some2015 cold cargo kokarakis

Operational and Design Measures to Carry Liquid Cargo at Subzero TemperatureDr. John KokarakisVice President Technology & Business Development, South Europe, Middle East, Africa Zone SNAME SOME SymposiumMay 2015, Athens

*SNAME SOME Symposium Athens 2015

Low temperatures reduce resistance to fracture

In some areas of the world it is anticipated to have subzero temperature cargo.Exposure to low temperatures increases the risk of brittle fracture.Cold cargoes: naphtha, gasoil, gasoline, gas condensate (freezing point < -40 oC)Modern ships increased fatigue damage & lower corrosion waste tolerance. First line of defense is fracture toughness.Quantify resistance of steel to fracture initiation and crack propagation.Arctic region is the new Eldorado


Grade A steel with no Charpy requirement


Ductile tearing fracture Brittle cleavage fractureHigh energy absorbed by ductile fractureIt is associated with large plastic strainIt materializes with large cracksOccurs @ lower thicknesses and lower loading rate


Behavior of steel at low temperatures - NDTDecrease Nil Ductility Temperature. Fine grains & addition of Ni-MnThe myth of yield strength!!!!!Brittle fracture below yield


Crack arrest curves with initial defect


47 J @ 0oC and less than 70% crystallinityNDT (or NDTT) must be > -18oCHeat treatment, welding, compositionNo S-curve transition (SS, Ni, Al)


Design guidelinesUtilization of high grades of steel as much as possibleAcceptable grade A steel when in contact with cold cargo.Fatigue resistant design of structural details.Establishment of toughness requirements for Grade A steel.


Operational guidelinesBallast water to heat cargo. For 200 m3/hr, DT is ~0.5 oC/hr initially.Cargo loaded and heated in parcels.Ballast exchange promotes heat transferBallast heating is safe for low flash point cargoes.Ballast top might freeze creating an insulator (de-icing)Valving on deck to be thermally insulatedUtilization of deck heaters (steam 130oC) to the extend practicable


Cargo heatingPart of the cargo can be warmed at the slop tanks and then mixed with the cold cargo. Cold cargo can cause freezing of the steam in the coil and cause fracture due to the volumetric expansion of ice. Boilers may not have the required capacity for heating the cargo.The heaters are to be kept in permanent operation or drained and isolated after each use so that they may not be rendered inoperative due to ice build-up or thermal oil gelation


Ships for cargoes of temperatures below -10CPrevention of excessive ice built-up in the ballast tanks located adjacent to the cargo tanks. Ice may be detrimental to the ship structure.Prevention of freezing of the heating medium in the cargo heaters and in the piping system.Maintenance of the temperature of the heated cargo in all heaters below its boiling point.Maintenance of the temperature of the cargo in the tanks below its flash point.Oil products are not to be directly heated by steam or thermal oil having a temperature exceeding the boiling point of the product.


Ships for cargoes of temperatures below -10CMaterials used in equipment and systems should be suitable for operation in freezing environment. Discharge rates may need to be reduced to ensure cargo pump drive motors are not overloaded due to the higher viscosity of cargo. Ability of high level alarms to remain active at freezing temperatures needs to be ensured. Relief arrangements must be suitable for the temperatures involved.


Risk analysis Potential overheating of the cargo due to insufficient circulation ( cargo pump failure etc.), which could lead to the creation of an explosive atmosphere.Freezing of the heating medium due to the low temperature/thermal inertia of the cargoExcessive ice built-up in the ballast tanks especially above the waterline.


Countermeasures for ice-buildupAir-bubbling installed on each frame promotes convective heat transfer.Air-bubbling ice-prevention systems keep the water in motion and carry warm water upward from the motion. Surface formation of ice is prevented naturally.Unlikely of the whole tank solidifying due to the insulating action of ice.Ice cannot be discharged at deballasting, reducing the deadweight.Steam injectionVertical heating coilsWater circulation



Transient heat transfer assumptions


ConclusionsCargo from Northern and Southern Russia as well as other Arctic zone regions bears the challenge of carriage of cargoes at sub-zero temperature. Steel at low temperatures, especially the popular grade A steel might turn from ductile to brittle. CVN energy combined with fracture surface appearance constitute the most reliable criteria for a fracture resistant design.Fracture toughness requirements for grade A steel must be included in the rules as a function of expected service temperature.Fracture resistant designs are not driven by strength considerations alone.Cargo needs to be heated to temperature acceptable to the receiving terminal. The technical team needs to determine the proper means of heating the cargo, within the time limits allowed and with the means available.


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some2015 cold cargo kokarakis

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