Can Galvanized steel be painted-Precautions to take

Can Galvanized Steel be Painted? Precautions to Take

According to the industry experts, galvanizing could present several challenges when undertaking painting operations. Life can be added to steel surfaces along with its electrochemical activity and surface chemistry with zinc coating. Thus, it results in conditions which lead to adhesion failures with regards to applied organic coatings. Successful painting can be achieved by recognizing the different surface conditions which are presented by weathered and new galvanizing. Effective cleaning operations are then employed for mitigating its effects. It is by choosing coating products which develop enduring and strong bond to galvanized surface that ultimate success is derived.

About Galvanizing

It is the term used for metallurgical process which applies zinc metal layer over steel surface for avoiding steel corrosion. During the reaction, zinc layer is found to sacrifice itself for protecting underlying steel substrate. The zinc during the electrochemical reaction functions as the anode, while steel represents the cathode. With adequate zinc being used, corrosion can be avoided to protect steel.

Galvanizing types

Zinc through HDG (hot dip galvanizing) process can be used for coating piping, structural steel along with other steel shapes. The process involves using of hot acid baths in combination to clean steel. It is to eliminate scale and rust followed by immersion and fluxing into molten pure zinc bath heated in range 820 – 860F. HDG achieves zinc thickness within the range of 2-8mils for steel varieties and dependent upon immersion time in bath. HDG thickness of range 20-30 mils is achieved with few reactive steels. Sheradizing and electroplating are the other methods used for applying zinc layer to steel.

Duration of protection provided to steel with zinc coating

Corrosion may take place with zinc. As exposed to atmosphere, chemical reaction begins with oxygen, carbon dioxide, moisture & soluble airborne salts such as sulfates and chlorides. Zinc corrosion rate depends upon environmental exposure and severity. According to reports, galvanized steel surface of zinc of 2 mils tend to develop just 5% rusting that too after around 35 years of getting exposure in the industry environment!

How galvanizing can be painted?

Replacing lost corrosion protection: Although atmospherically stabilized zinc corrosion rate is low, zinc layer’s thickness is reduced with time. Atmospheric exposure severity and original zinc thickness is likely to affect galvanizing life. With corrosion, zinc layer gets reduced and its capability to safeguard underlying steel substrate gets diminished, while galvanic protection provided by zinc is lost. Here, polymer overcoating application is to be considered for extending the structure life.

Using Duplex System for extending life of galvanizing

Situations may come where immediate overcoating of HDG will be necessary for extending the structure’s life beyond zinc layer’s longevity. Synergistic effect gets created to extend galvanizing life as new HDG is used to overcoat along with organic coating. The latter tends to act as a barrier by preventing moisture from penetrating, thus slowing down zinc layer corrosion. Moreover, life of galvanized coating is extended by factor from 1.4 – 2.7 times the total of lives that has been predicted for each layer of coating.

For enhancing appearance

HDG often is overcoated using organic coating, since metallic gray spangling’s natural appearance may be objectionable. This is to impart specific desired color through architectural rendering or to enhance its appearance. In such situations, adding of an overcoat is sure to extend the galvanized layer’s life.

Get in touch with us via Email: info@galvanizers.co.in or
Phone: (0265) 2632517 (O) / +91 8000842648

Batch Galvanized Vs Pre-galvanized Products-Applications and benefits

Batch Galvanized Vs Pre-galvanized Products | Applications and benefits

There is a common misconception among many that any type of zinc coating is termed as galvanizing. However, the truth is there are present various processes through which application of zinc coating is possible. HDG or hot dip galvanizing tends to refer to those coatings which are created through immersion of steelwork into zinc in molten form. Two variations are present of HDG process, namely, Pre-galvanizing and Batch Galvanizing.

About Batch Hot Dip Galvanizing

It is a process that is generally used for coating completely fabricated articles. Chemical cleaning is involved of work before immersing in galvanizing bath, specified with EN ISO 1461. The process given below offers full coverage including hollow section internal surfaces without the presence of any uncoated area. Highest corrosion protection level is also offered with the formation of thick coating.

Pregalvanized Steel product

The alternative available will be to take specific product like tubes, wires or sheet and use an automated process to galvanize them.

Pregalvanized Steel Sheet

It is considered to be among the most used of all pregalvanized products, specified with EN 10346. The sheet is uncoiled to be passed through reducing atmosphere before it gets immersed for short time period in galvanizing bath. On withdrawing it from galvanizing bath, there is used a mechanical wiper or air knife for eliminating excess zinc, to produce excellent surface finish. However, the result derived is thin coating varying between 7 and 42 μm depending upon the grade and most products having typical coating thickness of about 20 μm. Once galvanizing is completed, the sheet gets recoiled before the stockholder. It is uncoiled and then cut down for sale to produce uncoated edges.

Pre-galvanized Steel Tubes

Using automated procedure to EN 10240, it is possible to galvanize tubes. Here, immersion times re much shorter and on withdrawal, the tube bore may be blown down by steam to provide adequate surface finish. Coating thickness could be high by about 45-55 μm, even though most of the produced products may have significant thinner coating of about 20 to 30 μm. The tubes can be cut again for resale purpose to size to create uncoated edges.

Pre-galvanized Wire

Wire strands, from practical view point may be coated just using automated process, specified with EN 10244-2. If wiping procedures are used, then there will be shorter immersion times to eliminate excess zinc present and to achieve smooth finish. Again, coating thickness could vary with strand diameter and grade. However, it will be typically around 20 to 30 μm. Although it is not possible to galvanize individual strands to EN-ISO 1461, for such processing mesh can be found suitable for achieving thicker galvanized coating.

Coating comparison

It is essential to understand that both pregalvanized and hot dip galvanizing coatings tend to come with different characteristics. Also, as coating weights get specified for the steel sheet, weights tend to include the sheet’s both sides to ensure that coating life becomes half for equivalent coating weight that is specified within EN 10346.

Choose Tanya Galvanizers for all galvanizing needs

Those interested to get superior quality galvanizing can check out the different types of services offered by ‘Tanya Galvanizers’, the leading company in the domain. They are considered to be cost effective and known not to compromise on the quality aspect. They are completely reliable and can be trusted upon for providing the best and cost effective galvanizing solutions as and when required.

Get in touch with us via Email: info@galvanizers.co.in or
Phone: (0265) 2632517 (O) / +91 8000842648