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Inspection of Hot-Dip Galvanized Steel

This course is intended to train individuals on the proper inspection

techniques and requirements for hot-dip galvanized steel products. There are

four sections in this course:

Hot-Dip Galvanizing Process

Galvanizing Standards

Types of nspection

!epair

"pon completion of this course# you should $e a$le to recognize specification

requirements and perform all inspection steps to ensure conformance %ith the

requirements. &dditionally# any inspector %ho completes the course# and

passes the test '()* or $etter+ %ill receive a printa$le ,ertificate of,ompletion and %ill $e listed on the &G& %e$site as an inspector.

Disclaimer

The information contained in this course has $een compiled $y the &merican

Galvanizers &ssociation '&G&+# a not-for-profit trade association %hose mem$ers

represent the after-fa$rication hot-dip galvanizing industry throughout the "nited

States# ,anada# and eico. The &G& ma/es no endorsement and offers no

evaluation of any vendor0s products# %hether listed here or not.

Galvanizing Process

The term hot-dip galvanizing is defined as the process of immersing iron or steel in a

$ath of liquid zinc to produce a corrosion resistant# multi-layered coating of zinc-iron

alloy and zinc metal. The coating is produced as the result of a metallurgical reaction

$et%een the liquid zinc and the iron in the steel. The coating forms an equal thic/ness

on all surfaces immersed in the galvanizing /ettle. This process# similar to the one

seen inFigure 1# has $een in use since 1234 and has provided long-lasting#

maintenance-free corrosion protection at a reasona$le cost for many years. The three

main steps in the hot-dip galvanizing process are surface preparation# galvanizing# and

post-treatment# each of %hich %ill $e discussed in detail.

Figure 1: Model of the Hot-Dip Galvanizing Process


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Steel structures %ith visi$le evidence of corrosion are pictured in the series of photos

inFigure 2. !ust and corrosion can $e epensive for $usiness o%ners and tapayers

$ecause $uildings# roads# and $ridges# %ithout sufficient corrosion protection# may

need to $e repaired often or even re$uilt.

The process is descri$ed in more detail later in this section. t is inherently simple#and this simplicity is a distinct advantage over other corrosion protection methods.

Figure 2: Corroding teel tructures

Surface Preparation

The first step in the hot-dip galvanizing process is intended to o$tain the cleanest

possi$le steel surface $y removing all of the oides and other contaminating residues.This is achieved $y first hanging the steel using chains# %ires# or specially designed

dipping rac/s# as seen inFigure 3# to move the parts through the process. There are

three cleaning steps to prepare the steel for galvanizing.

Degreasing!Caustic Cleaning

5irst the steel is immersed in an acid degreasing $ath or caustic solution in order to

remove the dirt# oil# and grease from the surface of the steel. &fter degreasing the steel

is rinsed %ith %ater.


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Pic"ling

6et the steel is immersed in an acid tan/ filled

%ith either hydrochloric or sulfuric acid# as seen in

Figure 4# %hich removes oides and mill scale in a

process called 7pic/ling.8 9nce all oidation has$een removed from the steel# it is again rinsed %ith

%ater and sent to the final stage of the surface

preparation.

Figure #: $he Pic"ling $an"

Flu%ing

The purpose of the flu is to clean the steel of all oidation developed since the

pic/ling of the steel and to create a protective coating to prevent the steel from any

oidizing $efore entering the galvanizing /ettle. 9ne type of flu is contained in a

separate tan/# is slightly acidic# and contains a com$ination of zinc chloride and

ammonium chloride. &nother type of flu# top flu# floats on top of the liquid zinc in

the galvanizing /ettle# $ut serves the same purpose.

&fter $eing immersed in the degreasing# pic/ling# and fluing tan/s# the surface of the

steel is completely free of any oides or any other contaminants that might inhi$it the

reaction of the iron and liquid zinc in the galvanizing /ettle.

Galvanizing

9nce the steel has $een completely cleaned# it is ready for immersion in the liquid

zinc. The galvanizing /ettle contains zinc specified to &ST ;# a document that

specifies any one of three different grades of zinc that are each at least


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Post-$reatment

>hen the steel is removed from the galvanizing /ettle# it may receive

a post-treatment to enhance the galvanized coating. 9ne of the most

commonly used treatments is quenching. The quench tan/ contains

mostly %ater $ut may also have chemicals added to create apassivation layer that protects the galvanized steel during storage and

transportation. 9ther finishing steps include removal of zinc drips# or

icicles# $y grinding them off.

Time to First Maintenance

The estimated time to first maintenance for a hot-dip galvanized coating that

eperiences common atmospheric eposure can $e seen inFigure 7. Time to firstmaintenance is defined as the time to ?* rusting of the su$strate steel. The time to

first maintenance of hot-dip galvanized steel is directly proportional to the zinc

coating thic/ness.

Figure ': $ime to First Maintenance Chart for Hot-Dip Galvanized Coatings

Other orrosion Protection S!stems

There are many other types of corrosion protection# such as coating steel %ith oil#

grease# tar# asphalt# polymer coatings or paints# or corrosion protection materials such

as stainless and %eathering steel# sacrificial anodes# plating systems and impressed

current systems. These are some of the most commonly used corrosion protection

materials and systems and are sometimes used together %ith hot-dip galvanized steel.

ost of these materials rely on $arrier protection# %hile some of them rely on

cathodic properties to prevent corrosion of the steel. The most effective type of

corrosion protection that provides $oth $arrier and cathodic protection is hot-dip

galvanizing.


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There are also a %ide variety of zinc coatings used for corrosion protection. any

people use 7galvanizing8 to descri$e all of these coatings# $ut each has its o%n unique

characteristics and performance. These coatings have several applications $ased on

their properties and respective thic/nesses. The corrosion protection offered $y a zinc

coating is linearly related to its coating thic/ness. The most commonly used coatings

are hot-dip galvanized# metallized# zinc-rich paint# galvannealed or galvanized sheet#and electroplated. The relative thic/ness for each of these zinc coatings can $e seen in

the photomicrograph 'Figure 8+. elo% is a $rief eplanation of each type of zinc

coating.

Figure (: Photomicrogrpah of )inc Coatings* $hic"nesses

Metallizing

etallizing is the general name for the technique of spraying a metal coating on the

surface of non-metallic or metallic o$@ects. This process is accomplished $y feedingzinc in either %ire or po%der form into a heated gun# %here it is melted and sprayed

onto the surface to $e coated using com$ustion gases andAor auiliary compressed air

to provide the necessary velocity. The limitations of this process include a difficulty in

reaching recesses# cavities# and hollo% spaces# even coating thic/ness and cost.

)inc-+ich Paint

Binc-rich paint is applied to a clean# dry steel surface $y either a $rush or spray and

usually contains an organic $inder pre-mi. Paints containing zinc dust are classified

as organic or inorganic# depending on the $inder that they contain# and are discussed

in more detail later in this course.

Continuous Galvanizing

The continuous galvanizing process is a hot-dip

process %here a steel sheet# strip# or %ire is

cleaned# pic/led# and flued on a processing line

approimately ?)) feet '1?3 m+ in length# and

running at speeds $et%een 1)) to ;)) feet per

minute

Figure ,: Continuous Galvanizing Plant


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'=) to 1(? m per minute+. n the coating of a steel sheet or strip# the galvanizing

/ettle contains a small amount of aluminum# %hich suppresses the formation of the

zinc-iron alloys# resulting in a coating that is mostly pure zinc. & post-galvanizing# in-

line heat treatment process /no%n as galvannealing can also $e used to produce a

fully alloyed coating. Galvannealing is usually ordered $y those %anting to paint over

the zinc surface $ecause the presence of alloy layers on the steel surface promotespaint adhesion. & photo of a continuous galvanizing plant is seen inFigure 9and the

common plant setup is sho%n inFigure 10.

