Safety with cryogenic systems
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SAFETY WITH CRYOGENIC SYSTEMS. Safety aspects 1. Physiological 2. Suitability of materials and construction 3. Explosions and flammability 4. Excessive pressure.

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SAFETY WITH CRYOGENIC SYSTEMS

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Safety with cryogenic systems

SAFETY WITH CRYOGENIC SYSTEMS


Safety with cryogenic systems

Safety aspects1. Physiological2. Suitability of materials and construction3. Explosions and flammability4. Excessive pressure


Safety with cryogenic systems

1. PhysiologicalHazard - Frostbite (cold burns)Safety - Eye and body protectionSafety glasses, face shields, grease free leather gloves, proper footwear, apron and trouser clothing.Clothing – free from grease and oils.


Safety with cryogenic systems

Clothing for hydrogen service - minimum static electricity build-up.Clothing for oxygen service – minimum flammability.


Safety with cryogenic systems

Hazard Nitrogen Asphyxiation - due to spillage or leakage, in large vessels that have contained gaseous or liquid nitrogen, resulting in dilution of oxygen content-creates respiratory problem resulting in unconsciousness;may lead to death


Safety with cryogenic systems

Safety - use oxygen monitors (acceptable 16-25% ) -fresh air purged prior to entry -work in teams, with one team member outside working area. -safety rope and lifeline attached to person entering the tank and lifeline continuously monitored.


Safety with cryogenic systems

Hazard Excess pure oxygen -lung damage occurs if oxygen concentration in air exceeds 60% -prolonged exposure leads to bronchitis, pneumonia, lung collapse. -oxygen enriched air leads to flammability and explosion hazards.


Safety place oxygen detectors or monitors watch for fog or mist

Safety -place oxygen detectors or monitors -watch for fog or mist


Safety with cryogenic systems

2. Suitability of materials and constructionBrittle fracture :-Failure of materials at low temperature under impact.-occurs very rapidly resulting in instantaneous failure.


Safety with cryogenic systems

- failure causes severe damage if the equipment is under pressure - release of fluid such as oxygen may result in fire or explosion


Safety with cryogenic systems

Tests to determine material suitabilityDrop weight tests :NDT (nil ductility transition )temperature of the material - varies with material, thickness,hardness and other properties


Safety with cryogenic systems

Charpy impact test -low cost test - specifies minimum allowable impact value for various materials - stainless steel, aluminum, copper and brass have high impact resistance at low temperatures


Safety with cryogenic systems

Thermal stress -caused by thermal contraction of materials - thermal contraction leads to spillage of cryogen and possibility of fire or explosion - results in differential contraction when two dissimilar materials are joined


Safety with cryogenic systems

- contraction in long pipes is a serious problem - provision is made for change in length by using bellows, expansion joints, flexible hose


Safety with cryogenic systems

4. Over pressure - due to phase change from liquid to gas - systems containing liquid cryogen reach bursting pressure very rapidly, if not relieved and trapped in enclosures - in uninsulated systems the liquid vapourises more rapidly - more the fluid greater the pressure - liquid and vapour phase exists between TPT and CPT.


Safety with cryogenic systems

- entrapment of cold liqiuds and gases may occur in relief valves and burst discs resulting in overpressure - vent lines without rain traps may collect rainwater and freeze closed


Safety with cryogenic systems

Ullage space – vapour filled space above liquid is provided for safe cryogenic storage. - relief valves to be provided,inspected and maintained periodically - in event of freeze closing, ice plug is melted by inserting warm copper rod


Safety with cryogenic systems

Conclusion : Safety is ensured in cryogenic systems by following good operating procedures and practices. - to select materials and methods of construction compatible with properties of cryogens - eliminate sources of ignition - provide proper insulation and relief


Safety with cryogenic systems

- eliminate cracks, recesses,pores in the design and assembly of parts - provide adequate ventilation - keep the surrounding clean and free from contamination


Thank you

THANK YOU


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