8
16 6 3
18 7 3 12
20 8 4
Fabricators Guide to Pipe and Tube Galvanizing
In order to select adequate, yet economical detailsfor vents and drains, it is necessary to understandhow the product will be oriented as it is beinglowered into the baths. is is not somethingthat a fabricator could reasonably know without
prior guidance.
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Square or Rectangular Tube
Triangular corner cutouts, rather than round
holes, are suggested for fill or vent open-
ings in end closures on primary members
made of square or rectangular tube. Round
holes, however, remain suitable to be fill
or vent openings in secondary members
made from this type of tube. The following
table lists square-inch units for minimum
opening sizes in primary members, and
hole diameters in inch units for minimum
openings in secondary members.
Minimum Fill and
Vent Hole Size
Tube Cross Primary Secondary
Section* Member Member
(sq. in.) (sq. in.) (inches)
2.25 0.6 124.0 1.0 5/8
9.0 1.25 5/8
16.0 2.75 1
25.0 4.5 1-14
36.0 5.5 1-3/8
49.0 8.0 1-5/8
64.0 11.0 1-7/8
81.0 13.0 2
100.0 15.0 2-14
*Interior cross section, square or rectangular tube.
Qual i ty o f Open ing
The evenness of the edge of an opening
plays a significant part in helping Valmont
Coatings achieve a good looking galva-
nized coating around it. Regular openings
allow a smooth spill of molten zinc upon
withdrawal from the bath. Irregular, ragged
edge openings cause molten zinc to splat-
ter as it pours and should be avoided.
Good Avoid
Locat ion o f Open ings
Openings are best located where they
will help to fill, vent and drain the tubes
most rapidly. Their location on individual
components must be related to the listing
direction of the overall assembly.
(a) In Primary Members
Fill (Near end)
Lift Lift
Lift Lift
Vent (Far end)
Fill (Near end)
Vent (Far end)
Round single Square or rectangle single
Round assembly Square or rectangle assembly
(b) In Secondary Members
Perpendicular member
1/2 maximum
6. Product Filled Slowly, Gradually
from End to End
Slow immersion allows the bath and the
product to adjust for their very different
initial temperatures. Filling from end to
end allows flux on the interior surfaces
to be flushed out of the product.
7. Product Is Drained Through Original
Fill Holes
The sloped orientation of the work piece
on the lifting equipment facilitates drainage.
Further Ass i s tance
Valmont Coatings will provide help to
customers, upon request, to establish the
size and location of vent and drain holes
during the fabrication of an order.
If Valmont Coatings technicians determine
additional vent and drain fabrication is
necessary once a product is in the Valmont
plant, we will noti fy the customer, provide
costs for appropriate modifications and
request permission to install or modify
the holes.
Angled member
3/4 maximum
3/8 diameterPrimary fill
1/2 maximum
Dip direction
5/8 diameterPrimary fill
1/2 maximum
3/8 diameterSecondary vent
1/2 maximum
1-1/2 Pipe handrail
1/2 maximum
3/8 diameterSecondary fill
3/8 diameterSecondary vent
5/8 diameterPrimary vent
3/8 diameterSecondary fill
1/2 maximum
Pipe Handrail
5/8 diameterSecondary fill
Two cutouts 1 x 1-1/4 (1.25 sq. in.)Primary vent
5/8 diameterSecondary vent
3/4 maximum
Open end
3-1
/2
x2
-1/2T
ub
e
2-1/2
x2-1/2Tub
e
Dip direction
Tubular Bracket
Examp les
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Introduction and Purpose
Fabricated steel products that are to be
galvanized should have details that would
allow the galvanizers cleaning solutions
and molten zinc to flow freely through the
product at various stages throughout the
hot dip galvanizing process.
When such details are made, they elimi-
nate the formation of air pockets during
dipping. This helps to assure that the steel
is thoroughly cleaned and coated in all
corners. Improperly cleaned areas of steel
will not galvanize.