Figure 1: .%ample of a Continuous Process

.lectroplating

The electroplating process# or zinc-plated coating# has a dull gray color# a matte finish#

and a thin coating that ranges up to one mil '4? Cm+ thic/. This very thin coating

restricts the use of zinc-plated products to indoor eposures. The specification &ST

;== lists the classes of zinc-plated steel coatings as 5eABn ?# 5eABn (# 5eABn 14# and

5eABn 4?# %here 5e represents iron and Bn represents zinc# %hile the num$er indicates

the coating thic/ness in microns. The main uses for this type of coating include

scre%s# light s%itch plates# and other small products or fasteners.

"STM Specifications

There are certain specifications that have $een developed for hot-dip galvanizing in

order to produce a high-quality coating. The most commonly used specifications

design engineers and fa$ricators should $ecome familiar %ith in order to promote a

high-quality coating and ensure their steel design is suita$le for hot-dip galvanizing

are:


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/$M / 120!/ 120M:Standard Specification for Zinc (Hot-Dip a!"ani#ed$

%oating& on 'ron and Stee! roduct&

Single pieces of steel or fa$rications %ith different types of steel products

/$M / 10!/ 10M:Standard Specification for Zinc %oating (Hot-Dip$ on

'ron and Hard)are

5asteners and small products that are centrifuged after galvanizing to removeecess zinc

/$M / '&'!/ '&'M:Standard Specification for Zinc-%oated (a!"ani#ed$

Stee! *ar& for %oncrete +einforce,ent

!einforcing steel or re$ar

/$M / '(:Standard ractice for +epair of Da,aged and ncoated .rea&

of Hot-Dip a!"ani#ed %oating&

Touch-up procedures for coating $are spots on an eisting hot-dip galvanized

product

9ther commonly used specifications in the hot-dip galvanizing industry include:

/$M / 1#0!/ 1#0M:Standard ractice for Safeguarding .gain&t

/,ritt!e,ent of Hot-Dip a!"ani#ed Structura! Stee! roduct& and

rocedure for Detecting /,ritt!e,ent

/$M / 0(#!/ 0(#M:Standard ractice for Safeguarding .gain&t arpage

and Di&tortion During Hot-Dip a!"ani#ing of Stee! .&&e,!ie&

/$M / 0(!/ 0(M:Standard ractice for ro"iding Hig-ua!it Zinc

%oating& (Hot-Dip$

/$M &:Standard Specification for Zinc

/$M D &0(&:Standard ractice for reparation of Zinc (Hot-Dip

a!"ani#ed$ %oated 'ron and Stee! roduct and Hard)are Surface& for aint /$M . 0'&:Standard ractice for ea&uring %oating icne&&

agnetic-Fie!d or /dd-%urrent (/!ectro,agnetic$ /a,ination etod&

C/3!C/ G 1:Hot-Dip a!"ani#ing of 'rregu!ar! Saped .rtic!e&

45 1#&1Hot-Dip a!"ani#ed %oating& on Faricated 'ron and Stee!

.&&e,!ie&

Specification& and e&t etod&

et0s eamine a fe% of these specifications in more detail.

"STM " #$% for Structural Steel Products

The &ST & 14=A& 14= specification covers individual steel pieces as %ell as

assem$lies of various classes of material. The four material categories covered in

&ST & 14=A& 14= include structural steel and plates# strips and $ars# pipes and

tu$ing# and %ires. & fa$rication can have more than one material category such as a

frame assem$ly. &ny com$ination of these products can $e assem$led into a singlefa$rication and then can $e hot-dip galvanized# as seen inFigure 11.


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t is the responsi$ility of the designer and fa$ricator to ensure the product has $een

properly designed and $uilt $efore the hot-dip galvanizing process. The galvanizer

should $e made a%are of any necessary special instructions or requests in advance of

shipping the materials to the galvanizing plant. These requests should $e stated on the

purchase order for the hot-dip galvanizing.

t is the responsi$ility of the galvanizer to ensure compliance %ith the specifications

as long as the product has $een designed and fa$ricated in accordance %ith the

referenced specifications. Ho%ever# if the galvanizer has to perform additional %or/

in order to prepare the product for hot-dip galvanizing# such as drilling holes to

facilitate drainage or venting# it must $e approved $y the customer. 9nce the material

has $een hot-dip galvanized# it can $e fully inspected at the galvanizing plant prior to

shipment.

&ny materials re@ected $y the inspectors for reasons other than em$rittlement may $e

stripped# regalvanized# and resu$mitted for inspection. The &ST specifications &

13=A& 13=# &ST & =(3A& =(3# and &ST & =(? provide guidelines forpreparing products for hot-dip galvanizing. The requirements listed in &ST & 14=A&

14= include coating thic/ness# finish# appearance# and adherence. These are each

defined $elo% and discussed in more detail later in this course.

/$M / 120!/ 120M +e6uirements

Coating $hic"ness ! 7eightE dependent upon material category and steel

thic/ness

FinishE continuous# smooth# uniform

/ppearanceE free from uncoated areas# $listers# flu deposits and gross drossinclusions as %ell as having no heavy zinc deposits that interfere %ith intended

use

/dherenceE the entire coating should have a strong adherence throughout the

service life of galvanized steel

The hot-dip galvanized coating is intended for products fa$ricated into their final

shape that %ill $e eposed to corrosive environmental conditions. 9nce a product has

$een hot-dip galvanized# any further fa$rication# %hich very rarely occurs# may have

negative effects on the corrosion protection of the coating. The coating grade is

defined as the required thic/ness of the coating and is given in microns. &ll coating

thic/ness requirements in specification &ST & 14=A& 14=# as seen in a!e& 1 2# are minimumsF there are no maimum coating thic/ness requirements in either

specification.

$a8le 1: Minimum /verage Coating $hic"ness Grade 89 Material Categor9

From /$M /120;


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$a8le 2: Coating $hic"ness Grade From /$M / 120;

The time to first maintenance of hot-dip galvanized steel is directly proportional to the

thic/ness of the hot-dip galvanized coating. >ith all other varia$les held constant# the

thic/er the zinc coating# the longer the life of the steel. The aim of the finish and

appearance requirements is to ensure no coatings have pro$lem areas that are deficient

of zinc or have surface defects that %ould interfere %ith the intended use of the

product. n addition# the coating should have a strong adherence throughout the

service of the hot-dip galvanized steel.

"STM " #&% for Hard'are

The specification &ST & 1?=A& 1?= applies to hard%are products such as

castings# fasteners# rolled# pressed and forged products# and miscellaneous threaded

o$@ects that %ill $e centrifuged# spun# or other%ise handled to remove the zinc# as

seen inFigure 12.

Figure 12: Galvanized Fasteners

The requirements for &ST & 1?=A& 1?= are very similar to those reported earlier

for &ST & 14=A& 14=# ecept for the addition of threaded products and

em$rittlement requirements.

