Best ball valves for mild steel through hulls?

[AndyJ76]

My steel hulled ketch has through hulls consisting of steel threaded pipe welded to the hull, with ball valves attached to the top.
When I bought her, several of the handles had broken off (but the old owner graciously supplied a generous selection of mole grips)

I'll be getting her out of the water and I'd like to replace them with something better. I was originally thinking of nylon valves, although I'm concerned about their fire-resistance (sure, melting the ball valves would probably quench a fire pretty quickly, but I'd still have to abandon ship)

What would be the right material for attaching to mild steel to minimise galvanic corrosion? I was thinking DZR, with lithium grease applied to the thread.

Any other suggestions?

 

[PCUK]

Nylon is acceptable in steel hulls but not in the engine room. My 30 year old steel hull still has the original standard bronze skin fittings and valves with no signs of corrosion. The steel protects the bronze but the vast difference in area between the hull and the skin fittings negates any possibility of serious corrosion to the steel.

 

[AndyJ76]

How would that work in my situation? The "through hulls" are about a foot of steel pipe, welded to the hull. I imagine that they have good electrical continuity to the rest of the hull, but how would this affect the galvanic circuit at the top of the pipe?
At the top, the pipe will contain seawater across the junction of the ball valve and the pipe. Is any galvanic reaction greatly reduced due to the reduction in volume of the electrolyte?

 

[ianabc]

316 stainless ball valve

is standard on origami steel boats here

 

[PCUK]

Personally I'd cut off the extension tubes and put the fittings straight into the hull. You never know what is happening inside the tubes until they fall off.

 

[AndyJ76]

That's interesting, I hadn't thought of doing that. I had thought of extending the tubes until they were just above the waterline. I have very deep bilges, and I don't think I'd fancy having to reach right down to turn them on/off. (equally, I don't want to sink because my extension tubes have broken off)

What sort of things might cause the pipes to fail?

 

[Tranona]

What you have is pretty standard practice and if you have had no galvanic problems so far, replace with DZR. 316 is an alternative but you run the risk of crevice corrosion in the threads. No reason not to use glass filled plastic ones, but the US ones are nearly twice the price of DZR. Tru design from New Zealand are cheaper and widely used down under. The concern about using them in the engine space is probably overstated, stemming from MCA coding recommendations. They are however used extensively for that purpose in both N America and down under. The distributor here is Lee Sanitation.

 

[AndyJ76]

How do I know if they've suffered galvanic corrosion? My anodes are pretty obvious, but that's what they're supposed to do. What does unintentional galvanic corrosion look like?

 

[vyv_cox]

I have replied to your PM. If there is galvanic corrosion you will see pitting at the ends of the tubes adjacent to the valves.