Glossary of terms used in galvanizing of steel


Glossary of terms used in galvanizing of steel

Galvanizing is carried out to protect steel against corrosion. The process is carried out in several steps as shown in Fig 1.

Steps in galvaniing

Fig 1 Steps in the process of galvanizing

 The common terms used in galvanizing of steel are given below.

Abrasion resistance – It is the ability of the galvanized coating to resist damage caused by contact with hard, rough, or coarse media or objects.

Abrasive blasting – It is the process of using a forceful stream of particles, available in varying hardness, to remove residue and contaminants from steel surfaces to prepare for galvanizing.

Adherence – It is the act, action, or quality of zinc bonding to steel, measured in grams/Sq mm.

Aggressive environment – It is an environment that is particularly corrosive.

Alloy layers – It is the interior layers of the galvanized coating which comprised of iron/zinc intermetallics formed when molten zinc reacts with iron in the steel.

Aluminum – It is the element found in the galvanizing bath (added to molten zinc through a product commonly called “brightener bar”) that gives the hot-dip galvanized coating a shiny appearance.

Amphoteric – It is having the characteristics of an acid and a base and capable of reacting chemically either as an acid or a base.

Anion – It is a negatively charged ion, especially the ion that migrates to an anode in electrolysis.

Anode – It is the electrode of an electrolytic cell at which corrosion (oxidation) occurs, positive current flows from the anode through the electrolyte to the cathode. With respect to hot dip galvanizing, anode refers to zinc, which corrodes sacrificially to protect steel.

Anodic – exhibiting of the properties of an anode. Zinc is anodic to steel.

Application – It is the act of putting to use; specifically, the use to which galvanized steel will be put.

Aqueous – It is relating to, similar to, containing, or dissolved in water; watery.

Ash – It is the solid byproduct formed in the galvanizing process, consisting primarily of zinc oxides, that remains on the surface of the kettle; commonly referred to as “skimmings”.

Ash inclusions – It is the ash or skimmings carried out of the pot on parts; ash inclusions remain solidified in the coating.

Assemblies – It is the fitting together of manufactured parts into a complete structure, machine, or unit of a machine; assemblies sometimes require specific design features in order to be optimally galvanized.

Atmosphere – It is a surrounding influence or environment that affects the rate of corrosion; frequency and amount of moisture, humidity, chlorides, sulfides, and wind are some of the atmospheric components affecting corrosion rates

Barrier protection – It is the protection provided by inhibiting oxidation (rust) by an insoluble top coating such as zinc, which isolates steel from any electrolytes that would assist the corrosion process.

Bond strength – It is the strength with which two or more items are joined; the resistances that must be overcome in order to separate the joined materials, e.g. steel and zinc-iron alloy layers of the galvanized coating, or galvanized reinforcing steel and concrete.

Brown staining – It is the reactions between exposed inter metallic layers (specifically the iron portion of the layers) and oxygen, resulting in surface color changes from gray to brown.

Bracing – It is metal that is attached to a fabrication prior to galvanizing in order to provide support so that the steel does not change shape during heating and cooling. It can be temporary or permanent.
Cathode – It is the electrode of an electrolytic cell at which reduction occurs. Positive current flows from the anode (zinc) through the electrolyte to the cathode (steel).

Cathodic – It is exhibiting properties of a cathode. Steel is cathodic in relation to zinc.

Cathodic protection – It is the reduction or prevention of corrosion of a metal surface by making it a cathode in an electrolytic cell, using either a galvanic or impressed current. Zinc cathodically protects steel i.e. sacrificially giving up electrons to protect the steel from corrosive attack.

Caustic cleaning – It is the cleaning of steel in a solution with high alkalinity. In the hot dip galvanizing process, organic residues are removed by immersing steel in a tank of caustic solution.

Centrifuging – It is the process of removing excess zinc from small hot dip galvanized parts by placing them in a perforated, rapidly spinning cylindrical container.

Chemical cleaning – It is the process of immersing steel in chemical solvents to remove (dissolve) residues that would otherwise prevent the galvanized coating from forming.

