HDG Defect

8/20/2019 HDG Defect

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Bare Spots

Figure 24: Bare Spots

Bare spots, defined as uncoated areas on the steel surface, are the

most common surface defect and occur because of inadequate surface

preparation, welding slag, sand embedded in castings, excess aluminumin the galvanizing kettle, or lifting aids that prevent the coating from

forming in asmall area. Only very small areas, less than inch in the

narrowest dimension with a total of no more than !."#of the accessible

surface area, may be renovated using $S%& $ '(!. %his means narrow,

bare areas may be repaired) however, if they are greater than one inch*

square areas, the product must be regalvanized. +n order to avoid bare

spots, like those seen in Figure 24, the galvanizer must ensure the

surfaces are clean and no contaminants are present after pretreatment.

+f the size of the bare spot or total surface area causes reection, the

parts may be stripped, regalvanized, and then re*inspected for

compliance to the standards and specifications.


2/45

-hain and ire

&arks

Figure 26: Chain and Wire Marks

$nother type of surface defect occurs when steel is lifted and

transported around the galvanizing plant using a chain or wire. %hese

lifting aids can leave uncoated areas on the finished product that will

need to be repaired. %he superficial marks, like those seen in Figure 26 ,

left on the galvanized coatingfrom the lifting attachments are not

grounds for reection as long as marks can be

repaired. $S%& specifications do not allow any bare spots on the

finished galvanized part.


3/45

-logged %hreads

Figure 28: Clogged Threads

-logged threads are caused by poor drainage of a threaded section

after the product is withdrawn from the galvanizing kettle. %hese clogged

threads, as seen in Figure 28 , can be cleaned by using post*galvanizing

cleaning operations such as a centrifuge or by heating them with a torch

to about "!! / 012! -3 and then brushing them off with a wire brush to

remove the excess zinc. -logged threads must be cleaned before the

part can be accepted.


4/45

4elamination

4elamination or peeling creates a rough coating on the steel where the

zinc has peeled off. %here are a number of causes for zinc peeling.

&any large galvanized parts take a long time to cool in the air and form

zinc*iron layers after they have been removed from the galvanizingkettle. %his continued coating formation leaves behind a void between

the top two layers of thegalvanized 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 acceptable. +f the coating

does not meet the minimum specification requirements then the part

must be reected and regalvanized. +f delamination, as seen in Figure

29, occurs as a result of fabrication after galvanizing, such as blasting

before painting, then the galvanizer is not responsible for the defect.


5/45

4istortionFigure 30: Distortion

4istortion, as seen in Figure 30 , is defined as the buckling of a thin, flat

steel plate or other flat material such as wire mesh. %he cause of this is

differential thermal expansion and contraction rates for the thin, flat plate

and mesh than the thicker steel of the surrounding frame. +n order toavoid distortion, use a thicker plate, ribs, or corrugations to stiffen flat

sections or make the entire assembly out of the same thickness steel.

4istortion is acceptable, unless distortion changes the part so that it is

no longer suitable for its intended use.


6/45

4rainage Spikes

Figure 3: Drainage Spikes

4rainage spikes or drips are spikes or tear drops of zinc along the

bottom edges of the product. %hese result when the surfaces of the

product are processed horizontal to the galvanizing kettle, preventing

proper drainage of the zinc from the surface as the product is withdrawn

from the kettle. 4rainage spikes, as seen in Figure 31, are typically

removed during the inspection stage by a buffing or grinding process.

4rainage spikes or drips are excess zinc and will not affect corrosion

protection, but are potentially dangerous for anyone who handles the

parts. %hese defects must be removed before the part can be accepted.


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4ross +nclusionsFigure 32: Dross !n"lusions

4ross inclusions are a distinct zinc*iron intermetallic alloy that becomes

entrapped or entrained in the zinc coating. %his is caused by picking up

zinc*iron particles from the bottom of the kettle. 4ross, as seen in Figure

32 , may be avoided by changing the lifting orientation or redesigning the

product to allow for proper drainage. +f the dross particles are small and

completely covered by zinc metal, they will not affect the corrosion

protection and are acceptable. +f the dross particles are large, then the

dross must be removed and the area repaired.


