HRCSA coatings are easy-to-use, single-component coatings that cure by air oxidation and UV, much like regular alkyd paint. HRCSA are softer films that remain both active and flexible while continuously releasing corrosion inhibitors at the coating/metal interface. Essentially, HRCSAs possess both barrier properties against the ingress of corrosive materials and corrosion inhibitive properties. Two elements which accounts for it’s ability to resist undercutting in ways traditional hard film form coating systems cannot.
Hard Film Form Coatings Undercutting.
Unlike Hard Film Form coating (above), HRCSA will not “hide” active corrosion cells due do it’s calcite platelet structure. From a preservation point of view, this means that ACTIVE CORROSION CELLS CAN BE SEEN – a critical element for knowing where one stands wrt the true health of their structure.
HRCSA Does Not Undercut.
ASTM D5894 FHWA test (USA) JIS H8502 Japanese C-Nexco Test
ASTM 5894 above chart and testing protocal
Federal Highway Administration (US) Test Report
While engineers may be more familiar with other generic types of coatings such as alkyds, latexes, zincs, epoxies, urethanes (2-pack, polyaspartic and moisture-cured) the HRCSA coatings are a rather interesting and somewhat lesser known coatings type with a 30 plus year track history of targeting structure critical corrosion in areas where crevice corrosion, pack-rust and corrosion-frozen moving parts are shortening the service life of steel structures.
The essential formula of an HRCSA coating is (R-Ar-SO3)2–M.x (MA). The coating is made up of a non-polar alkylate (the R group with alkyl side chains containing 12 to 20 carbon atoms); a complex of calcium (M) sulfonate (SO3) and basic calcium (M) carbonate (A); one or more alkyds with which the sulfonate copolymerizes; drying oils; and an array of additives and anticorrosive pigments. The benzene ring (Ar) attached to the acidic sulfonate group gives the coating considerable polarity and ability to wet out surfaces. The carbonate is basic and inhibits corrosion. Platelets of the complex sulfonate carbonate crystals present a more tortuous path for the ingress of corrosive materials and also confer extra film strength.
(R-Ar – SO3)2 M . x (MA)
R = alkyl side chains 12 to 20 carbons M = Ca2+ or Mg2+ or Ba2+
A = CO32-
x = 10 to 20
As with any formulation, the nature of the ingredients and how they are assembled determines the level of in-service performance. On the one hand, the presence of calcium carbonate as hexagonal plate-like calcite crystals in an artificially grown sulfonate-carbonate lattice gives the HRCSA coating substantially better performance than a sulfonate-low cost amorphous calcium carbonate admixture in a non-HRCSA (high ratio calcium sulfonate).
What does the designation “high ratio” mean? It refers to the formulation having a high percentage of active sulfonate balanced with the right amount and type of artificially grown basic calcium carbonate. The ratio of active sulfonate to the Total Base Number basic carbonate (total base number TBN) is very important. For optimum performance, the ratio should be between 90 and 105 TBN (Total Base Number) and a minimum 9.5 to 11% active sulfonate. Calcium sulfonate alkyd coatings with lower active sulfonate percentages (3–5%) , or high TBN numbers (200–300) are markedly lower in performance characteristics. Engineered correctly, the result is a very flexible coating that possesses an active chemistry for the control of corrosion, especially crevice corrosion, where differential oxygen concentration cells exist.
Importantly, the HRCSA coatings exert minimal shrinkage stress, a beneficial attribute because cold weather can impart substantial hygrothermal stresses to overcoat systems, and, in turn, the deleterious stresses can then be imparted to underlying coatings.
The lower tensile strength of HRCSA coatings is highly advantageous. For instance, even at –10 C (+14 F), the HRCSA used in this work has an adhesion
value of 100–300 psi and does not disbond in overcoat scenarios, whereas high-build epoxies with tensile strengths close to 1,000 psi might disbond under similar conditions. Similar to certain high-quality penetrating sealer epoxies used for overcoating purposes, HRCSA coatings have the added ability to displace moisture, scavenge oxygen and neutralize acids inside crevices and connections.
