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FEM-based verification of the PN-EN standard-based stress concentration factor for the drum-pipe joint of a boiler

Dwornicka R.

Journal of Achievements in Materials and Manufacturing Engineering

2009

Vol. 37, nr 1

48-51

Purpose: The aim of this paper is to present the results of the comparative test between the PN-EN 12952-3:204/Ap1:2005 standard and FEM analysis as procedural tools for determining the stress concentration factor for the drum-pipe joint of a steam boiler. Design/methodology/approach: Geometrical properties of the drum and the pipe are defined. In the first step the stress concentration factor is calculated using the formulas presented in the PN-EN 12952-3:204/Ap1:2005 standard. Then two grid models are defined for unweakened (the drum alone) and weakened (the drum with the pipe) elements. Next, the maximum stresses are computed by FEM analysis conducted in the ANSYS system. A quotient of the maximum stresses gives the FEM-based stress concentration factor. A whole family of factors is created with a stable quotient between element wall thicknesses. Comparative plots of the families are created for both cases: standard-based and FEM-based approaches. Findings: There is rather a good conformity between plots derived from the PN-EN standard and from FEM analysis, with some slight differences due to the approximating character of the semi-empirical formulas presented in the PN-EN standard. Research limitations/implications: The plot presented for the PN-EN standard has limited precision for the geometry of the individual element. The standard presents as an alternative some semi-empirical formulas which are described as ‘approximating’. Ultimately, the numerical methods are more precise tools for determining the stress concentration factor. Practical implications: The results obtained allow the maximum stresses in the cycle to be determined precisely, due to the dependency of the final value on the preceding values in the computation procedure of the stress concentration factor. Originality/value: The calculated formulas may be significantly useful for determining the allowable cooling/heating rates of power plant devices.