Applying alkyd paints on fire protection pipes or other galvanized surfaces can cause severe paint film detachment, affecting corrosion protection and aesthetics. To address this quality issue, the author repeatedly emphasized the necessity of using phosphate-based primers or zinc yellow primers as a base, followed by the application of alkyd paints or alkyd-colored paints. The image illustrates a typical case of alkyd red paint detachment on galvanized pipes. All galvanized surfaces are alkaline, and alkyd paints react with the zinc in an alkaline environment, resulting in a phenomenon known as saponification, where the paint film loses its adhesion. Some suggest using epoxy primers, which are more expensive, but require maintaining a certain concentration and should not be too thick. After applying the epoxy primer, alkyd paints of various colors can be applied. However, this reverses the function of epoxy and alkyd paints. Specifically, epoxy primers are superior to alkyd paints indoors, while alkyd paints are more resistant to UV radiation outdoors. Different solutions should be chosen based on specific conditions, and adjustments and confirmations are required by technical personnel.
It should be noted that this type of error is quite common and should be a focus of attention for corrosion protection design and construction personnel.
Here are a few additional points regarding the ten birds:
1. This issue isn't limited to alkyd paints; all oil-based paints (note: this refers to paints containing fatty acids) exhibit this phenomenon, including alkyd-modified paints, alkyd-modified varnishes, phenolic-modified paints, and phenolic-modified varnishes, etc. The reason is that the fatty acids in oil-based paints react with zinc to produce fatty acid zinc (also known as saponification). Fatty acid zinc is a white, fluffy, powdery substance that causes detachment at the interface between the coating and the zinc surface due to a loss of adhesion.
2. In addition to using phosphate-based primers or zinc-yellow primers as a base, it is also possible to design using other primers that are inert to zinc surfaces to avoid this phenomenon, such as epoxy-based primers.
3. Some paints that can be used on carbon steel surfaces are not suitable for galvanized surfaces, such as red lead paint and zinc-rich paint.
4. Due to the low surface roughness of the galvanized surface, other inert primers used on galvanized surfaces differ from those used on steel surfaces cleaned by spraying. Primarily, primers for galvanized surfaces require enhanced adhesion to low-roughness surfaces. For example, adhesion promoters can be added to the primer formulation.
Article source: WeChat public account "Industrial Coating Engineer"
This article's content is sourced from the anti-corrosion forum: http://www.51fangfu.com/forum. The post was initiated by forum member "Zhang Zewu."