/$M / 10!/ 10M +e6uirements

Coating $hic"ness!7eightE depends on the material category and steel

thic/ness# values are listed in a!e 3

$hreaded ProductsE areas %ith threads are not su$@ect to the coating

thic/ness requirement

FinishE continuous# smooth# uniform


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.m8rittlementE high tensile strength fasteners '1?)/si+ and castings can $e

su$@ect to em$rittlement

/ppearanceE free from uncoated areas# $listers# flu deposits and gross dross

inclusions as %ell as having no heavy zinc deposits that interfere %ith intended

use

/dherenceE the entire coating should have a strong adherence throughout theservice life of hot-dip galvanized steel

There are fa$rication steps that may impair the corrosion protection of the hot-dip

galvanized coating# ho%ever# fla/ing or damage to the coating $ecause of this is not

case for re@ection. n all cases# good steel selection results in the formation of a higher

quality coating and finish on the product. The corrosion protection coating for

threaded products is applied after the product has $een fa$ricated and further

fa$rication may compromise the corrosion protection system. The one eception to

this rule is the internal threads of a nut that should $e over-tapped after the coating is

applied in order to accommodate the coating thic/ness change on the thread of the

$olts. n this case# the zinc on the $olt threads provides the corrosion protection to theuncoated threads in the nut.

There are certain fa$rication techniques that can induce stresses into the steel and lead

to $rittle failure. There are precautions given in &ST & 13=A& 13= that should $e

ta/en in order to prevent em$rittlement. n addition# selecting steels %ith appropriate

chemistries can help prevent em$rittlement of mallea$le castings. & reproduction and

summary of the ta$le given in &ST & 1?=A& 1?=# %hich is seen in a!e 3# gives

the different classes of products and the minimum coating thic/ness required $y the

specification.

$a8le 0: Minimum /verage Coating $hic"ness 89 Material Class From /$M /

10;


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"STM " ()( for *einforcing Steel

The specification &ST & 2;2A& 2;2 is applica$le eclusively to the hot-dip

galvanizing of reinforcing steel# other%ise /no%n as re$ar# as seen inFigure 13# and

is applica$le to all types of re$ar# $oth smooth and deformed. Ho%ever# %ire is not

included.

Figure 10: Hot-Dip Galvanized +e8ar

The requirements in &ST & 2;2A& 2;2 are also intended to produce a high qualityzinc coating for corrosion protection.

/$M / '&'!/ '&'M +e6uirements

4dentit9E the galvanizer is responsi$le for consistent material trac/ing if

necessary

Coating $hic"ness!7eightE material category and steel thic/ness

ChromatingE to prevent reaction $et%een cement and recently galvanized

material

FinishE continuous# smooth# and uniform

/ppearanceE free from uncoated areas# $listers# flu deposits and gross drossinclusions as %ell as having no heavy zinc deposits that interfere %ith intended

use

/dherenceE should $e tightly adherent throughout intended use of the

product

end DiametersE fla/ing and crac/ing due to fa$rication after the hot-dip

galvanizing process are not re@ecta$le

9nce re$ar is delivered to $e hot-dip galvanized# it is the galvanizer0s responsi$ility to

trac/ and maintain the identity of the product throughout the hot-dip galvanizing

process until shipment of the finished product. &gain# the analogous coatingrequirements in the areas of coating thic/ness# finish# and adherence are present in


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&ST & 2;2A& 2;2. Ho%ever# this single product specification introduces a fe%

ne% requirements that apply solely to hot-dip galvanized re$ar. n &ST & 2;2A&

2;2# the coating requirement is given in 7mass of the zinc coating per surface area8.

& summary of the ta$le given in &ST & 2;2A& 2;2 and the minimum required

coating thic/ness A %eight of the classes is seen in a!e 4.

$a8le #: Mass of )inc Coating From /$M / '&';

This specification also introduces a ne% requirement to the galvanized coating /no%n

as chromating. 6e%ly galvanized steel can react %ith %et cement and potentially form

hydrogen gas as a product. &s this evolved hydrogen gas travels through the concrete

matri to%ard the surface# voids can $e created %hich %ea/en the $onding %ith the

concrete or distur$ the smoothness of the concrete surface. n order to help prevent

and suppress this reaction# hot-dip galvanized re$ar is dipped into a %ea/ chromate

quench solution after $eing removed from the galvanizing /ettle.

The finish requirement for re$ar is along the same lines as the finish requirements

given in specifications &ST & 14=A& 14= and & 1?=A& 1?=. The coating is

intended for corrosion protection# so deficiencies that affect the coating0s corrosion

performance are grounds for re@ection. n addition# since re$ar is handled frequently

during its installation# any tears or sharp spi/es that ma/e the material dangerous to

handle are grounds for re@ection.

!e$ar is commonly $ent prior to the hot-dip galvanizing process. The ta$le $elo%

gives recommendations for $end diameters $ased upon the $are steel $ar diameter

$efore coating. Steel reinforcing $ars that are $ent cold prior to hot-dip galvanizing

should $e fa$ricated to a $end diameter equal to or greater than the specified values.Ho%ever# steel reinforcing $ars can $e $ent to diameters tighter than specified in

a!e 5providing they are stress relieved at a temperature of


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$a8le : Minimum Finished end Diameters From /$M / '&';

Other Galvanizing Standards

There are ,anadian and international specifications that could $e used to specify hot-

dip galvanizing on a pro@ect. The differences in these specifications and the &ST

specifications are minimal# and for the most part# only differ slightly in the minimum

coating thic/nessA%eight required for each type and thic/ness of product $eing hot-

dip galvanized.

Other Specifications for Hot-Dip Galvanizing (Taken from

CAN/CSA an !SO Stanars"

C/3!C/-G1 Hot Dip Galvanizing of 4rregularl9 haped /rticles

Scope

1. This standard specifies the requirements for zinc coating 'galvanizing+ $y the

hot-dipping process on iron and steel products made from rolled# pressed# or

forged shapes such as structural sections# plates# $ars# pipes# or sheets 1 mm

thic/ or thic/er.

4. &pplies to $oth unfa$ricated and fa$ricated products such as assem$led steelproducts# structural steel fa$rications# large hollo% sections $ent or %elded

$efore galvanizing# and %ire %or/ fa$ricated from uncoated steel %ire.

=. &pplies to steel forgings and iron castings that are to $e galvanized separately

or in $atches.

3. Does not apply to continuous galvanizing of chain lin/ fence fa$ric# %ire#

sheet# and strip.

?. Does not apply to pipe and conduit that are normally hot dip galvanized $y a

continuous or semicontinuous automatic process.

;. The values stated in S units are to $e regarded as the standard. The values in

parentheses are imperial units and are included for information only.


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45 1#&1 Hot Dip Galvanized Coatings on Fa8ricated 4ron and teel

/rticles

Scope: This Standard specifies the general properties of and methods of test for

coatings applied $y hot dipping in zinc 'containing not more than 4* of other metals+

on fa$ricated iron and steel articles.

t does not apply to:

1. Sheet and %ire continuously hot dip galvanizedF

4. Tu$e and pipe hot dip galvanized in automatic processF

=. Hot dip galvanizing products for %hich specific standards eist and %hich

may include additional requirements or requirements different from those of

this uropean Standard.

3. &fter-treatmentAovercoating of hot dip galvanized articles is not covered $y

this standard.

35$.ndividual product standards can incorporate this standard for the coating $y

quoting its num$er# or may incorporate it %ith modifications specific to the product.

n this section# the type of inspections performed on hot-dip galvanized steel %ill $e

discussed. The various inspections are used to verify the necessary specifications for

the galvanized product are met. These techniques for each test method are specified in

&ST & 14=A& 14=# & 1?=A& 1?=# or & 2;2A& 2;2# depending upon the type of

product $eing inspected. The most common inspections# listed $elo%# range from a

simple visual inspection to more sophisticated tests to determine em$rittlement or

adhesion.

Coating $hic"nessE magnetic gauges# optical microscopy

Coating 7eightE %eigh-galvanize-%eigh# and %eigh-strip-%eigh

Finish and /ppearanceE visual inspection

/dditional $ests

o /dherenceE stout /nife

o .m8rittlementE similar $end radius# sharp $lo%# and steel angle

o ChromatingE spot test

o endingE minimum finished $end diameter ta$le

ampling


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oating Thic+ness

The term coating thic/ness refers to the thic/ness of zinc applied to steel# %hile

coating %eight refers to the amount of zinc applied to steel for a given surface area.

