For Leak-Before-Break (LBB) assessment in nuclear piping system, it is required to accurately predict Elastic-Plastic Fracture Mechanics (EPFM) parameters. One of well-known method to predict EPFM parameter is GE/EPRI method using plastic influence function for fully plastic terms of EPFM parameter. However, the current plastic influence functions of GE/EPRI method are proposed only for limited pipe/crack geometries and strain hardening exponent. Thus, in the present study, the extension of plastic influence functions is pursued to thin-walled pipe with high strain hardening exponents for possible application to high toughness pipe using 3-D FE analyses.