Chromate quenching – It is treating metal in a tank of containing a solution of chromium compounds to produce a conversion coating consisting of trivalent and hexavalent chromium compounds. Chromate passivation sometimes is used on galvanized reinforcing bar to control reactions between zinc and concrete while the concrete cures, particularly the hydrogen evolution that adversely affects bonding. Chromate quenching other galvanized articles prevents the formation of wet storage stain.

Chromating – It is the chromate quenching of a galvanized article.

Cleaning – It is the process of chemically or mechanically removing unwanted residue or contaminants (mill scale, rust, dirt and oil) from the surface of a steel article prior to galvanizing.

Cleaning solutions – These are liquids used to remove unwanted residue or contaminants (mill scale, rust, dirt, and oil) from the surface of steel prior to galvanizing. Cleaning solution can be typically an alkali, caustic solution, hydrochloric or sulfuric acid, and zinc ammonium chloride flux solution.

Coating thickness – It is the thickness of the zinc coating, measured in mils (0.001 inches) or micrometers.

Cold galvanizing – It is the process used to touch up and/or repair hot dipped galvanized surfaces and providing barrier protection and some cathodic protection.

Cold working –It is bending or forming of steel at ambient temperature. This action induces stresses that may be released during the galvanizing process.

Containment – It is the act, process, or means to keep within prescribed limits.

Contraction – It is the shrinkage of steel due to cooling after removal from the galvanizing kettle.

Corrosion – It the chemical or electrochemical reaction between a material and its environment that produces a deterioration of the steel and its properties. Zinc chemically reacts with elements in the atmosphere, thereby sacrificially corroding to prevent corrosion of the underlying steel.
Delta layer – It is the second layer of zinc iron alloy growth from the base steel formed during the galvanizing process. The Delta layer’s chemical composition is approximately 90% zinc and 10% iron. The Delta layer is 60% harder than the base steel it protects from abrasion and corrosion.

Design – It is to create, fashion, execute, or construct steel according to plan so that it will yield a quality hot dip galvanized coating.

Diamond Pyramid Number – It is system of assigning values to metals quantifying their hardness.

Dissimilar metals – These are two or more different metals in contact. Due to varying surface conductivity, one or more metals may experience accelerated corrosion. Since zinc is high in the galvanic series, it preferentially corrodes to protect most dissimilar metals.

Dissolution – It is the act of dissolving, sundering, or separating into component parts.

Distortion – It is the deviation from the original size, shape or contour that occurs when the application of heat during the galvanizing process releases stress from the steel induced in the fabrication process or during the steel making process. Distortion is of concern when galvanizing asymmetric structural shapes and/or fabrications

Double dipping – It is the act of dipping steel, too large in one dimension to completely fit into the galvanizing pot, more than once in cleaning solutions and molten zinc metal in order to produce a coating that covers the entire surface of the steel.

Drainage – It is the act, process, or mode of becoming emptied or freed of cleaning solutions and/or zinc.

Dross – It is the byproduct of the galvanizing process that forms by reactions between zinc and loose particles of iron. Dross may exist at all depths of the pot, but usually sinks to the bottom.

Dross inclusions – dross that is carried out on to the work piece upon removal from the galvanizing pot.

Drossing – It is the process of removing dross buildup from the bottom of the pot.

Dry galvanizing – It is the dipping of steel in an aqueous zinc ammonium chloride solution and then thoroughly drying before immersing in the molten zinc bath.

Ductile iron – It is the molten iron treated with an element such as magnesium or cerium to induce a measurable degree of ductility to the iron. These additives do not affect galvanizing ability of iron.

Ductility – It is the ability of a material to be formed without fracturing. Galvanized steel is ductile within certain recommended bending radii.

Duplex system – It is the galvanized steel that has been coated with an additional corrosion inhibiting product, typically liquid or powder paint. The two separate coating systems work synergistically to provide enhanced corrosion protection.
Electrical isolation – It is the separation of two conductive materials from electrical contact. Galvanized steel is sometimes electrically isolated in order to prevent rapid consumption of the zinc coating.

Electrode – Anode or cathode are type of electrode.

Electrolyte – It is an ionized chemical substance or mixture, usually liquid that will conduct electric currents.

Embrittlement – It is the reduction in the normal ductility of steel due to a physical or chemical change that may occur when cold worked steel is immersed in molten zinc in the galvanizing pot.

