Raw water metal corrosion

[Steve DAntonio]

I came across this just today, while on an inspection of a 6 year old high end production motor yacht; it's something I see on a near-monthly basis, corroded raw water metallic plumbing, more often than not part of the air conditioning system. Because they run so often, failures are accelerated in HVAC raw water systems above all others.

Check your HVAC raw water plumbing, particularly in areas where not readily visible, this one was buried under an access deck plate in a lazarette, definitely out of casual sight.

 

[diver dave]

Thats very notable. btw, i have access to a XRF at work. This gives a complete elemental read of the alloy.

 

[DavidM]

Was that elbow made of real marine bronze?


David

 

[Comodave]

Nice hose clamp also, not a S/S screw.

 

[Xsbank]

“Stainless” corrodes, but that is an automotive clamp.

 

[O C Diver]

Yes, not all bronze is equal. Redid some manifold plumbing last month while in the boatyard. While most bronze fittings seem to come from China, the quality varies widely with actually alloys being all over the place. Really pays to buy name brand on that stuff. Interestingly I found only one manufacturer that offers true bronze pipe nipples (Groco). If you read the fine print, all the others I looked at were brass.

Ted

 

[Steve DAntonio]

Was that elbow made of real marine bronze?


David

If only there was a way to make that determination in the field. Anecdotally, I'd say no.

BTW, the hose clamp is stainless steel, including the screw, just not 316, it's automotive, 304. That staining isn't unusual in a damp, salty environment, eventually it can lead to a band failure.

 

[Steve DAntonio]

Yes, not all bronze is equal. Redid some manifold plumbing last month while in the boatyard. While most bronze fittings seem to come from China, the quality varies widely with actually alloys being all over the place. Really pays to buy name brand on that stuff. Interestingly I found only one manufacturer that offers true bronze pipe nipples (Groco). If you read the fine print, all the others I looked at were brass.

Ted

Agreed on buying from trusted sources, however, I've walked the aisles at many chandleries and have seen bins labeled "bronze" when I know the parts are brass. Any alloy with more than 1-2% zinc content technically isn't bronze. Any copper alloy with more than 15% zinc content cannot be used for raw water. Pipe nipples are often leaded red brass, they should look reddish, if they look yellow they almost certainly contain more than 15% Zn. I've seen these fail on many occasions.

More on brass vs. bronze here https://stevedmarineconsulting.com/know-your-underwater-alloys/

 

[Steve DAntonio]

Thats very notable. btw, i have access to a XRF at work. This gives a complete elemental read of the alloy.

Could I send you one of these the next time I encounter it?

 

[rslifkin]

BTW, the hose clamp is stainless steel, including the screw, just not 316, it's automotive, 304. That staining isn't unusual in a damp, salty environment, eventually it can lead to a band failure.

304 stainless clamps wouldn't worry me provided they're in an inspectable location, as in a clamp, you'll see signs of degradation well before failure.

Stuff like that elbow fitting is quite concerning, however. It probably looked pretty much fine up until it failed.