What is the difference between the Hydo Case and the Sus Case if the fluid density is the same in both? I understand the Hydro Case looks at the yeild strength, but if you allow the yeild (Sy) to equal the cold allowable (Sc) the output shows different stress values. Anyone?

By default the load case for HYD uses "PH" instead of "P1" (or P2, etc).

In addition, a load case designated as "HYD" has spring hangers locked (a rigid stiffness is used). This will change the load distribution throughout the system, resulting in different stresses.

Also, pay attention to the Configuration Directive to turn on/off the consideration of "insulation weight" in the hydrotest case.