This presentation is an overview of the work Mangoola Coal has done with Maintenance Technology Institute (MTI) within the Department of Mechanical and Aerospace Engineering at Monash University to understand the causes of failure relating to an incident in October 2016, and developing strategies to prevent similar failures in the future.

1. Understanding the Cause
Alan Burns – Mangoola Coal
Gerard Chitty – MTI, Monash University
1

2. • Incident Summary
• Post Incident investigation process
• Understanding the cause of the failure
• Conclusions & recommendations
Content

3. EX151 Incident
3

4. Background
The cabin on the Liebherr R9250
excavator is supported by four
resilient rubber mounts that are
secured to a cab “riser”.
The cab riser is retained by four
vertical bolts and two horizontal
bolts. These cab riser bolts
(30mm dia. x 300mm long) secure
the entire cab and riser to the LH
front chassis of the machine.
Cabin
Cab Riser

5. Background
At the time of the incident, the machine had approximately 32,000 SMU hours
on it with no previous faults reported on the cab riser bolts before the 13th of
May 2016

6. Events leading up to the Incident
13/5/2016 23/5/2016
• 2 broken bolts identified during service
• Work Order raised and task scheduled to replace broken bolts
• Maintenance Planner contacted the OEM
• Unsuccessful attempt made to remove and replace bolts
• Second unsuccessful attempt made to remove and replace broken bolts.
21/6/2016 7/7/2016

7. Events leading up to the Incident
250mm to the
broken part of
the bolt
Broken bolts were unable to be removed due to some misalignment and
inability to effectively reach approximately 250mm to the broken part of the
bolt

8. Events leading up to the Incident
13/5/2016 10/8/2016
• 3rd broken bolt identified during inspection.
• OEM notified and inspected the machine.
• Risk assessment / discussion was conducted involving a number of
personnel - combined experience of over 75 years
• Estimated 5 days to replace bolts as the cab and riser had to be
disconnected and removed from the machine
• Decision made to carry out an interim repair and implement additional
inspections to monitor the effectiveness of the repair.
• Inspections to be carried out at crib breaks - 12 and 4 on each shift.
• Plan to remove bolts at the November Shutdown unless results from
inspections determine otherwise.
11/2016

9. Events leading up to the Incident
13/5/2016 11/8/2016
• An incident occurred where a rock had rolled onto the track and made
contact with the support under the cab riser.
11/2016

10. Events leading up to the Incident
13/5/2016
12/8/2016
11/2016
• 4th broken bolt identified.
• Risk assessment/discussion conducted between Maintenance Personnel
• Reinforcement of interim repaired carried out
• Inspections to monitor the effectiveness of the repair being carried out
• Further reinforcement to the interim repair with gussets
• OEM records the broken bolt status in their internal system
13/8/2016
15/8/2016

11. Events leading up to the Incident
13/5/2016 11/20161/9/2016
• Cab to riser rubber mounts
replaced as a further control
measure to minimise cabin
movement.
Cabin
Cab Riser

12. Events leading up to the Incident
13/5/2016 11/201610/10/2016
• At 8:45pm, the cabin and cab riser dislodged from its normal position and
tipped over damaging hydraulic hoses, electrical harnesses and causing
minor structural damage to cab riser mounting.
• No Injuries were reported at the time of the incident.

13. The Investigation
• Investigations commenced.
• Required notifications made and the Resource Regulator visited the site
• ICAM investigation initiated on 12th October 2016.
• External facilitator and participates external and internal to Mangoola

14. The Investigation
Root Cause
• Failure of the design of the interim repair
• Monitoring program not detecting the failing state of the interim repair
• Failure of the bolts indicates misalignment between the riser and the
chassis mounts as the probable cause. The misalignment placing
additional stress on the bolts causing them to fatigue and progressively fail
over time.

15. The Investigation
Significant Learnings
• Failure of cab riser bolts not completely understood.
• Apart from the requirement to inspect bolts, there is no other definitive
requirements relating to planned maintenance of the cab or riser in OEM
manuals or site documentation.
• Interim repairs are common place and considered a routine part of
maintenance but there is no process or procedure that clearly deals with
the specific requirements involved in the management of interim repairs
• The integrity of the interim repair was heavily reliant on a routine
inspections being conducted each shift.
• Insufficient formal documentation to control the interim repair design and
monitoring given the length of time the interim repair was relied upon.
• Interim repair inspection criteria not clearly defined or communicated and
limited documented evidence of the routine inspections being conducted

16. The Investigation
Recommendations
• Develop an Interim Repair TARP / Procedure
• Communicate the requirement to maintain accurate and timely records for
ongoing monitoring of equipment.
• Review the Maintenance Strategy around Cab Riser maintenance
• Share learnings with OEM and other sites
• Review Mechanical Engineering Control Plan

17. Post Investigation
10/10/2016 31/1/2017
• Presentation to the Resource Regulator Representatives & District Check
Inspector on the implementation and completion of the recommended
actions.
• Perceived that the presentation was well received.

