What is Corrosion?
Corrosion is when a refined metal is naturally converted to a more stable form such as its oxide, hydroxide or sulphide state this leads to deterioration of the material.
Why corrosion occurs?
Metal corrodes when it reacts with another substance such as oxygen, hydrogen, an electrical current or even dirt and bacteria. Corrosion can also happen when metals like steel are placed under too much stress causing the material to crack.
What kind of paint can protect Corrosion?
One of the easiest and cheapest ways to prevent corrosion is to use barrier coatings like paint, plastic, or powder. Powders, including epoxy, nylon, and urethane, adhere to the metal surface to create a thin film. Today’s paint systems are a combination of different paint layers that serve different functions. The primer coat acts as an inhibitor, the intermediate coat adds to the paint’s overall thickness, and the finish coat provides resistance to environmental factors.
How to test anti-corrosion paint?
There are many technology of testing anti-corrosive paint. The most common is "natural Salt Spray Test" and another one is "Water condensation".
Test method followed by ISO 12944-6:2018
Standard for water condensation is ISO 6270-1
Standards for Natural Salt Spray is ISO 9227 & ASTM B117
How to test corrosion using method of salt spray ASTM B117?
Salt Spray Chamber. ASTM B117
Test Condition:
1.
Salt solution conentration : 5% wt
2.
pH of collected solution : 6.5- 7.2
3.
Air supply : 1.0 kg/cm2
4.
Temperature in the salt spray chamber: 35ºC
5.
Saturated air temperature: 47°C
6. Test duration: 1440Hr (according ISO 12944-6)
7.
Fogg collection: 1.2 ml/hr
8. Method of supporting article: Suspension
ASTM D1654
An X pattern is scribed into the powder coated test coupons, see Figure 1. The scribed test coupons are then exposed to ASTM B117 testing. After the exposure the rate the corrosion or loss of paint extending from a scribe mark as prescribed in bellow notation.
ASTM D714
This test method employs photographic
reference standards to evaluate the degree of blistering that may develop when
paint systems are subjected to conditions which will cause blistering.
Performance requirement to ISO 12944-6:2018
Assessment method Requirement
ISO 4628-2, Blistering 0 (SO)
ISO 4628-3, Rusting Ri 0
ISO 4628-4, Cracking 0 (SO)
ISO 4628-5, Flaking 0 (SO)
ISO 4628-6,A.2, Corrosion at scribe Max. 1.5mm as average value
ISO 4624, Pull Off Adhesion Min. 2.5 MPa for each measurement. 0% dhesive failure between substrate & first coat(Unless values are at least 5 MPa)
Thanks
If you have any question please feel free ask here
ReplyDelete