Details that allow a clear path for the
run-off of molten zinc when steel parts
are being withdrawn from the galvanizers
kettle result in a coating that is more evenly
formed throughout the product. Proper
details prevent unwanted zinc build-ups
which, ultimately, add to the customers
cost, look unsightly, and may interfere
with the fit-up of adjoining parts.
To determine how to avoid pockets and
traps when a product is being hot dip
galvanized, the fabricator must first
understand how a product will be oriented
as it is being lowered into and lifted from
the baths. This is not something that a
fabricator could reasonably be expected to
know without guidance from the galvanizer.
The purpose of this brochure is to acquaint
the fabricator with the principles that
Valmont Coatings uses to: (1) determine
how to position a work piece for lowering
into, and lifting from, the baths, and (2)how this leads to a determination of where
vents and drains should be located. The
focus of this section is on the fabrication
details for products made of open-sided
components.
Examples are provided to show how the
principles are applied to fabrications made
of open-sided components. However, since
the type and configuration of products are
so varied, Valmont Coatings relies on these
principles, coupled with the fabricators
knowledge of their own product, to help
them determine where vents and drains
are required.
Pr inc i p l es
1. Product Is Oriented to Maximize
Bath/Kettle Space
Bath width
Product width
Generally, products are set up for galvaniz-
ing so that their smallest dimension parallels
the bath width. Several identical pieces
can often be galvanized side by side at the
same time, thereby utilizing most of thewidth of the cleaning bath or zinc kettle.
2. Product Support Locations Depend
on Size, Configuration and Number
of Pieces per Lift
Product is set up for galvanizing either by
being placed into a rack, or by suspension
from a harness of wires that is attached
through a suitably placed hole at a corner
location near to the end of the product.
Rack
Use of a rack is preferable when: (1) there
are many identical pieces to be galvanized,
such as warehouse stock angle; (2) these
pieces are generally not more than 4 x 4
in cross-section; and (3) they are no more
than 20 in length. Items galvanized in a
rack do not need to be provided with a
pick-up hold.
Side view of loaded rack
Product
Fabricators Guide to Open Section Galvanizing
The majority of items that are hot dip
galvanized are suspended by wires
attached at one or more pick-up
points on each work piece.
Single Point Pick-Up
In general, Valmont will suspend from
a single corner pick-up point if: (1) the
geometry of the product is reasonably
streamlined along its length; (2) the product
would give minimal drag through molten
zinc as it was being moved along the
length of the kettle; (3) the length and
major cross-section dimension of the
product falls at or below the limits of the
graph given below; and (4) if the minor
cross-section dimension of the product
is not greater than 7.
Examples of products suited to single point pick-up
The graph is intended to provide only a
very approximate guideline as to whether
a product may be supported at a single
pick-up point.
Example: A product with a major cross-
section dimension of 20 and a minor
cross-section dimension of 7 and a
length of 11 will be lifted from a single
pick-up point.
The required pick-up hold size is 3/8
diameter for items weighing less than 100
pounds, and 5/8 diameter for heavier items.
Two Point Pick-Up
Any product for which rack or single point
pick-up is not practical is picked up from
a wire harness through a hole in each of
its two ends.
The required pick-up hold size is 3/8
diameter for items weighing less than 200
pounds, and 5/8 diameter for heavier items.
The product is arranged on the lifting
equipment so that it enters the bath at an
angle. The angular orientation is used to
encourage a flow of molten zinc to move
progressively along each component of
the product from one end to the other.
This provides a more uniform wetting
action between the steel and the zinc,
and better drainage upon withdrawal.
3. Choice of Top or Bottom Side
Is Based on Openness
Determination is made as to which of
two sides of a product will be first to
lowered into the bath. This is particula
significant when the ends (in the case
one point pick-up) or the sides (in the
of two point pick-up) are not the sam
Guidelines to help determine how a p
uct will be hung, based upon its widt
provided in Principle No. 1. It must als
determined which remaining side will
the top, and which will be the bottom
For each submersion of non-symmet
products, Valmont will choose the sid
is most open to be the bottom.