T%o different methods are used in order to measure the coating thic/ness of hot-dip

galvanized steel.

Figure 1#: Pencil-t9le Gauge

The first method to measure coating thic/ness involves using magnetic thic/ness

gauges. There are three different types of magnetic thic/ness gauges and all can $e

used quite easily in the galvanizing plant or in the field.

The first type of magnetic thic/ness gauge is very small and utilizes a spring-loaded

magnet encased in a pencil-li/e container# as seen inFigure 14. The tip of the gauge is

placed on the surface of the steel and is slo%ly pulled off in a continuous motion.

>hen the tip of the gauge is pulled a%ay from the surface of the steel# the magnet#

near the tip# is attracted to the steel. & graduated scale indicates the coating thic/ness

at the instant immediately prior to pulling the magnet off the surface of the steel. The

accuracy of this gauge requires it to $e used in the true vertical plane $ecause# due to

gravity# there is more error associated %ith measurements ta/en in the horizontal

plane or overhead positions. The measurement should $e made multiple times $ecause

the a$solute accuracy of this type of gauge is $elo% average and it is difficult to

determine the true coating thic/ness %hen only one reading is ta/en.

Figure 1: anana Gauge

& $anana gauge# as seen inFigure 15is the second type of thic/ness gauge. >ith thisgauge# coating thic/ness measurements are ta/en $y placing the ru$$er magnet


16/44

housing on the surface of the product %ith the gauge held parallel to the surface. &

scale ring is rotated cloc/%ise to $ring the tip of the instrument in contact %ith the

coated surface and rotated counter-cloc/%ise until a $rea/ in contact can $e heard and

felt. The position of the scale ring %hen the magnetic tip $rea/s from the coated

surface displays the coating thic/ness. This type of gauge has the advantage of $eing

a$le to measure coating thic/ness in any position# %ithout recali$ration or interferencefrom gravity.

Figure 1&: .lectronic!Digital $hic"ness Gauge

The electronic or digital thic/ness gauge# as seen inFigure 16is the most accurate

and argua$ly# the easiest thic/ness gauge to operate. The electronic thic/ness gauge is

operated $y simply placing the magnetic pro$e onto the coated surface and then a

digital readout displays the coating thic/ness. lectronic gauges have the advantage of

not requiring recali$ration %ith pro$e orientation# $ut do require cali$ration %ith

shims of different thic/nesses in order to verify the accuracy of the gauge at the time

it is $eing used. These shims are measured and the gauge is cali$rated according to

the thic/ness of the shim# and then this process is repeated for shims of different

thic/nesses until the gauge is producing an accurate reading in all ranges of thic/ness.

/$M . 0'&

The specification &ST =2; contains information for measuring coating thic/ness

using magnet or electromagnetic current. t also provides some tips for o$taining

measurements %ith the greatest accuracy# as %ell as descri$ing ho% the physical

properties# the structure# and the coating can interfere %ith the measurement methods.

The requirements for &ST =2;# as seen $elo%# are intended to ma/e the coating

thic/ness measurements using magnet or electromagnetic current as accurate as

possi$le.

/$M . 0'& +e6uirements

easurements on large products should $e made at least four inches from the

edge to avoid edge effects

easurement readings should $e as %idely dispersed as possi$le

There are some general guidelines# as seen $elo%# for reducing error and ensuring the

most accurate readings are $eing collected %hen using magnetic thic/ness gauge

instruments.


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Guidelines for +educing .rror

!ecali$rate frequently# using non-magnetic film standards or shims a$ove and

$elo% the epected thic/ness value

!eadings should not $e ta/en near an edge# a hole# or inside corner

!eadings ta/en on curved surfaces should $e avoided if possi$le Test points should $e on 7regular areas8 of the coating

Ta/e at least five readings to o$tain a good# 7true8 value %hich is

representative of the %hole sample

Figure 1': 5ptical Microscop9

The second method used to measure the coating thic/ness involves optical

microscopy# as seen inFigure 17. This is a destructive technique and is typically only

used for inspection of the coating of single specimen samples that have failed

magnetic thic/ness readings or for research studies. Since it is not a common method#

the accuracy is highly dependent on the epertise of the operator.

oating ,eight

The term coating %eight refers to the amount of zinc applied to a product for a given

surface area. T%o different methods can $e used to measure the coating %eight of hot-

dip galvanized steel.

The first method to measure the coating %eight involves using a process called %eigh-

galvanize-%eigh# and is only appropriate for single specimen samples. The zinc

coating %eight from this technique is underestimated $ecause the actual coating is

made up of $oth iron and zinc and this method %ill only measure the added zinc

%eight in the coating. n addition# it can $e very difficult to measure and calculate the

surface area of a comple steel fa$rication# and this ma/es coating %eight values even

less accurate.

>eigh-strip-%eigh is the second method used to measure coating %eight# and again isonly appropriate for single specimen samples. This method is destructive since it


18/44

removes the hot-dip galvanized coating during the measurement. This process

involves first %eighing the specimen# stripping it of all zinc coating that %as added#

and then %eighing it again. The difference in the %eights is then equal to the amount

of coating added during the galvanizing process. Ho%ever# this method is usually only

used on very small products li/e nails# and can $e inaccurate $ecause %hen the

coating is stripped there may $e some $ase metal stripped along %ith the coating. Thismeans that there may $e etra iron included in the %eight measurement# ma/ing for a

higher than actual zinc coating %eight.

Finish "ppearance

The inspection of finish and appearance is done %ith an unmagnified visual

inspection. This inspection is performed $y fully o$serving all parts and pieces of a

hot-dip galvanized product to ensure all necessary components and specifications

have $een met. t is done in order to o$serve surface conditions# $oth inside and out#

and chec/ all contact points# as %ell as %elds# @unctions# and $end areas.

/ppearance

The appearance of the hot-dip galvanized coating can vary from piece to piece# and

even section to section of the same piece. There are a num$er of reasons for the non-uniform appearance# $ut it is important to note appearance has no $earing on the

corrosion protection of the galvanized piece. This section %ill overvie% the resons for

differences in appearance.

Finish

This section %ill revie% a num$er of possi$le surface defects visi$le on the

galvanized coating. Some of these surface defects are re@ecta$le# as they %ill seriously

lo%er the corrosion protection# %hile others have little or no effect on the corrosion

performance and are accepta$le.

Different "ppearances

The appearance of hot-dip galvanized steel immediately after galvanizing can $e

$right and shiny# spangled# matte gray# or a com$ination of these. There are a num$er

of reasons for the difference in appearance# as eplored here# $ut regardless if the

piece is shiny or dull# the appearance has no effect on the corrosion performance. &nd

in time after eposure to the environment# all galvanized coatings %ill ta/e on a

uniform matte gray appearance.


19/44

#easons for Different Appearances

teel Chemistr9

The most common reason for galvanized steel to have different appearances is the

chemistry of the steel pieces. There are t%o elements of steel chemistry %hich moststrongly influence the final appearanceF silicon and phosphorous. oth silicon and

phosphorous promote coating gro%th# and this thic/er coating is responsi$le for the

differing appearance.

