If you have a question, we are here to answer! If you do not see your question here
, please send us a message using the input form to the right.
Hot-dip galvanizing provides an impenetrable barrier between the steel and corrosive elements in the atmosphere. It does not allow moisture and corrosive elements to attack the steel. Furthermore, zinc is anodic to steel. meaning that it sacrifices itself before the steel will corrode, until the zinc is completely consumed. In addition, the applied zinc layer forms a zinc patina layer which is so stable that hardly any zinc corrosion occurs.
Hot-dip galvanized steel is extremely resistant to corrosion in numerous environments. It is not uncommon for galvanized steel to last more than 70 years under normal atmospheric conditions. See the Zinc Coating Life Predictor on our website to get a good idea of how long the zinc coating will provide maintenance-free protection for the steel in your project.
Constant exposure to temperatures below 200°C is a perfectly acceptable environment for hot-dip galvanized steel. Good performance can also be obtained when hot-dip galvanized steel is exposed to temperatures above 200°C on an intermittent basis.
Note; in those cases where there is also high humidity and high levels of air pollution, there may be severe corrosion deterioration.
The corrosion rate of zinc and how long it provides protection is a function of coating thickness and the amount of corrosive elements in the atmosphere. For example, in rural environments where there is less exhaust from cars/trucks and factory facilities, galvanized steel can easily provide 75 to well over 100 years of protection and do so without any maintenance. Industrial and/or marine locations contain significantly more aggressive corrosion elements such as chlorides, and galvanized steel can provide 25 to 50 years of protection in those cases. The relationship between coating thickness and atmospheric conditions is contained in a calculation tool found on our website: Zinc Coating Life Predictor.
International standards exist for metals and metal coatings that specify corrosion under certain atmospheric conditions. These are defined in ISO 14713-1, ISO 9223 and ISO 9224. ISO 9225 addresses air pollution. Using these standards and the measured zinc coating thickness, you are able to estimate the maintenance-free protection life of a zinc coating. Also, our tool on the website(Zinc Coating Life Predictor) allows you to calculate the duration of protection for a given location.
Swimming pools all over the world are made of galvanized steel. An additional coating is only required in cases where there is direct contact between the galvanized steel and the pool water. This does depend on the situation. In constantly humid environments with chlorides, an additional coating is also desirable. Examples are shower areas and sometimes poorly ventilated technical areas in a swimming pool building.
Galvanized steel can be used in almost all conditions up to C5. The classification from C1 to C5 and above it CX, comes from the ISO 14713-1 and ISO 12944-2 standards. It is an agreed classification of atmospheric conditions. A C5 category hardly ever occurs in the Benelux countries but represents increased humidity and chloride content. In such a situation, the maintenance-free protection life of the zinc coating is less than in a more moderate climate. There can be as much as a factor of 4 difference between a C3 and a C5 atmosphere in terms of zinc corrosion. Nevertheless, hot-dip galvanized steel is applicable in a C5 corrosion category. An additional coating in the form of a wet paint will provide additional protection to the galvanized steel. When doing so, opt for a Duplex system.
See Technical Info Sheet number 10
Refer to the Code of Practice “Powder and Wet Paint on Galvanized Surfaces.”
The use of a steel structure made of galvanized steel in such applications is usually quite feasible as long as there is adequate ventilation and the galvanized steel is not in direct contact with the chemicals or road salt.
Hot-dip galvanized steel is very widely used in situations where it is partly above and partly below ground. Think of traffic sign posts, lampposts, tension pylons, fence posts, pipes, etc. So there is virtually no obstacle to doing this in an outdoor atmosphere. Only in very few cases can there be degradation of the zinc layer due to the structure and composition of the soil as well as placement. If in doubt, consult with your galvanizing plant about the application or ask your question via the Helpdesk on this site.
Due to its corrosion resistance, galvanized steel is generally well suited for use in aqueous environments. In hot water, however, galvanized steel can show typical pitting caused by potential increase of the zinc layer.
