Steady Numerical Simulation Research On Post Weld Heat Treatment Of Large Spherical Tank By Internal Combustion Method

In recent years with the development of the petrochemical and energy industry, thenumber of large spherical tank is increasing. And large spherical tank present a tendency oflarge-scale, the volume of large spherical tank is increasing from1500m3,2000m3to5000m3,6000m3,8000m3even10000m3. With further increase of volume, the temperatureunevenness of spherical tank shell is more obvious when post weld heat treatment by internalcombustion method as well as the difficulty of heat treatment is becoming bigger. A lot ofspherical tanks the crack phenomenon occur in use process. One of the main reasons is thatthe welding residual stress was not eliminated effective after heat treatment. The overall levelof welding residual stress remains high. The residual stress tests show that it can reach up to70%~90%of the yield strength, indicating the practical results of residual stress eliminatedby heat treatment are unsatisfactory. So there is a big controversy on effect of residual stresseliminated actually by a large tank use internal combustion method. The uniformity of heat isguarantee of heat treatment quality of the tank shell. There is a doubt in the industryuniformity of tank shell can meet the requirements during post weld heat treatment process byinternal combustion method. So it is necessary that doing a research on post weld heattreatment process by internal combustion. Numerical Simulation based on fluent software wascarried out to study a large spherical tank post weld heat treatment by internal combustionmethod.Supported by the Special Fund for Quality Supervision, Inspection and QuarantineResearch in the Public Interest of China “Research on Evaluation technique on effect of largespherical tank post weld heat treatment process”(Grant No.201410028), the large sphericaltank internal combustion post weld heat treatment was studied by numerical simulation. Themain research work and conclusions are summarized as follows:(1)In this paper, the numerical model of spherical tanks internal combustion post weld heat treatment was established. The large spherical tank internal combustion post weld heattreatment was analyzed. A simplified calculation method in the wall temperature of the layerspherical with insulation layer was present. The simplified geometric model was established,physical model was chosen in fluent software and the main calculation methods of theboundary conditions were determined.(2)The validations of numerical model of spherical tanks internal combustion post weldheat treatment. After a10000m3tank internal combustion method post weld heat treatmentprocess is numerical calculated, compute evolution and distribution of the flow field andtemperature field of inner spherical tank and wall temperature curve which shows a10000m3spherical tank internal combustion method post weld heat treatment can achieve temperatureuniformity specifications required by related standard.(3)Based on the numerical model of large spherical tank internal combustion methodpost weld heat treatment, to study the influence of thermal insulation material and thickness,air flow, diversion umbrella shape and installation position of the spherical tank on internalflow field and temperature field and the spherical shell temperature. Air flow of burner has agreat influence on spherical tank wall temperature. With the increase of air flow rate, thespherical tank wall temperature is decreases. But the air flow rate has little impact on thetemperature difference between the top and bottom of the spherical tank wall, temperaturedifference almost does not change. Large spherical tank in the internal combustion methodpost weld heat treatment, the thickness of the insulation layer has an upper limit. When thethickness of the insulation layer exceed the limit, increasing the thickness of the insulationlayer almost impossible to reduce the wall temperature of the maximum temperaturedifference. Diversion umbrellas can reduce the maximal difference of wall temperatures ofspherical tanks and make the wall temperatures more uniform. When the distance betweendiversion umbrella and the lower manhole is1/3spherical tank diameter and the Angle ofdiversion umbrella is100°, the temperature difference of the spherical tank wall temperatureis minimal.