8/45

5xcess

$luminum in 6alvanizing Bath

Figure 33: #$"ess %lu&inu& in 'al(ani)ing Bath

$nother type of surface defect, shown in Figure 33, is caused by an

excess amount of aluminum in the galvanizing bath. %his creates bare

spots and black marks on the surface of the steel. %he excess aluminum

can be avoided by ensuring proper control of the aluminum level in the

galvanizing bath by means of regular sampling and analysis, and by

adusting the levels in a regular and controlled manner. /or small areas

of bare spots, the part may be repaired as detailed in the specification. +f

this condition occurs over the entire part, then it must be reected and

regalvanized.


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/ish Boning

Figure 34: Fish Boning

/ish boning is an irregular pattern over the entire surface of the steel

part. %his is caused by differences in the surface chemistry of a large

diameter steel piece and variations in the reaction rate between the steel

and zinc. %hese reaction differences cause the thickness of the

galvanized coating to vary in sharply defined zones across the surface.

/ish boning, as seen inFigure 34, has no effect on the corrosion

protection provided by the zinc coating and is not cause for reection of

the hot*dip galvanized part.


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/laking

Figure 3*: Mi"rograph o+ Flaking

/laking results when heavy coatings develop in the galvanizing process,

usually 1 mils or greater. %his generates high stresses at

the interface of the steel and the galvanized coating and causes the zinc

to become flaky and separate from the surface of the steel. /laking can

be avoided by minimizing the immersion time in the galvanizing kettle

and cooling of the galvanized steel parts as quickly as possible. Figure

35 shows a micrograph of flaking. +n addition, using a different steel

grade, if possible, may also help avoid flaking. +f the area of flaking is

small, it can be repaired and the part can be accepted) however, if the

area of flaking is larger than allowed by the specifications, the part must

be reected and regalvanized.


11/45

/lux +nclusions

Figure 36: Flu$ !n"lusion

/lux inclusion can be created by the failure of the flux to release during

the hot*dip galvanizing process. +f this occurs, the galvanized coating will

not form under this flux spot. +f the area is small enough, it must be

cleaned and repaired) otherwise, the part must be reected. /lux spots

can increase if the flux is applied using the wet galvanizing method,

which is when the flux floats on the zinc bath surface. /lux deposits on

the interior of a hollow part, such as a pipe or tube, as seen in Figure 36 ,

cannot be repaired, thus the part must be reected. $ny flux spots or

deposits,picked up during withdrawal from the galvanizing kettle do notwarrant reection if the underlying coating is not harmed, and the flux is

properly removed.


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Oxide 7ines

Figure 3,: -$ide .ines

Oxide lines are light colored oxide film lines on the galvanized steel

surface. Oxide lines are caused when the product is not removed from

the galvanizing kettle at a constant rate. %his may be due to the shape of

the product or the drainage conditions. Oxide lines, as seen in Figure 37 ,

will fade over time as the entire zinc surface oxidizes. %hey will have no

effect on the corrosion performance) only the initial appearance will beaffected. %his condition is not a cause for reection of the hot*dip

galvanized parts.


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8roducts in

-ontact

Figure 38: /rodu"ts in Conta"t

$nother type of surface defect is caused by products that come in

contact with each other or are stuck together. %his usually occurs when

many small products are hung on the same fixture, which creates the

chance products may become connected or overlapped during the

galvanizing process, as seen in Figure 38 . %he galvanizer is responsible

for proper handling of all products in order to avoid this defect. +n

addition, if the surface of a product has a larger bare area than the

specified repair requirement allows, then that product must be reected

and regalvanized.


14/45

9ough

Surface -ondition

Figure 3: 1ough Sur+a"e Condition

9ough surface condition or appearance is a uniformly rough coating with

a textured appearance over the entire product. %he cause for this rough

surface condition is hot*rolled steel with a high level of silicon content.

%his can be avoided by purchasing steel with a silicon content less than

!.!:# of the steel by weight. 9ough surface condition, as seen in Figure

39, can actually have a positive effect on corrosion performance

because of the thicker zinc coating produced. One of the few situationswhere rough coating is cause for reection is if it occurs on handrails.

%he corrosion performance of galvanized steel with rough coatings is not

affected by the surface roughness.


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9uns

Figure 40: 1uns

9uns are localized thick areas of zinc on the surface. 9uns occur when

zinc freezes on the surface of the product during removal from the zinc

bath. %his is more likely to occur on thinner sections with large surface

areas that cool quickly. +n order to avoid runs, as seen inFigure 40 ,

adustments of the dipping angles can be made, if possible, to alter the

drainage pattern to a more acceptable mode. +f runs are unavoidable

and will interfere with the intended application, they can be buffed. 9uns

are not cause for reection.


