I am wondering how maximum stiffness of a flange connection on a short piece of piping at skid edge is calculated by Caesar II or by hand?
One example I saw from one pipe stress study report is:
a 8" 150 flange connection on a short piece of spool at skid edge. This short piece of spool serves as a connection pipe between a skid edge tie in point and a heat exchanger. stiffness is provided to the client because the tie point can not be treated as anchor point for Caesar II pipe stress study.
The stiffness results are:
The maximum stiffness of translation X=8000 lb/in
The maximum stiffness of translation Y=8000 lb/in
The maximum stiffness of translation Z=8000 lb/in



Thanks,
Glenn

Those look like arbitrary numbers since all are the same and there's no rotation terms.
I've seen some skid layouts where the connecting flange is at the skid boundary but is the flange, itself, is not anchored. Instead, the anchor is located back, away from the flange. This arrangement gives a good boundary and (some) flexibility at the flange.

The Codes say the system shall be analyzed "as a whole". Your approach here is common but illustrates why systems should be analyzed as a whole.

The system shall be analyzed "as a whole" is the best solution for this skid edge loading issue.
I will argue with my client by using ASME B31.3 319.4.3 whenever tie in point stiffness on short piece piping spool is asked.

319.4.3 Basic Assumptions and Requirements.
Standard assumptions specified in para. 319.3 shall be followed in all cases. In calculating the flexibility of a piping system between anchor points, the system shall be treated as a whole.