Wet exhaust- which metal?

[deblen]

Originally Posted by roverhi

300 series Stainless can work harden and crack if exposed to vibration especially in the corrosive environment of an exhaust. Think I'd stick with galvanized or un galvanized Iron pipe for cost and reliability. It will eventually corrode through but life span in measured in decades in most applications.

Getting Yanmar exhausts apart is a real bitch. Had to call in a mechanic to disassemble mine because it needed a humongous vise strong enough to clamp it in place so he could unscrew the pieces with an equally humongous pipe wrench and heating to a cherry red with an acetylene torch.

Mount the flange in a good vise.Rig a hacksaw so the blade goes thru the nipple.Hacksaw 2 slots about an inch apart & lengthways the nipple til you just about touch the flange threads.Put the nipple in the vise,cold chisel the one inch strip out,& then crush the nipple a bit with vise.
I agree-black iron nipple is the traditional thing to use & replace it every 2 yrs.

[UNCIVILIZED]

For anything steel, stainless & non, it's worth having the parts salt bath nitride. It GREATLY increases corrosion & wear resistance. As in several fold on some parts. Due to the process converting the outer layer of the metal, several molecules thick, into a hyper wear resistant alloy that rates about 80 on the Rockwell scale.
It may work on iron parts also, I'm not sure. One would need to check with a metallurgist.

[Mainstay]

i would get in touch with Deangelo Marine exhaust in Fort Lauderdale and ask them the same question. i know they use Monel for the systems they build.

[mholtzberg]

I know I am not a boat expert but, after studying the assembly diagram I have to ask if any of the bolts have been replaced. Because there are gaskets isolating the bigger major parts the only other way of getting galvanitic corrosion is from charges being transferred through the flange bolts, washers, and nuts. This could cause the action thaat you are seeing on the elbow.