Old posting but couple comments.

All three proposals have one common problem. Not enough space for the ancillaries. In some cases can be solved by high expense. 500 C is quite high temperature and normally floating ring designs are required.

As a general comment. Most pipe designers give insufficient space for the expansion joints. Add to that unnecessarily low spring rates, wrong movements... Pipe designers should realize that bellows element goes often well past the yield point and it has impact on force directions.

One of the biggest mistakes with the movement specification is to give equal movement in two directions. Lets assume the 500 C case. CAESAR II gives compression 50 mm and the stress engineer specifies 50/-50 mm movement for the expansion joint. Big mistake. 50 mm compression is a result of 480 C temperature difference. To have 50 mm expansion the pipe temperature should go to about -460 C. Expansion joint can be designed for these movements but it is less safe compared to the one where movements are specified correctly.

Just to remind again: Expansion joint with tie rods cannot have axial movement.

I have designed expansion joints well over 20 years, try to train engineers and have special design software and I battle with these issues every day - world wide.