Analysis of Causes for Longitudinal Cracking of Large-sized Heavy-wall Hydraulic Prop Pipe

According to the problem of the post-hot-rolling longitudinal over-length cracking of the large-sized heavy-wall S890 steel hydraulic prop pipe，relevant observation and inspections are conducted，and then the facts as follows are identified. The fracture is a transgranular cleavage brittle fracture，the microstructure is bainite，the strength，yield ratio and residual stress of the material are high，whereas its toughness is poor. The final analysis results show that because the bending of the tube is so serious，when being straightened，the violent swing of the bite end of the pipe leads to obvious plastic deformation，and occurrence of cracking，and furthermore due to the action of high residual stress and the low toughness of the material，the crack continues to expand，eventually resulting in the full-length crack failure of the tube. Accordingly，specific measures are taken to get the pipe body cracking stopped，including reducing cooling rate to get partial ferrite structure，and getting the pipe straightened after reducing its bending degree and residual stress.