16/45

9ust

Bleeding

Figure 4: 1ust Bleeding

9ust bleeding appears as a brown or red stain that leaks from unsealed oints after the product has been hot*dip galvanized. +t is caused by pre*

treatment chemicals that penetrate an unsealed oint. 4uring galvanizing

of the product, moisture boils off the trapped treatment chemicals leaving

anhydrous crystal residues in the oint. Over time, these crystal residues

absorb water from the atmosphere and attack the steel on both surfaces

of the oint, creating rust that seeps out of the oint. 9ust bleeding, as

seen in Figure 41, can be avoided by seal welding the oint where

possible or by leaving a gap greater than :;:1< 01.=mm3 wide in order to

allow solutions to escape and zinc to penetrate during hot*dip

galvanizing. +f bleeding occurs, it can be cleaned up by washing the oint

after the crystals are hydrolyzed. Bleeding from unsealed oints is not the

responsibility of the galvanizers and is not cause for reection.


17/45

Sand

5mbedded in -asting

Figure 42: Sand #&edded in Casting

$nother type of surface defect occurs when sand becomes embedded in

the castings and creates rough or bare spots on the surface of the

galvanized steel. Sand inclusions are not removed by conventional acid

pickling, so abrasive cleaning should be done at the foundry before the

products are sent to the galvanizer. %his type of defect also leaves bare

spots and must be cleaned and repaired or the part must be reected,

stripped, and regalvanized. Sand embedded in a casting can be seen

in Figure 42 .


18/45

Striations

Figure 43: Striations

Striations are characterized by raised parallel ridges in the galvanized

coating, mostly in the longitudinal direction. %his can be caused when

sections of the steel surface are more highly reactive then the areas

around them. %hese sections are usually associated with segregation of

steel impurities, especially phosphorous, created during the rolling

process in steel making. Striations, as seen in Figure 43, are related to

the type of steel galvanized and while the appearance is affected, the

performance of thecorrosion protection is not. Striations are acceptable

on most parts) however, if the striations happen to occur on handrails,

then the parts must be reected and regalvanized. Sometimes

regalvanizing does not improve the striations and the handrail must be

refabricated out of better quality steel.


19/45

Surface

-ontaminant

Figure 44: Sur+a"e Conta&inents

hen surface contaminants create an ungalvanized area where the

contaminant was originally applied, a surface defect may occur. %his is

caused by paint, oil, wax, or lacquer not removed during the

pretreatment cleaning steps. Surface contaminants, as seen in Figure

44, should be mechanically removed prior to the galvanizing process. +f

they result in bare areas, then the repair requirements apply and small

areas may be repaired, but a large area is grounds for reection and the

entire part must be regalvanized.


20/45

%ouch

&arks

Figure 4*: Tou"h Marks

$nother type of surface defect is known as touch marks, which are

damaged or uncoated areas on the surface of the product. %ouch marks

are caused by galvanized products resting on each other or by

the material handling equipment used during the galvanizing operation.

%ouch marks, as seen inFigure 45 , are not cause for reection if they

meet the size criteria for repairable areas. %hey must be repaired before

the part is accepted.


21/45

eeping

eld

Figure 46: Weeping Weld

eeping welds stain the zinc surface at the welded connections on the

steel. %hey are caused by entrapped cleaning solutions that penetrate

the incomplete weld. +n order to avoid weeping welds for small

overlapping surfaces, completely seal weld the edges of the overlapping

area. /or larger overlapping areas, the area cannot be seal welded since

the volume expansion of air in the trapped area can cause explosions in

the galvanizing kettle. %o avoid weeping welds in large overlapping

areas, the best plan is to provide a :;:1< 01.=mm3 or larger gap between

the two pieces when welding them and let the zinc fill the gap between

the pieces. %his will actually make a stronger oint when the process is

complete. eeping welds, as seen in Figure 46 , are not the

responsibility of the galvanizer and are not cause for reection.


22/45

elding

Spatter

Figure 48: Welding Spatter

elding spatter appears as lumps in the galvanized coating adacent toweld areas. +t is created when welding spatter is left on the surface of the

part before it is hot*dip galvanized. +n order to avoid welding spatter,

welding residues should be removed prior to hot*dip galvanizing. elding

spatter, as seen in Figure 48 , appears to be covered by the zinc coating,

but the coating does not adhere well and can be easily removed. %his type

of defect can leave an uncoated area or bare spot if the zinc coating is

damaged and must be cleaned and properly repaired.


