The Principals of Salt Corrosion

Salt corrosion and the challenge of effective salt removal has plagued people ever since metal and salt first came into contact. It was never a harmonious partnership, with salt corrosion always having the upper hand.

What is Salt Corrosion?

Metallic corrosion is the process of either stealing or donating electrons, when the electrons are stolen or donated, the metal atoms become charged and will dissolve in the water. Salt water is a much better conductor that fresh, so the rate of electron movement increases speeding up the corrosion process. Total salt removal is the only way to arrest this corrosion process. Even the smallest amount of residual salt will allow the reaction to continue.

Aluminium Corrosion is Different

At first Aluminium corrodes very quickly, much faster than Iron or Steel, but once an oxidised surface has developed, it bonds very tightly providing a protective surface, this is the process of anodising to protect aluminium.

When salt is present, the chloride (Cl-) ions attack this oxidised layer, penetrating and exposing fresh aluminium. This then corrodes only to be stripped off again in a never ending cycle. So the natural protection Aluminium gets from an oxide coating is useless against salt! This is why anodising fails to offer any long term protection against salt corrosion.

Anything that is exposed to salt water, salt air or ground salts will be a candidate for salt corrosion. Even when the salt is dry it is still a problem since salt is hydroscopic, attracting moisture. Any available will allow the corrosion to continue, often unseen until it is too late and the damage is done.

Because of salt's hydroscopic property, removing salt residues is not an option if your equipment is to survive long term, it has to be thorough. The ability of SX50 and Buster 50 to neutralize salt, makes salt removal a very simple operation. Once the salt is neutralised, corrosion is halted!

Prevention is Cheaper than Repair and Replacement

Some Salt Removal Methods can be Costly!

A customer decided not to use SX50 because his mechanic's suggested a "better method"....

"...The recommendation was 3:1 water and hydrochloric acid left in the system for 3/4 hr then flushed out. This seemed to work very effectively although I only left it for 1/4 hr before flushing the system..."

We decided to get some expert advice from an Industrial Chemist who specialises in chemical/metal corrosion.

"...The use of uninhibited hydrochloric acid (HCl) on ANY metal surface would not be recommended. Any HCl purchased "off the shelf" would not have an inhibitor system added to it - this means that the acid will not stop acting when it reaches "clean metal" but will continue to etch into the metal surface.

Effectively, uninhibited hydrochloric acid continues to etch into the metal surface at the same rate that it removes scale or rust. If you have a motor which has varying depths of scale - as most do - this means that the acid will be eating through scale in some parts of the motor, but will be eating through the base metal where the scale is thin.

Further, HCl will cause pitting of the surface as it will follow a corrosion pathway in areas of the metal that may be heat stressed - possibly leading to breakthrough. Further, residual chloride ion will continue to promote corrosion on ferrous parts even after the acid has been flushed out.

Finally, HCl will "de-zinc" brass and bronze leading to "sponginess" in the metal and loss of mechanical strength in yellow metal components.

SX50, on the other hand, has a number of advantages:

1. It's a "soft" acid - effective at removing scale, but weak at attacking base metals.
2. It has a "three way" inhibitor system - with specific inhibitors for ferrous metals, aluminum & "yellow metals". This means that it will quickly etch to the metal surface and then stop reacting once it hits base metal.
Further, these inhibitors, in combination with the film forming protective agents present in SX50, protect the metal from ongoing corrosion.
3. Being chloride free, SX50 will not cause "chloride corrosion" as seen with HCl - in fact the exact opposite is true – SX50 displaces chloride ion at the metal surface and protects the metal against salt attack.
4. Finally, the film forming agents within SX50 have a lubricating effect on seals and bushes...."

Bruce Heath, BAS App Chem, Grad Dip Tech Mgt MBA MRACI-CChem