The formation of a conductive layer of corrosion products on the zinc will increase the surface potential. In borderline cases, it even occurs that this potential of the
zinc becomes higher than the equilibrium potential of the ízer. The cathodic protection is then no longer present. Usually this occurs at temperatures above 50 degrees Celsius, but not necessarily. Dissolved substances in the water play a major role, especially the presence of bicarbonates and nitrates promote potential increase. At the location of defects in the zinc layer, the iron will then locally corrode very strongly. This is because the anode, in this case the iron, has a comparatively small surface area compared to the zinc that is cathode. The critical potential at which pitting can occur depends, as mentioned above, on the substances dissolved in the water. In particular, ions that form insoluble salts with Zn2+ clog the pores more quickly, and the critical potential at which pitting occurs is then higher. On the other hand, hypotheses have also been made assuming that the formation of ZnO under the influence of certain dissolved substances can take place at lower temperatures. In particular, Hoxeng and Prutton conducted research in this area and concluded that presence of calcium, magnesium, silicates, chlorides and sulfates inhibits potential rise of zinc.
In short; therefore, in addition to temperature, the composition of the liquid is also important. At a temperature of 75 degrees Celsius, the rate of deterioration is at almost maximum. This application of hot-dip galvanized steel is not recommended.
Despite the fact that galvanized steel has been used in agricultural applications for 150 years, a barn does have some rusting of the steel. Sometimes after only one year. The cause is mostly due to barn manure. Increasingly, stables are no longer mucked out daily and only the hard fraction of fecal matter is removed. This is called a potting shed. Aggressive acids produced by urine and feces can then remain present against the galvanized steel for a very long time. Unfortunately, the element zinc cannot withstand long-term moisture and chemicals where the pH drops below 5.5. Rapid corrosion of the zinc is then to be expected. One can prevent this by more frequent and better fattening or providing the underside of the barn walls with a resistant coating.
It is a fact that under the influence of UV light, bitumen can form organic acids. When these come into contact with zinc via water, this can lead to (local) corrosion of the zinc layer. However, the bitumen can be coated with an anti-UV ironing or spreading layer to prevent this phenomenon as much as possible. This is actually about the resistance of zinc to such an organic acid. Zinc does not have this property. Zinc dissolves at a pH lower than 5.5. It is better to choose another solution for this.
Disinfectants or disinfectants are used in all kinds of situations where food or plants etc. are grown or stored. In order to prevent mold and insect infestation, such disinfection will have to take place periodically. This in itself is not a problem, as long as it is realized that the zinc coating may react with the agent to be used. Therefore, the contact time with the agent will have to be as short as possible (see the agent’s instructions for use) and afterwards, rinse excessively with clean tap water. Make sure that no puddles of residual agent remain near the columns and thus can react with the zinc for a longer period of time.
The requirements for discontinuous hot-dip galvanizing are laid down in EN-ISO 1461. For galvanized steel pipes, standard EN 10240 applies if they are automatically galvanized. For duplex systems, EN-ISO 15773 and NEN 5254 apply as well as the code of practice “powder and wet coating on galvanized substrates“.
Layer thickness depends on the thickness, roughness, chemistry of the steel as well as the design of the object being galvanized. Any or all of these factors can produce zinc layers of non-uniform thickness.
Unlike a paint coating, for example, zinc coating thickness is the result of a chemical reaction between zinc and iron. Of importance are steel chemistry and surface conditions as determinants of zinc coating thickness. If the steel is left in the molten zinc for longer than optimum, this can have two effects: 1) it can increase the coating thickness, but only marginally; 2) it can significantly increase the coating thickness and cause a brittle, i.e., fragile, zinc coating.
For zinc to develop its protective patina of zinc carbonate that is highly stable and non-reactive, it requires a wetting and drying cycle similar to that present in the atmosphere. Salt spray tests keep the zinc wet and essentially wash off the zinc corrosion products as they develop, accelerating the corrosion rate of zinc. This laboratory test in no way reflects the performance of zinc coating in practice. Therefore, no conclusions can be drawn from it and certainly do not apply as a comparison to organic coatings.
