Fasteners SS vs HT Carbon Steel

Not enough information.

What does the pipe carry, etc. etc?

Don't you have a specification?

Have you considered throwing darts at a board with SS ans CS targets instead of numbers? That'll be as good as any thing.

Corrosion is not any more inmost cases a problem since protection caps have been already since a long time developed and are available of the shelf.

You can use SS in stead of CS ONLY if the resistance requirements are equal.

Use whichever is the strongest.

and depends on the flange material too. SS for SS, CS for CS (kinda sorta)

How frequent is the dismantling?

How high is the pressure?

It would be good practice to replace the bolts regularly, if not at every use to reduce risk of shearing due to repeated stretching of the bolts.

Details are important. If corrosion is not a consideration, then high tensile steel will outlast ss. In our lab we have eliminated the use of ss socket head bolts because they wear out too quickly. High tensile steel is only permitted, but, corrosion is not a problem.

I Use Both 316 L Stainless Steel and K500 Monel Coated with (Baked On) Xylan for the ease of removal in jobs where they have to be removed often.

Most of my projects are Offshore submerged in seawater.

Note Rosemount's torque spec for 316 SS fasteners that is lower than the other materials, half that of carbon steel (CS), used to fasten a flanged manifold valve to the process flanges of a DP transmitter.

I'm not a materials guy, but I suspect it's lower tensile strength.

The installers tell me that they ALWAYS use anti-seize compound to allow disassembly.

High pressure piping typically use fasteners per ASTM A193 spec. Within this spec are both SS and carbon steel fasterners but the SS variety has a lower tensile strength compared to the carbon steel. Therefore, as others have pointed out, more info is required about your application. Have a look at Portland Bolt. They have lots of info on fastener standards. We use this resource quite often.

Your first concern is which codes govern the piping installation. But after that, why would want to replace HT steel with stainless? Stainless galls (making it difficult to remove), it's not as strong as steel and it's more expensive.