The amount of silicon added during the steel ma/ing process to deoidize the steel

can create differences in appearance of galvanized products. The recommended

silicon composition is either less than ).)3* or $et%een ).1?* and ).4?*. &ny steels

not %ithin these ranges are considered reactive steels and are epected to form zinc

coatings that tend to $e thic/er.

n addition to producing thic/er coatings# highly reactive steels tend to have a matte

gray or mottled appearance instead of the typical $right coating. This difference in

appearance is a result of the rapid zinc-iron intermetallic gro%th that consumes all of

the $right# pure zinc. This gro%th of the intermetallic layer is generally out of the

galvanizer0s control# $ecause they usually do not have prior /no%ledge of the steel0s

composition. Ho%ever# this increased coating thic/ness can $e $eneficial in some

respects $ecause time to firrst maintenance is directly proportional to coating

thic/ness.

nFigure 18# the micrograph on the left sho%s a regular zinc-iron alloy# %hile the

micrograph on the right sho%s an irregular zinc-iron alloy. These clearly sho% themicroscopic level differences that can occur due to the amount of silicon in the steel

$eing hot-dip galvanized.

Figure 1(: +egular vs C

are Spots

lasting Damage

,hain and >ire ar/s

,logged Holes

,logged Threads

D > .

Delamination

Distortion

Drainage Spi/es Dross nclusions

cess &luminum in Galvanizing ath

F > 5

5ish oning

5la/ing

5lu nclusions

9ide ines

P > +

Products in ,ontact

!ough Surface ,ondition

!uns

!ust leeding

> $

Sand m$edded in ,asting

Striations Steel Surface ,ondition
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23/44

Surface ,ontaminant

Touch ar/s

? > )

>eeping >eld >elding lo%outs

>elding Spatter

>et Storage Stain

Binc S/immings

Binc Splatter

/isual Defects. "-0are Spots

are spots# defined as uncoated areas on the steel surface# are the most common

surface defect and occur $ecause of inadequate surface preparation# %elding slag#

sand em$edded in castings# ecess aluminum in the galvanizing /ettle# or lifting aids

that prevent the coating from forming in a small area. 9nly very small areas# less than

1 inch in the narro%est dimension %ith a total of no more than ).?*of the accessi$le

surface area# may $e renovated using &ST & 2(). This means narro%# $are areas

may $e repairedF ho%ever# if they are greater than one inch-square areas# the product

must $e regalvanized. n order to avoid $are spots# li/e those seen in Figure 24# thegalvanizer must ensure the surfaces are clean and no contaminants are present after

pretreatment. f the size of the $are spot or total surface area causes re@ection# the

parts may $e stripped# regalvanized# and then re-inspected for compliance to the

standards and specifications.

Figure 2#: are pots
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24/44

Figure 2: lasting Damage

lasting Damage

lasting damage creates $listered or fla/ing areas on the surface of the galvanized

product.lasting damage follo%s a$rasive $lasting prior to painting of the galvanized

steel. t is caused $y incorrect $lasting procedures creating shattering and

delamination of the alloy layers in the zinc coating. lasting damage# as seen in

Figure 25# can $e avoided %hen careful attention is paid to preparation of the product

for painting. n addition# $last pressure should $e greatly reduced according to &ST

D ;=(;. Since $lasting damage is induced $y a post-galvanizing process# the

galvanizer is not responsi$le for the damage.

Figure 2&: Chain and 7ire Mar"s

Chain and 7ire Mar"s

&nother type of surface defect occurs %hen steel is lifted and transported around the

galvanizing plant using a chain or %ire. These lifting aids can leave uncoated areas on

the finished product that %ill need to $e repaired. The superficial mar/s# li/e those

seen inFigure 26# left on the galvanized coating from the lifting attachments are not

grounds for re@ection as long as mar/s can $e repaired. &ST specifications do not

allo% any $are spots on the finished galvanized part.


25/44

Figure 2': Clogged Holes

Clogged Holes

,logged holes are holes partially or completely clogged %ith zinc metal. & goodeample is the screen sho%n inFigure 27. The zinc %as trapped $ecause liquid zinc

%ill not drain easily from holes less than =A1)8 '(mm+ in diameter due to its high

surface tension. ,logged holes can $e minimized $y ma/ing all holes as large as

possi$le. The trapped zinc can $e removed $y using active fettling %hen the part is in

the galvanizing /ettle# vi$rating the cranes to @ostle the parts# or $lo%ing compressed

air onto the galvanized products. This condition is not a cause for re@ection# unless it

prevents the part from $eing used for its intended purpose.

Figure 2(: Clogged $hreads

Clogged $hreads

,logged threads are caused $y poor drainage of a threaded section after the product is

%ithdra%n from the galvanizing /ettle. These clogged threads# as seen inFigure 28#

can $e cleaned $y using post-galvanizing cleaning operations such as a centrifuge or

$y heating them %ith a torch to a$out ?)) 5 '4;) ,+ and then $rushing them off %ith

a %ire $rush to remove the ecess zinc. ,logged threads must $e cleaned $efore the

part can $e accepted.


26/44

/isual Defects. D-1

Figure 2,: Delamination

Delamination

Delamination or peeling creates a rough coating on the steel %here the zinc has peeled

off.There are a num$er of causes for zinc peeling. any large galvanized parts ta/e a

long time to cool in the air and form zinc-iron layers after they have $een removed

from the galvanizing /ettle. This continued coating formation leaves $ehind a void

$et%een the top t%o layers of the galvanized coating. f there are many voids formed#

the top layer of zinc can separate from the rest of the coating and peel off the part. f

the remaining coating still meets the minimum specification requirements# then the

part is still accepta$le. f the coating does not meet the minimum specification

requirements then the part must $e re@ected and regalvanized. f delamination# as seen

inFigure 29# occurs as a result of fa$rication after galvanizing# such as $lasting

$efore painting# then the galvanizer is not responsi$le for the defect.

Figure 0: Distortion

Distortion

Distortion# as seen inFigure 30# is defined as the $uc/ling of a thin# flat steel plate or

other flat material such as %ire mesh.The cause of this is differential thermal

epansion and contraction rates for the thin# flat plate and mesh than the thic/er steel

of the surrounding frame. n order to avoid distortion# use a thic/er plate# ri$s# or

corrugations to stiffen flat sections or ma/e the entire assem$ly out of the same

thic/ness steel. Distortion is accepta$le# unless distortion changes the part so that it is

no longer suita$le for its intended use.


27/44

Figure 01: Drainage pi"es

Drainage pi"es

Drainage spi/es or drips are spi/es or tear drops of zinc along the $ottom edges of the

product.These result %hen the surfaces of the product are processed horizontal to the

galvanizing /ettle# preventing proper drainage of the zinc from the surface as the

product is %ithdra%n from the /ettle. Drainage spi/es# as seen inFigure 31# are

typically removed during the inspection stage $y a $uffing or grinding process.

Drainage spi/es or drips are ecess zinc and %ill not affect corrosion protection# $ut

are potentially dangerous for anyone %ho handles the parts. These defects must $e

removed $efore the part can $e accepted.

Dross 4nclusions

Dross inclusions are a distinct zinc-iron intermetallic alloy that $ecomes entrapped or

entrained in the zinc coating. This is caused $y pic/ing up zinc-iron particles from the

$ottom of the /ettle. Dross# as seen inFigure 32# may $e avoided $y changing the

lifting orientation or redesigning the product to allo% for proper drainage. f the dross

particles are small and completely covered $y zinc metal# they %ill not affect the

corrosion protection and are accepta$le. f the dross particles are large# then the drossmust $e removed and the area repaired.

Figure 02: Dross 4nclusions


28/44

Figure 00: .%cess /luminum in Galvanizing ath

.%cess /luminum in Galvanizing ath

&nother type of surface defect# sho%n inFigure 33# is caused $y an ecess amount of

aluminum in the galvanizing $ath. This creates $are spots and $lac/ mar/s on the

surface of the steel.The ecess aluminum can $e avoided $y ensuring proper control

of the aluminum level in the galvanizing $ath $y means of regular sampling and

analysis# and $y ad@usting the levels in a regular and controlled manner. 5or small

areas of $are spots# the part may $e repaired as detailed in the specification. f this

condition occurs over the entire part# then it must $e re@ected and regalvanized.

