Technical definition
Copper is a measurement of the concentration of copper present in the heating system water, expressed in milligrams per litre (mg/L). Depending on the laboratory method used, this may represent total copper, including both dissolved copper and copper contained within fine suspended corrosion products or debris.
Copper is widely present in heating systems through copper pipework, heat exchangers, fittings and copper-containing alloys such as brass. When these materials are exposed to unsuitable water chemistry, copper can be released into the circulating water through corrosion or chemical attack.
Copper is therefore an important indicator of the condition of copper-containing components and the overall corrosiveness of the system water.
Simplified definition
Copper measures the amount of copper present in the heating system water.
Higher levels can indicate that copper pipes, heat exchangers or fittings are corroding, or that copper-containing corrosion products are already circulating within the system. Testing copper helps identify deterioration before it develops into leaks or component damage.
Copper is important because elevated levels can indicate corrosion of copper-containing materials or the presence of existing copper corrosion products within the heating system.
An abnormal or elevated Copper result may indicate:
Corrosion of copper pipework, heat exchangers or fittings.
Unsuitable system-water pH.
Insufficient or ineffective corrosion-inhibitor protection.
Elevated chloride or other aggressive dissolved salts.
Residual soldering flux or other installation contaminants.
Inappropriate or inadequately flushed cleaning chemicals.
Oxygen entering the system through leaks or repeated topping-up.
Existing copper corrosion products being disturbed and circulated.
Changes in water chemistry following draining, flushing, refilling or maintenance.
Copper corrosion can result in both dissolved and insoluble corrosion products. As corrosion progresses, these materials may circulate through the system or deposit on internal surfaces.
Elevated copper can therefore be associated with:
Pinhole leaks or deterioration of copper pipework.
Damage to copper-containing heat exchangers.
Formation of corrosion products and deposits.
Fouling of narrow waterways, valves and heat exchangers.
Reduced component life.
Leakage or premature failure in more severe cases.
Copper ions can also interact with other metals within a mixed-metal heating system. Deposited copper on less noble metals can potentially create local electrochemical conditions that increase corrosion risk, so elevated copper may have implications beyond the component from which it originated.
Copper testing is therefore useful when investigating overall system corrosion and should be considered alongside parameters such as Dissolved Copper, Iron, Aluminium, pH, Chloride, Conductivity, Suspended Solids and inhibitor concentration.
Copper should not normally be assessed in isolation. An elevated result shows that copper is present in the system water, but it does not by itself determine whether the copper originates from active corrosion or historic corrosion products.
It is particularly useful to distinguish between Copper and Dissolved Copper:
Dissolved Copper measures copper that is chemically dissolved in the water and can be particularly useful as an indication of active or recent metal dissolution.
Copper, where the laboratory method represents total copper, may include both dissolved copper and fine particulate copper-containing corrosion products.
For example, high total Copper with relatively low Dissolved Copper may indicate that older corrosion products or debris are circulating within the system. Conversely, elevated Dissolved Copper can provide stronger evidence that copper is actively being released into the water.
Small quantities of copper may also be present in the original filling water, so results are most useful when compared with the filling-water concentration, previous test results, system materials and known treatment history.