Environment – It is the complex of physical, chemical, and biotic factors (climate, soil, and living things) that act upon metal and ultimately affect the corrosion rate.

Eta layer – It is the fourth outer layer of the galvanized coating solely comprised of zinc.

Excess zinc – It is the extra amounts of zinc that may accumulate on the steel because of chemical composition of the steel or the profile of the steel.

External venting – These are the holes that prevent high-pressure gas buildup in enclosed fabrications dipped in the molten zinc of the galvanizing bath.

Finishing – It is the final stages of inspection and preparing galvanized steel so that it complies with specification.

Flux – These are the chemicals used to protect steel from oxidation prior to entering the molten zinc containing pot.

Flux inclusions – It is the flux carried out onto the steel from the top flux blanket incorporated in the wet process. It occurs only in the wet galvanizing process.

Fluxing – It is the process by which steel is dipped in aqueous zinc ammonium chloride to remove undesirable substances and to protect it from further oxide formation prior to entering the galvanizing bath

Galling – It is a condition whereby excessive friction between high spots on two different steel parts results in localized welding.

Galvanizing – It is the act of coating steel with zinc in order to provide barrier and cathodic protection from corrosion.

Galvanizing temperature – It is the temperature at which the molten zinc bath is kept in order to react with the steel. Typically this temperature is between 443 deg C) and 454 deg C.

Gamma layer – It is the first layer of zinc iron alloy growth from the base steel formed during the galvanizing process. The chemical composition of this layer is approximately 75 % zinc and 25 % iron. Gamma layer has a diamond pyramid number (DPN) of 250 compared to the base steel’s DPN of 159.

Grinding – It is mechanically removing material from a work piece with a grinding wheel or abrasive belt.

Grit blasting – It is abrasive blasting with small irregular pieces of steel, malleable cast iron or hard nonmetallic. materials.
Handling – It is the process by which steel articles are carried throughout the galvanizing facility, by chain, wire, hook, or racked in a fixture.

Hardness – It is the resistance of metal to plastic deformation, usually by indentation. The term may also refer to stiffness or temper or to resistance to scratching, abrasion or cutting.

Holding devices – These are the fixtures used to connect fabrications/parts to be galvanized to handling equipment in the galvanizing facility.

Hot rolled steel – It is the steel deformed plastically at such a temperature and strain rate that re- crystallization takes place simultaneously with the deformation thus avoiding strain hardening. This is the most common type of steel galvanized.

Hydrochloric acid – It is the solution used in the cleaning stages of the galvanizing process and consisting of one hydrogen ion and one chloride ion (chemical formula: HCl) in mixture with water.

Hydrogen embrittlement – It is a condition of low ductility in metals resulting from the absorption of hydrogen.

Identification – It is the marking/labeling steel so that different customer products can be distinguished from one another after galvanizing.

Impact resistance – It is the ability to avoid damage due to contact with a forceful motion or object. Galvanized coating’s uppermost, pure zinc Eta layer is relatively soft and absorbs impact shock, protecting the underlying alloy layers.

Inspection – It is coating thickness and surface condition verifications.

Intermetallics – These are interior layers of the galvanized coating that have distinct proportions of the alloying metals iron and zinc; e.g. Delta, Gamma & Zeta layers.

Internal stress – it is also known as residual stress, stress present in a steel member or fabrication that is free of external forces or thermal gradients.

Internal venting – These are holes on the inside of enclosed fabrications that allow cleaning solutions, zinc, and any gases to freely flow throughout the structure.
Kettle – It is molten zinc filled tank or pot where the metallurgical bonding of zinc and steel takes place. Lifting points – These are connectors (sometimes temporary) directly on the steel work pieces article that help the galvanizer in handling the work piece throughout the galvanizing process.

Masking –This is the process of using a material to produce intentionally ungalvanized areas, typically used in areas that are to be welded, on faying surfaces, or areas where the galvanized coating is not necessary for uniform corrosion protection.

Matte – It is dull, lacking or deprived of shine. Matte gray galvanized appearance may result from steel chemistry or may be intentionally induced when the galvanized steel’s use defines reflectivity limits.

Mechanical cleaning – It is the removing of residues or impurities from steel using mechanical force such as grinding or sand blasting.