The ASTM A123 mentioned is the American standard for hot-dip galvanizing. It was developed entirely separately from the international standard. However, there are many similarities. However, the galvanizers in the Benelux work according to the ISO 1461 and therefore cannot issue a statement that they comply with the American standard.
There are international standards for metals and metal coatings that specify corrosion under certain atmospheric conditions. These are defined in ISO 14713-1, ISO 9223 and ISO 9224. ISO 9225 addresses air pollution. Using these standards and the measured zinc coating thickness, you are able to estimate the maintenance-free protection life of a zinc coating. Also, our tool on the website (Zinc Coating Life Predictor) allows you to calculate the protection life for a given location.
All affiliated galvanizing plants work according to the provisions of EN-ISO 1461. However, you must indicate when ordering that you wish the galvanization work to be carried out according to this standard. If you have additional wishes or requirements, you must also make these known in advance. In the case of layer thickness measurements you must also mention this in advance, otherwise you run the risk that your material has not been measured. After all, a galvanizing plant carries out random measurements without paying specific attention to order numbers and batches.
Only in those cases where there is a Duplex system where the galvanized steel is subsequently provided with a paint system or powder coating, rounding off is stipulated in various standards and in the code of practice “powder and wet coating on galvanized substrates.” In the case of hot-dip galvanizing, there is no standard stating this. However, rounding off is preferable. Sharp corners are easily damaged when bumped during logistics or assembly. A rounded edge is much less vulnerable.
The material to be galvanized that is offered to the galvanizing plant is best to comply with EN-ISO 14713-2. This provides guidelines and recommendations on the proper way to manufacture the item before it is galvanized. One of those issues is the cutting edge of a thermal cut sheet. The heat introduced into the cutting edge changes the structure of the steel surface such that reduced zinc coating properties are created. Namely, a lesser zinc coating thickness and a lesser zinc coating cohesion that results in a lesser bond with the steel. The previously mentioned standard therefore states that this cutting edge should be treated afterwards by grinding away this zone. If this is not done or is insufficient, the zinc layer thickness at the location will be less. Is this a reject according to EN-ISO 1461? No: the standard clearly states that layer thickness measurements may not be carried out on cut edges and within 10 mm of the cut edges.
Galvanizers can double-dip galvanize the materials in such a case. They first dip one half into the molten zinc, remove it, turn it over and dip the other half into the zinc bath. It does require additional measures such as additional suspension holes and countersink holes. The result is usually less attractive than if the object can be dipped in 1 time.
In particular, care must be taken to ensure that pretreatment fluids and molten zinc can flow easily through the object and reach all nooks and crannies. This means that holes must be placed in the right places. This for inflowing and venting zinc from tubular configurations, welding slag must be removed, overlapping surfaces sealed or vented. Design and fabrication details are included in the Good and Safe Galvanizing checklist.
The hot-dip galvanizing process is suitable for different types and sizes. Virtually every galvanizing plant has a different zinc bath dimension. Hoisting weight can also sometimes play a role. On this site you will find a list of galvanizing plants with the corresponding dimensions. In critical cases; where the object is close to the bath dimensions, it is preferable to contact the relevant galvanizing plant.
Minimizing possible warping and deformation can easily be done in the design stages of the project by selecting steel of as much equal thickness as possible. Also, the object will preferably be designed symmetrically. Welding composition also plays an important role. Try to design complex objects so that they consist of several separate parts that can be linked by flange connections after galvanizing. Some assemblies may benefit from the use of temporary bracing to help maintain their shape and/or alignment.
When galvanized parts are used for friction-fast joints, they must be brushed, sanded blasted or painted with zinc silicate paint to increase surface roughness and thus slip factor. In many cases it is referred to as slip factor or coefficient of friction. There is no set number as a coefficient for a zinc coating. Many studies indicate that it varies quite a bit.
