Aluminium is a pretty resolute material thanks to the thin aluminium oxide layer it forms upon exposure to the environment, giving it natural protection from corrosion. But did you know it is possible to create an even more effective outer coating? Welcome to the world of the anodised aluminium pipe.
The naturally formed oxide film covering an aluminium pipe comes with one weakness. Other elements can react with it, leading the protective layer to erode away and exposing the aluminium underneath.
This makes aluminium more susceptible to wear, corrosion and other factors which can weaken it and ultimately lead to holes and cracks appearing.
Preventing this is possible by increasing the thickness of the aluminium oxide coating through an electrochemical process called anodising.
What is anodising?
Aluminium oxide is second only to diamond on the Mohs Hardness Scale. The thicker the layer created, the greater resistance against wear and corrosion.
The aluminium pipe to be anodised is placed in tank filled with an electrolyte-heavy solution. Sulphuric acid is commonly used, although other acids including phosphoric acid, chromic and organic are also suitable.
It is then connected to the positive terminal of a battery. A sacrificial plate is connected to the negative terminal, placed into the electrolyte solution and the battery turned on.
With the circuit completed, an electrical current passes through it. Negative ions are attracted to the aluminium pipe, a reaction takes place and an oxide coating is formed.
The strength of the electrical current and how long the process runs for determines the thickness of the final aluminium oxide layer.
Anodised aluminium pipe for aesthetic reasons
There are other reasons for anodising aluminium pipe beyond protection. A layer of aluminium oxide makes the metal surface easier to dye.
The process creates pores which can be filled with dye pigments. The colour left by dying aluminium is permanent and cannot be scratched way.
Electrocolouring is another method of colouring aluminium made possible for anodising. The anodised material is introduced to inorganic metallic salts through an electrolyte.
The anodised aluminium becomes one electrolyte and graphite the other. The oxide precipitates in the pores, adding dark colours to the oxide layer.
At a more basic decorative level, anodising acts as an excellent primer for coating aluminium pipe with regular paint.
Because anodising is a naturally occurring reaction, the appearance of aluminium pipework left with its original anodised finish will vary greatly from pipe to pipe.
For some, this is part of the appeal of anodised aluminium pipe. The beauty is in the different characteristics, similar to how stone, wood, slate and oxidised copper differ.
If it is therefore desired for all anodised aluminium pipe to appear uniform, one of the above listed colouring methods is necessary.
Lifespan of anodised aluminium pipe
With so many factors in play, it can be difficult to give a guarantee of how long anodised aluminium pipe will last.
Factors which can impact its lifespan include the thickness of the oxide coating, the effectiveness of the electrochemical process and how aggressive the environment is where the pipe is being installed.
In the event of an anodised aluminium pipe cracking, a moisture cured pipe sealant can be easily used to repair the damage.
The sealant is extruded directly into the split in the pipe, where it will harden almost instantly to fill the crack.
Downsides of anodised aluminium pipe
There is one major downside of anodised aluminium pipe which you can probably – cost. The additional protection and attractive finish make it a premium product. Such a premium product in fact that it will often push the cost of a project towards breaking point.
Is it worth breaking the budget for? If you can afford it, then yes. Low maintenance, long-lasting and aesthetically pleasing pipework is not always easy to come by.
Many materials will tick one or two boxes but not all three. Anodised aluminium does. You get what you pay for, as they say.
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