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et Storage Stain

et storage stain is a white, powdery surface deposit on freshly galvanizedsurfaces. +t is caused by newly galvanized surfaces being exposed to fresh

water , such as rain, dew, or condensation that react with the zinc metal on

the surface to form zinc oxide and zinc hydroxide. +t is found most often on

tightly stacked and bundled items, such as galvanized sheets, plates,

angles, bars, and pipes. et storage stain can have the appearance of

light, medium, or heavy white powder on the galvanized steel product.

5ach of these appearances can be seen from right to left in Figure 49.

One method to avoid wet storage stains is to passivate the product after

galvanizing by using a chromate quench solution. $nother precaution is to

avoid stacking products in poorly ventilated, damp conditions. 7ight or

medium wet storage stain will weather over time in service and is

acceptable. +n most cases, wet storage stain does not indicate serious

degradation of the zinc coating, nor does it necessarily imply any likely

reduction in the expected life of the product. >owever, heavy wet storage

stain should be removed mechanically or with appropriate chemical

treatments before the galvanized part is put into service. >eavy storage

stain must be removed or the part must be reected and regalvanized.


24/45

?inc

Skimmings

Figure *0: in" Ski&&ing !n"lusions

Skimming deposits are usually caused when there is no access to remove

the skimmings during the withdrawal of the steel from the galvanizing

kettle. %he skimmings on the liquid zinc surface are trapped on the zinc

coating. +n order to remove zinc skimmings without harming the soft zinc

coating underneath, lightly brush them off the surface of the galvanized

steel during the in*house inspection stage with a nylon*bristle brush. ?inc

skimmings, as seen in Figure 50 , are not grounds for reection. %he zinc

coating underneath is not harmed during their removal and it meets the

necessary specifications.


25/45

?inc Splatter

Figure *: in" Splatter

?inc splatter is defined as splashes and flakes of zinc that loosely adhere to

the galvanized coating surface. ?inc splatter is created when moisture on

the surface of the galvanizing kettle causes liquid zinc to @pop< and splash

droplets onto the product. %hese splashes create flakes of zinc loosely

adherent to the galvanized surface. ?inc splatter, as seen in Figure 51, will

not affect the corrosion performance of the zinc coating and is not cause for

reection. %he splatter does not need to be cleaned off the zinc coating

surface, but can be if a consistent, smooth coating is required.


26/45

$dherence

%est

Figure *2: Stout ni+e Test

%esting of the zinc coating adherence to the steel is achieved using a stout

knife. %he steps used in this test are listed below and a photo of the test

being performed can be seen in Figure 52 . %he coating shall be deemed

@not adherent< if it flakes off and exposes the base metal in advance of the

knifepoint. %he test is not an attempt to pare or whittle the zinc coating. +f

the coating is adherent the knife should put a slight mark in the zinc metal

surface, but should not cause any delamination of the coating layers.

Adhesion Test with a Stout Knife

• 8ush down point of stout knife

• -oating must not flake off exposing the base metal

• 4o not perform at edges or corners of the product

• Ao paring or whittling with knife is acceptable


27/45

Bending %est

%he hot*dip galvanized coating on a steel bar must withstand bending

without flaking or peeling when the bending test is preformed in accordance

with the specifications in $S%& $ =:. %here are various tests used to

assess the ductility of steel when subected to bending. One test may

include the determination of the minimum radius or diameter required to

make a satisfactory bend. $nother test may include the number of repeated

bends that the material can withstand without failure when it is bent through

a given angle and over a definite radius.

9ebar is commonly bent prior to the hot*dip galvanizing process. Steel

reinforcing bars bent cold prior to hot*dip galvanizing should be fabricated

to a bend diameter equal to or greater than the specified value in $S%& $

'2';$ '2'&. >owever, steel reinforcing bars can be bent to diameters

tighter than the specified values if they are stress relieved at a temperature

of !! to !"! / 0=(! to "2! -3 for one hour per inch 01"mm3 of diameter.

-hromating %est

%he specification to determine the presence of chromate on zinc surfaces

is $S%& B 1!. %his test involves placing drops of a lead acetate solution

on the surface of the product, waiting " seconds, and then blotting it gently.

+f this solution creates a dark deposit or black stain, then there is

unpassivated zinc present. $ clear result indicates the presence of a

chromate passivation coating.

5mbrittlement %est


28/45

hen there is suspicion of potential embrittlement of a product, it may be

necessary to test a small group of the products to measure the ductility.