Liquid surface
A table-like stand, for instance, would
lowered legs first.
Product length (Feet)
MajorCrosssectiondimension(Inches)
5
10
20
30
40
50
60
6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
9 8 7
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4. Potential Air Pockets and Zinc
Traps Are Identified
Once it has been determined how a
product is likely to be picked up and
oriented, it is possible to identify places
where air pockets could potentially form
during submersion, and also where molten
zinc could be prevented from draining
during withdrawal.
The illustrations provide examples of
frequent problem areas and the proper
methods to avoid them.
Further Ass i s tance
Valmont will provide help to custome
upon request, to establish the size an
location of vent and drain holes durin
fabrication of an order.
If Valmont Coatings technicians deter
additional vent and drain fabrication is
necessary once a product is in the Va
plant, we will notify the customer, pro
costs for appropriate modifications a
request permission to install or modif
the holes.
Detail needed:1/2 diameter hole madeat each corner preventsair pocket formation
Liquid surface
Dip direction
Air pocket
Venting at structural panel point
Detail needed:1/2 diameter hole madeat each corner preventsa trap for galvanizing liquids
Liquid surface
Withdrawal
Trapped liquid
Draining at structural panel point
Detail needed:1/2 diameter hole madein a corner of the web, andas close to the plate aspossible, prevents airpocket formation
Liquid surface
Dip direction
Air pocket
Hanging wire
Venting at base of post
Air pocket
Liquid surface
Dip direction
Hanging wire
1/2 diameter pick-up / vent hole 2 diameter hole forfilling and drainingat the lower rightcorner of the back wall
Venting and draining of enclosure body
Detail needed:1/2 diameter pick-up holein flange, and as close aspossible, also serves as avent to prevent formationof an air pocket. Seeenlarged detail.
Venting and draining of a stand
Construction: Angle legs and braces; sheet or placetop and shelf with brake formed flanges.
Liquid surface Dip direction
Air pocket
Air pocket
Detail needed:
1/2 diameter hole made in the angle anddownturned flange of top prevents airpocket formation. Holes need to be asclose to the top corner as possible.
Detail needed:
1/2 diameter hole made in theangle and downturned flangeof the shelf prevents air pocketformation. Holes need to be asclose to the inside corner of theshelf as possible.
Alternative: 1/2 diameter holesin the top surface of the shelf asclose to the corner as possible.
Detail needed:
1/2 diameter hole made in each angle prevents a trap forgalvanizing liquids. Holes need to be as close to the topsurface of the shelf as possible.
Alternative: 1/2 diameter holes in the topsurface of the shelf as close to thecorner as possible.
Note 1:
1/4gap.Ifno gap,provide1/2diameterholeintheend ofthehorizontalleg ofbraceangle.
Detail needed:
1/2 diameter hole made inthe leg of each angle prevents atrap for galvanizing liquids. Holesneed to be as close to the cornerof the angle and the base plateas possible.
Hanging wiretypically four places
Seenote 1
Seenote 1
Seenote 1
Shelf
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Introduction and Purpose
This article describes major causes of
distortion that become evident after hot
dip galvanizing and suggests ways to
reduce the risk.
Considering the volume of products that
are hot dip galvanized, the occurrence of
distortion is quite infrequent. When it does
happen, however, distortion is a serious
concern to the fabricator and galvanizer
alike, involving extra costs and possibly
delays to remedy the problem.
An understanding of the causes of
warpage during galvanizing can lead to
measures that will eliminate or substantially
reduce the problem.
Overv i ew
In many instances, the potential for distor-
tion has been put i nto the product before
its arrival at the galvanizing plant. Distortion
can be due to:
residual stresses induced at the mill dur-
ing rolling of structural sections or plate;
residual stresses created by bending
or welding;
lack of symmetry in simple sections
such as channels or in built up sections;
a combination of thick and thin material
in the same assembly;
assemblies made so large that they
require double dipping to be coated
over their entire surface.