The hot-dip galvanizing process is suitable for different types and sizes. Virtually every galvanizer has a different zinc bath size. Lifting weight can also sometimes play a role. On this site you will find a list of galvanizing plants with the corresponding dimensions. Sometimes assemblies are larger than the bath dimensions but the galvanizing plant can still provide the object with a zinc coating. In that case, the (too large) object is galvanized in 2 stages. First the largest piece and in a second pass the remaining piece. This can be either a width dip in the case of a frame or a length dip in the case of a beam. Also called reversal dip in case of a frame. In cases where the dimensions of the object approach the specified bath dimensions, please contact your galvanizer.
The primary reason for these openings is to allow internally trapped air and flux residues to escape. During galvanizing itself, a closed zinc layer is thus applied over the entire (including internal) surface. It also ensures that excess zinc can flow away easily. It also prevents dangerous situations. In the case of trapped liquid, there may be an explosion when immersed. Consider the gas law and what happens when the temperature increases from ambient to 450°C. If there is any doubt about safety, the galvanizing plant will not proceed with galvanizing until adjustments have been made or it has been demonstrated that the proper adjustments have actually been made.
See also the publication: Checklist good and safe galvanizing
When chain welds are used, there is a possibility that a zinc layer will not be formed between the openings of the two joined parts, because the pretreatment fluids have not been able to do their job sufficiently. After all, no zinc layer is formed on a non-pure steel surface. By leaving at least a 2.5 mm gap between the contact surfaces, the pretreatment fluids are able to flow in and out, improving the conditions for zinc coating formation.
Yes, but because masking or anti-zinc materials may not be 100% effective for your application and purpose, please contact your galvanizer for suggestions.
Only in those cases where there is a Duplex system where the galvanized steel is subsequently provided with a paint system or powder coating, rounding off is stipulated in various standards and in the code of practice “powder and wet coating on galvanized substrates.” In the case of hot-dip galvanizing, there is no standard stating this. However, rounding off is preferable. Sharp corners are easily damaged when bumped during logistics or assembly. A rounded edge is much less vulnerable.
Excessive use of welding spray or the use of unsuitable welding spray, can lead to ungalvanized spots. This is because the material to be galvanized must be delivered free of surface contaminants. At a galvanizing plant, the steel is cleaned with the aim of getting a good zinc layer. The steel is first degreased and then pickled. Paint, oil, grease, welding sprays, welding slag, labels, line, etc.; are not removed in this pretreatment. As a result, the steel is insufficiently clean in the affected area, making zinc coating impossible.
Although in principle stainless steel cannot be galvanized, in practice it sometimes turns out to work. Lower grades of stainless steel in particular (known as SS 304) can often be galvanized. However, it is usually a matter of trial and error. Perhaps by sending a test piece to the galvanization plant to see if it will indeed work. After all, it is a waste of effort, money and the environment to use the entire object as a trial.
A clear overview of all recommendations and guidelines on modifications that make an object suitable for galvanizing is summarized in our publication which is based on ISO 14713-2. In particular, the table advising on the diameter of holes to be applied is a must.
In the pretreatment of a galvanization plant, acid is used to remove any fly rust or rust. However, substantially developed layers of rust, can lead to ungalvanized spots provided that the galvanizer leaves the parts dipped in the pickling liquid for a sufficient period of time. Heavily rusted parts will show a pockmarked surface after galvanizing. The galvanizing process will allow this uneven surface to lead to comments. Thus, it is not the case that pits and craters created by rust will be filled by zinc.
Unlike paint, for example, it will not necessarily be necessary to bevel or round off the edges. After all, paint involves a liquid and this tends to form a sphere because of surface tension (Vanderwaals forces). This means that paint pulls back from edges during the drying process. How different is it in hot-dip galvanizing. In that case, in fact, a chemical bond is formed between the zinc and the iron. So there is no (drying) liquid but a metallurgical bond. This bond is no different on a sharp edge than in other places. However, a sharp edge is more likely to be damaged than a rounded edge. Damage can occur by bumping and sliding during all kinds of logistic operations and during assembly work. Recommendation is to choose a rounded edge of at least 1 mm.
