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Marine Safety Investigation Unit
MARINE SAFETY INVESTIGATION REPORT
Safety investigation into the failure of a deck crane
on board the Maltese registered bulk carrier
SEAPACE
in the port of Bécancour, Canada
on 13 August 2014
201408/012
MARINE SAFETY INVESTIGATION REPORT NO. 22/2015
FINAL
2
The MSIU gratefully acknowledges the assistance and cooperation of the Transportation
Safety Board of Canada, during the safety investigation of this accident.
Investigations into marine casualties are conducted under the provisions of the Merchant
Shipping (Accident and Incident Safety Investigation) Regulations, 2011 and therefore in
accordance with Regulation XI-I/6 of the International Convention for the Safety of Life at
Sea (SOLAS), and Directive 2009/18/EC of the European Parliament and of the Council of 23
April 2009, establishing the fundamental principles governing the investigation of accidents
in the maritime transport sector and amending Council Directive 1999/35/EC and Directive
2002/59/EC of the European Parliament and of the Council.
This safety investigation report is not written, in terms of content and style, with litigation in
mind and pursuant to Regulation 13(7) of the Merchant Shipping (Accident and Incident
Safety Investigation) Regulations, 2011, shall be inadmissible in any judicial proceedings
whose purpose or one of whose purposes is to attribute or apportion liability or blame, unless,
under prescribed conditions, a Court determines otherwise.
The objective of this safety investigation report is precautionary and seeks to avoid a repeat
occurrence through an understanding of the events of 13 August 2014. Its sole purpose is
confined to the promulgation of safety lessons and therefore may be misleading if used for
other purposes.
The findings of the safety investigation are not binding on any party and the conclusions
reached and recommendations made shall in no case create a presumption of liability
(criminal and/or civil) or blame. It should be therefore noted that the content of this safety
investigation report does not constitute legal advice in any way and should not be construed
as such.
© Copyright TM, 2015.
This document/publication (excluding the logos) may be re-used free of charge in any format
or medium for education purposes. It may be only re-used accurately and not in a misleading
context. The material must be acknowledged as TM copyright.
The document/publication shall be cited and properly referenced. Where the MSIU would
have identified any third party copyright, permission must be obtained from the copyright
holders concerned.
MARINE SAFETY INVESTIGATION UNIT
Malta Transport Centre
Marsa MRS 1917
Malta
3
CONTENTS
LIST OF REFERENCES AND SOURCES OF INFORMATION ............................................4
GLOSSARY OF TERMS AND ABBREVIATIONS ................................................................5
SUMMARY ...............................................................................................................................6
1 FACTUAL INFORMATION .............................................................................................7
1.1 Vessels, Voyage and Marine Casualty Particulars .....................................................7
1.2 Description of Vessel .................................................................................................8
1.2.1 MV Seapace ...........................................................................................................8
1.3 Narrative .....................................................................................................................8
1.4 Post-accident Investigation .......................................................................................10
1.5 Post-accident Actions ...............................................................................................11
1.6 Damage to the Vessel’s Structure .............................................................................13
1.7 Vessel’s Manning .....................................................................................................15
1.8 The Crane Operator ..................................................................................................15
1.9 The Deck Cranes ......................................................................................................15
1.10 The Slewing Ring Bearing .......................................................................................16
1.11 Follow up Investigation ............................................................................................18
2 ANALYSIS.......................................................................................................................23
2.1 Aim ...........................................................................................................................23
2.2 Cause of the Accident ...............................................................................................23
2.3 Cause of Bearing Failure ..........................................................................................24
2.4 Design of the Slewing Bearing .................................................................................25
2.5 Rocking Test .............................................................................................................25
2.6 Grease Analysis ........................................................................................................26
2.7 Maintenance Issues ...................................................................................................26
3 CONCLUSIONS ..............................................................................................................29
3.1 Immediate Safety Factor ...........................................................................................29
3.2 Latent Conditions and other Safety Factors .............................................................29
3.3 Other Findings ..........................................................................................................30
4 RECOMMENDATIONS ..................................................................................................30
LIST OF ANNEXES .................................................................................................................31
4
LIST OF REFERENCES AND SOURCES OF INFORMATION
American Bureau of Shipping. (2007). ABS requirements of Guide for Certification
of Lifting Appliances
Crew members – MV Seapace
Deck crane operator – Canada
International Atomic Energy Agency. (2007). Application of Reliability Centred
Maintenance to Optimize Operation and Maintenance in Nuclear Power Plants.
