Technical definition
Sebacate is a measurement of the concentration of sebacate ions present in the heating system water, expressed in milligrams per litre (mg/L). Sebacate is the ionised form of sebacic acid, an organic dicarboxylic acid, and its salts—such as sodium sebacate—can be used as organic corrosion inhibitors in aqueous heat-transfer and coolant formulations.
Within heating-system water analysis, sebacate is primarily a treatment-related parameter rather than a naturally significant component of mains water. Fernox Laboratories specifically lists Citrate and Sebacate under its available testing for Organic Inhibitors & Additives, indicating that the measurement is used to characterise treatment chemistry within circulating system water.
Simplified definition
Sebacate is an organic chemical that can be used as part of a corrosion inhibitor package in heating and cooling systems.
Testing its concentration can help determine whether the expected treatment chemistry is present and whether it may have become diluted, lost or incorrectly dosed.
Sebacate is important because it can act as a marker for certain organic corrosion-inhibitor formulations. Fernox's laboratory capability specifically categorises sebacate as an organic inhibitor/additive parameter, so its concentration can provide useful information about the treatment condition of the system water.
A low or unexpected Sebacate result may indicate:
Insufficient sebacate-containing inhibitor within the system.
Dilution caused by repeated topping-up with fresh water.
Loss of treated water through leaks, draining or maintenance.
A system that has been refilled without the correct treatment being restored.
Incorrect initial dosing.
A change from one inhibitor formulation to another.
Use of a treatment product that does not contain sebacate, in which case a low result may be completely normal.
An unusually high Sebacate result may indicate:
A relatively high concentration of a sebacate-containing treatment product.
Over-dosing of an inhibitor or additive.
Introduction of another sebacate-containing chemical.
A change in the treatment regime or system-water concentration.
Sebacate salts are used industrially as dicarboxylate corrosion inhibitors, including in heat-transfer and coolant formulations. Their function is to help reduce corrosion of metallic surfaces as part of an inhibitor package.
Maintaining the intended inhibitor concentration is important because inadequate corrosion protection can contribute to:
Corrosion of steel, aluminium, copper and other system metals.
Formation of iron oxide and magnetite sludge.
Increased dissolved and suspended corrosion products.
Radiator cold spots.
Restricted circulation.
Fouling of pumps, valves and heat exchangers.
Reduced heat-transfer efficiency.
Leakage and premature component failure.
Fernox describes central-heating inhibitors as being used to protect systems against corrosion, sludge and scale-related problems, and recommends that inhibitor concentration is maintained and checked as part of system servicing.
Sebacate should therefore be considered alongside parameters such as Molybdate, Molybdenum, Boron, Phosphorus, pH, Conductivity, Iron, Copper and Aluminium when assessing the system's treatment chemistry and corrosion protection.
Sebacate should not normally be assessed in isolation. Its significance depends heavily on the specific treatment product being used.
A low Sebacate concentration does not automatically mean that the heating system is inadequately inhibited. Many corrosion inhibitors use different chemical technologies, so a system treated with a non-sebacate formulation may legitimately contain little or no sebacate. Fernox Laboratories' classification of sebacate as an organic inhibitor/additive rather than a general water-quality mineral reinforces this treatment-dependent interpretation. (Fernox)
Similarly, the presence of sebacate is not itself evidence that corrosion is occurring. It is primarily evidence of a particular type of organic treatment chemistry.
The result is most useful when compared with the known inhibitor product and intended dosage, previous water-test results and other inhibitor-related parameters. A significant reduction over time may indicate dilution or treatment loss, while an unexpected increase may indicate additional dosing or a change in treatment chemistry.
