The degree and type of corrosion allegedly associated with the failed shafts was of such a minor nature that it didn’t raise any obvious alarm bells when the two incidents were compared.
Boroscope inspection in the field is only going to highlight plainly obvious corrosion. The boroscope inspection is carried out to confirm removal of the ‘ Mud’ and deposits not the type of corrosion EC are talking about.
There is no EC requirement to check for corrosion.
The chance of seeing the weld area with the naked eye from the bottom of the box is compromised due to the change in profile of the shaft and dripping oil.