Abstract: Cracks occur frequently around the two pairs of welding neck flange at the short inlet cone section of the FCC flue gas turbine in certain petrochemical company in recent years.So there＇re hidden dangers of weld fracture.There＇s serious flange deformation inside the short section.The flange clearance is decreased from 8mm to 1.5mm and it＇s impossible to carry out the start-up and thermal fastening.There is risk of flue gas leakage around the flange.These may affect the safe and stable operation of the flue gas turbine.This paper analyzes the weld cracking and flange deformation from such aspects as pipeline layout,metal material,welding process and operating conditions.It is discovered that high temperature creep,intergranular cracking,deteriorating weld toughness and ductility and too large preload occur easily around the weld junction.These are the causesfor the failure.The paper then puts forward corresponding suggestions for improvement in the light of the cause analysis.