Exhaust system

[Steve Michel]

Has anyone used all black iron pipe for the exhaust system on a 25XP?

[Tom Glennon]

Steve,
Use brass! I replaced the exhaust manifold and pipes on my cat 30, and got some really valuable advice from that associations former "guru" Dick Dickens.  He was vehimently opposed to Iron pipe, as it will rust out in the marine environment.

Home Depot, or Lowes should have all the nipples and elbows you may need.

[cholder]

I replaced the factory schedule 10 stainless steel pipe with screw coupled schedule 40 stainless steel when the water injection point failed due to corrosion of the weld damaged material.  The replacement is readily done by any good plumber except for welding in the injection pipe into a short straight pipe.  That I had done by a local welding shop for a small charge.  Actually, I had two done so I've one as a spare.

My repair was done several years ago and has worked well since with lots of hours on the engine.  

If I had to do the fix again, I'd use schedule 80 pipe since the heavier wall size allows more material left over after cutting the screw threads.  

The reasons these pipes fail are that hot salt water is extremely corrosive, stainless steel is only corrosion resistent in an oxygen rich atmosphere when the oxide coat can form and the heat of welding damages the material.  

By the way, its very important to pick the grade of stainless steel with care.  Grade 316 is commonly used for marine work but isn't the best for all conditions.