Some causes of distortion can arise at the
galvanizing plant. These can be due to:
poorly selected pick-up points for
handling product through the process;
random laydown of product after
galvanizing, especially of products
leaning against each other or against
other objects, that may establish
a deformed set in the product
during cooling.
The remainder of this article details causes
of distortion that can be controlled by the
fabricator or the galvanizer and describes
preventive measures that can be applied
to each case.
Causes and Prevent ion
Cause: Bending
While a product may have the correct form
in the as fabricated condition, stresses
induced in the product during bending
operations at the fabricating plant may be
released when the product is galvanized.
The galvanizing temperature, 820 to 870
F, is at the low end of the stress relieving
temperature range. Consequently, stresses
induced by bending may be released
during galvanizing with a resultant
change in shape or dimension of the
fabricated product.
Consider the case of a plate section that
has a curve rolled into it so that when
several such sections are joined, they form
a circle. As a result of galvanizing, the plate
would relax to a greater radius than thedimension originally fabricated.
Prevention:
Installation of temporary struts across the
chord of the circle will enable the curved
section to retain its form. The struts would
be structural angles or channels bolted or
welded into position. Their size will be pro-
portional to the size and thickness of the
plate section. The struts should be located
at the quarter points of the height of the
section as shown below.
Control of Distortion in Galvanized Products
1/4 H
H
1/4 H
After galvanizing, it would be necessary
for the fabricator to remove the struts
and repair the area where they had been
joined to the plate.
Valmont would be pleased to assist in
establishing strut and end connection
details based on each particular case.
Cause and Prevention: Welding
There are several actions the fabricator
should take to minimize the potential for
distortion due to the release of stresses
in welds. Those actions are as follows:
avoid over welding;
use as few weld passes as possible;
place welds near the neutral axis;
balance welds around the neutral axis;
use backstep welding;
make weld shrinkage forces work
in the desired direction;
balance shrinkage forces with
opposing forces;
use a well planned, balanced welding
sequence;
remove weld shrinkage forces during
and after welding;
reduce the welding time.
More information on these points and
much additional guidance on minimizing
distortion in weldments is given in the
brochure, Distortion . . . How to Minimize
It With Sound Design Practices and Con-
trolled Welding Procedures, Plus Proven
Methods for Straightening Distorted
Members, written by Omer W. Blodgett,
P.E., and Duane K. Miller, P.E., and
published by Lincoln Electric Company.
Valmont will be pleased to furnish a
complimentary copy upon request.
Cause: Lack of Symmetry in Product
The potential for warpage is greatly
reduced when a product is symmetrical
about its horizontal and vertical neutral
axes. When a symmetrical section such
as a simple I-beam is galvanized, thermal
expansion forces above and below the
neutral axis balance each other and l eave
the beam free of distortion.
However, in the case of unsymmetrical
sections, such as a wide flange beam
with a rectangular structural tube welded
to its top flange, a geometric imbalance
has been created. The wall of the tube is
considerably thinner than the flange of the
beam. Consequently, the tube material will
be thoroughly heated to the temperature
of the galvanizing bath, while the bottomflange of the beam lags behind it in coming
up to bath temperature. As a result, the
tube material is expanding fast, but the
cooler bottom flange is unable to keep
pace. If such a beam were to be galva-
nized in the configuration shown, it would
experience upward bowing distortion.
Prevention:
This problem can be prevented in any of
three ways, depending upon economics
and desire to maintain the integrity of the
corrosion protection:
(a) Galvanize the sections back-to-back if
there are a number of identical pieces on
the order that allow this to be an option.
Beams would be bolted back-to-bac
using pie spacers to separate the bea
to allow the flanges to be cleaned an
galvanized. The bolts would be remo
after galvanizing when the sections h
cooled. Spots where the spacers con
the beam flanges would be repaired w
galvanizing repair material. Valmont w
be pleased to assist in the determina
of the number and size of bolts to use
Separation and touch up of the sectio
would be the customers responsibilit
unless other arrangements are made
(b) Fabricate and galvanize the I-beam
tube as separate loose pieces. Then,
them together after galvanizing. Touc
welds with galvanizing repair material
(c) Redesign the section to makeit symmetrical.
