Cracked Welded Joints on Ladle Turret Rotating Arm

Cracked welded joints occurred on a “S” type ladle turret rotating arm and support structure. O’Donnell Consulting was asked to perform analysis on the structure including at the welded joints.

The design comprises a rotating 20 foot vertical arm with a cantilevered horizontal arm. Molds attached to the horizontal arm rotate about a secondary axis that is perpendicular to the horizontal arm. The most severe crack was observed in the weld joint between the vertical arm 8×10 inch steel tubes and the overlaid 1/2 inch steel plate used to support the counterweights. This crack traversed the whole circumference of the vertical arm. Cracks were found in other regions of the arm as well.

The objectives of the analysis were to determine the general state of stress within the arm, especially at the welded joints and to determine deformation behavior.

The analysis results showed that the displacements of the arm proper are within acceptable limits and that the arm will develop relatively low stress levels due to the conservative design loading conditions imposed (1.5 dynamic load factor). Two of the loading conditions, a loaded ladle horizontally bumping the locating stops (LC2) and the inertial resistance of a loaded ladle to arm motion (LC3) produced stresses of less than 5 ksi.

The support frame developed stresses of up to 20 ksi in the vertical gusset plates and the web when subjected to a vertical load due to a fully loaded ladle in one bay and nothing in the other bay (LCIB). This loading is the most critical condition. Replacing the gussets with larger ones reduced the stresses in the gussets to less than 12 ksi. The stresses in the web were reduced to 18 ksi.



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