The three Zinc iron alloy layers that form during the galvanizing process are all harder than the steel it is designed to protect and therefore have excellent wear resistance. Only the pure zinc layer (solidification layer) is softer and will wear faster.
See Technical Data Sheet 12
Depending on product mix, square footage per ton and steel surface condition, the costs for hot-dip galvanizing and paint systems are roughly equivalent on an initial cost basis. However, as with any investment, lifetime costs must be considered when making a project decision on which corrosion prevention system to use. When choosing hot-dip galvanizing, life-cycle costs, that is, maintenance costs over the useful life, are almost always lower than for a paint system. Paint systems require maintenance, partial repainting and some complete repainting.
First of all, the variety of galvanized items is wide. Structural steel (angle lines, pipes, wide flange beams, I-beams, H-beams), grating material, stair treads, expanded metal, corrugated sheets, wire, cable trays, wall plate, castings, bolts and nuts. The industries that use hot-dip galvanized steel vary quite a bit. From bridge and highway (reinforcing steel for bridge decks, girders, columns, light poles, road signs, guardrail, fencing), water and wastewater treatment plants (walkway grid, expanded metal, railings), architectural (facades, visible structural steel) parking garages (rebar for concrete decks, visible structural steel columns and wheel washers and barriers), pulp and paper mills (structural steel, walkways, railing), OEMs (engine housings, foundation frames, heat exchangers), etc.
Examples of projects
Virtually all steel products can be galvanized. Especially in those cases that involve an outdoor application or an indoor application where the industrial appearance is considered important. Attention must be paid to the design and desired galvanizing holes and hanging options.
There are also products that are not suitable for galvanizing because of their composition, material thickness or size. Also steel types that have a special alloy to obtain certain properties sometimes cannot be galvanized. Examples include spring steel, wear-resistant steel, self-hardening steels, and the like.
On average, the weight of the article increases by about 5.5% as a result of zinc being incorporated during the electroplating process. However, that figure can vary greatly based on numerous factors. Material thickness, shape, size and steel chemistry all play an important role, and other factors such as black weight, the different types of steel being welded together and the chemical composition of the zinc bath can also have an effect.
See Technical Info Sheet number 13
There are no known studies that conclude that zinc corrosion products are harmful to the environment. Unfortunately, it is sometimes taken that way because zinc simply falls under the heading of “heavy metals.” This designation says nothing at all about dangerous or not dangerous. On the contrary, zinc is essential for good health. Zinc is a naturally occurring element on earth and necessary for all organisms to live. It is a recommended component of our diet (Daily Recommended Allowance is 15 mg for men and 11 mg for women) and necessary for reproduction. It is used in baby ointments, vitamin preparations, surgical instruments, sunscreen, shampoo and lozenges.
Primarily the difference is that in discontinuous hot-dip galvanizing the objects are first fabricated and then completely immersed in the liquid zinc. A completely sealing zinc layer of relatively large thickness is created. In continuous galvanizing, a steel strip on a coil is first galvanized and only then is an object fabricated from it. The zinc layer is considerably thinner and not at all present on the machined edges of the fabricated object. There is also no protective zinc layer in drill holes.
The process steps are somewhat similar, but the production equipment is quite different. Discontinuous hot-dip galvanizing is a more manual process in which structural steel (fabricated plate, profiles, angle lines, channels, pipe, tube, pipe, fasteners) is suspended by use of steel wire, chain or hook on crane elevators and immersed in the pretreatment fluids and then in the zinc bath. Continuous hot-dip galvanizing is fully automated and involves unwinding the coil, moving it through the cleaning steps and through the zinc bath, blowing off and coiling it back onto a coil.
Discontinuous galvanized steel will provide long-term protection against corrosion in most atmospheric conditions for 50 to 100 years because of an average zinc coating thickness of 80 microns. Galvanized sheet is suitable for interior applications because of its relatively thin coating (typically 20 microns), unless painted/coated after galvanizing.