Distortion in structural channels is typ
a uniform bow in the weak direction w
the toes of the channel pointing away
the radial center. This distortion can
be minimized by the back-to-back m
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Cause: Poorly Selected Pick-up Points
When a long, slender product is picked
up at both ends for transport through the
galvanizing process, a potential is created
for the product to become bowed.
When the hot, galvanized product is being
withdrawn from the zinc bath, some of the
deflection caused by the products own
empty weight can be permanently set into
the product. The yield strength of mildsteel can be temporarily reduced during
immersion in the zinc bath. The problem
is compounded in slender products that
have inadequate drainage openings that
allow a substantial weight of molten zinc to
be retained and delayed from leaving the
product during withdrawal.
Prevention:
Long, slender products should be
equipped with lifting lugs located at the
quarter points of the length of the product
to overcome the possibility of experiencing
this kind of distortion.
Drainage opening should be placed and
sized according to recommendations in
the articles of Fabricators Guide to Pipe
and Tube Galvanizing and Fabricators
Guide to Open Section Galvanizing to
minimize containment
of excess zinc.
Cause: Poor Laydown
After Galvanizing
Permanent deforma-
tion may occur when a
batch of hot galvanized
products is laid down haphazardly and
flexed out of shape during cooling.
A structural member set down on its side
on blocks that are too far apart can easily
sag in its weak direction under its own
weight. If it is set down that way while still
hot, it may permanently retain some por-
tion of that distortion.
Prevention:
In both cases, this type of problem c
be reduced by arranging the parts aft
galvanizing as straight and as free fro
external forces as possible during co
When a product has acquired an une
pected bow during galvanizing, settin
it down while hot and applying weigh
to restore the part to straightness du
cooling may be helpful.
Further Ass i s tance
Upon request, Valmont will provide he
to customers about countermeasure
distortion during the fabrication of an
Section A-A
Cause: Thick and Thin Material
in Assembly
Thin material in an assembly expands faster
than thicker materials nearby because it
takes less time to be fully heated to the
galvanizing temperature. Distortion will take
place in thin material when thicker material
restrains it from free expansion.
Consider the case of a steel sheet or plate
placed on a structural frame and securely
attached by welds around it s perimeter.
Imagine that the sheet or plate is only
half as thick as the material in the frame.
The sheet soon reaches the galvanizing
temperature of about 850 F and its
maximum potential expansion. The frame,
being thicker, is still cooler and has not yet
had the opportunity to expand as muchas the sheet. Since the sheet cannot push
its growth outwards at the edges because
of the welds, its increase in size results in
one or more buckles in the sheet surface.
Distortion due torestrained expansion.
Section A-A
Prevention:
Two approaches can be taken to avoid
this condition.
(a) Galvanize the sheet and frame separately
and join them after galvanizing.
(b) Use the same thickness of material
for frame and sheet.
Cause: Size of Assembly Requires
Double Dip
The potential for warpage increases when
an item is so large that the galvanizer must
dip one portion at a time in order to fully
coat it.
The portion immersed in the zinc is sub-
jected to much higher temperature and
greater thermal expansion than the portion
projecting from the kettle, especially during
the first dip. The differential heating and
expansion between the two portions can
cause distortion that will not be removed
when the remainder of the product is
placed into the molten zinc.
Simple pipes and poles do not experience
distortion from double dipping, probably
because of their symmetry and simplicity
of design.
Whenever possible, it is preferable to size a
product so that it can be totally immersed
in a single dip.
Even though a product is small enough to
be immersed in a single dip, it is important
that fill and drain holes be large enough to
enable the part to be immersed and with-
drawn rapidly to avoid differential expansion.
L
1/4 L1/4 L
Considering the volume of products that arehot dip galvanized, the occurrence of distortion isquite infrequent. When it does happen, however,distortion is a serious concern to the fabricator andgalvanizer alike, involving extra costs and possiblydelays to remedy the problem.
