случайных воздействий ветровой нагрузки на

OCC = сокращение от "occasional"

Еще есть такие виды нагрузок на трубопровод, как длительная (Sustained = SUS), рабочая (operating = OPE), нагрузка при гидроиспытаниях HYD и т.д.

http://www.whatispiping.com/load-cases
a. Hydrotesting case: Pipelines are normally hydrotested before actual operation to ensure absence of leakage. Water is used as the testing medium. So during this situation pipe will be subjected to water weight and hydrotest pressure.
Accordingly our first load case in Caesar II will be as mentioned below
1. WW+HP HYD
b. Operating case: When operation starts working fluid will flow through the piping at a temperature and pressure. So accordingly our operating load cases will be as mentioned below:

2. W+T1+P1 OPE for operating temperature case
3. W+T2+P1 OPE for maximum system temperature case
4. W+T3+P1 OPE for minimum system temperature case

c. Sustained Case: Sustained loads will exist throughout the plant operation. Weight and pressure are known as sustained loads. So our sustained load case will be as follows:
5. W+P1 SUS
d. Occasional Cases: Piping may be subjected to occassional wind and seismic forces. So to check stresses in those situations we have to build the
following load cases:
6. W+T1+P1+WIN1 OPE Considering wind from +X direction
7. W+T1+P1+WIN2 OPE Considering wind from -X direction
8. W+T1+P1+WIN3 OPE Considering wind from +Z direction
9. W+T1+P1+WIN4 OPE Considering wind from -Z direction
10. W+T1+P1+U1 OPE Considering seismic from +X direction
11. W+T1+P1-U1 OPE Considering seismic from -X direction
12 W+T1+P1+U2 OPE Considering seismic from +Z direction
13 W+T1+P1-U2 OPE Considering seismic from -Z direction

While stress analysis the above load cases form load case 6 to load case 13 is generated only to check loads at node points.
To find occasional stresses we need to add pure occassional cases with sustained load and then compare with code allowable values. Following sets of load cases are built for that purpose.
14. L6-L2 OCC Pure wind from +X direction
15. L7-L2 OCC Pure wind from -X direction
16. L8-L2 OCC Pure wind from +Z direction
17. L9-L2 OCC Pure wind from -Z direction