I've pretty well determined that if you post an opinion (or known fact) on this forum, there will be at least 1 person that disputes it with their reasoning. When you get 5 or 6 or 7 people who who dispute it, then its worth listening to. Let's all remember that we're building BOATS, not nuclear power facilities. We're installing parts and pieces on a vessel that will be exposed to some of nature's most harsh environmental conditions; an environment which no one understands completely. "So I put a piece of metal on my boat and it corroded"..."The plastic fittings I put on got too much sun damage and eventually cracked" Yeah, duh! Point out any one production or custom boat that's more than 10 or 15 years old that has been used in saltwater, and if its all original (ie. nothing repaired or replaced), then I'll shutup.
One last plug for SST fittings below the waterline
In the water/wastewater treatment facilities I build, we have 2 standards for metals that will be in submersion: aluminum and SST. You think that saltwater is bad, take a look at some of the fluids that come through these facilities. We build and design systems that forcefully incorporates excessive amounts of chlorine (gas and liquid), lime, carbon, ammonia, fluoride, sulfuric acid, and many other chemicals that you don't even want to look at without protective safety gear. Of course, different metals have their correct applications, and we avoid using them in a quick-sure-fail environment. The desalinization equipment we install is primarily constructed of SST. That is equipment that processes saltwater...and the components are in constant submersion. Other than the appearance, we don't find too many differences in 304 vs. 316. In general, we use SST for the fabrication of a variety of submersed applications, such as pipe fittings, brackets, trays, bolts, etc. Since much of our work is rehab and additions, we often remove old SST components so the system can be up-sized, and almost without fail, those pieces are in excellent shape.
We don't use SST fittings when installing chlorinators. For this, its almost always SCH80 PVC or bronze. The purpose of a chlorinator is force extremely high concentrations of chlorine into the system, often times 25% to 50% by volume. No matter what type of material you use for this application, the components are subject to frequent maintenance and replacement.
Saltwater is less than 2% chlorides. Chlorides have been identified to be corrosive to SST at water temps higher than 50C, or about 120F. Still, the exposure needs to be continuous and it takes a long time to matter. Since the water I fish in only ever gets to the mid 80's (in the heart of scallop season), I won't be too concerned. SST thru-hulls for me!
Hopefully, this is my last post on this thread