Metalizing – It is forming a metallic coating by atomized spraying with molten zinc or by vacuum deposition. It is also called spray metalizing. It is applying an electrically conductive metallic layer to the surface of another material.

Metallurgical bond – It is the bonding of iron/zinc inter-metallic layers to the base steel.

Mill lacquer – It is the organic protective coating applied to steel parts, usually pipes or tubes, to protect the parts during shipping; this material cannot be removed by the usual galvanized cleaning methods.

Mill scale – It is a heavy, imbedded iron oxide layer formed during hot fabrication or heat-treatment of steels.

Nickel – It is the common element found in the galvanizing pot to suppress the reactivity of silicon and phosphorus in the steel.
Organic contaminants – Theses are surface impurities (dirt, grease, oil and paint markings) that will hinder the formation of the galvanized coating, usually removed in the caustic cleaning stages of the galvanizing process.

Overtapping – It is cutting female fastener threads of nuts or threaded holes larger than standard to account for the increased diameter of the galvanized (male) mating part.

Passivation –It is changing of a chemically active metal surface to a much less reactive state.

Patina – It is the relatively insoluble zinc carbonate layer that forms as the galvanized coating weathers, providing added corrosion protection and abrasion resistance.

Phosphating – It is forming of an adherent phosphate coating on steel by immersion in a suitable aqueous phosphate solution, commonly used to promote better adhesion of paint to galvanized steel.

Phosphorus – It is naturally occurring element commonly found in steel, particularly reactive in molten zinc metal.

Pickling – It is removing surface oxides from steels by immersion in ambient temperature, dilute hydrochloric acid or hot (82 deg C) sulfuric acid.

Pinhole – It is small hole left in a weld area that allows low viscosity liquids to enter and become pressurized under the high temperature conditions of the molten zinc bath.

Pitted surfaces – These are the areas of steel where small, sharp cavities exist, usually formed by corrosion.

Polarization – It is the partial or complete polar separation of positive and negative electric charges in a nuclear, atomic, molecule or chemical system.

Post treatment – It is subjecting the steel to specific processes after it has been galvanized.

Pre flux – It is the process of fluxing steel before it enters the galvanizing pot as opposed to using a top flux layer, which would be located on top of the molten zinc in the pot.

Pre treatment – It is subjecting steel to specific processes before galvanizing.

Progressive dipping – It is the act of dipping steel more than once in cleaning solutions and molten zinc metal in order to produce a coating that covers the entire surface of the steel. It is commonly done when the steel article/fabrication is too large to fit entirely into the pot in one dip.

Quenching – It is rapid cooling by dipping galvanized steel in a tank filled with a liquid solution which is usually water or a dilute chromate or phosphate solution.

Racking – It is the process of arranging articles on a rack in order to transport them more efficiently through the galvanizing process.

Repair – It is performing finishing work piece after galvanizing in order to meet standards or specifications, or coating areas of steel that have been exposed due to post galvanizing fabrication, installation, or extremely rough handling.

Residue – These are contaminants (oil, grease, dirt, rust and mill scale) that unless removed, will prevent complete galvanizing of the steel surface.

Return current path – It is the path through which the current in an electric cell returns to the source.

Rinsing – It is removing of any active solution from the surface of steel by immersion in water rust, corrosion product consisting of hydrated iron oxides.

Rust – It is the corrosion product consisting of hydrated iron oxides.

Rust staining – It is the reaction between exposed inter-metallic layers (specifically the iron portion of the layers) with oxygen, that cause mild red or brown staining.

Salt water – It is the water with high concentrations of sodium chloride or other salts.

Scale – It is a thick layer of imbedded oxidation (rust) products on the steel.

Seal welding – It is a weld used primarily to obtain tightness and prevent the flow of cleaning solutions and zinc into otherwise enclosed areas, to prevent flash steaming that causes localized ungalvanized areas.

Service life – It is the anticipated length of time zinc will protect steel. The amount of time until enough of the galvanized coating is consumed and 5% of the substrate steel surface area shows signs of rust.

Shot-blasting – It is the abrasive blasting of steel with metal shot, usually to remove deposits or mill scale more rapidly or more effectively than can be done by sand-blasting or chemical cleaning.