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Part 1 General
1.01 Scope
These guidelines cover the galvanized
coating applied to general steel articles,
structural sections, fabricated steel
assemblies and threaded fasteners.
Note: These guidelines do not apply to the
galvanized coating on semi-finished prod-
ucts such as wire, tube or sheet galvanized
in specialized or automatic plants.
1.02 Quality Assurance
A.Relevant Standards:
American Society for Testing and
Materials (ASTM)
A 53 Pipe, Steel, Black and
Hot-Dipped Zinc Coated
Welded and Seamless
A 123 Zinc (Hot-Dip Galvanized)
Coatings on Iron and
Steel Products
A 143 Safeguarding Against
Embrittlement of Hot-Dip
Galvanized Structural Steel
Products and Procedure for
Detecting Embrittlement
A 153 Zinc Coating (Hot-Dip) on Iron
and Steel Hardware
A 325 High Strength Bolts for Structural
Steel Joints
A 384 Safeguarding Against Warpage
and Distortion During Hot-Dip
Galvanizing of Steel Assemblies
A 385 Providing Quality Zinc
Coatings (Hot-Dip)
A 563 Carbon and Alloy Steel Nuts
A 780 Repair of Damaged Hot-Dip
Galvanized Coatings
B 6 Zinc (Slab Zinc)
B. Certification
When requested by the purchaser/
designer, a Certificate of Compliance shall
be provided stating that the galvanizing
complies with ASTM Specifications and
Standards and all other applicable
requirements specified herein.
C. Inspection and Tests
Inspections, tests and samples shall
conform with ASTM A 123 or A 153 as
applicable. Inspections and tests shall
include the following:
1. visual examination of samples or
finished products, as appropriate;
2. tests to determine thickness or
weight of zinc coating per square
foot of metal surface;
3. adhesion.
1.03 Submittals
The original and two copies of Certificates
of Compliance shall be forwarded to the
Architect/Engineer.
1.04 Handling, Transport and Storage
Galvanized articles shall be loaded and
stored as follows to prevent the formation
of wet storage stain:
(a) The material shall be loaded in such
a manner that continuous drainage
could occur.
(b) In storage, the articles shall be raised
from the ground and, i f necessary,
separated with strip spacers to provide
free access of air to most parts of the
surface. They shall also be inclined in
a manner which will give continuous
drainage. Under no circumstances shall
galvanized steel be allowed to rest on
cinders or clinkers; nor shall it be stored
on wet soil or decaying vegetation.
Suggested Guidelines for Hot Dip Galvanizing
Part 2 Products
2.01 Steel Materials
A. Structural shapes, plates and bars
that are to be galvanized shall be
manufactured from steel conforming
to ASTM A 36 or A 572 except that
silicon (Si) content shall be in the range
of 0 to 0.04% or 0.15 to 0.20%, and
phosphorus (P) content in the range
of 0 to 0.02%. Steel with chemistry
conforming to the formula Si + 2.5P
0.09 is also acceptable. Mill certificates
shall be furnished.
Note: Hot dip galvanized coatings result
from metallurgical reactions between
molten zinc and steel. Galvanized coatings
formed on steel of normal reactivity havea two-part composite structure. One part,
a layer of iron-zinc alloy formed during
galvanizing, metallurgically bonds the
coating to the underlying steel. The other
part of the coating is an outer layer of
uniform appearance that has a chemical
composition similar to the zinc in the
galvanizing bath. Certain percentages of
silicon and phosphorus in the chemistry
of some steels increase the reactivity
between the steel and molten zinc during
galvanizing and produce coatings of a
different structure and appearance.
Galvanized coatings on steels with
increased reactivity, due to the silicon
and/or phosphorus levels, may be matte
grey, mixed shades of grey, or include
localized outbursts of grey colored iron-
zinc alloy in otherwise bright surfaces.