/isual Defects. F-O

Figure 0#: Fish oning

Fish oning

5ish $oning is an irregular pattern over the entire surface of the steel part.This is

caused $y differences in the surface chemistry of a large diameter steel piece and

variations in the reaction rate $et%een the steel and zinc. These reaction differences

cause the thic/ness of the galvanized coating to vary in sharply defined zones across

the surface. 5ish $oning# as seen inFigure 34# has no effect on the corrosion

protection provided $y the zinc coating and is not cause for re@ection of the hot-dip

galvanized part.


29/44

Figure 0: Micrograph of Fla"ing

Fla"ing

5la/ing results %hen heavy coatings develop in the galvanizing process# usually 14

mils or greater. This generates high stresses at the interface of the steel and the

galvanized coating and causes the zinc to $ecome fla/y and separate from the surface

of the steel. 5la/ing can $e avoided $y minimizing the immersion time in the

galvanizing /ettle and cooling of the galvanized steel parts as quic/ly as possi$le.

Figure 35sho%s a micrograph of fla/ing. n addition# using a different steel grade# if

possi$le# may also help avoid fla/ing. f the area of fla/ing is small# it can $e repaired

and the part can $e acceptedF ho%ever# if the area of fla/ing is larger than allo%ed $y

the specifications# the part must $e re@ected and regalvanized.

Figure 0&: Flu% 4nclusion

Flu% 4nclusions

5lu inclusion can $e created $y the failure of the flu to release during the hot-dip

galvanizing process. f this occurs# the galvanized coating %ill not form under this

flu spot.f the area is small enough# it must $e cleaned and repairedF other%ise# the

part must $e re@ected. 5lu spots can increase if the flu is applied using the %et

galvanizing method# %hich is %hen the flu floats on the zinc $ath surface. 5lu

deposits on the interior of a hollo% part# such as a pipe or tu$e# as seen in Figure 36#

cannot $e repaired# thus the part must $e re@ected. &ny flu spots or deposits#pic/ed

up during %ithdra%al from the galvanizing /ettle do not %arrant re@ection if theunderlying coating is not harmed# and the flu is properly removed.


30/44

Figure 0': 5%ide =ines

5%ide =ines

9ide lines are light colored oide film lines on the galvanized steel surface . 9ide

lines are caused %hen the product is not removed from the galvanizing /ettle at a

constant rate. This may $e due to the shape of the product or the drainage conditions.9ide lines# as seen inFigure 37# %ill fade over time as the entire zinc surface

oidizes. They %ill have no effect on the corrosion performanceF only the initial

appearance %ill $e affected. This condition is not a cause for re@ection of the hot-dip

galvanized parts.

/isual Defects. P-*

Figure 0(: Products in Contact

Products in Contact

&nother type of surface defect is caused $y products that come in contact %ith each

other or are stuc/ together. This usually occurs %hen many small products are hung

on the same fiture# %hich creates the chance products may $ecome connected or

overlapped during the galvanizing process# as seen inFigure 38. The galvanizer is

responsi$le for proper handling of all products in order to avoid this defect. naddition# if the surface of a product has a larger $are area than the specified repair

requirement allo%s# then that product must $e re@ected and regalvanized.

+ough urface Condition

!ough surface condition or appearance is a uniformly rough coating %ith a tetured

appearance over the entire product.The cause for this rough surface condition is hot-

rolled steel %ith a high level of silicon content. This can $e avoided $y purchasing

steel %ith a silicon content less than ).)=* of the steel $y %eight. !ough surface

condition# as seen inFigure 39# can actually have a positive effect on corrosion

performance $ecause of the thic/er zinc coating produced. 9ne of the fe% situations


31/44

%here rough coating is cause for re@ection is if it occurs on handrails. The corrosion

performance of galvanized steel %ith rough coatings is not affected $y the surface

roughness.

Figure 0,: +ough urface Condition

Figure #: +uns

+uns

!uns are localized thic/ areas of zinc on the surface. !uns occur %hen zinc freezes on

the surface of the product during removal from the zinc $ath. This is more li/ely to

occur on thinner sections %ith large surface areas that cool quic/ly. n order to avoid

runs# as seen inFigure 40# ad@ustments of the dipping angles can $e made# if possi$le#

to alter the drainage pattern to a more accepta$le mode. f runs are unavoida$le and

%ill interfere %ith the intended application# they can $e $uffed. !uns are not cause forre@ection.

+ust leeding

!ust $leeding appears as a $ro%n or red stain that lea/s from unsealed @oints after the

product has $een hot-dip galvanized.t is caused $y pre-treatment chemicals that

penetrate an unsealed @oint. During galvanizing of the product# moisture $oils off the

trapped treatment chemicals leaving anhydrous crystal residues in the @oint. 9ver


32/44

time# these crystal residues a$sor$ %ater from the atmosphere and attac/ the steel on

$oth surfaces of the @oint# creating rust that seeps out of the @oint. !ust $leeding# as

seen inFigure 41# can $e avoided $y seal %elding the @oint %here possi$le or $y

leaving a gap greater than =A=48 '4.3mm+ %ide in order to allo% solutions to escape

and zinc to penetrate during hot-dip galvanizing. f $leeding occurs# it can $e cleaned

up $y %ashing the @oint after the crystals are hydrolyzed. leeding from unsealed@oints is not the responsi$ility of the galvanizers and is not cause for re@ection.

Figure #1: +ust leeding

/isual Defects. S-T

Figure #2: and .m8edded in Casting

and .m8edded in Casting

&nother type of surface defect occurs %hen sand $ecomes em$edded in the castings

and creates rough or $are spots on the surface of the galvanized steel. Sand inclusions

are not removed $y conventional acid pic/ling# so a$rasive cleaning should $e done at

the foundry $efore the products are sent to the galvanizer. This type of defect also

leaves $are spots and must $e cleaned and repaired or the part must $e re@ected#stripped# and regalvanized. Sand em$edded in a casting can $e seen in Figure 42.


33/44

Figure #0: triations

triations

Striations are characterized $y raised parallel ridges in the galvanized coating# mostly

in the longitudinal direction. This can $e caused %hen sections of the steel surface are

more highly reactive then the areas around them. These sections are usually associated

%ith segregation of steel impurities# especially phosphorous# created during the rolling

process in steel ma/ing. Striations# as seen inFigure 43# are related to the type of steel

galvanized and %hile the appearance is affected# the performance of the corrosion

protection is not. Striations are accepta$le on most partsF ho%ever# if the striations

happen to occur on handrails# then the parts must $e re@ected and regalvanized.

Sometimes regalvanizing does not improve the striations and the handrail must $e

refa$ricated out of $etter quality steel.

Figure ##: urface Contaminents

urface Contaminant

>hen surface contaminants create an ungalvanized area %here the contaminant %as

originally applied# a surface defect may occur.This is caused $y paint# oil# %a# or

lacquer not removed during the pretreatment cleaning steps. Surface contaminants# as

seen inFigure 44# should $e mechanically removed prior to the galvanizing process.

f they result in $are areas# then the repair requirements apply and small areas may $e

repaired# $ut a large area is grounds for re@ection and the entire part must $e

regalvanized.


