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May 15 - May 19, 2017

Which single type of paint system can be used to protect both stainless steel and carbon steel welded together?

Selected Answers

From jiyash bhaskaran of Samsung engg on October 18, 2017:
For SS/CS weld joints, when selecting the paint system, the following things have to be considered. 1) If the paint contains conductive pigments like free Zn ions, zinc phosphate can be used as zn ions are not free. 2) the operating temperature of the service: for example, epoxy mastic or high build epoxy can be applied up to 120 C, while silicone acrylic binder can go up to 250 C.Silicone aluminium can go up to 450C. Depending on the exposure conditions and service, all these paints can be used on SS/CS weld joints

Epoxy mastic or zinc phosphate self-primer can be used on weld joints to protect both metals at the joint. The main problem is galvanic corrosion, which can occur if any pinhole is present on weld joint. So, low voltage holiday test should be carried out on the weld joint. If the surface is exposed to ambient conditions,  then a polyurethane topcoat should be used for UV protection.

From Bryant Chandler of Greenman-Pedersen, Inc. on May 18, 2017:
Bill Slama hit all the essential points for a coating system. Further selection of the coating type would be based on the type of exposure, heat, UV, chemical, etc. It would be essential to do a holiday/pinhole test to verify no pinholes present in the carbon steel.

From William Slama of International Paint/Ceilcote Products on May 16, 2017:
Any non-conductive coating system (but not a zinc primer) can be used, depending on the specific operating conditions that the coating will be exposed to, especially if it will be used in immersion. However, one must be aware of the potential galvanic corrosion that could be caused by the potential voltage difference between the stainless steel and the carbon steel if large areas of the stainless steel are exposed. Then a pinhole in the coating on the carbon steel will be exposed to the galvanic corrosion with a great anode area of the exposed stainless steel, resulting in very rapid corrosion. In many cases the corrosion engineer will actually specify that all of the immersed stainless steel also be coated to eliminate that potential effect.

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Tagged categories: Carbon Steel; Coating Materials; Coating selection; Stainless steel

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