See Technical Info Sheet number 15
Cold zinc does not exist. The term is often used in reference to painting with zinc-rich paint. By definition, hot-dip galvanizing means a metallurgical reaction between zinc and iron. There is no such reaction when zinc-rich paints are applied and the adhesion and abrasion resistance is much less. Can only be used as a repair or life extension.
See Technical Info Sheet number 2
There are four main process steps:
Discontinuous hot-dip galvanized fasteners generally have about 5 to 10 times more zinc on the surface and are suitable for use in all outdoor and indoor applications. Electrogalvanized fasteners will have disappointing performance when used outdoors, especially when used to join hot-dip galvanized steel structural members. They will then show rust marks fairly quickly because the zinc layer thickness is much lower.
See Technical Info Sheet number 17
See also the publication: Galvanizing – Different techniques for galvanizing
It is then almost certain that fasteners were used that were not hot-dip galvanized but were zinc coated in some other way. Most likely, these bolts and nuts were electrogalvanized.
Discontinuous hot-dip galvanized fasteners generally have about 5 to 10 times more zinc on the surface and are suitable for use in all outdoor and indoor applications. Electrogalvanized fasteners will have disappointing performance when used outdoors, especially when used to join hot-dip galvanized steel structural members. They will then show rust marks fairly quickly because the zinc layer thickness is much lower.
See Technical Info Sheet number 17
See also the publication: Galvanizing – Different techniques for galvanizing
The so-called duplex coatings; the combination of zinc and paint as corrosion protection, produces a synergistic effect. The result is about 1.5x the sum of the corrosion protection each system would provide separately. In addition, duplex coatings provide excellent safety markings and color coding. Repainting galvanized steel that has been in use for many years also extends the life of the zinc coating. Sometimes there are applications that are always, after several years of use, still painted. A common example is high-voltage pylons.
Refer to the Code of Practice “Powder and Wet Paint on Galvanized Surfaces.”
Galvanized coatings can be easily and effectively painted, not only for aesthetics or safety, but also to extend their life. The age and degree of weathering of the galvanized coating determine the degree of surface pre-treatment required to apply a quality paint system to galvanized steel. Advice should be sought from the paint supplier.
Refer to the Code of Practice “Powder and Wet Paint on Galvanized Surfaces.”
As pretreatment before wet painting, galvanized steel is often “shot blasted” to remove oxides and obtain some coarsening to ensure good adhesion. The skill of blasting the zinc coating in such a way as to avoid damage lies in the hands of the person blasting. Over-intensive blasting can cause the zinc coating to come loose. This is because the zinc layer is harder than the underlying steel. The steel can still deform somewhat during blasting, but the hardness of the zinc layer does not allow this deformation. Loosening of the zinc layer is the result. Often oval spots with a clear rim appear. It is recommended that these spots be touched up by grinding the edges flat and compensating for the lack of zinc coating on these spots by a thicker layer of paint.
In the large numbers of apartment complexes that have been installed since the turn of the century, a lot of duplex treated material is used. Often it is the railings around balconies and in stairwells that are coated after galvanization. Unfortunately, it is not readily apparent whether there are how many layers of wet paint/powder coating are involved. For example, sometimes a 1 layer powder coating system is applied when there is an increased risk of corrosion due to inadequate cleaning and/or sea salts left behind after wind when installed on the coast. Because a 1 layer powder coating does not completely seal, the zinc will slowly corrode. A white deposit of zinc corrosion products will then form through the pores in the powder coating. Eventually, the coating will detach from the zinc layer and the whole thing will have to be re-treated or repaired. Rarely can other causes be blamed for white deposits.
Refer to the Code of Practice “Powder and Wet Paint on Galvanized Surfaces.”
Despite the fact that not very many studies have been conducted, many materials made of high-strength steel are already being galvanized daily. Especially in the case of trailer construction, this is a nice way to save weight. There are no known situations where there are problems or incidents. If you want to switch to a particular type of high-strength steel, you may want to have a trial conducted at your galvanizing plant and hire a laboratory to examine the properties of the steel after galvanizing.