34/44

Figure #: $ouch Mar"s

$ouch Mar"s

&nother type of surface defect is /no%n as touch mar/s# %hich are damaged or

uncoated areas on the surface of the product. Touch mar/s are caused $y galvanized

products resting on each other or $y the material handling equipment used during the

galvanizing operation. Touch mar/s# as seen inFigure 45# are not cause for re@ection

if they meet the size criteria for repaira$le areas. They must $e repaired $efore the

part is accepted.

/isual Defects. 2-3

Figure #&: 7eeping 7eld

7eeping 7eld

>eeping %elds stain the zinc surface at the %elded connections on the steel.They arecaused $y entrapped cleaning solutions that penetrate the incomplete %eld. n order to

avoid %eeping %elds for small overlapping surfaces# completely seal %eld the edges

of the overlapping area. 5or larger overlapping areas# the area cannot $e seal %elded

since the volume epansion of air in the trapped area can cause eplosions in the

galvanizing /ettle. To avoid %eeping %elds in large overlapping areas# the $est plan is

to provide a =A=48 '4.3mm+ or larger gap $et%een the t%o pieces %hen %elding them

and let the zinc fill the gap $et%een the pieces. This %ill actually ma/e a stronger

@oint %hen the process is complete. >eeping %elds# as seen inFigure 46# are not the

responsi$ility of the galvanizer and are not cause for re@ection.


35/44

Figure #': 7elding lo@outs

7elding lo@outs

>elding $lo%out is a $are spot around a %eld or overlapping surface hole.These are

caused $y pre-treatment liquids penetrating the sealed and overlapped areas that $oil

out during immersion in the liquid zinc. This causes localized surface contamination

and prevents the galvanized coating from forming. n order to avoid %elding

$lo%outs# as seen inFigure 47# chec/ %eld areas for complete %elds to insure there is

no fluid penetration. n addition# products can $e preheated prior to immersion into

the galvanizing /ettle in order to dry out overlap areas as much as possi$le. >elding

$lo%outs cause $are areas that must $e repaired $efore the part is accepta$le.

Figure #(: 7elding patter

7elding patter

>elding spatter appears as lumps in the galvanized coating ad@acent to %eld areas. t

is created %hen %elding spatter is left on the surface of the part $efore it is hot-dip

galvanized. n order to avoid %elding spatter# %elding residues should $e removed

prior to hot-dip galvanizing. >elding spatter# as seen inFigure 48# appears to $e

covered $y the zinc coating# $ut the coating does not adhere %ell and can $e easily

removed. This type of defect can leave an uncoated area or $are spot if the zinc

coating is damaged and must $e cleaned and properly repaired.


36/44

7et torage tain

>et storage stain is a %hite# po%dery surface deposit on freshly galvanized surfaces.

t is caused $y ne%ly galvanized surfaces $eing eposed to fresh %ater# such as rain#

de%# or condensation that react %ith the zinc metal on the surface to form zinc oide

and zinc hydroide. t is found most often on tightly stac/ed and $undled items# suchas galvanized sheets# plates# angles# $ars# and pipes. >et storage stain can have the

appearance of light# medium# or heavy %hite po%der on the galvanized steel product.

ach of these appearances can $e seen from right to left inFigure 49.

9ne method to avoid %et storage stains is to passivate the product after galvanizing

$y using a chromate quench solution. &nother precaution is to avoid stac/ing products

in poorly ventilated# damp conditions. ight or medium %et storage stain %ill %eather

over time in service and is accepta$le. n most cases# %et storage stain does not

indicate serious degradation of the zinc coating# nor does it necessarily imply any

li/ely reduction in the epected life of the product. Ho%ever# heavy %et storage stain

should $e removed mechanically or %ith appropriate chemical treatments $efore the

galvanized part is put into service. Heavy storage stain must $e removed or the part

must $e re@ected and regalvanized.

Figure #,: 7et torage tain

Figure : )inc "imming 4nclusions

)inc "immings

S/imming deposits are usually caused %hen there is no access to remove the

s/immings during the %ithdra%al of the steel from the galvanizing /ettle. Thes/immings on the liquid zinc surface are trapped on the zinc coating. n order to


37/44

remove zinc s/immings %ithout harming the soft zinc coating underneath# lightly

$rush them off the surface of the galvanized steel during the in-house inspection stage

%ith a nylon-$ristle $rush. Binc s/immings# as seen inFigure 50# are not grounds for

re@ection. The zinc coating underneath is not harmed during their removal and it meets

the necessary specifications.

)inc platter

Figure 1: )inc platter

Binc splatter is defined as splashes and fla/es of zinc that loosely adhere to the

galvanized coating surface.Binc splatter is created %hen moisture on the surface of

the galvanizing /ettle causes liquid zinc to 7pop8 and splash droplets onto the product.

These splashes create fla/es of zinc loosely adherent to the galvanized surface. Binc

splatter# as seen inFigure 51# %ill not affect the corrosion performance of the zinc

coating and is not cause for re@ection. The splatter does not need to $e cleaned off the

zinc coating surface# $ut can $e if a consistent# smooth coating is required.

"dditional Tests

/dherence $est

Figure 2: tout Anife $est

Testing of the zinc coating adherence to the steel is achieved using a stout /nife. The

steps used in this test are listed $elo% and a photo of the test $eing performed can $e

seen inFigure 52. The coating shall $e deemed 7not adherent8 if it fla/es off and

eposes the $ase metal in advance of the /nifepoint. The test is not an attempt to pare

or %hittle the zinc coating. f the coating is adherent the /nife should put a slight mar/in the zinc metal surface# $ut should not cause any delamination of the coating layers.


38/44

/dhesion $est @ith a tout Anife

Push do%n point of stout /nife

,oating must not fla/e off eposing the $ase metal

Do not perform at edges or corners of the product

6o paring or %hittling %ith /nife is accepta$le

ending $est

The hot-dip galvanized coating on a steel $ar must %ithstand $ending %ithout fla/ing

or peeling %hen the $ending test is preformed in accordance %ith the specifications in

&ST & 13=. There are various tests used to assess the ductility of steel %hen

su$@ected to $ending. 9ne test may include the determination of the minimum radius

or diameter required to ma/e a satisfactory $end. &nother test may include the

num$er of repeated $ends that the material can %ithstand %ithout failure %hen it is

$ent through a given angle and over a definite radius.

!e$ar is commonly $ent prior to the hot-dip galvanizing process. Steel reinforcing

$ars $ent cold prior to hot-dip galvanizing should $e fa$ricated to a $end diameter

equal to or greater than the specified value in &ST & 2;2A& 2;2. Ho%ever# steel

reinforcing $ars can $e $ent to diameters tighter than the specified values if they are

stress relieved at a temperature of hen there is suspicion of potential em$rittlement of a product# it may $e necessary

to test a small group of the products to measure the ductility. These tests are usually

destructive to the zinc coating and possi$ly to the product as %ell. Products suspected

of em$rittlement shall $e tested according to the specification &ST & 13=.Depending on the service conditions the product %ill $e eposed to# one of three

em$rittlement tests may need to $e performed. These em$rittlement tests include the

similar $end radius test# sharp $lo% test# and steel angle test. The em$rittlement test

uses a /no%n force to provide a stress that should $e lo%er than the yield stress of the

part. f there is a fracture or permanent damage created during the testing process# the

parts must $e re@ected.