Silicon – It is naturally occurring element commonly found in steel. Silicon is particularly reactive in molten zinc metal.

Skimmings – It is a galvanizing byproduct comprised mainly of zinc oxides. The skimmings are recyclable.

Skip welding – It is alternating the weld so that it is not continuous or complete.

Spangle – It is the characteristic crystalline form exhibited by the solidified, hot dipped zinc coating.

Stenciling – It is the process by which lettering or a design through which a substance (ink, paint, or metallic powder) is forced onto a surface to be printed. It is commonly used to mark steel fabrications but generally does not remain after the galvanizing process.

Storage – It is the area where galvanized articles are staged for pick-up or delivery.

Strain age embrittlement – It is the loss in ductility accompanied by an increase in hardness and strength that occurs when low carbon steel is aged following plastic deformation. The degree of embrittlement is a function of aging time and temperature, occurring in a matter of minutes at the galvanizing temperature but requiring a few hours to years at room temperature.

Stress relieving – It is heating to a suitable temperature, holding long enough to reduce residual stresses and then cooling slowly enough to minimize the development of new residual stresses.

Structural – steel member of specific cross-sectional dimensions used in fabrication and/or construction.

Sulfuric acid – It is a solution used in the cleaning stages of the galvanizing process that consists of two hydrogen ions and one sulfate ion (chemical formula: H2SO4) in a water mixture.

Surface preparation – It is stages of cleaning that prepare the steel for finishing (galvanizing)
Tank – It is a container for chemicals used in the galvanizing process. Steel is dipped sequentially in solution containing tanks.

Temporary bracing – It is the metal that is attached to a fabrication prior to galvanizing in order to provide added support so that the steel does not change shape during heating and cooling. Temporary bracing is removed after galvanizing.

Touch up – It is performing finishing work after galvanizing in order to meet standards or specifications, or coating areas of steel that have been exposed due to post galvanizing fabrication, installation, or extremely rough handling.

Venting – It is providing holes in fabrications to be galvanized to allow entrapped, heated liquids and gases to escape as pressure increases.

Vibrating – It is the process of removing excess zinc by rapidly shaking galvanized articles.

Weepage – It is the leaching out of trapped liquid solutions in galvanized structures, primarily through pinholes or gaps in welds that were not sealed over by zinc.

Weld residue – It is the impurities left from the welding process. Weld residue will inhibit localized formation of the galvanized coating.

Weld slag – It is the material resulting from the combination of weld material and weld flux. Weld slag will inhibit localized formation of the galvanized coating.

Wet galvanizing –It is using a liquid flux layer floated on top of the molten zinc. In the galvanizing process, final cleaning occurs as the material passes through the flux blanket before entering the molten zinc bath.

Wet storage stain – It is the white surface oxide and hydroxide that forms on newly galvanized steel when excessive moisture is present in poorly ventilated storage.

White rust – It is white, sticky substance comprised of basic zinc carbonate. It forms when galvanized surfaces are constantly covered by water or water containing sulfides or chlorides.

Zinc – It is the major element found in the galvanizing pot that provides both barrier and cathodic protection for steel.
Zinc ammonium chloride – It is the typical component of the flux solution used in the cleaning phase of the galvanizing process.

Zinc carbonate patina – It is relatively insoluble zinc carbonate layer that forms as the galvanized coating weathers, providing added corrosion protection and abrasion resistance.

Zinc hydroxide – It is corrosion product formed in response to the presence of moisture on galvanized articles.

Zinc oxide – It is basic corrosion product formed almost instantaneously on freshly galvanized articles after withdrawal from the molten zinc metal.

Zinc patina – It is relatively insoluble zinc carbonate layer that forms as the galvanized coating weathers, providing added corrosion protection and abrasion resistance.

Zinc solder – It is the material used to touch-up and/or repair hot dip galvanized surfaces.

Zinc iron alloy layers – These are inner layers of the galvanized coating formed from inter diffusion reactions between iron in the base steel and molten zinc metal, (e.g. Delta, Gamma, and Zeta)

Zinc rich paint – This is also called cold galvanizing. It is the material used to touch up and or repair hot dipped galvanized surfaces, providing barrier protection and some cathodic protection.