Application Research On Structure And Strength Of Fillet-Groove Weld For Large Tanks

The fillet-groove weld of large tanks is located at the connection between the bottom shell and bottom plate?or the bottom edge plate?.The local stress of fillet-groove weld is very high due to the structural transition and the local stress fluctuates due to large margin during the operation of the tank.The bottom plate is in long-term contact with the medium,and which leads to the corrosion easily,especially when the medium with stress corrosion property.As the fillet-groove weld of the inner side of the tank wall is within the tensile stress zone,the possibility of stress corrosion damage is higher.The fillet-groove weld and corrosion medium could be insolated by reinforce-and-protect structure and the local stress could be declined substantially.The optimal structure type of reinforce-and-protect structure was selected by the simulation of finite element analysis method for the combination of the tank shell and reinforce-and-protect structure.The main contents of the paper are as follows:?1?Four kind of structure type,including concave arc type,protruding arc type,bending type and piping type are analyzed.A whole protection system includes reinforce-and-protect structure,shell,bottom plate,detector tube and then leakage indicator could be established.?2?The local stress of fillet-groove weld is very high due to the structural mutation.The local stress could be reduced substantially by reinforce-and-protect structure which can also insulate the fillet-groove weld and corrosion medium,and the possibility of fatigue failure reduced sharply.The main factor of corrosion or stress corrosion cracking is eliminated.?3?The local stress of fillet-groove weld is declined substantially by four kind of reinforce-and-protect structure through simulation with ANSYS.The stress condition of six positions in the fillet-groove weld was analyzed by dimensionless parameter?/and R/T₁,and the results show that the optimal structure is concave arc type.The stress of internal and external surfaces of fillet-groove weld could be reduced by 55%and 40%with the optimal concave arc type when R=7¹1T₁ and?=0.75⁰.85T₁.?4?The fillet-groove weld has a larger safety margin of stress by reinforce-and-protect structure during the effect of destructive load in short time?e.g.earthquake?.Under the action of alternating loads in daily operation,the alternating stress can be reduced lower than the critical value of fatigue failure,which avoids the generation and expansion of cracks.