18. Post Investigation
• Notification that another inspector was taking over the investigation.
• Section 155 notice was going to be issued to provide information.
• Intention to conduct interviews
• Section 155 notice received
• Interviews commence
10/10/2016 9/3/201714/3/2017 31/3/2017

19. Post Investigation
10/10/2016
• Second Section 155 notice received.
11/5/2017

20. Post Investigation
10/10/2016
• Interviews Continued
5/5/2017 - 11/7/2017

21. Post Investigation
10/10/2016 13/11/201716/8/201722/11/17 & 29/11/17
• Notified that the investigation was being handed over to the Investigation
Unit.
• 3rd Section 155 notice received
• Interviews Continued

22. Post Investigation
10/10/2016 5/12/2017 25/9/2018
• 4th Section 155 notice received
• Investigation to continue into 2018
• Enforceable Undertaking

23. Enforceable Undertaking Action
• Engage the Maintenance Technology Institute within the Department of
Mechanical Engineering at Monash University to understand the root cause
of failure and provide recommendations to eliminate such failures in the
future

24. Understanding the Cause
Learnings from Liebherr R9250 Cab Riser Detachment Failure
at Glencore Mangoola Mine
Dr Daya Dayawansa, Amanda Gonzago, Tony Carpinteri, Dr Michael Lo & Gerard Chitty (MTI)

25. Understanding the Root Cause of Failure
Methodology Adopted
The methodology adopted are as follows:
1. Review available failure information
2. Conducted preliminary FEA on the cab riser to understand the structural behavior
and determine the instrumentation plan and sensors locations.
3. Install MTI’s Structural Monitoring System (SMS) on excavator EX151 with additional
instrumentation.
4. Conduct specific testing to determine major influencing practices that effect the cab
riser connection bolts.
5. Conducted FEA based on measured SMS data.
6. Conduct fatigue assessments based on measured data and FEA.
7. Development a comprehensive risk management strategy to minimise risk of failure.

26. Instrumentation used
The instrumentation consisting the following :
• The MTI Structural Monitoring System (SMS) which monitors the structural performance of
the machine and identify how the machine is being operated.
• The system includes
– 10 strain gauges on the boom stick and main frame
– 3 position inclinometers on the boom, stick and bucket
– Pressure transducers to measure boom, stick and bucket strut and swing forces.

27. Cab Riser Instrumentation
Strain gauge
Terminations
to SMS logger
M30x300 bolt
The instrumentation of the cab riser consisted of the following:
• The six instrumented connection bolts
• Three displacement transducers to measure any movement between the
riser chassis.
• 1 tri-axial accelerometer and some additional strain gauge on the
connection block
The strain gauges were zeroed prior to installation so that the pretension
of the bolts could be measured at the time of install.
Instrumented bolt installed on
the outer rear of the riser
Position of vertical and horizontal bolts
Displacement transducers
Tri-Axial
Accelerometer
Front
Horizontal Bolt
Transverse
measurement
Vertical
measurement
Chassi
s
Riser

28. Bolt Pretention Measurements
Pretension applied to a bolted connection has the ability to significant
change fatigue loading on the bolt.
The OEM specified a torque of 1920 Nm to tension the bolts which is
equivalent to ~ 57% of proof load (570 MPa) for the bolt.
Measured bolt tensions after the installation:
Bolt
Notation
Instrumented Bolt Pretension Stress
(MPa)
Pretension Stress
(% Proof Stress)
B SG01 – Vertical Bolt Front (Outer) 755 75.5
A SG02 – Vertical Bolt Front (Inner) 180 18
E SG03 – Horizontal Bolt Front 590 59
F SG04 – Horizontal Bolt Rear 980 98
C SG05 – Vertical Bolt Rear (Inner) 125 12.5
D SG06 – Vertical Bolt Rear (Outer) 275 27.5

29. Operator Practices – Normal Digging
SMS Dashboard
showing no alarms

30. Operator Practices – Sudden Impact with Side Load
SMS Dashboard showing operating
practice causing strength alarms

31. Normal Operations with High Damaging Dig Conditions
High fatigue life usage in rear connection bolts mostly when digging not ripped coal was dug.
Sudden increase in Bolt SG06
cumulative damage