The vast majority of steels can be hot-dip galvanized. The chemical composition of the steel is important in assessing whether a thick or thin zinc layer will form or whether the appearance is shiny or dull. The designation S275 says everything about the properties and strength of the steel but relatively little about the chemical composition and thus formation of the zinc layer. Usually the experience is that S355 produces a somewhat larger zinc layer thickness than S275.
See Technical Info Sheet number 18
Actually, steels as with the trade name HARDOX are intended as wear plates and are often used untreated or only with a decorative shop paint as shovel loading shovels or in agricultural implements. Because of its wear-resistant property, the steel is also used by shipyards. The composition of this steel is such that it is both hard and tough. It is better not to galvanize the material because there have been frequent problems with it. Many times the sheets crack during immersion in the hot zinc bath or immediately after during cooling.
Applying galvanized reinforcement reduces the amount of concrete required. The galvanized bars require less cover thickness of the concrete because there is much less chance of concrete rot. Especially in the case of precast concrete elements, volume and weight can be saved with the advantage of less material use and fewer transport movements. Abroad, the use of galvanized reinforcing steel is often prescribed by governments. For example, in the construction of tunnels and viaducts. This prevents concrete rot and therefore very costly repairs resulting in traffic disruption.
Research has shown that galvanized steel exhibits better adhesion to concrete than untreated steel. Thus, there is nothing to fear regarding adhesion when prescribing hot-dip galvanized rebar.
Reinforcement is usually fabricated after galvanizing. Do not bend reinforcing bars with a radius of more than 8 times the radius of the bar to minimize the possibility of loosening of the zinc coating.
The moment rebar comes in contact with fresh concrete, a reaction will occur at the zinc surface due to the high pH of concrete. The pH value of concrete is between 12.5 and 13.5, a value you can never encounter under atmospheric conditions.
The principle of the reaction Zn + 2H₂O→Zn(OH)₂ + H₂(g)
The released hydrogen, one of the smallest atoms, will easily diffuse through the liquid concrete and disappear. Already immediately, a passive layer (zinc patina) consisting of:
Zn(OH)₂ + 2H₂0 + Ca(OH)2₂ ->- Ca(Zn(OH)3)₂ – 2H₂0
After formation of this layer, hydrogen egress will come to a halt after only a few hours.
Also, some of the hydrogen will diffuse into the steel. The fear of hydrogen embrittlement of the steel has proved unfounded after research by TNO.
Tensile testing has shown that there is virtually no difference between untreated steel and galvanized steel applied as reinforcement.
There is no good method for determining the adhesion of a zinc coating. After all; adhesion is one of the most important characteristics of this process. Namely, a metallurgical bond is formed on the steel surface between zinc and iron by a diffusion process. By definition, this is an inseparable bond. The reason why the zinc layer sometimes detaches from the substrate after mechanical loading is because of the hardness differences between the zinc-iron alloy layers and the steel. Steel is somewhat softer and yields by denting while the hard zinc layer does not dent and therefore comes loose. People used to talk about the hammer test but it has disappeared from ISO standards. In America, in exceptional cases, the zinc layer is tested by carving with a sturdy and pointed knife (kind of oyster knife). Sometimes one still comes across a Dolly test. This form of testing is intended for organic coatings and completely unsuitable for zinc coatings because the results of the test mean nothing.
Compared to paint systems, hot-dip galvanizing has less to similar initial application costs and, almost always, lower life-cycle costs. The lower life-cycle costs of a hot-dip galvanized project make hot-dip galvanized steel the right choice for today and tomorrow.
The fresh zinc layer is highly reactive and wants to form zinc oxide and zinc hydroxide corrosion products that eventually form the stable zinc carbonate. When galvanized steel is directly stacked or stored in humid conditions that do not allow free flowing air, the zinc forms excessive layers of zinc hydroxide, also known as white rust. Most of it can be easily removed with a cleaning or nylon brush. Preventing the possibility of white rust formation as much as possible can be done in the following ways.
