This short blog will cover some of the coatings that are advisable for Ductile Iron Pipe in above ground applications including well housings, pit, plants, and outdoors, etc. Also, how do you specify the metal coating including finish coat, primers, surface preparation, etc?
If nothing is specified, Ductile Iron Pipe is usually provided with an asphaltic coating nearly 1-mil thick. Generally considered for aesthetic purposes, this coating is commonplace for above and below ground applications.
When it comes to above ground applications like bridge crossings, pump stations, and pipe on supports installations, asphaltic coatings are used. For specialized above ground conditions there are other coatings available such as epoxies. Installations that may use such coatings include chemical environments, corrosive wet walls, etc. In addition, some installations need the pipe to be primed for finishing coat. The coating type as required by the purchaser might depend on a number of criteria including temperature resistance, appearance, gloss retention, resistance to a given environment and sunlight and coat finish computability, etc.
Though carbon steel and ductile iron can be both ferrous metals, there are innate differences between the two which means that the same surface preparation or coating application cannot be used. If you attempt to apply specifications of steel surface preparation to Ductile Iron, it could lead to damaged pipe surfaces with subsequent lowered effectiveness of coating and longevity.
Usually coating manufacturers need some kind of surface preparation pre-application as warranty condition.
Since what they recommend for surface preparation is dependent on the paint type, and the final service environment, the technical data sheet of the coating manufacturer should be checked every time a special coating is made use of. It should be noted that recommendations provided on technical data sheets of coating manufacturer may not hold good for ductile iron pipe. Therefore, it is important to consult the pipe manufacturer as regard to the coating type, application method and surface preparation type that go into it.