In the paper the interaction of several loads like pressure, axial force, bending moment and torsional moment are analyzed, taking into account the deterioration due to cracks and the influence of residual stresses. A nonlinear, power law, of structure material is considered. General relationships for total participation of specific energies introduced in the structure by the loads, as well as for the critical participation have been proposed. On these bases: - a new strength calculation methods was developed; � strength of tubular cracked structures and of cracked tubular junction subjected to combined loading and strength were analyzed. Relationships for critical state have been proposed, based on dimensionless variables. These theoretical results fit with experimental date reported in literature. On the other side stress concentration coefficients were defined. Our one experiments onto a model of a pipe with two opposite nozzles have been achieved. Near one of the nozzles is a crack on the run pipe. Trough the experiments the state of stress have been obtained near the tubular junction, near the tip of the crack and far from the stress concentration points. On this basis the stress concentration coefficients were calculated.

The paper presents the particularities of accomplishing risk analyses with the purpose of establishing the safety distances � SD, between the pipes belonging to the natural gas national transmission system � NTS and facilities (people, animals, buildings, crops, orchards, forests etc.) placed in the their vicinity. In order to check if the distances between the National Gas Transportation Pipeline- NGTP and neighboring facilities are SD, the authors developed a procedure and a software for the risk assessment, which make use of a set of formulas validated by experimental results presented in the paper and information from the data base (built by the authors and presented briefly in our work) regarding the supervision of the technical state and recording of the accidents that took place in the last 19 years on the NGTP from NTS. Also, in the paper, one describes the way the technical solutions verified using the procedure and the software built by the authors can be selected and ranked (in view of implementation) by applying the ALARP principle and the cost � benefit analysis.