The paper summarizes an effort in improving structural integrity of the railroad tank cars. Damage tolerance analysis is performed on a DOT 111A100W1 general purpose tank car. Stress distributions and potential fatigue critical locations are determined using global and local finite element models. Welding residual stresses in an unconstrained TC128-B butt weld are obtained using neutron diffraction technique. Fatigue crack growth analysis under a tank car service load spectrum is carried out and inspection intervals are determined for various postulated initial flaws. Two materials are considered, a generic steel (presumably representing A516-70), and A515 for older tank cars.