39/44

Sampling

& sampling protocol has $een developed $y &ST to ensure high quality products

$ecause the inspection of the coating thic/ness for every piece of material galvanized

in a pro@ect %ould not $e practical. &ST & 14=A& 14= states for a unit of products

%hose surface area is equal to or less than 1;) inI '1)=4 cmI+# the entire surface of

each test product constitutes a specimen. n the case of a product containing more

than one material category or steel thic/ness range# that product %ill contain more

than one specimen. n addition# products %ith surface areas greater than 1;) inI '1)=4

cmI+ are multi-specimen products. There are four important terms used in the &ST

specifications and each is defined $elo%.

ampling $erms

=otE unit of production or shipment from %hich a sample is ta/en for testing

ampleE a collection of individual units of product from a single lot

pecimenE the surface of an individual test product or a portion of a test

product %hich is a mem$er of a lot or a mem$er of a sample representing that

lot

$est ProductE an individual unit of product that is a mem$er of the sample

5or single specimen products# each randomly selected product is a specimen. n

thic/ness measurement tests# five measurements are ta/en %idely dispersed over the

surface area of the specimen in order to represent the total coating thic/ness. The

mean value of the five coating thic/nesses for one specimen must have a minimumaverage coating thic/ness grade of not less than one grade $elo% the minimum

average coating thic/ness for the material category. nFigure 53# the separation of a

lot into a sample and individual specimen is sho%n.

Figure 0: ingle pecimen Product ampling

& multi-specimen product is defined as having a surface area that may $e larger than

1;) inI '1)=4 cmI+# have multiple steel thic/nesses# or contain more than one coating

category. n order to test coating thic/ness of products %hose surface area is greater

than 1;) inI '1)=4 cmI+# they are su$divided into three continuous local sections %ith

equivalent surface areas# each of %hich constitutes a unique specimen. n the case of

any such local section containing more than one material category or steel thic/ness


40/44

range# that section %ill contain more than one specimen. n Figure 54# the separation

of a lot into a sample and individual specimen is sho%n.

Figure #: Mutli-pecimen Product ampling

5or products hot-dip galvanized to either &ST & 14=A& 14= or & 1?=A& 1?=#

a!e 6is used to determine the minimum num$er of specimens for sampling from a

given lot size.

3o< of Pieces in =ot 3o< of pecimens

= or less &ll

3 to ?)) =

?)1 to 14)) ?

14)1 to =4)) (

=4)1 to 1)#))) 1=

1)#))1J 4)

$a8le &: Minimum 3um8er of pecimens for /$M / 120 and / 12

5or re$ar hot-dip galvanized according to &ST & 2;2# the information $elo% is

used to determine the minimum num$er of samples per lot# measurements per sample#

and the total num$er of measurements required for each of the different coating

thic/ness measurement techniques.

Magnetic $hic"ness:

o = samples per lot

o ? or more measurements per sample

o 1? measurements# at the minimum# comprise the average

Microscop9 Method:

o ? samples per lot

o 3 measurements per sample

o 4) measurements# at minimum# comprise the average

tripping and 7eighing:o = samples per lot


41/44

The minimum average coating thic/ness for a lot is the average of the specimen

values and must meet the minimum for the material category. The minimum for an

individual specimen is one grade $elo% the minimum for the material category. &n

individual measurement has no minimum# $ut $are areas are not allo%ed on the part.

The final inspection of a part shall include thic/ness measurements and visual

inspection. &ll parts that do not meet the requirement must $e resorted andreinspected or re@ected and then regalvanized.

*epair

f the galvanized product does not meet all of the requirements of the specification# it

must $e repaired or re@ected along %ith the lot it represents. >hen repair of the

product is allo%ed $y the specification or $are spots are present# the galvanizer is

responsi$le for the repair unless directed other%ise $y the purchaser. The

specifications allo% for some retesting of products that represent lots or retesting after

the lot has $een sorted for non-conformance. The coating thic/ness of the repairedarea must match the coating thic/ness of the surrounding area. Ho%ever# if zinc-rich

paint is used for repair# the coating thic/ness must $e ?)* higher than the

surrounding area# $ut not greater than 3.) mils $ecause mud crac/ing tends to result

%hen the paint coating is too thic/. The maimum sizes for allo%a$le areas that can

$e repaired during in-plant production are defined in the specifications as summarized

$elo%.

Ma%imum ize of +epaira8le /rea

/$M / 120!/ 120M:

o 9ne inch or less in narro%est dimensiono Total area can $e no more than ).?* of the accessi$le surface area to

$e coated or =; square inches per piece# %hichever is less

/$M / 10!/ 10M:

o The $are spots shall have an area totaling no more than 1* of the total

surface area to $e coated# ecluding threaded areas of the piece

/$M / '&'!/ '&'M:

o 6o area given

o f the coating fails to meet the requirement for finish and adherence#

the $ar may $e stripped# regalvanized# and resu$mitted

o Damage done to the coating due to fa$rication or handling shall $e

repaired %ith a zinc-rich formulation

o Sheared ends shall $e coated %ith a zinc-rich formulation

+epair Methods

&ny repairs made to galvanized products must follo% the requirements of &ST &

2()# %hich defines the accepta$le materials and the required procedures. !epairs are

normally completed $y the galvanizer $efore the products are delivered# $ut under

certain circumstances# the purchaser may perform the repairs on their o%n. The touch-

up and repair materials are formulated to deliver an ecellent color that matches either

$rightly coated# ne%ly galvanized products or matte gray# aged galvanized products.


42/44

aterials used to repair hot-dip galvanized products include zinc-$ased solder# zinc-

rich paint# and zinc spray metallizing# and are eplained in the follo%ing sections.

3inc-0ased Solder

Figure : )inc-ased older

Soldering %ith zinc-$ased alloys is achieved $y applying zinc alloy in either a stic/ orpo%der form. The area $eing repaired needs to $e preheated to approimately ;)) 5

'=1? ,+. The most commonly used solders for repair# as seen inFigure 55# include

zinc-tin-lead# zinc-cadmium# and zinc-tin-copper alloys.

urface Preparation

&ccording to &ST & 2()# the surface to $e reconditioned shall $e %ire $rushed#

lightly ground# or mildly $last cleaned. n addition# if %ire $rushing or light $lasting is

inadequate# all %eld flu and spatter must $e removed $y mechanical methods. The

cleaned area also needs $e preheated to ;)) 5 '=1? ,+ and %ire $rushed %hile heated.

Pre-flu may also $e necessary to provide chemical cleaning of the $are spot. 5inally#special care should $e given to insure that the surrounding galvanized coating is not

overheated and $urned $y the preheating.

/pplication

The soldering method is the most difficult of the three repair methods to complete. &

high level of caution must $e ta/en %hile heating the $are spot to prevent oidizing

the eposed steel or damaging the surrounding galvanized coating. Solders are

typically not economically suited for touch-up of large areas $ecause of the time

involved in the process and $ecause heating of a large surface area to the sametemperature is very difficult. >hen the repair has $een completed# the flu residue

needs to $e removed $y rinsing the surface %ith %ater or %iping %ith a damp cloth.

Final +epaired Product

The final coating thic/ness for this repair shall $e agreed upon $et%een the galvanizer

and the purchaser# and is generally in the 1 to 4 mil range. The thic/ness shall $e

measured $y any of the methods in &ST & 14=A& 14= that are non-destructive.

Binc-$ased solder products closely match the surrounding zinc and $lend in %ell %ith

the eisting coating appearance.


43/44

3inc-*ich Paint

Figure &: )inc-+ich Paint

Binc-rich paint is applied to a clean# dry steel surface $y either a $rush or spray as

seen inFigure 56# and usually contains an organic $inder pre-mi. Binc-rich paints

must contain either $et%een ;?* to ;


44/44

3inc Spra! Metallizing

Figure ': )inc pra9 Metallizing

Binc spray# %hich is also referred to as metallizing# is done $y melting zinc po%der or

zinc %ire in a flame or electric arc and pro@ecting the liquid zinc droplets $y air or gas

onto the surface to $e coated# as seen in Figure 57. The zinc used is nominally

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