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

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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.

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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).

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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

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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.

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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

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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.

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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.

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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.

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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).

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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.

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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.