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Cracked Rivets Found With NDT

by | 15 Sep 2021

Cracked rivets were found by NES NDT staff in the Dolly Car Winder intermediate shaft bearing support structure which was allowing excessive movement of the bearing during operation of the Winder.

Situation: Routine condition monitoring surveys by NES staff found excessing axial vibration levels/movement of the winder bearing housings during operation causing concern for site engineering management

Recommendations: NES staff recommended Motion Amplification be conducted to identify cause/s and specific locations of the movement.

Response: Site management arranged the Motion Amplification service provided by NES and this found the movement was due to inadequate strength in the support structure and in particular in the rivetted mounting blocks the bearing housings were sitting on. Ultrasonic NDT was then arranged and NES staff carried out this work identifying 5 out of 8 cracked support rivets under one of the shaft bearings. Photo shows one of 2 bearing support blocks where 2 thick plates are secured with rivets to make up the block. The diagram shows 5 out of 8 cracked rivet locations (red dots) in one of the blocks.

Follow-up: NES engineering staff designed replacement one-piece blocks for the bearing supports, to remove the rivetted block design, and the repairs were successful in removing the excessive movement and elevated vibration levels in the Winder drive assembly with a more stable support.

Wrap-up: The Winder drive assembly has been in use for a number of decades and various modifications had been made over that long period for different reasons with varying degrees of success. This problem was identified through the use of a number of techniques and technologies used by NES and the outcome has provided the client site with an improved performance of this critical infrastructure for the site.


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