For combined mechanical and thermal loads, the analytical method to calculate the fracture mechanics parameter J for cracked pipes in the annex A16 of the RCC-MR 2002 code presents two options: the first one is the RSE-M method and the second option is based on a strong interaction where the mechanical and thermal loads are affected. It is then shown for this second option that the J parameter is strongly over-estimated for a significant mechanical load level.
A new equation is proposed based on a summation of the mechanical Jme and of the thermal Jth corrected to take into account the interaction. This interaction depends on the relative significance of the mechanical loads compared to the thermal loads, and takes into account the nature of the mechanical loads: It is then shown that the amplification due to the mechanical loads has to be limited, according to the nature of the mechanical loads (axial load, bending moment, pressure,…) and the type of defect (circumferential or longitudinal, semi-elliptical shape,…) under consideration. A validation is realized using a F.E. calculation data: several defects are considered, with different mechanical loads and thermal load (linear gradient of temperature, thermal shock,…).