Effect of Loading Modes on the Limit Behaviors for Pipe Bends Under Combined Loads

Pipe bends are widely used in industrial piping and pipelines. Because of their flexibility properties, they can accommodate thermal expansions and absorb other externally induced loads. Under severe loading conditions, bends exhibit significant cross-section ovalization, associated with strains well beyond the elastic limit and fail because of excessive cross-section ovalization. The past references provide several studies on the ovalization induced loading capacity change. The main aim of the study is to establish the effects of load history on the calculated failure load, when a bend is subjected to a combination loading of in-plane bending, torsion and internal pressure. The results of the investigation show that geometric nonlinearity is a significant consideration when calculating plastic failure loads of pipe bends subject to combined loads. The limit load is path independent of the loading sequence in the cases of bending and torsion combinations. In the cases of pressure and moment combinations the proportional and pressure-moment load cases exhibit significant geometric strengthening, whereas the moment-pressure load case exhibits a little. The results according to the ASME Boiler and Pressure Vessel Code may show overall conservative in all loading conditions.

Deformation Behaviors of Partial Diameter-Enlargement Part Worked under Combination Loading of Torsion and Pressure

We have proposed a new cold processing method to form a partial diameter-enlargement part in a hollow shaft. Using the processing method, the diameter-enlargement part with a large deformation is formed easily by applying compressive stress at yield stress level and cyclic torsional stress on two ends of specimen. In the present paper, processing experiments were conducted using the processing machine developed originally based on the processing principle, and deformation behaviors on the diameter-enlargement part were measured. In addition, the simulation analysis method in the processing was developed by the finite element method (FEM), the behaviors of stress and strain on processed part were analyzed, and deformation mechanism was investigated. It is clarified that the processing conditions affect the deformation behaviors base on the experiments and analysis.

Research the Coiled Tubing Deformation under Internal Pressure and Cyclic Bending

The tendency for coiled tubing grow in diameter and thin in wall under a combination loading of internal pressure and cyclic bending. The deformation mechanisms are described. The results show that the trends in coiled tubing deformation behavior are according with the context of theory: when the internal pressure exists, the tubing grew in the diameter; except for neutral point, the tubing thin in wall and the position in tensile is much thinner than in pressure; by the time of cycle increasing. The tubing grew in diameter and ovality, thin in wall.

Mechanism Study on the Coiled Tubing Deformation under a Combination Loading

The tendency for coiled tubing to grow in diameter and thin in wall under a combination loading of internal pressure and cyclic bending. This can occur in spite of the fact that nominal stresses due to internal pressure loading are well within elastic limits in both hoop and radial directions. The deformation mechanisms are described. Fatigue tests of 10 coiled tubing specimens are finished. The results show that the trends in coiled tubing deformation behavior are according with the context of theory.