Presentation on theme: "Transport of hydrogen and LPG : Safety Issues Presented by."— Presentation transcript:
Transport of hydrogen and LPG : Safety Issues Presented by
Hydrogen Properties: Lower Explosion limit with air – 4% Upper Explosion limit with air – 75 % Lower Explosion limit with Oxygen – 4% Upper Explosion limit with Oxygen – 95% Self Ignition Temperature – 585 C Maximum burning speed with air – 346 m/s Colour – Colourless Smell – No odour
Modes of Transport Truck deliverling liquid hydrogen SS inner Vessel CS outer jacket Temperature - -253 o C Pressure – 7.8 bar
Truck delivering Gaseous Hydrogen: Standard tube Trailer : Pressure - 200 bar Capacity – 300 kg Hydrogen delivery through Pipelines MOC – Carbon Steel
General Causes of Accident For Pipelines: Release through ends of pipe Release through a hole in pipeline For Road Tankers: Instantaneous release of complete inventory Catastrophic failure Failure of tubes Leak from loading/unloading valves
Effects of Accidents Instantaneous release of compressed hydrogen can lead to formation of Vapour cloud, which if ignited can explode. In case of catastrophic failure of cryogenic liquid hydrogen pipe or vessel, a pool is formed with continuos evaporation occurring. There is high possiblity of pool fire to occur.
Case Study- Motorway accident of Cessalto Causes of Accident : Dense fog so low visibility High Speed of vehicle Not enough safe distance between two vehicles Due to crash increase in Temperature of the cylinder Crack in cylinder leading to Fire
Effect of Accident 250 cars were affected, 12 people killed 70 people were injured
Direct or Indirect Sources of Risk Lack of Protection in back part of the Tube Trailer : Directly affects : Loading/Unloading valves Pipeline Links
Lack of Protection for Trailer Wheels and fuel Tank : Potential Source of combustible material and Heat in case of accident Lack of lifting points : Useful for Isolation Lack of Equipment to evaluate pressure inside the cylinder from a safe distance
Safeguards Detection system coupled with alarms Types of Hydrogen composition Detector : Catalytic Electro chemical Semi-conducting Oxide (Recommended) Thermal conductivity Mass Spectrometer Sonic
Detection system for Hydrogen Flames Different types of system : Temperature Sensor Heat sensitivity Cable Optical Thermal conductivity Broadband imaging Narrow band imaging
Typical transmission and distribution Piping system
MOC requirements Hardness : 22 HRC Ultimate tensile strength : 950 MPa Should be homogeneous with fine grains Should have reduced non metallic inclusion. Components free from internal and surface defects.
Underground piping system: safety aspects Preferable to have no flanged joints Should have electrical discontinuity between underground and above ground Should be protected from frost, vehicular load from vehicles above the ground Should have proper cathodic protection Uniform pipe coating.
Above ground piping : safety aspects Welded connection are recommended Should be earthed after suitable intervals Should be protected from environmental corrosion
Identification of hazards Damage by third parties Hydrogen embrittlement External corrosion Leaks at valve packing, gaskets Over pressurisation of pipeline Improper inerting procedure Improper operation and maintenance Abnormal loads due landslide etc
Mitigating measures Control of third party interference Increased thickness of pipe Nondestructive test on welds Inerting of pipe Isolation valves : ball, gate valves Emergency Isolation valves – Typically gate valves – Fail close arrangement – At the beginning and at each user end.
Each casting to be hydraulically leak tested Excess flow shut down valve Leak detection Physical protection : concrete coating or encasement
General safety requirements No smoking Personal protective equipments Use of non sparking tools Work permit required while doing maintenance work Positive isolation before maintenance
Proper purging and inerting prior to welding Use of fire watch while welding or cutting Temporary grounding while maintenance and repair Hazardous work permit required before shut down, start up
Embrittlement and environmental damage mechanisms in presence of hydrogen Hydrogen Stress cracking (HSC) – Material becomes brittle or may fail under high stress in presence of hydrogen. – Optimum around room temperature. – Negligible at cryogenic conditions. – From tests critical stress intensity factor is detected. (below which hydrogen induced crack growth does not occur) – Nickel alloys are particularly susceptible. – Fracture occurs in brittle manner under sustained load conditions.
Hydrogen assisted fatigue – Accelearation of fatigue crack growth and degradation in fatigue endurance limits. – Carbon and low alloy steels show degradation even at low pressures. – Not generally observed in pipeline applications due to relatively constant pressure.
Stress corrosion cracking – Typically in underground applications. – External corrion and not influenced by hydrogen. – Untempered martensite in weld areas, microbial activity, coating defects, inadequate cathodic protection are causes. –
Hydride formation – Degradation of metal properties due to precipitation of metal hydrides. – Applied stress promotes formation of hydrides. – Titanium, magnessium, niobium alloys are susceptible.
Metallurgical control Heat treatment – Tampering : increases toughnes – Normalising : gives fine grain structure Sulfide shape control – Sulfides : have elongated shape and akin to crack – Rare earth metals modify shape of sulfides – Globular sulfides do not reduce toughness.
Killed steel – Control of residual oxygen improves toughness – Alluminium is added to control oxygen level it also forms nitrides which forms fine grains.
LPG properties CASE STUDY Fire and Explosion of LPG carrying truck. 07.01.2001 Jamnagar to Varanasi. LFL (%vol): 1.9 UFL (% vol): 9.5 Auto-ignition temperature = 460 o C. UN hazard code = 2.1
Events Poor visibility and fog near Kanpur. Collision with ply-carrier. LPG tanker skids along the slope by the side of road. Shearing of liq/vapour lines of bullet. Profuse leakage. Fire to LPG BLEVE = Boiling Liquid Expanding Vapour Explosion
Other similar cases… LPG carrier derailed at Waverly Tennessee in USA LPG tanker rollover in Virginia
Recommendations Stop traffic passing nearby. Anything that can cause spark must not be used. Contact fire brigade. If leak is small then try to plug the hole if possible. Use dry fire extinguisher to extinguish small fire. Try to cool the tank with water. (BLEVE requires 10-15 min after fire starts)
Precautions The MOC of carrier must not crack in cryogenic conditions. (vaporizing LPG at 1 atm can reach -40 o C) Driver and crew must know the hazards of LPG. Proper training must be given to handle emergency situations. Dry fire extinguisher must be available all the time. For knowledge for public DANGER sign must be displayed on the carrier.
For transport of LPG bottles/cylinders.. Cool the bottles with water. Transfer the bottles away from the source of fire. Piped gas – better mode of transport. Proper system required at the receiving point.