Report IAEA-TECDOC-1590
Managers – MV Seapace
Transportation Safety Board of Canada
5
GLOSSARY OF TERMS AND ABBREVIATIONS
AB Able seaman
ABS American Bureau of Shipping
Co. Company
Fe Iron
gt Gross tonnage
IACS International Association of Classification Societies
IHI Ishikawajima-Harima Heavy Industries Co. Ltd.
Inc. Incorporated
kW Kilowatt
LT Local time
LTD. Limited
m Metres
mm Millimetre
MSIU Marine Safety Investigation Unit
MT Metric tonnes
MV Motor vessel
NDT Non-destructive testing
No. Number
PMS Planned maintenance system
rpm Revolutions per Minute
SWL Safe working load
TSB Transportation Safety Board of Canada
UTC Coordinated Universal Time
WMMP Wuhan Marine Machinery Plant Co. Ltd.
6
SUMMARY
On 13 August 2014, at about 18541, deck crane no. 4 on board the Maltese registered
bulk carrier, Seapace experienced a catastrophic failure while discharging salt in the
port of Bécancour, Quebec, Canada.
The deck crane’s combined cabin unit and jib parted from its pedestal base and fell
into cargo hold no. 5, striking the open hatch cover as it toppled over.
The stevedore operating the deck crane became trapped inside the cabin and it took
the shore emergency services some time to extricate him from the wreckage and land
him ashore. The crane operator sustained serious injury to one of his legs and minor
injuries to his head.
Discharging operations were suspended and the managers arranged for the cargo to be
discharged by shore cranes until such time the remaining cranes could be thoroughly
inspected.
The safety investigation concluded that the immediate cause of the accident was the
failure of the slewing ring due to pre-existing upper and lower circumferential fatigue
cracks. The fatigue cracking initiated at the undercut fillets above and below the
extended nose portion of the nose ring.
Three safety recommendations were issued to the ship managers and the crane
manufacturers to enhance the operational safety of the deck cranes.
1 Local time zone was UTC-5, Daylight Saving Time (Summer Time).
7
1 FACTUAL INFORMATION
1.1 Vessels, Voyage and Marine Casualty Particulars
Name Seapace
Flag Malta
Classification Society American Bureau of Shipping
IMO Number 9486025
Type Bulk Carrier
Registered Owner Courtesy Shipping Inc
Managers Thenamaris Ships Management
Construction Steel (Double bottom)
Length overall 189.99 m
Registered Length 185.00 m
Gross Tonnage 33036
Minimum Safe Manning 16
Authorised Cargo Bulk cargo
Port of Departure Casablanca, Morocco
Port of Arrival Bécancour, Canada
Type of Voyage International
Cargo Information 36,824 tonnes of industrial salt
Manning 22
Date and Time 13 August 2014 at 1854 (LT)
Type of Marine Casualty Serious Marine Casualty
Place on Board Deck crane no. 4
Injuries/Fatalities One serious injury
Damage/Environmental Impact Damage to deck crane no. 4, hatch cover; coaming
of cargo hold no. 5, shear strake and the deck
railing
Ship Operation Normal Service – Alongside/moored /
Discharging cargo
Voyage Segment Arrival
External & Internal Environment Overcast with good visibility, light drizzle
Persons on Board 22
8
1.2 Description ofVessel
1.2.1 MV Seapace
Seapace is a 33036 gt, bulk carrier owned by Courtesy Shipping Inc. and managed by
Thenamaris Ships Management Inc., Athens, Greece. The vessel was built by
Taizhou Sanfu Ship Engineering Co. Ltd, Taizhou City, China in 2010, and is classed
with American Bureau of Shipping (ABS). It is understood that Seapace is the 57th
vessel of a series of 443 sister ships that were constructed between 2008 and 2014 by
various shipyards located in China.
