The Features of Corrosion Exhaustion of Tanks Resource and Assessment of Intensity of Stress State Increasing in Welds

Ammosov G.S., Ivanov Dj.S., Ammosov A.P.

 

The paper is devoted to a wear of elements of tanks for storage of oil and oil products during their long-term operation under conditions of sharply continental climate of the North. Based on field observations of a large number of tanks, the most significant technological defects caused by welding of joints and their structural elements are found, the features of a stress-strain state in the areas of structural elements connections which cause a static accumulation of the depth of a corrosion damage. It is found that the pitting corrosion is most prevalent in tanks bottom leading to stop of their further operation. Defects: undercuts, craters, shells, fistulas and through cracks in a weld wall, rim welds of tanks. A significant rate of expansion and growth of pore depths of corrosion damage in comparison with other types of technological defects was observed. The article presents a mathematical model of a rate of corrosion depending on a molar amount of metal and average stress values in metal sections calculated using a tank radius and a stress concentration factor. A rate of corrosion is a factor of deepening of further growth of elastic-plastic deformation in a heat-affected zone (HAZ), which in turn causes micro- and macrocracks. A comparison of a corrosion rate of these areas with taking into account a yield strength of a reservoir main metal and HAZ of welded joints is a key factor for determining the ultimate life of reservoirs.

Key words: tanks, resource, weld, weld defects, corrosion damage, corrosion rate, concentration ratio, stress, yield strength, risk assessment, accident.

Science and Education, 2017, No.1, pp.75-80