Maritime bulk cargo transportable moisture limit requirements for iron ore shipments

Transcription

1 Maritime bulk cargo transportable moisture limit requirements for iron ore shipments Ken Williams, Tom Honeyands, Ralph Holmes, Rolando Orense, Alan Roberts, Michael Pender, David McCallum and Tobias Krull A summary of the AMIRA P1097 iron ore fines TML project

2 Transportable Moisture Limit The TML represents the upper limit of a Group A classified (liable to liquefy) bulk commodity can inherently contain which ensures sufficient cargo stability is attained for safe shipborne transportation 2009 A number of ships in distress carrying Iron Ore Fines (IOF) 08/2009 Hodasco 15 Calcutta to China. Capsized sank off Malaysia DWT 09/2009 Black Rose From India to China. Sank off Paradip port, India DWT 09/2009 Vinalines Mighty Paradip India to China. Developed a list DWT October 2010, the DSC released a circular (IMO, 2010) which stated that iron ore fines may liquefy and should be treated as such TML Investigation begins when DSC formed a correspondence group, subsequently major iron ore companies were asked to form the technical working group (TWG) for iron ore fines TML investigation. April 2012 AMIRA P1097 project commenced

3 Presentation Overview Current IMO TML test options Development of new IOF TML test Failure modelling within the ship Sliding failure Liquefaction Ore characterisation and liquefaction resistance P1097 Project summary Iron ore fines TML requirements

4 IMO SPECIFIED TML TESTS

5 IMO Defined TML Tests Devices and Size Fraction Limitations (1) Flow Table (-7mm) (2) Penetration (-10mm small cell) (-25mm large cell) (3) P/F (-5mm) Iron Ore Fines typically sub 10mm, can be as large as sub 16mm

6 TML Methods Overview TML is 90% of the Flow Moisture Point (FMP) value for the Flow Table and Vibration Test. TML is the intercept between the Proctor Fagerberg compaction curve and the 70% saturation line Three methods prescribed by IMO: Flow Table Test Based on hydraulic slumping of cements. Refined for mineral concentrates. Proctor Fagerberg Test Based on soil compaction science. Refined for mineral concentrates. Vibratory Penetration Test Based on loss of shear strength due vibrational energy Validated by comparison with concentrate TML values from the flow table test.

7 X+12% 14.0% X+10% 12.0% Flow Table Test ( 7mm) Penetration Test (Full size) Proctor Fagerberg Test ( 5mm) TML (%) 10.0% X+8% X+6% 8.0% X+4% 6.0% A B C E Iron Ore Sample Material was scalped to the specified size limit for flow table and Proctor-Fagerberg test Results show variability of over 1% moisture content between tests One of the three IMO methods for TML determination fit the broad spectrum of IOF size distributions The penetration test provides excessively conservative moisture values Some below the dust extinction moisture level No direct relationship apparent between any of the tests and the effects on IOF cargo stability during a ship voyage

8 DEVELOPMENT OF NEW IRON ORE FINES TML TEST

9 Comparison of TML Test Results by varying PF parameters Variations: 1. Upper Particle Size: -5mm size to Full Size 2. Moisture equilibrium: 5 mins and 12 hour 3. Consolidation: 350g hammer (C energy) and 150g hammer (D energy) 4. Percentage of void saturation: 70% and 80% Examples of partially to fully saturated samples in PF test

10 Proctor Fagerberg Curve Example Compaction data from ship survey Proctor Fagerberg curves defined by test results Sr = Percentage of void space filled with water Void ratio = total void volume/total solids volume Optimum Moisture Content (OMC) defined by lowest void ratio= highest dry bulk density

11 16.0% X+14% different moisture equilibration times Comparison of Test Results Size variation between -5mm and full size TML (%) 14.0% X+12% X+10% 12.0% 10.0% X+8% variation between 70% or 80% saturation using the 150g hammer different hammer weights 8.0% X+6% X+4% 6.0% A B C E 350g Proctor Fagerberg ( 5mm, no equil) 350g Proctor Fagerberg (FS, 24h equil) 350g Proctor Fagerberg (FS, no equil) 150g Proctor Fagerberg (FS, 24h equil) 150g Proctor Fagerberg (FS, 24h equil, Sr=80%)