The vessel has a length overall of 189.99 m, a moulded breadth of 32.26 m and a
moulded depth of 18.0 m. The vessel has a summer draught of 12.80 m. Seapace has
five cargo holds and is equipped with four deck cranes. The vessel is classed as a
handy sized bulk carrier.
Seapace is powered by a 6-cylinder MAN-B&W 6S50MC-C single acting slow speed
diesel engine, producing 9480 kW at 127 rpm. This drives a fixed pitch propeller to
give a service speed of about 14.20 knots.
The vessel is operated on the spot market under charter and trades worldwide.
1.3 Narrative
On 01 August 2014, Seapace completed loading 36824 metric tonnes (mt) of
industrial salt at Casablanca, Morocco. At about 0318 on the same day, the vessel
departed her berth and after dropping her outward pilot at 0330, she headed towards
Bécancour, Canada.
On 11 August, at about 0812, the vessel picked up the St. Lawrence River pilot at
Les Escoumins pilot station. At 1825 on the same day, Seapace embarked her next
pilot at Québec City, Quebec and disembarked the Escoumins pilot. Seapace arrived
off Bécancour at about 2236 and made fast two tugs to come alongside. The vessel
completed her mooring operations at 0100 on 13 August.
9
On completion of the port formalities, the chief mate ordered the bosun to pick up all
of the crane jibs from their stowed position and prepare them for the cargo
discharging operations that were scheduled to start at 0800 that day.
At 0740, hatch covers on cargo hold nos. 1, 3 and 4 were opened. At 0800, the
stevedores boarded, but due to issues with the grab and power connections,
discharging operations did not start until 0905 in cargo hold no. 3. Thereafter,
discharging operations also started in cargo holds nos. 1 and 4 with deck cranes
nos. 1, 2 and 4 in operation.
At 1635, discharging was suspended in cargo hold no. 1 because the stevedores
complained of the ship’s grab leaking excessive cargo. The grab was exchanged for a
shore grab and discharging resumed in that cargo hold at 1712.
At about 1800, the crane operator on deck crane no. 1 relocated to deck crane no. 4
for the final two hours of his shift to discharge cargo from cargo hold no. 5. He found
the deck crane difficult to operate as he had to apply a lot of force on the control
levers to move the jib. He also noticed that when he slewed the deck crane, it made a
strange noise. He initially reported the matter to his foreman who arranged for the
duty crew to diagnose the problem. The deck crane was visually checked and the
operator was given the all clear to operate it.
At about 1845, the deck crane operator hoisted a load of salt and was in the process of
slewing it outboard when it made a strange noise and stopped. He released the load
and picked up another but the deck crane would not slew outboard. The attending
stevedore on deck reported this to the deck cadet on duty, who informed the duty able
seaman (AB). The duty AB was in the process of walking aft towards cargo hold
no. 5 when he heard a loud bang and thought that a grab had fallen on deck. On
reaching cargo hold no. 5, he saw that the deck crane no. 4 cabin had detached from
the pedestal and fallen into the cargo hold no. 5 (Figure 1).
The master, who was on his way to his cabin from the mess room, also heard the loud
bang and on reaching his cabin, he looked out of the porthole where he saw the
collapsed deck crane. He alerted the crew on his VHF radio and public announcement
system. He also notified the emergency services immediately, using the on board
10
mobile telephone. He contacted his Company’s emergency response team and
informed the team members of the accident.
Figure 1: Deck crane no. 4 cabin in cargo hold no. 5, resting on the cargo of salt
The Police, fire and ambulance services all arrived on site within minutes of each
other, at about 1924. After providing first aid to the deck crane operator, they
extricated him from the wreckage and used a shore crane and recovery basket to land
him ashore at 2045. The deck crane operator was subsequently treated for a fractured
tibia and minor injuries to his head. The excavator and its driver, who was working in
the cargo hold, narrowly escaped damage and/or injuries.
1.4 Post-accident Investigation
At about 2256 on 13 August 2015, an investigation team from the Transportation
Safety Board of Canada (TSB) boarded Seapace. The team immediately took control
of the accident site and carried out a preliminary assessment on the same day. TSB
returned on board on 14 August to carry out a technical investigation into the
circumstance and causes as to why the slewing ring of deck crane no. 4 had failed
11
catastrophically. The investigation team was joined by an MSIU representative on 14
August 2015.
