PSI - Issue 80

M. Bennebach et al. / Procedia Structural Integrity 80 (2026) 136–145 Author name / Structural Integrity Procedia 00 (2019) 000–000

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A physical demonstrator has been designed and manufactured, in a reduced scale, representative of a chemical polymerization reactor. The demonstrator shown in Figure 2 is 1.7 m high and 1.1 m in diameter. It is made of P265GH steel whose mechanical properties are detailed in EN10028 (2009). A synthesis of main characteristics is given table 1.

Table 1: main mechanical characteristics of P265GH Material

P265GH

Young’s modulus Yield strength

201000 MPa

265 MPa 460 MPa

Ultimate tensile strength

Fig. 2. (a) CAD model of the equipment, (b) nomenclature of the pressure vessel parts

A finite element model of the equipment, subjected to different service loadings was done in commercial software Abaqus. Special attention was dedicated to welded zones between the lower coil and the shell, representing critical areas as pointed out by the FE model and from service experience. The pressure vessel is modelled using shell elements (S4R type) and the welds are modelled according to the IIW recommendations for the hot spot stress approach. In general, to limit modelling and computational efforts, simple models and relatively coarse meshes are preconized. Models with either thin plate or shell elements or with solid elements may be used. When using plate or shell elements, these are arranged in the midplane of the plates. In simplified models, the welds may be omitted except for cases where the results are affected by local bending, due for example to plate offsets or to interaction between welds close to each other. In such cases, the welds may be modelled by vertical or inclined plate elements having appropriate stiffness or by introducing constraint equations or rigid links to couple node displacements. For complex cases, solid elements may be used, allowing the weld to be modelled with prismatic elements. If isoparametric 20 nodes elements are used, one element is sufficient in thickness direction due to the quadratic displacement function and linear stress distribution. By reduced integration, the linear part of the stresses can be directly evaluated at the surface and extrapolated to the weld toe. It should be noted that when the weld is not modelled, extrapolation must be done to the intersection point. Figure 3 illustrates typical finite element models and extrapolation paths.