Thoughts triggered by the design error of the tail hook

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This post was last edited by B0SS on 2019-12-2 at 17:39. Recently, it was found that in the workshop, the angle of the tail hook on several devices was not set at 90° relative to the direction of the lifting center line of the device’s shaft studs. As shown in the drawings below, the shaft lugs are located at 30° and 210°, while the tail hook is at 135° (the correct angle should be 120°). The actual position is 15° clockwise offset from the correct position. If it is detected before welding, the shaft lug can be rotated by 15° to ensure that the lifting line of the shaft lug is perpendicular to the axis of the tail hoist (as the tail hoist interferes with the existing skirt plate gussets). Since the equipment has been manufactured and fully heat-treated. What methods can be used to achieve safe lifting while saving costs and minimizing the amount of work that needs to be redone? Method 1: Add another tail lift at an angle symmetric to the lifting center line of the existing tail lifts, as shown in the figure. During lifting, use the method of lifting two shaft lugs along with the two tail lifts to ensure that the equipment can be lifted symmetrically. Method 2: Cut off the existing tail sling, leaving the position of the internal support tube unchanged. Move the tail lift to the rib plate and align it with it (the rib plate is roughly at the position of the lifting center line). See the figure below: A bevel is applied to the weld joint between the tail hanger and the skirt base to ensure full penetration; the upper edge of the skirt base reinforcement plate is connected to the fillet weld of the tail hanger. However, the use of these two methods is conditional on the fact that, in the absence of internal support tubes, the stress calculations for the tail lift are satisfactory, and moving the position will not result in insufficient strength of the gusset plates or excessive stress in the skirt cylinder. If the calculation is not satisfactory, then the internal support tube and the tail hook must be cut off together and moved again; as for the connection of the external tail hook, method 2 mentioned above applies. The above methods are alternatives used when no other options are available; it is still recommended that designers, during the design process, take into account the requirements for on-site assembly in addition to ensuring the safety of the equipment.