On the same day, TSB issued a seizure letter2 to the master of Seapace. TSB required
the remaining parts of the slewing bearing on deck crane no. 4 pedestal and the deck
crane cabin assembly to be dismantled so that the Board could conduct metallurgical
tests, which would assist the safety investigation determine the cause of the failure.
1.5 Post-accident Actions
On 14 August 2014, Transport Canada Marine Safety & Security boarded the vessel
and after inspecting the vessel recorded four deficiencies. These deficiencies related
to the collapse of deck crane no. 4 and the structural damage caused by its collapse.
Transport Canada Marine Safety & Security also restricted the use of deck cranes nos.
1, 2, and 3 until such time a thorough inspection could be undertaken to confirm that
they were safe for further use.
On the same day of the accident, ABS boarded the vessel to assess the damage to the
deck crane and associated structure. The Classification Society surveyor was unable
to examine the slewing ring because of limited safe access. The surveyor, however,
required that deck cranes nos. 1, 2, and 3 be tested before they were put back into
service. The managers were required to carry out the following tests / inspections on
all deck cranes in the presence of an attending class surveyor:
1. Slewing ring to be opened for thorough examination;
2. Slewing ring to be subjected to NDT and Hardness Testing;
3. Deck cranes to be tested to the equivalent of an initial / five yearly crane survey;
and
4. Deck cranes to be examined and operationally tested to the equivalent of an
annual survey.
On 16 August, the managers hired a local workshop company and arranged for the
damaged crane cabin and jib to be taken off the vessel. The jib was detached from the
2 Seizure to thing(s) with the consent of the owner, Section 19, Canadian Transportation Accident
Investigation and Safety Board Act.
12
crane cabin and landed ashore. Thereafter, the crane cabin was lifted out of cargo
hold no. 5 and landed ashore (Figure 2).
Figure 2: Deck crane assembly being landed ashore
At the same time, the electro-hydraulic grab that was in use when the accident
occurred was weighed. The combined weight of the grab and its contents was found to
be 20.3 tonnes.
On 22 September 2014, following an initial assessment of the accident, TSB sent a
Marine Advisory Letter to the International Association of Classification Societies
Limited (IACS), advising them of the catastrophic failure of the slewing ring on deck
crane no. 4 on board Seapace. As TSB was unable to determine how many vessels
may have been fitted with similar cargo handling cranes and slewing ring bearings, it
recommended that IACS advises its members of the accident and recommend that
they take appropriate measures to ensure the integrity of any similar unit in service on
board their respective vessels. This letter can be found in Annex A.
13
1.6 Damage to the Vessel’s Structure
The accident resulted in deck crane no. 4 becoming a total loss. The forward part of
cargo hold hatch cover no. 5 was indented because of the initial impact of the deck
crane cabin. The hatch cover required repairs as the impact had distorted the hatch
cover and therefore the crew were unable to close the hatch cover (Figure 3).
Figure 3: Damage to hatch covers no. 5
The hatch coaming on the starboard side was also damaged where the deck crane’s jib
had landed. In the same area but on the outboard side, associated hand railings and
the vessel’s shear strake were damaged (Figures 4 and 5).
An inspection of the grab that was in use at the time of the accident indicated that the
closing mechanism had become distorted due to heavy impact on the concrete
quayside. The grab was considered beyond economical repair.
Damages relating to the seaworthiness of the vessel, i.e. hatch cover, coaming and
railings were repaired prior to the vessel’s departure from Bécancour on 22 August
2014.
14
Figure 4: Damage to hatch coaming, railings and shear strake in way of hold no. 5
Figure 5: Damage to hatch coaming, railings in way of hold no. 5 and grab
15
1.7 Vessel’s Manning
The Minimum Safe Manning Certificate issued by the flag State Administration
required the vessel to be operated by 16 persons, including seven officers. At the time
of the accident, the vessel was manned in excess of the minimum safe manning
requirement of Transport Malta’s Merchant Shipping Directorate.
The master and crew were all Filipino nationals and the working language was
English, which was understood by everyone on board. At the time of the accident, the
deck was manned by the third mate, a deck cadet and an AB.