In some instances, steels with increased
reactivity produce galvanized coatings
that are very thick and consequently
brittle. Galvanized coatings on the steel
chemistries suggested in these guidelines
should have acceptable adhesion and
be substantially free from iron-zinc alloy
outbursts. However, the coatings will tend
to be thicker on steels having higher levels
of silicon. For steels with silicon content in
the range of 0.15 to 0.20%, phosphorus
may increase the steel reactivity, but
the galvanized coating should not show
substantial iron-zinc alloy outbursting.
B. Steel for fasteners shall conform to
the following ASTM specifications for
each category:
General
Category Bolt Nut
Material Material
Carbon A 307 A 563 Gr. A
Steel Gr. A or B
High A 325 A 563 Gr. DH
Streng th Type 1 or 2 or, A 194 Gr. 2H
Tower Bolts A 394 A 563 Gr. A
C. Steel for sheet metal articles shall
conform to ASTM A 569 or A 570.
D. Steel for pipe or tubing shall conform
to ASTM A 53 or A 595 Gr. A or B.
Note: Avoid use of steels with an ultimate
tensile strength greater than 150 ksi.
2.02 Zinc for Galvanizing
Zinc for galvanizing shall conform to
ASTM B 6.
2.03 Fabrication
Fabrication practice for products to be
galvanized shall be in accordance with
the applicable clauses of ASTM A 143,
A 384 and A 385. Care shall be taken to
avoid fabrication techniques that could
cause distortion or embrittlement of the
steel during galvanizing. Before fabrication
proceeds, the Architect/Engineer shall be
notified of potential warpage problems
which may require modification in design.
All welding slag and burrs shall be removed
prior to delivery to the galvanizer.
Holes and/or lifting lugs to facilitate handling
during the galvanizing process shall be
provided at positions as agreed between
the designer, fabricator and galvanizer.
Unsuitable marking paints shall be av
and consultation by the fabricator wit
galvanizer about the removal of greas
paint and other deleterious material s
be undertaken prior to fabrication.
Surface contaminants and coatings w
would not be removable by the norma
chemical cleaning process in the galva
operation shall be removed by the fab
using blast cleaning or some other me
2.04 Surface Preparation
Steel shall be prepared utilizing a cau
bath, acid pickle and flux. Where appro
the steel can be blast cleaned and flu
2.05 Galvanizing
A. Steel members, fabrications, and
assemblies shall be galvanized aft
fabrication by the hot dip process
accordance with ASTM A 123.
B. Bolts, nuts and washers, and iron
steel hardware components shall
galvanized in accordance with AS
153. Nuts and bolts shall be supp
accordance with ASTM A 194, A
A 325, A 394 or A 563, as applica
Products shall be safeguarded ag
steel embrittlement in conformanc
with ASTM A 143.
All articles to be galvanized shall b
handled in such a manner as to a
any mechanical damage and to m
mize distortion.
When the galvanizer detects desig
features which may lead to difficul
during galvanizing, he shall point
them out to the fabricator and
arrange for modifications to be
made prior to dipping.
The composition of metal in the
galvanizing bath shall not be less
than 98% zinc.
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End cross section,when required
Individual areas, or allsurfaces for speciallength, at end of section
Any localized area
Entire top of flange, orany localized area
2.06 Coating Requirements
A. Thickness/Weight:The thickness
or weight of the galvanized coating
shall conform with paragraph 5.1 of
ASTM A 123 or Table 1 of ASTM A
153, as appropriate.
B. Surface Finsh:The galvanized
coating shall be continuous, adherent,
as smooth and evenly distributed as
possible and free from any defect that
is detrimental to the stated end use of
the coated article.
The integrity of the coating shall be
determined by visual inspection,
coating thickness measurements,
and adhesion testing.
Where slip factors are required to
enable friction grip bolting, these
shall be obtained after galvanizing by
suitable treatment of the faying surfaces
in accordance with the latest edition
of the Specification for Structural
Joints Using ASTM A 325 or A 490
Bolts as approved by the Research
Council on Structural Connections
of the Engineering Foundation.