%hese tests are usually destructive to the zinc coating and possibly to the

product as well. 8roducts suspected of embrittlement shall be tested

according to the specification $S%& $ =:. 4epending on the service

conditions the product will be exposed to, one of three embrittlement tests

may need to be performed. %hese embrittlement tests include the similar

bend radius test, sharp blow test, and steel angle test. %he embrittlement

test uses a known force to provide a stress that should be lower than theyield stress of the part. +f there is a fracture or permanent damage created

during the testing process, the parts must be reected.

Sampling

$ sampling protocol has been developed by $S%& to ensure high quality

products because the inspection of the coating thickness for every piece of

material galvanized in a proect would not be practical. $S%& $1:;$1:&

states for a unit of products whose surface area is equal to or less than 2!

inC 0!:1 cmC3, the entire surface of each test product constitutes a

specimen. +n the case of a product containing more than one material

category or steel thickness range, that product will contain more than one

specimen. +n addition, products with surface areas greater than 2! inC

0!:1 cmC3 are multi*specimen products. %here are four important terms

used in the $S%& specifications and each is defined below.

Sampling %erms


29/45

• Lot D unit of production or shipment from which a sample is taken for

testing

• Sample D a collection of individual units of product from a single lot

• Specimen D the surface of an individual test product or a portion of a

test product which is a member of a lot or a member of a sample

representing that lot

• Test Product D an individual unit of product that is a member of the

sample

/or single specimen products, each randomly selected product is a

specimen. +n thickness measurement tests, five measurements are taken

widely dispersed over the surface area of the specimen in order to

represent the total coating thickness. %he mean value of the five coating

thicknesses for one specimen must have a minimum average coating

thickness grade of not less than one grade below the minimum average

coating thickness for the material category. +n Figure 53, the separation of a

lot into a sample and individual specimen is shown.

$ multi*specimen product is defined as having a surface area that may be

larger than 2! inC 0!:1 cmC3, have multiple steel thicknesses, or containmore than one coating category. +n order to test coating thickness of


30/45

products whose surface area is greater than 2! inC 0!:1 cmC3, they are

subdivided into three continuous local sections with equivalent surface

areas, each of which constitutes a unique specimen. +n the case of any

such local section containing more than one material category or steel

thickness range, that section will contain more than one specimen.+n Figure 54, the separation of a lot into a sample and individual specimen

is shown.

/or products hot*dip galvanized to either $S%& $1:;$1:& or

$":;$":&, Table 6 is used to determine the minimum number of

specimens for sampling from a given lot size.

No. of Pieces in Lot No. of Specimens

: or less $ll

= to "!! :

"! to 1!! "

1! to :1!! (


31/45

:1! to !,!!! :

!,!!E 1!

Table 6: Minimum Number of Specimens for ASTM A1! and A1"!

/or rebar hot*dip galvanized according to $S%& $'2', the information

below is used to determine the minimum number of samples per lot,

measurements per sample, and the total number of measurements

required for each of the different coating thickness

measurement techniques.

• Ma#netic Thic$ness:

o : samples per lot

o " or more measurements per sample

o " measurements, at the minimum, comprise the average

• Microscop% Method:

o " samples per lot

o = measurements per sample

o 1! measurements, at minimum, comprise the average

• Strippin# and &ei#hin#:

o : samples per lot

%he minimum average coating thickness for a lot is the average of the

specimen values and must meet the minimum for the material category.

%he minimum for an individual specimen is one grade below the minimum

for the material category. $n individual measurement has no minimum, but

bare areas are not allowed on the part. %he final inspection of a part shall

include thickness measurements and visual inspection. $ll parts that do not


32/45

meet the requirement must be resorted and reinspected or reected and

then regalvanized.

9epair

+f the galvanized product does not meet all of the requirements of the

specification, it must be repaired or reected along with the lot it represents.

hen repair of the product is allowed by the specification or bare spots are

present, the galvanizer is responsible for the repair unless directed

otherwise by the purchaser. %he specifications allow for some retesting of

products that represent lots or retesting after the lot has been sorted for

non*conformance. %he coating thickness of the repaired area must match

the coating thickness of the surrounding area. >owever, if zinc*rich paint is

used for repair, the coating thickness must be "!# higher than the

surrounding area, but not greater than =.! mils because mud cracking

tends to result when the paint coating is too thick. %he maximum sizes for

allowable areas that can be repaired during in*plant production are defined

in the specifications as summarized below.

