Study On Safety Assessment Of A Liquid Natural Gas Spherical Tank

Finite element method was used to analyze the stress intensity factors for a spherical tank used in liquid natural gas storage,and procedures based on MATLAB software were prepared to conduct safety assessment for the tank,according to the national standard GB/T 19624-2004.This subject is of practice value for the safety of liquid natural gas tanks.A spherical tank was selected,the diameter is 12 m,the thickness is 40 mm,while the design pressure is 1.6MPa.The tank was manufactured with the Q345 R steel.3D models were established by using software ANSYS,stress distributions were analyzed and the stress intensity factors for the tank with certain sizes of crack were calculated.By comparing the results with which calculated according to the GB/T19624-2004,the stress intensity factors are different less than 10% with each other.It indicates that the results are reasonable.Routine assessment method proposed by the GB/T19624-2004 was used in the safety assessment for the tank,while both of the calculating results of stress intensity factors from GB/T19624-2004 and finite element method were used in the assessments.Defects sized from 4mm×4mm to 32mm×320mm were concerned in the assessments.The assessment results show than when the size of defect grows to 32mm×128mm,the tank with semi-elliptical surface crack is still safety,and this defect size for embedded crack can even reach to 32mm×320mm.Conclusions can be made that while the size of the defect is of the same,tanks with surface defect will be of more risk than with embedded defect.That is the surface defects are more dangerous than embedded defect.