12 Outcomes from PF test work Standard 350 g PF hammer (C Energy) over compacts the iron ore fines when compred to Sponsors in hold data The 150 g hammer(d energy) levels compacts the iron ore fines at void ratios more reflective of ship hold data The OMC occurs at the degree of saturation (Sr) 90% for all of the ores. OMC indicates maximum particulate contact and greatest inter particulate strength. A12 hour minimum equilibration time is recommended as it best reflects the moisture state of the ore within the ship hold prior to disembarkation. Therefore a PF test recommendation from the TWG group and supported by the AMIRA P1097 work for IOF is: Use of a the 150g D energy hammer for use in the PF test Minimum moisture equilibration time of 12 hours minimum As the OMC is greater than or equal to 90% void saturation, a conservative TML value based on the intercept between the PF curve and 80% void saturation. OMC >=90% TML= 80%

13 Inter lab Reproducibility Comparison of the PFD80 Test Results Averages X+16% X+14% TBS ATC Williams X+12% TML (%) X+10% X+8% X+6% X+4% X+2% X+0% A B C E G H I J K L Iron Ore Sample N i 1 (A i B ) 2N i 2 A - TML results from lab 1 B - The TML results from lab 2 N the number of tests. Standard deviation of about 0.17% in gross water content.

14 SHIP FAILURE MODELLING

15 SHIP FAILURE MODELLING PURPOSE: VALIDATION THAT PFD80 MOISTURE LEVELS ENSURE SAFE SHIPBORNE TRANSPORTATION FOR IOF CARRYING VESSELS Two Potential Cargo Failure Scenarios: 1. Dynamic motion induced shear failure Sliding failure 2. Cyclic failure due to excessive pore water pressure Liquefaction induced failure

16 What size vessels ship IOF? World iron ore carrying vessel mix by % total Iron Ore voyages in 2012 (TWG Marine Report)

17 TWG Marine Report (TWG 2013b) on vessel motions and forces summary The contribution from vibrations associated with engines is negligible. Vertical and the transverse motions are significant compared to longitudinal motion. For vertical and transverse motions, accelerations in Handysize vessels are up to twice those of Capesize vessels. Capesize vessels have a natural roll period of 10 seconds or 0.1 Hz Hold 1 (forward hold) experiences the largest accelerations. Real world accelerations measured during voyages are typically lower than those predicted by voyage calculations. The observed vessel accelerations are less than 1 G, typically 0.1 G. Handy size vessels represent worst case scenario

18 HANDY Size vessel motion example Example of a Handy size hold cross sectional size Handy vessel 12,000 DWT Bay of Biscay (Atlantic Ocean) Worst case handy vessel motions: 2 m/s 2 rolling and heaving accelerations Angle of roll: - Typically less than 20 o for multiples events - not greater than 30 o for single event

19 Shear (Sliding) failure mode Animation for generation of a sub-surface bulk failure plane CoG of material Wet layer depth Insipient failure

20 Continuum modelling of a non-saturated sub-surface circular failure plane Roll Heave y O Non-saturated material R W Circular-sector curve radius Bulk material weight + α CoG Centre of gravity θ R R Circular failure plane θ S L Surcharge angle Gravity torque distance R L CoG φ f Tangential failure angle to the horizontal surface θ s x φ f W CL

21 Fundamental stress analysis inputs Example: Ore B at approx. PFD80 moisture Flow properties at ore B relating to PFD80 moisture content.

22 Cape Size Hold 1 Continuum modelling of sub-surface failure Interpretation of results CoG shift = 9.34m Filling ratio = 0.5 After failure levelled surface R = 38.8 o f = 51.3 o Failure at 38.8 o Roll angle Safety factor > 1.29 (based on 30 o Roll angle) Assessment valid for wet layer heights less than 1.6 m 10 5 New CoG m Allowed maximum wet layer depth = 1.61 m Original CoG Circular failure plane

