Factor F in nozzle reinforcement calculation

[Biss73]

Hi,
Does anybody know the reason why a Factor F less than one cannot be used on openings that are not integrally reinforced? Is it to prevent creative repads that are not all-around or uneven?
Regards,
Serge

 

[DriveMeNuts]

My assumption is that placing a re-pad around a nozzle is a very approximate/clumsy way of reinforcing the nozzle opening.

The re-pad does reduce stresses however it also distorts the stresses local to the nozzle so that the factor F can no longer accurately estimates the axial and hoop local membrane stresses.