How are grooved pipe fittings rust-proof？

How are grooved pipe fittings rust-proof？
For grooved pipe fittings, due to the particularity of their materials, cast iron is basically used at present, so anti-rust treatment is very critical. At present, there are two main methods for this process, and Numerous tubes
We will briefly introduce the more skilled craftsmanship used by parts manufacturers - below.
1. Spray painting, this process has been used for a long time, and at present, 30% of enterprises are still using it.
2. Plastic spraying, due to the many defects of the spray painting process, since 2008, many grooved pipe fittings companies have started to use the plastic spraying process for anti-rust treatment.