- 22 November 2016
- Posted by: Stm Coatech
- Category: Educational Articles
The relatively new polyurea two-component thermosets are chemically somewhat similar to the polyurethanes and are available as aliphatic and aromatic products. They are produced by the reaction of an isocyanate with an amine resin component rather than a polyol, as with polyurethanes. Polyureas can be used by themselves or as hybrids with polyurethanes. They cure very radiply to form soft to hard elastomers for use on concrete floors or containments. They have the same advantages as %100 solids high-build coatings. Polyaspartic variations produce aliphatic products that have longer pot lives so that they can be applied by brush, roller or spray.
Polyurea spray coatings technology is one of the new developments of the last 20 years. This technology combines fast curing, even at very low temperatures, and water insensitivity with exceptional mechanical properties, chemical resistance and durability.
The development of new raw materials and improved spray equipment has made it possible to overcome the initial problems of this technology such as substrate wetting, intercoat adhesion and surface finish quality.
The latest development programs are focussing on the extension of the application fields through the introduction of MDI-prepolymers combining low viscosity with low NCOcontent, resulting in slower reactivity and/or higher flexibility. Alternatively, prepolymers with higher NCO-content produce coatings with superior hardness.
Inevitably coatings get damaged by external forces or by a number of long-term degradation processes that affect the constituents of the coating. Typically this results in coating defects that expose the pipe steel to the environment around the pipeline and this corrosion risk is and can be controlled by cathodic protection.
Polyurea polymers are designed to compete with tri laminate products such as FBE, 3LPP and 3LPE, providing higher performance coatings at competitive costs. The application processes required are simple and efficient and the equipment systems utilized are inexpensive when compared to the costs of systems used in the application of FBE, Tri-Laminate and similar coating technologies and not to mention about the field joints which is compatible on all of the above with added advantage of cost, speed and minimum back to service time.
Polyurea is characterized by many essential properties which make it an effective corrosion resistant coating.
Resistance to water is perhaps the most important characteristic since water, as a universal solvent, in combination with other materials can take various form and can create very corrosive environment and have a damaging effect on the steel substrates. The extremely low rates of water absorption and moisture vapor transfer are essential features which makes it an effective coating barrier which very few coating can match.
The dielectric strength is a key property of polyurea which helps in breaking the electric circuit set up during corrosion reaction and makes it suitable to be used as a corrosion resistant coating by resisting passage of electron. Polyurea has a dielectric strength of > 16 KV and this combined with low moisture absorption makes it an ideal anti corrosion coating.
Polyurea coating’s high resistance to ionic passage is a desired coating characteristic and prevents transfer or passage of chlorides, sulphides, or similar ions which accelerates corrosion. Resistance to ionic passage is a contributing factor to chemical resistance and polyurea is good for chemicals between pH 12 and pH 4 particularly the alkalis.
The strong adhesion prevents the problem caused by temperature gradient, osmosis and electro-osmosis and retains its integrity for longer time and thus enhancing the life of the coating. A strong adhesion also prevents undercutting.
A well formulated elastomeric Polyurea has a good resistance to abrasion, impact and scouring and the loss is < 6mg on C17 wheel comparable if not better than most of the anti-corrosive coatings being patronized to day.
One of the characteristics which make polyurea unique is its retention of physical property on ageing which makes it weather and age resistant and make it suitable as a coating for long term protection. A well formulated Polyurea retains more than 90 % of its physical even after ageing.
A very good external corrosion control on steel pipelines is achieved by combining polyurea distributed with a cathodic protection. The coating provides the first, and major, defense against corrosion and further, in case of its damage, the cathodic protection serves to prevent pitting or general corrosion where the pipe steel is exposed by damage to the coating. Coating damage is to be expected on all pipelines using traditional coatings and the degree of damage with Polyurea is minimal or none unless these are very roughly handled and hence the degree of risk is very less.
A good protective coating application always comes down to preparation of the substrate or material it is applied to. Preparation is normally in the form of shot blasting or ultra-high water blasting depending on where the application is to take place and the material it is to be applied to. There are cold applied formulas which can be applied using brush, roller or squeegee.
*Pipe and Pipeline Coatings and Linings
*Joint Filling and Caulking
*Waste Water Retention
*Truck Bed Liners
*Amusement and Water Parks
*Flooring and Parking Decks
*Landscape Water Features
*Extremely fast curing. Very fast set and return to service (5-20 seconds)
*Can be applied in sub-zero temperatures
*Can be built up to any thickness (mm) in one hit
*Very high abrasion resistance
*Very high corrosion protection
*Very high chemical resistance
*No atmospheric or environmental resistance
*Comes in most colours for structural enhancement
*Water-sensitivity during application.
*High-build, %100 solids.
*Can be soft to hard elastomers.
*Can be used in hybrids with polyurethanes.
*Used on concrete floors or containments.REFERENCES:
1.Huntsman, Polyurea Spray Coatings, Date of access: 11 November 2016, http://www.huntsman.com/polyurethanes/Media%20Library/a_MC1CD1F5AB7BB1738E040EBCD2B6B01F1/Products_MC1CD1F5AB8081738E040EBCD2B6B01F1/Adhesives_former_MC1CD1F5B06E31738E040EBCD2B6B01F1/Technical%20presentati_MC1CD1F5B098A1738E040EBCD2B6B01F1/files/ecc_8-_marc_broekaert_-huntsman_polyurethanes.pdf
2.IridexPlastic, POLYUREA – A Modern Alternative For Anti-Corrosion Protection Of Steel Structures, Date of access: 11 November 2016, http://www.iridexplastic.ro/images/inthepress/Poliurea-eng.pdf
3.GMW Restoration Services, Polyurea Coatings, Date of access: 11 November 2016, http://gmwrestorationservices.ca/polyurea-coatings/