32. FE Modelling Results
FE Results showed that
• 34% of the measured transverse
displacement was due to the
deflection of the riser and the
remaining 66% was due to the
riser sliding relative to the chassis
which caused bolt bending.
• In the vertical directions, almost
all of the measured displacements
are due to the cab riser sliding
which causes bolt bending.
Transverse
Longitudinal
Vertical
Strain gauge

33. Fatigue Assessment – Axial + Bending Loads
BS7608 was used to estimate the fatigue life considering only axial loads and both axial
and bending.
Comparison of the estimated fatigue life for bolts are summarised in table below
`
The analysis showed that:
• Bending of the connection bolts due to sliding the movement of the riser accounted
for ~85% of the fatigue damage.
• The estimated fatigue life of the bolts were significantly different with the lowest
estimated fatigue life being ~4500 hours in Bolt D.
• The estimated fatigue life of horizontal bolts were higher than the vertical bolts.
Estimated Fatigue
Life (Hrs)
Bolt Notation Instrumented Bolt Axial Axial + Bending
B SG01 – Vertical Bolt Front (Outer) 60000+ 12500
A SG02 – Vertical Bolt Front (Inner) 50000+ 12500
E SG03 – Horizontal Bolt Front 50000+ 20000+
F SG04 – Horizontal Bolt Rear 50000+ 20000+
C SG05 – Vertical Bolt Rear (Inner) 60000+ 10000
D SG06 – Vertical Bolt Rear (Outer) 20000+ 4500

34. Design concepts
1. The bolted connections should be designed to prevent bolt bending as the
sliding movement contributed to 85% of the bolt fatigue.
2. Another weaknesses of the connection design is that if one bolt is broken, it
can not be replaced without completely removing the riser and cabin
assembly.
Chassis
Cab riser
block
Connection
features a tapered
section to prevent
movement.
Use bolt and nut
arrangement for easy
replacement where
possible
(1) (2)

35. Conclusions
The following conclusions can be made:
• The pretension of the bolts at installation
– Varied significantly between each bolt.
– Not all bolts achieved the recommended pretension.
– Currently the pretension set to 57% of proof stress is relatively low.
– Procedure to achieve recommended pretension of bolts was not provided by the
OEM.
• Sudden application of vertical force with side force causes significant stresses in
the excavator structure and the cab riser connection bolts and high relative
movement between the cab riser and the chassis.
• The operating conditions and operator practices have a large influence on the life
of the bolts. High fatigue life usage occurred when digging coal not ripped.
• The movement of the cab riser relative to the chassis with the current bolt
connection design cause bolts to experience significant bending during
operations, which contributed to 85% of the fatigue damage.

36. Recommendations
The following recommendations can be made for the study:
• Higher attention should be given to pretension of the bolts:
– Adopt a bolt pretension procedure to ensure all the bolts are tensioned to the
specified value which includes a bolt pretension sequence and re-tightening
processes.
– The pretensions should be checked at the next schedule day after.
• With the current connection detail bolts should be inspected every 3 months and
replaced every year to avoid bolt crack initiation/failure.
• Inspect the attachment block (of the two horizontal bolts) every 5000 hours.
Cracks in these areas will lead to loss of pretensions in the horizontal bolts.
• Conduct operator awareness training programs to eliminate stress spikes which
cause strength alarms and reduce the number of fatigue alarms provided by
utilising the SMS real-time feedback which will improve production and minimise
cumulative damage.
• The connections between cab riser and chassis should be redesigned to prevent
the movement of the cab riser w.r.t. the chassis (prevent bolt bending).

37. Key Learnings
Key Learnings from the investigation can be summarised as follows:
• Understanding the loading the structure/structural component experiences during
operations is critical in understanding the Root Cause of the Failure.
• Most mining structures will experience fatigue cracking. The crack initiation and
the crack growth rate will depend on:
– Magnitude of the stress cycles experienced by the component (operating
conditions)
– The number of stress cycles (operating conditions)
– Fatigue category of the connection (design)
• To develop a comprehensive risk management strategy to maintain structural
integrity of dynamic structures the loading/stresses experienced by the structures
should be clear understood and the inspection frequencies should be based on
estimated crack growth rates for each component
• FEA is great engineering tool. However the loading used for the analysis and
boundary conditions used in the FE models are critical to get accurate
results/predictions

38. Acknowledgements
End of
Presentation