1.8 The Crane Operator
The crane operator was a Canadian national. He was 44 years old and had been a
crane operator for about 13 years. He had received initial training before he started
operating cranes. More recently, for the past two years, he had been a trainer as well.
1.9 The Deck Cranes
The vessel was equipped with four electro-hydraulic deck cranes that had been
manufactured by Wuhan Marine Machinery Plant Co. Ltd (WMMP), China under
licence from Ishikawajima-Harima Heavy Industries Co. Ltd (IHI), Japan.
The deck crane type was SS360200-280, the slim version, and had a safe working
load (SWL) of 36 mt. When used with a grab, its SWL was reduced to 28 mt.
The deck cranes had been commissioned on 29 March 2010. They were proof tested
to a load of 41 mt at a radius of 28 m. The original slewing bearing on crane no. 4
had been replaced after approximately seven months of the vessel coming into
service. The slewing bearing that failed on 13 August 2014, was the replacement3 of
the original bearing fitted by the manufacturer of the crane and had approximately
46 months of service at the time of failure.
The deck cranes were subject to a planned maintenance schedule as required by the
vessel’s safety management system. The wear assessment of the deck cranes was
3 The slewing bearing was supplied by the original manufacturer.
16
done by means of tilting clearance measurements. These assessments, which are
more commonly known as ‘rocking tests’ (Annex B), were required to be undertaken
every six months, in accordance with the vessel’s planned maintenance system
(PMS). The last tests were made on 30 January 2014 by the vessel’s crew and were
within the maximum allowable tolerances. A copy of these tests can be found in
Annex C.
The vessel’s PMS also required grease samples to be taken every six months. The last
sample was obtained on 18 February 2014 and tested ashore. The results of the grease
samples for all four cranes indicated that they within the accepted parameters value
range. The full results can be found in Annex D.
On 19 February 2014, all the deck cranes were examined by the ABS surveyor in
Singapore, in accordance with the annual thorough examination of cargo gear and
cranes. The Register of Lifting Appliances did record the deck cranes to be found in a
satisfactory condition. However, it did not record whether a rocking test was carried
out as specified in the ABS Requirements of Guide for Certification of Lifting
Appliance 2007, Notice No. 64 (Annex E) and the planned maintenance system.
1.10 The Slewing Ring Bearing
The slewing ring bearing assembly was fabricated by Dalian Metallurgical Bearing
Co. Ltd, China under the standard JB/T2300 of the type 133.34.2300.00.03 (three-
row) roller slewing ring bearing with internal gear (Figure 6).
4 Notice No. 6 is effective as from 01 May 2011.
17
Figure 6: Cross Section of Slewing Bearing
5
The main function of the slewing bearing was to provide a rotational attachment point
to secure the rotating deck crane to the fixed pedestal mount (Figure 6). The three
main parts were the supporting ring, the retaining ring and the nose ring. The
supporting ring raceway sat on the upper thrust rollers (A) which in turn sat on the top
raceway of the nose ring (D) and bore the weight of the cabin and jib. Radial rollers
(B) between the supporting ring radial raceway (outer) and the nose ring radial
raceway (inner) controlled radial movement.
5 Courtesy of TSB Engineering Branch Final Metallurgical Report, Annex F.
18
The retaining ring joined directly to the periphery of the supporting ring and was
bolted to the bottom of the cabin assembly, encasing the lower (auxiliary) thrust rollers
(C) between the retaining ring raceway and the bottom raceway of the nose ring to
prevent tipping. The nose ring was bolted directly to the pedestal. The deck crane
was rotated by two hydraulically operated pinion gears on the bottom of the cabin that
engaged with the internal circumferential gear of the nose ring.
1.11 Follow up Investigation
After landing the damaged deck crane cabin ashore, the TSB team dismantled the
slewing ring bearing in order to transport it to the laboratory for further testing.
Preliminary inspection of the slewing ring indicated:
i. a progressive failure initiated separation of the roller raceways from the nose ring
of the bearing assembly (Figure 7).
ii. that fatigue and overstress zones were observed on a macroscopic level in the
area of the rupture (Figure 8).
