Is Stainless Steel Really Worth the Extra Cost Over Carbon Steel?

A lot depends on just what you are transporting in the pipes, and what your cleaning protocols are. Paper mills are great proving grounds for piping material experiments. Cast iron, carbon steel, black iron, 304L, 316L, titanium, thin wall, tubing, Schedule 40 and 80, all coexist in a pulp mill. Plus many other exotic metals used in niche applications I have little personal knowledge of. Applications such as compressed air systems that exist with steel or iron that should never have been constructed with those materials if the eventual full cost of operation was ever considered.
Scale, corrosion, carbon leaching into the product, pipe wall & fitting erosion are all long term considerations that are often balanced against the design life of the project, which can easily be under or over estimated. Projects with a 5 year economic life running for 25-30 years, and 50 year infrastructure projects that the business couldn’t support for 3 years.

The engineering staff that can pick through those economic guard rails is truly a treasure.

My personal experience consists only of accidentally leaving gardening tools outside in the rain. A little moisture turns carbon steel to rust.

My gut feeling is that sooner or later, the higher cost of stainless steel will be exceeded by the cost of replacing corroded carbon steel pipes.

Here is some more information:

https://www.piyush-steel.com/blog/carbon-steel-vs-stainless-steel-pipe-what-to-choose/