On several sites, Bluefield has seen pendant rope equaliser pins, walking out or with failed retainer bolts. Of course, this is a serious situation as if left un-actioned the pin will fall out and the boom pendant ropes can end up on the deck of the shovel and risk more catastrophic failures. The pf interval of this failure mode is relatively slow and they should be easily managed in a scheduled fashion without affecting the reliability of the shovel.
The cause of this failure mode seems to be fatigue of the bolts that secure the pin retainers in place, as shown in the exaggerated view in figure 1 below. The maintenance tasks designed to manage this failure mode are simple condition based inspections of the bolts. Of course, there are NDT checks of the pins at a greater frequency and replacement of pins at the end of life, to manage the failure modes associated with the pin itself.
To manage this failure mode, it is important to identify cracked or broken bolts, and then correct the situation before the pin starts to move. Once the pin moves a significantly greater amount of effort is required to correct the condition, as the load may have to be taken off the pin to reposition it.
Figure 1 – Exaggerated view of load causing fatigue of the bolts
Also, we see that the corrective tasks recommended when broken bolts are detected, is to replace the broken bolts. However, given that this failure mode is fatigue related, we are recommending that when one bolt is found to be broken or cracked, that the most appropriate action should be to replace all of the bolts retaining the pin as they should all have similar levels of fatigue.
By correcting the condition of the bolts in this manner, it will minimise the amount of work required to maintain this area and maximise the reliability of the system.
Of course, this failure mode is also similar for many other retaining pins on mining equipment. Not addressing the defects identified during PM inspections is another problem that we have written about in other articles. (See related article)