19
Figure 7: Inner part of slewing ring showing area of fracture where the raceway separated
Figure 8: Outer part of slewing ring showing fatigue and overstress zones
Fatigue zone
Crane Pedestal
Over stress zone
Lower roller segments
Over stress zone
Upper roller segments
Fatigue zone
20
During the separation of the slewing bearing from the main bottom section of the cabin
unit, the TSB team also found that:
i. three out of 64 fastening bolts did not meet the specifications;
ii. one bolt was 152 mm instead of the required 305 mm and was of a coarse thread
of M54 * 4.75 instead of M45 * 2.0 fine thread (Figure 9);
iii. the third bolt was missing the first 25 mm of thread (Figure 10); and
iv. one bolt was bent (Figure 11).
Figure 9: Length of bolt 152 mm instead of 305 mm length
Figure 10: Missing thread
21
Figure 11: Bent bolt with signs of rubbing
On 26 June 2015, the TSB team completed the examination of the failed slewing
bearing under laboratory conditions and issued a report. The engineering report
concluded that:
i. the slewing bearing failed as a result of separation of the nose portion from
the gear portion of the nose ring;
ii. the nose portion separated due to fatigue cracking which initiated at the
undercut fillets machined between the nose and gear portions of the nose
ring and progressed to the point that the nose ring could no longer resist the
applied loads and separated in overstress fracture;
iii. fatigue cracking of the nose ring likely initiated as a result of vibrations
generated due to operation with spalled raceways and contaminated
lubricant;
iv. the particulate that contaminated the slewing bearing grease was generated
internally due to deterioration of the outer radial raceway of the supporting
ring;
v. the outer radial raceway likely deteriorated due to a combination of
corrosion and spalling6 when moisture migrated between the supporting
ring and the retaining ring;
6 Spalling is a process which leads to the breaking up into fragments.
22
vi. the chemical composition of the steel used for the bearing components met
the grade requirements of the engineering drawings;
vii. the hardness of the nose ring, supporting ring and retaining ring core
materials was less than the minimum value specified on the engineering
drawings;
viii. although the bearing raceways met the specified requirements with regards
to hardness, the depth of the hardened layer on the radial raceways was
insufficient;
ix. the lower core hardness and insufficient depth of the hardened layer would
have reduced the load-bearing capacity of the raceways. This would have
made them more vulnerable to plastic deformation and premature rolling
contact fatigue, resulting in sub-surface spalling; and
x. there was no seal in the design of the supporting ring/retaining ring
assembly to prevent moisture ingress.
A copy of the full metallurgical report can be found at Annex F.
23
2 ANALYSIS
2.1 Aim
The purpose of a marine safety investigation is to determine the circumstances and
safety factors of the accident as a basis for making recommendations, to prevent
further marine casualties or incidents from occurring in the future.
2.2 Cause of the Accident
Evidence indicated that the bearing failed in the overstressed extension of pre-existing
upper and lower circumferential fatigue cracks. The fatigue cracking initiated at the
undercut fillets, above and below the extended nose portion of the nose ring (Figures
7, 8 and 12).
Figure 12: Failure mechanism
7
7 Courtesy of TSB Engineering Branch Final Report, Annex F.
24
It would appear that the primary fatigue cracks grew slowly under high-frequency,
low-amplitude cyclic loading. When the primary fatigue cracks were close to each
other near the bow and port sides of the nose ring, the crack fronts turned and
continued to propagate in the circumferential directions. At some point, the remaining
intact nose ring material could no longer support the applied loads and the nose
portion of the nose ring was torn from the gear portion. As the slewing bearing
separated, it allowed the cabin and the jib to fall from the pedestal into the cargo hold.
It is understood that the final overstress fracture occurred when the crack propagation
in the circumferential direction had covered about 40% of the circumference. It was
estimated that about 70% of the entire fracture area failed in fatigue.
2.3 Cause of Bearing Failure
Evidence indicated that corrosion damage at the bottom edge of the raceway may have
been the initiating event for the extensive spalling damage noted to this raceway
(Figure 12).
It is considered that once deterioration of the radial raceway began, either through
corrosion or spalling, the resulting contamination of the lubricant would have led to the
extensive damage that was observed in the engineering laboratory.
