Welding Simulation Of Fully-Welded Ball Valves And Strength Evaluation

Fully-welded ball valve has been applied in large oil and gas pipelines, and its quality is directly related to the safety of the transportation of national energy. Considering the limitations of application, post-welded heat treatment can not be applied, thus the welds must have high strength. At the mean time, the severe application conditions of the long distance pipeline call for strict technological requirements of the resistance to load capacity. It is important to properly control the distributions of welding residual stress and make out the ultimate load of pipelines for optimizing the processing parameters and saving in material.Based the plastic-elastic method, the 3D FEM analysis model of fully-welded ball valve was built in ABAQUS software, and according to the measured residual stress, residual stress was simulated of fully-welded ball valves with multi-layer welding using“element birth and death”technique. After that, by applying inner pressure and bending load, the stress distribution of the ball valve after the failure of pipeline was got. The results showed that the failure happened at the location where the valve and pipeline joined. According to the requirements of ASMEⅧ-2, the stresses were classified and evaluated by drawing equivalent stress lines at the key locations of the valve, which indicated that the fully-welded ball valve was safe when the pipeline failed.To further study the load capacity of the valve, inner pressure was changed and the ultimate load was got with applied wall thickness. In the further checking, it was found that the practical wall thickness was far greater than designed wall thickness. By analysing models with different wall thickness under applied inner pressure, the minimum wall thickness was got.