Black pipe, brass or copper?

[Marty Levenson]

Hello - haven't posted for quite a while, but still learning a lot by lurking!

A dozen years ago I replaced my exhaust system, using black steel. It is rusting out now (salt water), and I wonder about other replacement options. I know not to use galvanized, so am considering brass or copper. Are those insanely expensive? Any other downsides? Does it have to be 1 1/4"....could I save money by using a smaller diameter, or would that risk back pressure? The muffler is plastic.

I'll probably end up with the black metal again as it will likely outlast my sailing years. If so, what is the best thread sealant to use?

Many thanks in advance.

[Antibes]

Skipping to your last question, no thread sealant is needed.

[ndutton]

Thread sealant might not be needed but I prefer it anyway. Pictured is the sealant I used, available from McMaster-Carr.

As for hot section pipe material, the USCG is specific about what is allowable due to the high temperatures in use. In the 'ABYC and USCG Standards' forum category open 'ABYC Exhaust Standards'. In post #1 click on the link then scroll down to the table on page 6 of the pdf. Allowable materials for gasoline engine hot sections are at the top of the table under 'Dry Exhaust.' If it's listed, you can use it. If not listed, then no. Note that Wet Exhaust in the table applies to downstream of the water injection point.

Be sure to read the footnotes especially footnote 12 - Schedule 80 pipe if it's threaded.

[Marty Levenson]

Great

Neil: Greatly appreciate the link to that table. I also prefer to use the thread sealant as well.

[Tim]

Mine is a combination of bronze fittings, brass pipe, steel pipe and steel fittings. The joints are sealed with a high temp sealant from Permatex. The brass and bronze I got from WM, the black steel pipes from Home Depot. The tee, elbows and pipes are 1.25 inches. The rubber exhaust hose is connected with a bronze fitting that is 1.5 inch hose barb x 1.25 npt threads. The water inlet hose is connected with a bronze 1.25 x .5 inch reducing bushing and a bronze .5 inch npt x .5 inch hose barb.

[Bob Adams]

Hello - haven't posted for quite a while, but still learning a lot by lurking!

A dozen years ago I replaced my exhaust system, using black steel. It is rusting out now (salt water), and I wonder about other replacement options. I know not to use galvanized, so am considering brass or copper. Are those insanely expensive? Any other downsides? Does it have to be 1 1/4"....could I save money by using a smaller diameter, or would that risk back pressure? The muffler is plastic.

I'll probably end up with the black metal again as it will likely outlast my sailing years. If so, what is the best thread sealant to use?

Many thanks in advance.

You never want to use brass fittings in a salt water system. The salt water will dissolve the zinc in the brass leaving behind a weak honeycomb of pure copper. You will not see this from the outside of the fitting (all will look fine) but the inside is being eaten away until the fitting snaps off. Bronze is the better choice.

[ndutton]

I think Bob is talking about brass for general use aboard as opposed to the specific topic of this thread, exhaust hot sections because the hot section has no water, salt or otherwise and neither brass nor bronze are approved for exhaust hot section use according to the standard referenced in post #3.

[Dave Neptune]

The salts will get there when the exhaust is cooling down. My big concern is electrolysis due to all the dissimilar metals, kind of a battery of sorts.

Dave Neptune