C.Adhesion:The galvanized coating
shall be sufficiently adherent to
withstand normal handling during
transport and erection.
Part 3 Execut ion
3.01 Welding
Where galvanized steel is to be welded,
adequate ventilation shall be provided.
If adequate ventilation is not available,
supplementary air circulation shall be
provided. In confined spaces, a
respirator shall be used.
Welding shall be performed in ac-
cordance with the American Welding
Society publication D19.0-72, Welding
Zinc Coated Steel.
All uncoated weld areas shall be
touched up.
A. Galvstop Service
Successful welding of galvanized steel
requires pre-planned, plain, uncoated
areas conforming to fabrication
requirements. Valmonts Galvstop
service is an adaptable method to
provide specific uncoated areas of
any size, shape or location. Extra
preparation work is not required.
Requirements must be provided.
Note: Galvstop is only applicable on
external surfaces and accessible
internal surfaces.
3.02 Touch Up and Repair
A. Mechanical Damage
Areas damaged by welding, flame
cutting, or during handling, transport
or erection shall be repaired by one of
the following methods whenever the
damage exceeds 3/16 in width on flat
surfaces, or 1/10 on cut ends:
(1) Cold Galvanizing Compound
Surfaces to be reconditioned
with zinc-rich paint shall be clean,
dry, and free of oil grease and
corrosion products.
Areas to be repaired shall be
power disc sanded to bright
metal. To ensure that a smoothreconditioned coating can be
effected, surface preparation
shall extend into the undamaged
galvanized coating.
Touch-up paint shall be an organic,
cold galvanizing compound hav-
ing a minimum of 65% zinc dust
in the dry film.
The paint shall be spray-or brush-
applied in multiple coats until a
dry film thickness of 4 mils mini-
mum has been achieved. A finish
coat of aluminum paint shall be
applied to provide a color blend
with the surrounding galvanizing.
Coating thickness shall be verified
by measurements with a magnetic
or electromagnetic gauge.
(2) Zinc Based Solder
Surfaces to be reconditioned
with zinc based solder shall be
clean, dry, and free of oil, grease
and corrosion products.
Areas to be repaired shall be wire
brushed and given a thin layer of
acidic paste flux.
Heat shall be applied slowly and
broadly close to, but not directly
onto, the area to be repaired.
The zinc-based solder rod shall
be rubbed onto the heated metal
until the rod begins to melt. A
flexible blade or wire brush shall
be used to spread the melt over
the area to be covered. The zinc
based solder shall be applied toa minimum thickness equivalent
to that of the undamaged coating.
Coating thickness shall be verified
by measurements with a mag-
netic or electromagnetic gauge.
(3) Metallizing
Surfaces to be reconditioned
with zinc metal spray shall be
clean, dry, and free of oil, grease
and corrosion products.
The area to be repaired shall
be grit blasted to white metal,
followed by zinc metal spraying
to a coating thickness equivalent
to that of the undamaged coating,
and seal coated using an alumi-
num vinyl paint.
B. Wet Storage Stain
Any wet storage stain shall be
removed by the galvanizer if formed
and discovered prior to leaving the
galvanizers plant, unless l ate pick-up
or acceptance of delivery has neces-
sitated the material being stored in
unfavorable conditions. In any event,
wet storage stain shall be removed
before installation to prevent premature
failure of the coating. Wet storage stain
shall be removed as fol lows:
(1) The objects shall be arranged
so that their surfaces dry rapidly.
(2) Remove light deposits with a stiff
bristle (not wire) brush. Heavier
deposits are to be removed by
brushing with an acidic-basedmetal cleaner. The surfaces
cleaned shall be thoroughly
rinsed with water.
(3) A coating thickness check must
be made in the affected areas to
ensure that the zinc coating
remaining after the removal of
wet storage stain is sufficient to
meet or exceed the requirements
of the specification.
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Notes
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7002 North 288th Stree
Valley, NE 68064 USA
p 1.800.825.6668
f 1.402.359.6070
www.valmontcoatings.com