Finite Element Analysis Of Welding Residual Stress For HP40Nb Ethylene Pyrolyzing Tubes

Ethylene cracking furnace is core equipment of ethylene cracking device. Furnace tube as the key component of ethylene cracking furnace is crucial. Because of its excellent properties of high temperature resistance,anti-carburizing, oxidation resistance and resistance to fatigue, HP40 Nb alloy is extensively used in the manufacture ofethylene cracking furnace tube. However, long term exposure to the environment of pyrolysis gas, ethylene cracking furnace tube bear carburizing, carburizing cracking, bending, bulging, creep cracking, oxidation, thermal fatigue cracking failures. And, as the weakest link of furnace tube, cracking tube welded joints cracking in the operation of cracking furnace, often causing large economic losses. Welding residual stress is the main reason for cracking furnace tube failure. So it is significance to study tube residual stress distribution for failture analysis and service period prediction of furnace tube.In this paper, to study the welding progress of φ63mm × 6.4mm cracking tube, welding temperature field is simulated by using finite element analysis software ABAQUS and writing FEA procedures based on "Element Birth and Death" technology. Stress-strain field is simulated by geting into result file obtained from welding temperature field as a predefined field. Physical and mechanical properties of materials change with temperature. The magnitude and distribution of welding temperature field and residual stress field are predicted. The results showed that: The axial stress and hoop stress around the circumferential direction almost has a homogeneous distribution except the start of welding and its vicinity; the hoop residual stress distribution on the inside and outside surfaces have the similar distribution; the axial residual stress distribution on the inside and outside surfaces have opposite distribution.Welding repair furnace tube cracking failure and prolong its service cycle. In this paper, the repair welding residual stress distribution of weld seam zone and heat affected zone are predicted. The result shows that residual stress caused by repair welding increases than before, and hoop stress and axial stress do not increase uniformly. Secondly, the influence of different repair length,repair width and repair depth on the residual stress distribution are studied in this paper. The results show that: the shorter the length of repair, the maximum residual stress values higher, with the increasing of welding length, stress amplitude decreases. The narrower the width of repair, the residual stress is higher, with the increase of the repair width, the stress reduces, and the influence on the distribution of internal surface residual stress increases. Different repair depth has little effect on the external surface residual stress distribution, while as the repair depth increase, the welding residual stress of inner surface increase.