STUDY ON LIMIT LOAD OF DOUBLE PIPE BEND COMBINED FITTINGS

摘要

Pipe bends and double pipe bends combined fittings including Back-to-back pipe combination (BB) and Face-to-face pipe combination(FF) play an important role in pressure pipeline system. Their carrying capacity will affect the integrity and safe operation of whole piping system directly. In this paper plastic limit loads for double pipe bends combined fittings (BB and FF) are analyzed by finite element method with elastic-perfect-plastic constitutive relation and the corresponding limit load equations are proposed which extends the range of pipe geometry λ. Results show that the limit load equations available in references fail to be used for double pipe bends combined fittings and are unsafe, especially for FF combination. The limit loads increase with pipe thickness and bend radius in the meantime. The value of r/t is the main factor affecting limit load solutions. Detailed analysis also demonstrates that with applied load increasing, initial yielding appears in the FF combination firstly and finally overall yielding will happen. While the stress situation of BB combination is close to that of a single pipe bend. Eventually these proposed finite element based results are validated with experiment data and shows that finite element based solutions are believable.