&aximum Size of 9epairable $rea

• ASTM A 1!'A 1!M:

o One inch or less in narrowest dimension

o %otal area can be no more than !."# of the accessible surface

area to be coated or :2 square inches per piece, whichever is less

• ASTM A 1"!'A 1"!M:


33/45

o %he bare spots shall have an area totaling no more than # of

the total surface area to be coated, excluding threaded areas of the piece

•

ASTM A (6('A (6(M:o Ao area given

o +f the coating fails to meet the requirement for finish and

adherence, the bar may be stripped, regalvanized, and resubmitted

o 4amage done to the coating due to fabrication or handling shall

be repaired with a zinc*rich formulation

o Sheared ends shall be coated with a zinc*rich formulation

9epair &ethods

$ny repairs made to galvanized products must follow the requirements of

$S%& $ '(!, which defines the acceptable materials and the required

procedures. 9epairs are normally completed by the galvanizer before theproducts are delivered, but under certain circumstances, the purchaser

may perform the repairs on their own. %he touch*up and repair materials

are formulated to deliver an excellent color that matches either brightly

coated, newly galvanized products or matte gray, aged galvanized

products. &aterials used to repair hot*dip galvanized products include zinc*

based solder, zinc*rich paint, and zinc spray metallizing, and are explainedin the following sections.


34/45

?inc*Based Solder

/igure ""F ?inc*Based Solder

Soldering with zinc*based alloys is achieved by applying zinc alloy in either

a stick or powder form. %he area being repaired needs to be preheated to

approximately 2!! / 0:" -3. %he most commonly used solders for repair,

as seen in Figure 55 , include zinc*tin*lead, zinc*cadmium, and zinc*tin*

copper alloys.

Surface 8reparation

$ccording to $S%& $ '(!, the surface to be reconditioned shall be wire

brushed, lightly ground, or mildly blast cleaned. +n addition, if wire brushing

or light blasting is inadequate, all weld flux and spatter must be removed by

mechanical methods. %he cleaned area also needs be preheated to 2!! /

0:" -3 and wire brushed while heated. 8re*flux may also be necessary to

provide chemical cleaning of the bare spot. /inally, special care should be

given to insure that the surrounding galvanized coating is not overheated

and burned by the preheating.

$pplication


35/45

%he soldering method is the most difficult of the three repair methods to

complete. $ high level of caution must be taken while heating the bare spot

to prevent oxidizing the exposed steel or damaging the surrounding

galvanized coating. Solders are typically not economically suited for touch*

up of large areas because of the time involved in the process and because

heating of a large surface area to the same temperature is very difficult.

hen the repair has been completed, the flux residue needs to be removed

by rinsing the surface with water or wiping with a damp cloth.

/inal 9epaired 8roduct

%he final coating thickness for this repair shall be agreed upon between the

galvanizer and the purchaser, and is generally in the to 1 mil range. %he

thickness shall be measured by any of the methods in $S%& $ 1:;$ 1:&

that are non*destructive. ?inc*based solder products closely match the

surrounding zinc and blend in well with the existing coating appearance.

?inc*9ich 8aint

/igure "2F ?inc*9ich 8aint


36/45

?inc*rich paint is applied to a clean, dry steel surface by either a brush or

spray as seen in Figure 56 , and usually contains an organic binder pre*mix.

?inc*rich paints must contain either between 2"# to 2# metallic zinc by

weight or greater than 1# metallic zinc by weight in dry film. 8aints

containing zinc dust are classified as organic or inorganic, depending on

the binder they contain. +norganic binders are particularly suitable for paints

applied in touch*up applications around and over undamaged hot*dip

galvanized areas.

Surface 8reparation

$ccording to $S%& $ '(!, the surface to be repaired shall be blast cleaned

to SS8-*S8!;A$-5 Ao.1 near white metal for immersion applications

and SS8-*S8 near bare metal for less aggressive field conditions.

hen blasting or power tool cleaning is not practical, hand tools may be

used to clean areas to be reconditioned. %he blast cleaning must extend

into the surrounding, undamaged, galvanized coating.

$pplication

%his method of repairing galvanized surfaces must take place as soon as

possible after preparation is completed and prior to the development of any

visible oxides. %he spraying or brushing should be in an application of

multiple passes and must follow the paint manufacturer Gs specific written

instructions. +n addition, proper curing of the repaired area must occur

before the product is put through the final inspection process. %his repair

can be done either in the galvanizing plant or on the ob site and is the

easiest repair method to apply because limited equipment is required. ?inc*


37/45

rich painting should be avoided if high humidity and;or low temperature

conditions exist because adhesion may be adversely affected.


