Technical definition
Aluminium is a measurement of the concentration of dissolved aluminium present in the heating system water, expressed in milligrams per litre (mg/L).
Aluminium is widely used within modern heating systems, particularly in boiler and heat-pump heat exchangers, radiators and other components or alloys. Fernox includes Aluminium as a dedicated laboratory parameter within its postal water-testing services.
Aluminium components normally rely on a thin, protective oxide layer at their surface. Suitable system-water chemistry and corrosion inhibition help maintain protection of metallic components. If aluminium is detected at an unexpectedly elevated concentration in the circulating water, it can therefore be an important indication that aluminium-containing components are being affected by corrosion or unsuitable water chemistry.
Simplified definition
Aluminium testing measures how much aluminium is present in the heating system water.
Because aluminium is used in components such as some heat exchangers and radiators, an unusually high level can indicate that an aluminium component may be corroding. Testing it helps identify this before corrosion develops into more serious system damage.
Aluminium is important because an elevated concentration within circulating system water can provide evidence of corrosion or deterioration of aluminium-containing components.
An abnormal or elevated Aluminium result may indicate:
Corrosion of aluminium components within the heating system.
Unsuitable system-water pH for the materials installed.
Insufficient or ineffective corrosion-inhibitor protection.
Contaminants interfering with the effectiveness of the inhibitor.
Poor initial system cleaning or residual installation contaminants.
Changes in water chemistry following draining, flushing, refilling or maintenance.
Repeated introduction of fresh water and oxygen through leaks or frequent topping-up.
Existing corrosion products being released or dissolved into the circulating water.
The relationship between aluminium and pH is particularly important. Fernox highlights pH control as an important part of corrosion protection and formulates Protector F1 with buffering to maintain system water within an appropriate range; the product is specifically designed for mixed-metal systems that include aluminium.
If system-water conditions become unsuitable, aluminium surfaces can become more vulnerable to deterioration. An elevated aluminium result can therefore be particularly useful when it occurs alongside an abnormal pH or inhibitor concentration.
Aluminium corrosion can potentially contribute to:
Damage to aluminium heat exchangers and other components.
Formation of corrosion products and deposits.
Increased suspended or dissolved material within the system water.
Restricted waterways or fouling of components.
Reduced heat-transfer performance.
Leakage where corrosion becomes severe.
Premature failure of expensive system components.
Fernox also notes that contaminants such as flux residues, existing corrosion sludge and residual cleaning agents can adversely affect inhibitor performance, potentially allowing corrosion to continue even where treatment has been added.
Testing aluminium is therefore particularly valuable as part of a wider corrosion assessment. For example, elevated Iron may indicate corrosion of ferrous components, elevated Copper may indicate deterioration of copper-containing components, and elevated Aluminium can help identify deterioration associated with aluminium-containing parts of the system.
Aluminium should therefore be considered alongside parameters such as pH, inhibitor concentration, Iron, Copper, Conductivity, Chloride and Suspended Solids when assessing the condition of the heating system.
Aluminium should not normally be assessed in isolation. The significance of the result depends on whether aluminium components are actually present within the heating system and on the wider water chemistry.
A detectable aluminium concentration does not automatically mean that significant corrosion is occurring. Small quantities may originate from the filling water or other sources, so the result is most useful when compared with the original filling-water concentration, previous test results and the materials installed within the system.
The combination of elevated aluminium, unsuitable pH and/or insufficient inhibitor protection would provide stronger evidence that corrosion of an aluminium-containing component should be investigated than an aluminium result alone.
It is also important to consider chloride and overall conductivity. Aggressive water chemistry can affect corrosion behaviour, while appropriate treatment and pH control are intended to protect mixed-metal systems, including aluminium. Fernox's current Protector F1 is specifically formulated for corrosion and scale protection in systems containing aluminium and uses pH buffering as part of that protection strategy.
The Aluminium result should therefore be interpreted against the system materials, filling-water chemistry, treatment regime, appliance manufacturer's requirements and other corrosion-related laboratory parameters.