Examination of the bearing suggested that the area with the most extensive and long-
term damage was that portion of the supporting ring/retaining ring assembly located
opposite to and in line with the jib, where the outer radial raceway showed the greatest
material loss.
This was also the area where corrosion ingress had occurred between the bolted
supporting ring/retaining ring assembly. This suggested that the bearing failure began
in the portion of the bolted assembly least protected from the elements, since there was
no cab or jib on that side. This was also where the assembly was loaded in tension as
that portion of the slewing bearing prevented the crane from tipping.
Spalling of the outer radial raceway would have created excessive amounts of debris in
the bearing grease. The contamination was not present at the time of sampling of
grease in February 2015. This contaminated grease then migrated throughout the
25
bearing with rotation of the assembly. Operation of the upper rollers over the
contaminated lubrication initiated and accelerated the spalling observed on either side
of the soft zone in the top raceway of the supporting ring.
The operation of the rollers over this spalled area, combined with the deterioration of
the radial raceway and contamination of the lubricant, would probably have generated
sufficient vibration in the assembly to act as the driving force to initiate fatigue
cracking in the cantilevered portion of the nose ring. This vibration would also have
acted to propagate the fatigue cracking and appears to be consistent with the high cycle
nature of the fatigue propagation.
As the slewing bearing was lubricated by an automatic pressurised greasing system, it
was unlikely that the failure occurred from lack of lubrication to the bearing. The
mismatched and bent securing bolts (Figures 9 to 11) between the slewing bearing and
cabin also did not contribute to the failure of the bearing.
2.4 Design of the Slewing Bearing
Bearing failures are rare on relatively new vessels. However, this was the second
bearing to have failed on Seapace. Although the nature of failure of the first bearing
is not known, the design of this type of bearing is such that the outer diameter of the
retaining ring is larger than that of the supporting ring. This generates a lip around the
entire bearing, where moisture and debris can collect. Moreover, the joint between the
supporting ring and the retaining ring had no gasket, O-ring or sealant to prevent
moisture ingress.
2.5 Rocking Test
The last rocking test which had been carried out was on 30 January 2014. It was
required to be carried out every six months. The test following the one carried out on
30 January had been scheduled to be undertaken but was eventually not carried out
because on 30 July, the vessel was at sea and the test could only be done while the
vessel was either alongside or at a sheltered anchorage. Although the rocking test was
not carried out as required, it was doubtful whether the test would have detected the
problems on the deck crane.
26
A rocking test is a simple method that can be undertaken by ship’s crew to determine
the wear on the bearings. However, it neither determines whether fatigue cracking has
begun, nor does it determine the condition of the raceways. As long as they are within
manufacturers recommended tolerances, the deck crane may be operated.
The alternate to a rocking test is an ultrasonic inspection of the nose ring from the
inner diameter and/or acoustic monitoring during movement of the slewing bearing.
This method may be better suited to identify progressive bearing deterioration before
failure. However, this method (or any other method using liquid penetrant or
magnetic particles) would require sophisticated equipment, immobilisation of the
crane and training that may not be suited for ship’s crew and therefore would require
that it is undertaken by a shore contractor.
2.6 Grease Analysis
The results of the grease analysis sampled on 14 February indicated a high iron (Fe)
content on all four samples taken from the deck cranes. Moreover, the ‘particle
quantifier index’ was also noted to be high. The concluding remarks on the report,
which stated that the samples were within limits and had passed, were misleading.
The fatigue noted on the slewing bearing would indicate that this had occurred over a
period of time and not since the last grease sample was tested. This was further
supported by the average number of hours the cranes had been in use since. It was
possible that the grease samples sent for testing were not representative of the actual
condition of grease since one would have expected a higher amount of iron content to
be present in the grease.
2.7 Maintenance Issues
It would appear that, a prima facia, these reports were neither scrutinised nor
compared with previous results. In view of the previous failure of the slewing
bearing, there was a strong case to monitor the results of the grease samples as they
would have been a good indicator of the condition of the bearings.
27
During the course of the safety investigation, the MSIU did not come across evidence
which indicated that the findings of the 14 February grease sample were discussed /
communicated to the manufacturer for his guidance. The fact that the samples were
found within limits led the crew members to make an ‘unspoken’ assumption about
the safety of the deck crane. It was also indicative that if analysed, the test results
were seen in isolation.