%he coating thickness for the paint must be "!# higher than the

surrounding coating thickness, but not greater than =.! mils, and

measurements should be taken with either a magnetic, electromagnetic or

eddy current gauge. /inally, the surface of the painted coating on the

repaired area should be free of lumps, coarse areas, and loose particles.


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?inc Spray &etallizing

/igure "'F ?inc Spray

&etallizing

?inc spray, which is also referred to as metallizing, is done by melting zinc

powder or zinc wire in a flame or electric arc and proecting the liquid zinc

droplets by air or gas onto the surface to be coated, as seen in Figure 57 .

%he zinc used is nominally ."# pure or better and the corrosion

resistance of the wire or powder is approximately equal.

Surface 8reparation

$ccording to $S%& $ '(!, the surface to be reconditioned shall be blast

cleaned to SS8-*S8";A$-5 Ao. near white metal and must be free of oil,


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grease, weld flux residue, weld spatter and corrosion products. %he blast

cleaning must extend into the surrounding, undamaged, galvanized

coating.

$pplication

?inc spraying of the clean, dry surface must be completed by skilled

workers and should take place within four hours after preparation or prior to

development of visible oxides. Spraying should also be done in horizontal

overlapping lines, which yield a uniform thickness more consistent than the

crosshatch technique. %he zinc coating can be sealed with a thin coating of

low viscosity polyurethane, epoxy*phenolic, epoxy, or vinyl resin. %he

details of the application sequence and procedures can be found in

$AS+;$S -1.(*:. %he application of zinc spray can be done either in

the galvanizerGs plant or at the ob site. +n addition, if high humidity

conditions exist during spraying, adhesion may be degraded.


%he renovated area shall have a zinc coating thickness at least as thick as

that specified in $S%& $ 1:;$ 1:& for the thickness grade required for

the appropriate material category. %hese thickness measurements should

be taken with either a magnetic or an electromagnetic gauge for best

results. %he plain zinc sprays or the sprays with aluminum additives both

provide a good match for newly galvanized, bright surfaces. /inally, the

surface of the sprayed zinc coating should be free of any lumps, coarse

areas, and loose particles.


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6alvanizing Standards

%here are certain specifications that have been developed for hot*dip

galvanizing in order to produce a high*quality coating. %he most commonly

used specifications design engineers and fabricators should become

familiar with in order to promote a high*quality coating and ensure their

steel design is suitable for hot*dip galvanizing areF

• ASTM A 1!'A 1!M: Standard Specification for Zinc (ot!"ip

#al$ani%ed& 'oating on )ron and Steel *roduct

Single pieces of steel or fabrications with different types of steel products

• ASTM A 1"!'A 1"!M: Standard Specification for Zinc 'oating (ot!

"ip& on )ron and ard+are

/asteners and small products that are centrifuged after galvanizing to

remove excess zinc

• ASTM A (6('A (6(M: Standard Specification for Zinc!'oated

(#al$ani%ed& Steel ,ar for 'oncrete -einforce.ent

9einforcing steel or rebar

• ASTM A ()*: Standard *ractice for -epair of "a.aged and

/ncoated rea of ot!"ip #al$ani%ed 'oating

%ouch*up procedures for coating bare spots on an existing hot*dip

galvanized product

Other commonly used specifications in the hot*dip galvanizing industry

includeF


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• ASTM A 1+!'A 1+!M: Standard *ractice for Safeguarding gaint

.brittle.ent of ot!"ip #al$ani%ed Structural Steel *roduct and

*rocedure for "etecting .brittle.ent

• ASTM A !)+'A !)+M: Standard *ractice for Safeguarding gaint

arpage and "itortion "uring ot!"ip #al$ani%ing of Steel e.blie

• ASTM A !)"'A !)"M: Standard *ractice for *ro$iding ig!ualit

Zinc 'oating (ot!"ip&

• ASTM , 6: Standard Specification for Zinc

• ASTM - 6!)6: Standard *ractice for *reparation of Zinc (ot!"ip

#al$ani%ed& 'oated )ron and Steel *roduct and ard+are Surface for

*aint

• ASTM !(6: Standard *ractice for eauring 'oating Ticne b

agnetic!Field or dd!'urrent (lectro.agnetic& a.ination etod

• /AN'/SA 0 16+: ot!"ip #al$ani%ing of )rregularl Saped rticle

•

S2 1+61 ot!"ip #al$ani%ed 'oating on Fabricated )ron and Steel e.blie

Specification and Tet etod


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$S%& $ 1: for

Structural Steel8roducts

/igure F Single /abrication

with &ultiple &aterial -ategories

%he $S%& $ 1:;$ 1:& specification covers individual steel pieces as

well as assemblies of various classes of material. %he four material

categories covered in $S%& $ 1:;$ 1:& include structural steel andplates, strips and bars, pipes and tubing, and wires. $ fabrication can have

