Assesment of the temperature loading influence on crack resistance of a tank with a semi-eliptical crack

Abstract

Reservoir parks are the main place of storage of petroleum products. There has been a tendency transition to the use of larger tanks in recent years, which is economically justified. However, it is leads to fire risk increase to accumulate large quantities of petroleum products. Tank fire is one of the most dangerous emergency event, which can lead not only to significant material damage but also to ecological human losses in case of spreading of fire to other tanks. To ensure safety and test the bearing capacity in these conditions determination of the stress-strain state in such tanks must be performed taking into account the temperature load. If there is an initial crack in the tank wall the assessment of crack resistance should be performed. In a previous work the authors determined the stress intensity factor (SIF) distribution along the semi-elliptical crack front in the RVS-5000 tank under hydrostatic pressure. The estimation of a stress-strain state of a steel vertical tank with an initial semi-elliptical crack under the thermal loading is performed in this article. It is suppoused that the part of wall of the tank, located closest to the fire epicenter, is heated unevenly in height: from 300 degrees at the top to 200 degrees at the bottom. On the other part of the tank the temperature reaches 70 degrees. The temperature within wall thickness is considered constant. Given the asymmetric nature of the temperature distribution, a discrete model was developed for the entire tank. After determining the stress-strained state in the whole tank under hydrostatic pressure and temperature load, a fragment with a semi-elliptical crack was calculated separately. The stresses determined from the calculation of the whole tank are used like an external load, applied on fragment boundaries. The difference of results of direct and energetic method of SIF calculation are in the range of 5%. Taking into account the temperature loading leads to an increase in the SIF values by about 20 % in comparison to the results of the calculation only under hydrostatic pressure.