23 Critical Roll Angles for Sub surface Failure at PFD80 Moisture Content Critical roll angle degrees Hold Ore A Ore B Ore C Ore E Ore F Ore G Ore J Cape size No. 1~ No No Panamax size No. 1 ~ Handymax size No No. 2 ~ Handy size No. 1 ~ In all cases, ship has to exhibit roll angles greater than 30 o to induce sub surface sliding failure

24 Numerical Modelling of liquefaction Computer program FLIP (Finite Element Analysis of Liquefaction Process) was used This modelling work attempted to investigate the cyclic response of partially saturated iron ore cargo (Sr = 80%), with and without the wet base. A 3 m wet base was assumed based on seepage analysis. Calibrated to Cyclic triaxial test results

25 Liquefaction failure modelling outcomes The development of excess pore water pressure (EPWP) is slow no EPWP development at the base, indicating no occurrence of liquefaction. Vertical ore displacement is also very small, showing that any deformation is related to localised shearing of the ore due to roll motion and not due to liquefaction The rate of increase in pore water pressure and settlement is related to the rate of increase in roll amplitude (i.e., the faster the rate of increase in roll angle, the faster EPWP). In the case where the 3 m wet base has lost all strength, settlement of the cargo surface was higher due to increased cargo consolidation. However, cargo stability was still maintained due to ore wall confinement and ore overburden above the wet base which prevented the occurrence of liquefaction induced flow type failure.

26 Ore Characterisation and liquefaction resistance

27 Cyclic resistance to liquefaction type failure Cyclic test results Shear stress (kpa) Excess pore pressure (kpa) Initial liquefaction 95% of initial confining pressure Shear strain (%) liquefaction based on strain DA strain 7.5% (simple shear) 5.0% (triaxial) Cyclic resistance 12 iron ore fines tested The cyclic stress ratio after 500 motion cycles was defined as the maximum cycles iron ore fines would experience Cyclic triaxial test work was compared to material parameters of goethite and median particle sizing

28 Goethite content versus cyclic resistance Ore F 35% goethite content line Goethite has high water holding capability, thereby cyclic resistance increases with goethite content TWG have proven that IOF with greater than 35% goethite have sufficient cyclic resistance to liquefaction in worst case ship motions (see TWG research at twg.com) Ore F exhibits free draining type behaviour

29 Goethite content versus median particle sizing increased particle sizing increases cyclic resistance of iron ore fines tested

30 Summary Bulk Strength Iron ore fines still retain significant bulk strength at the PFT D80 moisture level. Sliding Failure localised surface failures are possible but will not cause global cargo instability, sub surface failure modelling predicts that cargo movement will not occur under extreme vessel motions CTT tests Liquefaction resistance increases with increasing goethite content, particle size and higher porosity. Liquefaction failure Modelling of the liquefaction potential of iron ore fines at the PFT D80 moisture level subjected to expected vessel motion predicted that build up in excess pore water pressure and cyclic deformation were small and liquefaction did not occur. Conclusion The modified Proctor/Fagerberg test is the most appropriate TML test for iron ore fines as modifications were made to calibrate this test to the specific conditions encountered in shipping of iron ore fines. The resulting test is known as the PFT D80 test.

31 IMO TML compliance documents for IOF IMO Circular DSC.1/Circ.71) IMSBC Code 2013

32 Current IMO iron ore fines TML requirements (as per the iron ore fines schedule defined in IMO Circular DSC.1/Circ.71) Iron Ore Fines with less than 35% goethite content Is a group A cargo and requires TML determination with any one of four IMO authorised TML methods as per: The modified Proctor/Fagerberg test procedure for Iron Ore Fines if OMC 90% This method is the preferred method for iron ore fines TML determination, however any one of the other three existing TML methods described in the IMSBC can also be used in preference to the above method. Iron Ore Lump or Iron Ore Fines with 35% or greater goethite: Is a group C cargo and does not require a TML determination

33 TML Requirements Continued Test is valid for 6 months or when the product changes Producer has to ensure loaded cargo is below TML Conducted through a moisture management plan approved by the national competent authority (back of IMSBC Code) Australian competent Authority: Australian Maritime Safety Authority (AMSA)

34 ACKNOWLEDGEMENT The authors would like to thank AMIRA International and the project Sponsors in providing the support in project co-ordination, financial assistance and technical information for the AMIRA P1097 project.