Shaft modification or manufactured new one

I have a damaged shaft which is part of a RBC system in a sewage treatment plant. But, this is shorter by 300 mm that I am requiring. My question is can I add a piece of 300 mm to the shaft (welded or mech. coupling), to complete the total required length? Or, is it dangerous necessitating a new shaft.

The shaft specs are:

  • Material= carbon steel
  • OD= 600
  • thickness= 30mm
  • actual Length= 6400mm
  • final length including the 300mm=6700mm
  • RPM=1-5

Attached you can see a draft of the shaft.
I am thinking of using a shaft coupling, or welding to join the 300 mm missing length (and of course do the recalculation of the stresses and deflection).

Question: Repair or replace?



  • How does the 600 mm diameter relate to the 150mm diameter?
  • Is this a turned down solid shaft, or a 600 mm round shell mounted on a 150 mm shaft?
  • Is it a weldment or are shaft and shell mechanically coupled?
  • 150 mm shaft diameter for a 6.4 m span does not seem good.
  • Per ANSI/CEMA B105.1 Welded Steel Pulley Design, pulley shell strength should not be included in the shaft strength calculations.
  • It is not clear the usage, design, loading or fabrication of this component, but it may not have been designed per industry standards.

Above is a snippet.

@dvd, Sometimes it’s better knowing the questions to ask, right? :)