Store galvanized steel under a canopy and stack it with wood (stop wood) and sloped so that there is enough free flowing air between each galvanized article to prevent white rust.
See Technical Info Sheet number 1
Steel composition is the main determinant of the thickness and appearance of the galvanized coating. Structural steel produced by steel companies around the world has a wide variety of chemical additives, thus also different reaction phenomena during hot-dip galvanizing that affect the appearance.
There are further various additives that galvanizers can put into their zinc bath to influence the appearance of the coating cq. enhance by making it glossy, spotty or matte gray. The appearance of the coating (matte gray, glossy, spotty) usually does not change the corrosion protection of the zinc coating.
See Technical Info Sheet number 18
The chemical steel composition and surface condition of the steel are the main determinants of the thickness and appearance of the galvanized coating. Structural steel produced by the steel companies has a wide variety of additives, thus also different reaction phenomena during hot-dip galvanizing that affect the appearance.
There are further various additives that galvanizers can put into their zinc bath to influence and/or improve the appearance of the coating by making it shiny, spotty or matte gray. The appearance of the coating (matte gray, glossy, spotty) does not change the corrosion protection of the zinc coating.
See Technical Info Sheet number 18
The fresh zinc layer is highly reactive and wants to form zinc oxide and zinc hydroxide corrosion products that eventually form the stable zinc carbonate. When galvanized steel is directly stacked or stored in humid conditions that do not allow free flowing air, the zinc forms excessive layers of zinc hydroxide, also known as white rust. Most of it can be easily removed with a cleaning or nylon brush. Preventing the possibility of white rust formation as much as possible can be done in the following ways.
Store galvanized steel under a canopy and stack it with wood (stop wood) and sloped so that there is enough free flowing air between each galvanized article to prevent white rust.
See Technical Info Sheet number 1
White rust forms on new and fresh galvanizing as soon as there is humidity preventing the zinc layer from reacting with ambient air to form a zinc patina layer. Especially in the case of transport by sea in sealed containers, there is a high probability of the formation of white rust. This may be less than expected if on arrival the materials are removed from the container as soon as possible and exposed to dry outside air. It is not recommended to store the materials for weeks at a time on the unloading quay in closed containers, because the corrosion of the zinc layer can proceed so rapidly that locally there is hardly any zinc layer left.
Whiskers are a type of hair that forms on electrogalvanized steel, especially under specific conditions such as in data centers. This phenomenon occurs, for example, on cable trays. On hot-dip galvanized steel, as far as we know, this phenomenon does not occur. Therefore, it is a good thing to perform cable trays in hot-dip galvanized steel.
Zinc whiskers are tiny zinc filaments that grow from steel surfaces that have been electrogalvanized. The electrogalvanizing process forms a continuous layer of zinc atoms under compressive stress. The atoms are compressed, causing zinc whiskers to protrude out from the surface. These whiskers break off, become airborne through air cooling systems, invade hardware equipment and cause short-circuit damage to IT systems and even uncontrolled system resets. Most frustratingly, they are rarely detectable. Investigations rarely find clues pointing to the real problem. This is because zinc whiskers usually evaporate due to the same short circuits they cause.
The conditions in data centers are subject to fluctuations in temperature and humidity, which can lead to the growth of these hairs on electrogalvanized steel. When moisture is present, the zinc will crystallize and grow from a point in a manner more or less similar to how a hair grows. Careful attention must be paid to air circulation to avoid problems when electrogalvanized steel is still used. Incidentally, whiskers also form when silver and tin are used.
Zinc is a base metal and will sacrifice itself (i.e. corrode, give up its electrons) to protect most metals. So it is recommended that galvanized steel be insulated so that it does not come into direct contact with dissimilar metals. Rubber or plastic, both nonconductive, are often used to provide this insulation. Some combinations can, however, be used without danger of corrosion damage. For example, using stainless steel bolts and nuts to mount galvanized parts.
See Technical Info Sheet number 4
