# Corrosion test
## What is corrosion?
Without going too much into chemical details, we can define "corrosion" as a completely natural phenomenon that causes the deterioration of a material (typically a metal), which is caused by a chemical or electrochemical reaction with the elements in the environment.
When we think about corrosion, we all have in mind a detached layer of metal from a surface. And that's correct, that's the final result of the corrosion. But what it's worse, is that this process is never ending: the environment causes the oxidation of a metal layer, which detaches from the surface and exposes another metal layer to the corrosive environment and so on.

That's why corrosion can cause dangerous and expensive damage to everything from vehicles to underwater pipes.

Fortunately, there are methods to prevent and control corrosion that can reduce or eliminate its impact.

## How to fight corrosion

First of all, you have to consider that there is not just one type of corrosion:
- uniform
- intergranular
- pitting
- crevice
- stress cracking
- hydrogen induced cracking
- galvanic

You have to know your enemy, to fight it!

When you know that your environment is potentially corrosive (such as salty water, or even H2S environment), and the type of corrosion that it can cause, you need to make the correct material choice. Of course you cannot use Carbon Steel: you will prefer materials such as Stainless Steel, Duplex SS or Nickel Alloys.
If a complete pipeline made of UNS N06625 is too expensive (we bet it is!!) you can make a pipeline with carbon steel pipes, with UNS N06625 cladding.

## How to evaluate materials

Ok, you know the corrosion attack, you chose the material. And this is theory. But how can you know that the actual material used to make your products really resists to corrosion? That's where corrosion testing comes in!
Since the material behavior is affected by the actual chemistry and heat treatment performed, you have to test the project material to be sure that it really behaves as intended.
There are a lot of tests available, each specific for a type of material and corrosive environment, such as:
- ASTM A262
- ASTM G28
- ASTM G48
- HIC test
- SSCC test

and many many more.
As a general rule of the thumb, the harder a material is, the more it is subject to corrosion (and particularly tenso-corrosion).