more than one material category such as a frame assembly. $ny

combination of these products can be assembled into a single fabrication

and then can be hot*dip galvanized, as seen in Figure 11.

+t is the responsibility of the designer and fabricator to ensure the product

has been properly designed and built before the hot*dip galvanizing


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process. %he galvanizer should be made aware of any necessary special

instructions or requests in advance of shipping the materials to the

galvanizing plant. %hese requests should be stated on the purchase

order for the hot*dip galvanizing.

+t is the responsibility of the galvanizer to ensure compliance with the

specifications as long as the product has been designed and fabricated in

accordance with the referenced specifications. >owever, if the galvanizer

has to perform additional work in order to prepare the product for hot*dip

galvanizing, such as drilling holes to facilitate drainage or venting, it must

be approved by the customer. Once the material has been hot*dip

galvanized, it can be fully inspected at the galvanizing plant prior to

shipment.

$ny materials reected by the inspectors for reasons other than

embrittlement may be stripped, regalvanized, and resubmitted for

inspection. %he $S%& specifications $ =:;$ =:&, $S%& $ :(=;$ :(=&,

and $S%& $ :(" provide guidelines for preparing products for hot*dip

galvanizing. %he requirements listed in $S%& $ 1:;$ 1:& includecoating

thickness, finish, appearance, and adherence. %hese are each defined

below and discussed in more detail later in this course.

$S%& $ 1:;$ 1:& 9equirements

• /oatin# Thic$ness ' &ei#ht D dependent upon material category

and steel thickness

• 3inish D continuous, smooth, uniform


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• Appearance D free from uncoated areas, blisters, flux deposits and

gross dross inclusions as well as having no heavy zinc deposits that

interfere with intended use

• Adherence D the entire coating should have a strong adherence

throughout the service life of galvanized steel

%he hot*dip galvanized coating is intended for products fabricated into their

final shape that will be exposed to corrosive environmental conditions.

Once a product has been hot*dip galvanized, any further fabrication, which

very rarely occurs, may have negative effects on the corrosion protection of

the coating. %he coating grade is defined as the required thickness of the

coating and is given in microns. $ll coating thickness requirements in

specification $S%& $ 1:;$ 1:&, as seen in Table 1 2 , are minimums)

there are no maximum coating thickness requirements in either

specification.

%able F &inimum $verage -oating %hickness 6rade by &aterial -ategory 0/rom $S%&

$1:3 %able 1F -oating %hickness 6rade 0/rom $S%& $ 1:3

%he time to first maintenance of hot*dip galvanized steel is directly

proportional to the thickness of the hot*dip galvanized coating. ith all

other variables held constant, the thicker the zinc coating, the longer the life

of the steel. %he aim of the finish and appearance requirements is toensure no coatings have problem areas that are deficient of zinc or have

surface defects that would interfere with the intended use of the product. +n

addition, the coating should have a strong adherence throughout the

service of the hot*dip galvanized steel.


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%ypes of +nspection

+n this section, the type of inspections performed on hot*dip galvanized

steel will be discussed. %he various inspections are used to verify the

necessary specifications for the galvanized product are met. %hese

techniques for each test method are specified in $S%& $ 1:;$ 1:&, $

":;$ ":&, or $ '2';$ '2'&, depending upon the type of product being

inspected. %he most common inspections, listed below, range from a

simple visual inspection to more sophisticated tests to determine

embrittlement or adhesion.

• -oating %hickness D magnetic gauges, optical microscopy

• /oatin# &ei#ht D weigh*galvanize*weigh, and weigh*strip*weigh

• 3inish and Appearance D visual inspection

• Additional Tests

o Adherence D stout knife

o mbrittlement D similar bend radius, sharp blow, and steel

angle

o /hromatin# D spot test

o ,endin# D minimum finished bend diameter table

• Samplin#

Documents

HDG Defect