Analysis of differences in the requirements of national regulations and USA standards in the development of the tank bottom differential subsidence

UDK: 621.642.39.03

Key words: tank, bottom, ANSYS, FEM, stress-strain state, SAG, differential settlement.

Authors: A.A. Tarasenko, A.A. Gruchenkova; M.A. Tarasenko (Tyumen Industrial University, RF, Tyumen)

The article analyzes the national and foreign regulatory documents in part of the requirements for the allowable size of bottom local settlement.  Choosing a method to deal with the corrosive destruction of tanks metal structures, many Russian experts prefer to increasing the thickness of the bottom structure due to corrosion allowance. In some cases, it leads to a redistribution of the existing stresses in the tank operation, because the bottom of the vertical steel tank is "absolutely flexible membrane", and the deformation limits of steel structures reasonable for typical projects, in this case, are questionable and require additional theoretical justification. For this reason, there was a question about the possibility of bringing the former requirements for local settlement of tank bottoms, the thickness of metal structures which are increased by the allowance for corrosion. The authors of the task to determine the bottom stress-strain state of the vertical steel tank RVS-20000 the most widespread in the Russian Federation, for two cases: a thickness of 6 mm and 9 mm - with different sizes of  local settlement of the bottom central part. To obtain the results were used the analytical solutions of the flexible membrane on base elastic deformation problem and numerical methods in mechanics of solid deformable body, in particular the finite element method. According to the results of the analytical calculation were obtained the maximum sag value of local settlement zones, as well as the values of the tensile stresses acting in the center of the settlement zone, for the most unfavorable case - is when under the membrane missing the subgrade. According to the results of numerical calculation in PC ANSYS were obtained analytical dependences between the vertical and radial component of the settlement zone. To model the settlement zone has been selected by a factor of soil bed 3 MN/m³, this choice is justified need to obtain real values of tank bottoms deformations, constructed on the territory of Western Siberia. Analysis of the dependences showed that the magnitude of the settlement zone vertical component in national standards significantly overstated in contrast to the requirements of the American standard API: for the bottom sheet 6 mm and 9 mm at 52% and 65%, respectively. By increasing the thickness of the tank bottom central part up to 9 mm allowable interval of local settlements radial dimensions is increased by 37% from the maximum possible at the regulatory documents of the Russian Federation. According to the authors, to change the way to appointment the value of allowable settlement in the national regulatory documents, you can identify more realistic requirements for steel structures also with a corrosion allowance. Thus, national regulations need to be harmonized with international standards in the terms of requirements for allowable geometric dimensions of tank bottom central part local settlements.
References
1. Gorelov A.S., Gorkovenko A.I., Stress-deformation condition of the tank bottom
at presence of a heterogeneity local area in its ground foundation
(In Russ.), Izvestiya vysshikh uchebnykh zavedeniy. Neft' i gaz, 2008, no. 3,
pp. 120–122.
2. Gorelov A.S., Neodnorodnye gruntovye osnovaniya i ikh vliyanie na
rabotu vertikal'nykh stal'nykh rezervuarov (Inhomogeneous ground base
and their influence on the work of vertical steel tanks), St. Petersburg:
Nedra Publ., 2009, 220 p.
3. Konovalov P.A., Mangushev R.A., Sotnikov S.N. et al., Fundamenty
stal'nykh rezervuarov i deformatsii ikh osnovaniy (Foundations of steel tanks
and deformation of their bases), Moscow: Publ. of Assotsiatsii stroitel'nykh
vuzov, 2009, 336 p.
4. API 653, Tank inspection, repair, alteration, and reconstruction, 4th ed.,
USA, Washington, 2009.
5. Timoshenko, S.P. and Woinowski-KriegerS., Theory of plates and shells,
2nd ed., McGraw-Hill, New York, 1959.
6. Vasil'ev G.G., Tarasenko A.A., Chepur P.V., Guan' Yu., Seismic analysis of vertical
steel tanks RVSPK-50000 using a linear-spectral method (In Russ.), Neftyanoe
khozyaystvo = Oil Industry, 2015, no. 10, pp. 120–123.
7. Tarasenko A.A., Chepur P.V., Tarasenko D.A., Numerical simulation of vertical
steel tank deformation while differential settlements developing (In Russ.),
Neftyanoe khozyaystvo = Oil Industry, 2015, no. 4, pp. 88–91.
8. Tarasenko A.A., Chepur P.V., Chirkov S.V., Study of inherent stiffness of veltical
s teel cylindrical tanks (In Russ.), Neftyanoe khozyaystvo = Oil Industry, 2014,
no. 10, pp. 121–123.