Shaft Coating in Marine Enviroment (inside&out)

[boo1]

We are trying to select a coating system for marine shafting. The shaft material is 4340 carbon steel. Both the interior and exterior must be coated. The shafts vary in dia. from 6" to 14" and lenght 5' to 14'.

 

[AJohnson]

Hey Boo1,

Take a look at electroslag surfacing. It's expensive, but works quite well. Andy

 

[WKTaylor]

Are You going for strength or toughness with 4340 stl??? High strenth steel in a marine environment is a REAL problem child no matter what coating is used [SCC and pitting]. If at lower strength levels [for tougness], then may be better.

Is 4340 absolutely necessary... VS, say a high-grade marine environment qualified SSTL?

Is the shaft exposed-to, or worse, submerged in sea-water or bilge-water?

Caution: shafts with coatings of any substantial thickness, [especially applied to interior surfaces], MAY be a nightmare to balance.

Regards, Wil Taylor

 

[boo1]

We are overhauling a existing hovercraft. So they are exposed to constant salt spray. The balancing issue is a consideration for the final material selections.

The coating systems we are considering are :
1. Nylon 11 powder coating
2. Inorganic zinc rich coatings prime coating for interior, poly system exterior
3. Amine 2500
4. High Solids

 

[rustbuster1]

Organic coatings such as immersion-grade amine adduct-cured epoxy or 100% solid epoxy novolac can provide excellent corrosion protection, but all organic coatings will have to be adequately maintained.

On the metal side, why not consider electroless Ni - many plating companies have baths that can accommodate the sizes you list, the coating is uniform thickness and hydrogen cracking should not be a problem if the plater is advised of the material; or thermal spray coating - D-gun or HVOF coating of 316SS will be very durable. Other metals including bronzes and copper-nickel alloys are also available as T/S coatings. This can be done in a shop or in the field, although special tools are needed to T/S coat in side small bores.

Happy hovering!

 

[Knorris]

If you need information about corrosion coatings for offshore. Contact National Thermospray in houston. They replace all the Cr-coatings with hvof process coatings and they repair the ceramic coatings on the tensioner rod offshore and even do the machining offshore. Visit

http://www.hvof.com

 

[BarryMartin]

You can also look a electroplated coatings of various metals depending on your conditions. Take a look at

http://www.brushplating.com.

 

[111121]

From: T.Anderson
For external application, you could consider laser cladding.
Materials including stainless steels (316)and nickel alloys (alloy 625) can be metallurgically bonded to alloy steels including 4340 with minimal dilution (1% to 3%), very small heat affected zone and virtually no distortion. The coating is fully dense and will pass Aust. Std. pressure vessel weld bend codes, so adhesion is not a problem. Coatings can be strategically placed and deposition thickness can be varied to suit your application, starting from 0.25mm or thicker. Shafts up to 10 tonne weight and 7 metres long have been clad using lasers in Australia.