CORROSION PROTECTION FOR STEEL

Corrosion costs industries billions each year.  Corrosion protection of steel causes structural instability and poses a serious safety hazard. It causes severe disruption and financial implications in maintaining and replacing structures, and also appears aesthetically as though structures are old and failing.

ZINGA is different from other anti-corrosion methods because it combines both passive and active protection. Zinga can be easily applied as a film galvanizing system that not only delivers active cathodic protection but also provides a passive physical shield.

Where there is steel, there is corrosion. Corrosion-related spending has risen to billions. Indeed, countries like the United States, Britain, Germany and other industrialised countries have an individual corrosion related expenditure of more than ten billion US dollars. This means that the cost of corrosion is significantly higher than the sums spent on industrial coatings worldwide.*

A common method to protect steel from attack by corrosion is to coat the structure with different types of paints. One part of the coating system contains anti-corrosive pigments and additives, whereas other coatings react with surface humidity.  A common way that these coatings work is by forming a protective barrier to block the contact between the air / oxygen and the metal itself. Many of these systems are very effective, but if they begin to show bubbles, cracks or other defects in the coating, the barrier will be broken and the protection will be lost.

Preparation of the surface and the application process must be perfect for the coatings to work effectively. In coastal climates especially, a completely intact coating that has been applied too thinly may allow chloride ions on the surface to penetrate the paint film to the steel surface underneath. It usually costs four to five times more to correct the errors than the original cost of coating, because of all the extra work in rectifying and re-coating.*

The inefficiencies of coatings is a primary reason for the practice of hot dip galvanising to protect steel. Hot dip galvanising eliminates many issues that may arise with surface treatment. However, hot dip galvanising also has its own limitations and best practice guidelines to ensure the effective protection for steel.

Hot dip galvansing can increase the risk of twisting thinner steel parts. Even a very small rotation can cause significant issues. Some steel alloys have a different surface structure than ordinary steel and can therefore prove difficult to obtain a uniform design across the various alloys. Cast iron structures are difficult to hot dip because dipping in a liquid zinc bath with temperature at 450 degrees would lead to bursts.

*Information taken from Zingametall

Advantages Of Using Zinga Over Hot Dip Galvanising

During the early 1970’s, a system for film galvanizing called ZINGA was developed in Belgium. ZINGA can be used on structures that cannot be removed or moved easily. It can also be used on items that were previously treated by hot dip, such as high-voltage masts, pier legs, super sized storage tanks, bridges and traffic sign posts.

ZINGA film galvanising system offers the same type of cathodic protection as hot dip, but it is applied in the same manner as a paint or coating system. The liquid galvanisation consists of atomised zinc particles, resins and binders. This easy application has been proven to work well for repairs and can restore and increase the zinc coating thickness. The great results seen by using Zinga for repairs convinced more and more manufacturers to also use this method. This process also helps eliminate the problems with rotation of thin steel parts. Even iron can be galvanized if the application takes place at ambient temperature.

Film galvanising combines cathodic, galvanic and barrier protection. Application can be done by brush, roller or spraying. Zinc content in the dry layer is at least 96%. It can be applied in a humidity up to 95% (avoid water droplets on the ground) and in temperatures down to minus 15 degrees Celsius. The zinc coating dries within 15 minutes and a second layer can be applied after an hour. Due to these fast curing properties, film galvanising is now widely used in the offshore sector and on foundations of ports and bridges.

Zinga’s cured colour is grey which may not suit every application. However ZINGA can be over painted if required, but it does not require any extra finishing coating to complete the galvanising system. The longevity of the product can be seen in the performance of the surface on the Kalvoya bridge outside Oslo. The bridge was treated with ZINGA nearly 30 years ago and it is only now that a further refurbishment is being considered. An added advantage is that it has been found that a new application of Zinga will not require any further blasting, it will only require the surface to be cleaned under high pressure (700 bar). Tensile tests have demonstrated that the almost 30 year old ZINGA layer still has an adhesion of 11 MPa.

This example clearly demonstrates that it is possible to keep virtually all types of steel and iron constructions maintenance-free for a long period, and gives the structure full cathodic protection. This is provided the surfaces are properly cleaned and sandblasted prior to first application.

Kalvoya bridge in Oslo was treated with ZINGA film galvanizing system almost 30 years ago.

1985 – 2013

Corrosion protection of steel - Kalvoya bridge coated in Zinga