Dear Gents,
Kindly, I look for some help in order to understand the meaning and logic of Appendix 2-9: Split Loose Flanges



Any help would be greatly appreciated.

It is as you describe:
If you have a ring (usually) flange which is actually two pieces then for flange stress analysis you have to multiply Mo with 2. It is considered that flange section is made weaker up to two times, if you split it in the half. For ring type flanges, thickness is directly proportional to the Mo so you will need double thickness for each ring. Take a ring, find Mo, double Mo, find the thickness and split the ring to the half.
For double ring you have one ring above to another ring.You do not want the two splits to fall one to another, so the splits shall be located at 90 degrees each other.From the other hand two rings make the construction stronger. Take 2 rings, find Mo for one ring, find 0.75Mo, find the thickness of each ring and split the ring to the half. Put one up to another as above indicated.

Dear pastyl,

Thank you very much for your clear and detailed explanation.