Blast case for piping system

Normally, Blast case(Drag force) is converted into wind pressure while modelling in Caesar II with shape factor. when a piping system is going through a different blast pressure area, we can not input different wind pressure in CII. So I have changed shape factor which is calculated based on blast pressure(Shape factor - arrived from drag force calculation formula, F=DAF*Cd*P*OD*100 N/m, Cd-Shape factor).

Do any one come across to this and comments if any.

Kotees.