isnatums

Just for the Health of It

Corrosion Control & Protection

Steel Grades

corrosion prevention

A – Steel surface largely covered with adhering mill scale but little, if any, rust.

B – Steel surface which has begun to rust and from which the mill scale has begun to flake.

C – Steel surface on which the mill scale has rusted away or from which it can be scraped, but with slight pitting visible under normal vision.

D – Steel surface on which the mill scale has rusted away and on which general pitting is visible under normal vision.

St – Hand and power tool cleaning

St2 – Thorough hand and power tool cleaning. When viewed without magnification, the surface shall be free from visible oil, grease, and dirt, and from poorly adhering mill scale, rust, paint coatings and foreign matter.

St3 – Very thorough hand and power tool cleaning.  As for St2, – the surface shall be treated much thoroughly to give a metallic sheen arising from the metallic substrate.

Sa – Blast Cleaning

Sa1 – Light blast cleaning. When viewed without magnification, the surface shall be free from visible oil, grease and dirt, and from poorly adhering mill scale, rust, paint coatings and foreign matter.

Sa2 – Thorough blast cleaning. When viewed without magnification, the surface shall be free from visible oil, grease and dirt and from most of the mill scale, rust, paint coatings and foreign matter. Any residual contamination shall be firmly adhering.

Sa2.5 – Very thorough blast cleaning. When viewed without magnification, the surface shall be free from visible oil, grease and dirt, and from mill scale, rust, paint coatings and foreign matter. Any remaining traces of contamination shall show only as slight stains in the form of spots or stripes.

Sa3 – Blast-cleaning to visually clean steel. When viewed without magnification, the surface shall be free from visible oil, grease and dirt, and shall be free from mill scale, rust, paint coatings and foreign matter. It shall have a uniform metallic colour.

Protective Coatings

In the previous chapters we discussed the importance of surface preparation. To prevent and control the surface from further corrosion, the application of protective coatings need to be carried out before oxygen and water and other corrosive agent reactivate the substrate.

Choice of appropriate types of coatings should be made depending on what the substrate is subjected to the type of environment, characteristic and purpose. For instance, they must,

a) Develop strong adhesion to the substrate.

b) Must inhibit corrosion.

c) Act as a barrier to corrosive substrate.

d) Provide a good base for subsequent coats.

The last line of defence in combating corrosion is the primer. The performance of a coating system is ultimately dependent upon the ability of the primer to withstand the attack of corrosive agent from the surrounding environment and to inhibit the activity of these agents where they may be held on the substrate by the overlaying coatings.

The primer is the most important in any coating system. All other coatings are permeable by water and oxygen. In addition some soluble corrosive substance may pass through the coating film. The primer should neutralize these materials before reaching the steel substrate. Certain compounds are able to chemically inhibit and neutralize corrosive agents

Leave a Reply

Your email address will not be published. Required fields are marked *