WELDING RESEARCH deg direction was 44033 N, as shown in Fig. 6A, which was applied on the area of 912073 mm2 resulting in a pressure of 0.048 MPa. The finite element grids (see Fig. 6B) show the pressure applied to the surface that is a 90- deg section in the designed roll. Analyses were conducted to evaluate the individual effect of pressure and temperature on stress. It was found that the stress induced by pressure was much smaller than the temperature changes. Therefore, a constant pressure was applied in the analyses. Only the thermal load was applied as a cyclic load. Weld residual stresses and welding processes were not modeled in this study because PWHT was used in producing the roll, and PWHT may reduce residual stresses from welding. In addition, the roll served in a high-temperature environment was essential for the creep process to reduce the weld residual stress further. A follow-up study (Ref. 22) was conducted to include weld residual stress during the creepfatigue analyses. It was found that the same conclusions can be obtained with and without weld residual stress during the creepfatigue analyses. A Fully Coupled Heat Transfer and CFD Analysis A fully coupled heat transfer and CFD analysis was conducted to simulate the effect of highpressure air cooling inside the roll on the roll temperature, which was one of the proposed methods to improve the creep-fatigue life of the furnace roll in this study. The CFD analysis was governed 436-s WELDING JOURNAL / NOVEMBER 2016, VOL. 95 by incompressible Navier-Stokes equations. The equations can be readily found in the ABAQUS manual (Ref. 26) and the CFD textbook (Ref. 31) and will not be discussed here. The CFD model and boundary conditions are discussed in detail below. Fig. 10 — Effect of coolto temperature between cycles on maximum principal stress. A — Cool to 204C after 10 loading cycles; B — Cool to 427C after 10 loading cycles. Fig. 11 — Cracks observed near the welded joint (Ref. 21). Fig. 12 — Evolution of temperature, effective creep strain, and maximum principal stress at location 1 of Fig. 10 for case 1: cool to 204C between cycles. Fig. 13 — Hoop stress near a weld at 427C and observed cracks. A — Hoop stress; B — failed roll; C — crack 1 near a weld; D — crack 2 near a weld. A A B C D B
Welding Journal | November 2016
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