A proactive maintenance model is based on a preventive maintenance philosophy, or a
period of running hours or calendar time. Preventive maintenance is thus based on a
hypothesis that the equipment being maintained has a lifespan which may be
objectively calculated (otherwise, time intervals would not be recommended by the
manufacturer).
Although the bearing failed about 46 months after it had been replaced, it may be
submitted that it was in its middle region of its life8. The problem in this particular
case was that corrosion was a variable which did not seem to have been considered.
Thus, whereas the failure rate of most components would be constant during the
middle region of their lifespan, in this particular case, corrosion had reduced the
duration of the useful life of the bearing.
The importance of following the manufacturer’s recommendations is crucial in terms
of a planned maintenance policy on board. However, the operating context (i.e. the
marine environment) introduces a number of variables, which would make it
extremely challenging for the manufacturer to consider all the variables into the
equation. That resulted in a situation where predictive maintenance9 was difficult to
achieve.
8 Structural failure was therefore not correlated to the age of the bearing.
9 Proactive maintenance has two components – preventive and predictive.
28
THE FOLLOWING CONCLUSIONS AND
RECOMMENDATIONS SHALL IN NO CASE CREATE
A PRESUMPTION OF BLAME OR LIABILITY.
NEITHER ARE THEY BINDING OR LISTED IN ANY
ORDER OF PRIORITY.
29
3 CONCLUSIONS
Findings and safety factors are not listed in any order of priority.
3.1 Immediate Safety Factor
.1 The bearing failed in the overstress extension of pre-existing upper and lower
circumferential fatigue cracks. The fatigue cracking initiated at the undercut
fillets above and below the extended nose portion of the nose ring.
.2 The final overstress fracture occurred when crack propagation in the
circumferential direction had covered about 40% of the circumference.
.3 Corrosion damage at the bottom edge of the raceway may have been the
initiating event for the extensive spalling damage noted to this raceway.
.4 The operation of the rollers over this spalled area, combined with deterioration
of the radial raceway and contamination of the lubricant, would probably have
generated sufficient vibration to initiate fatigue cracking in the cantilevered
portion of the nose ring.
3.2 Latent Conditions and other Safety Factors
.1 The design and construction of the slewing bearing was such that a visual
examination of the condition could not be easily undertaken.
.2 The design of the slewing bearing did not help the prevention of moisture
ingress between the supporting and retaining ring.
.3 The operating context (i.e. the marine environment) introduced a number of
variables, which made it extremely challenging for the manufacturer to
consider all the variables into the equation. That resulted in a situation where
predictive maintenance was difficult to achieve.
30
3.3 Other Findings
.1 The latest grease analysis stated that the grease samples were within limits
whereas the iron content was noted to be high.
.2 The rocking tests were overdue but could not be carried out because the vessel
was at sea.
4 RECOMMENDATIONS
In view of the conclusions reached and taking into consideration the safety actions
taken during the course of the safety investigation,
Thenamaris Ships Management is recommended to:
22/2015_R1 Review their grease sampling procedure and monitoring
programmeto ensure that it provides atrue analysis of its condition.
Wuhan Marine Machinery Plant Co Ltd is recommended to:
22/2015_R2 Review the design of the bearing to take into account the lessons
highlighted in this investigation.
22/2015_R3 Adopt a Reliability Centred Maintenance (RCM) philosophy with
the participation of its customers to enhance the reliability and cost
effectiveness of maintenance of deck cargo cranes.
31
LIST OF ANNEXES
Annex A Transportation Safety Board of Canada Marine Safety Advisory Letter
No. 08/1410
Annex B Deck Crane Slewing Ring Rotation Test
Annex C Deck Crane Rocking Test Measurement – 30 January 2014
Annex D Quality Control Report on Four Grease Samples from MV Seapace
Annex E ABS Requirements of Guide for Certification of Lifting Appliance 2007,
Notice No. 6 – May 2011
Annex F Metallurgical Report11
10
This Annex is being reproduced by permission of the Transportation Safety Board of Canada.
11 This Annex is being reproduced by permission of the Transportation Safety Board of Canada.
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