Upload
others
View
36
Download
0
Embed Size (px)
Citation preview
General Propellant Safety*Evaluate Safety and Handling Before
Finalizing Propellant Selection
Some Considerations• Toxicity
• harmful to the environment or human
health when coming in contact
• Exothermal Decomposition• rapid reactions can be dangerous by
releasing lots of heat
• Explosive• decomposes or rearranges with extreme
rapidity, yielding much gas and heat
• Volatility• how readily a substance vaporizes
• Flammability• ability to ignite and combust
• Cryogenic• boiling points below -150°C
• Hypergolic• fuels that ignite spontaneously upon
contact
Hyperbolic Fuels
Hazard Symbol Ex.
Nitrous Oxide Properties• Non-cryogenic, liquid oxidizer
• Density and vapor pressure are highly
dependent on temperature
• Colorless, odorless
• Can displace air and cause asphyxiation
• Can get cold and cause frostbite
• Possibility of rapid exothermic
decomposition
• Avoid direct contact with skin
• Open cylinder valve slowly
• Thermodynamic Properties of N2O• Tables of properties for range of
temperatures
• Chemical Properties and Hazards• Data sheet from PRAXAIR
• Instructions for danger relief
Linde N2O Vapor Pressure
N2O Density
Nitrous Material CompatibilityIncompatible• Organic compounds
• Materials not rated for oxygen use
• Copper, nickel, other catalysts
• Viton, FKM, FPM are chemical compatible but
are swelling significantly when exposed to
N2O (spl.ch)
• Certain grades of elastomers such as Viton®
or Neoprene® are known to swell (AGIA)
Compatible• 304 and 316 Stainless Steel, Aluminum, PTFE
and other Teflon's, Kalrez/FFKM
• PTFE, PCTFE, FEP, PEEKTM, and EPDM
(AGIA)
Elastomer O-rings
Stainless Steels
Nitrous Pros/ConsPros
• Decent availability
• Nontoxic
• Relatively “safe”, only if handled with
caution and safe practices by knowledgeable
personnel
• Easy storage in cylinders
Cons
• Density (therefore performance) highly
dependent on temperature
• Need to have high system pressures to
stay above vapor pressure
• Greenhouse gas
• Susceptible to two phase flows
Two Phase Flow Regimes
Common for Performance Cars
Nitrous Dangers• Decomposition can occur at elevated temperatures
or in contact with incompatible materials
• Explosions have occurred• Industrial and rocketry projects
• Sources like contaminations, local heating,
adiabatic compression/water hammer,
combustion instabilities, electrostatic discharge,
reverse flow of hot chamber gas into tank vapors
• Freezing of valves and/or vents• Temperature decreases with venting
• Good solubility in oil, grease, plastics, and other
hydrocarbons• Creates highly explosive material
• Be very carful of seals, Viton has been used, if
swelling is observed then try Kalrez
(FFKM/FFPM)
• Asphyxiation from vapors
• More on dangers and suggestions• SPL, Is nitrous oxide safe?
• Air Force, Nitrous Oxide Explosive Hazards
• Aspirespace, Hybrid Safety
• More in google drive Scaled Composites
Hybrid Motor
Linde N2O Storage Facility
Nitrous Safety and HandlingRecommendations
• Be extremely attentive when ox cleaning lines
• Use nitrous and pressurant filters • 500 to 150 micron for gases (AIGA)
• Max pressurizing rate of 20 psi/s (SpaceDev)
• Keep nitrous temperatures low
• Electrically ground tanks
• Remote testing operations
• Decent injector pressure drop to avoid
combustion instabilities
• Never run cold flows with nitrous• Use water or CO2
• Avoid nitrous vapors going through engine
• Avoid two phase flow by further pressurizing
with inert gas• N2 or He
• Note that N2 is soluble in N2O, but should be
fine if pressurizing for short periods
• AIGA Safe Practices for N2O• Additional Info
AIGA Oxidizer Pipe Velocity
Vapor Lock and Temperature Effects on Filling• Vapor lock
• When the flow of liquids stops due to
vaporization of the liquid
• Flow is driven by pressure differential
• NO2 Filling• Sometimes use a pump, but not always
needed
• As vapor in NO2 tanks build, the pressure
differential decreases
• To keep pressure difference use small tank
vent, or maintain temperature differential • Temperature drives NO2 vapor pressure
• Can use ice around run tank and cool
down by venting
• Could use warm water over fill tank, not
hot though
NOS Fill Station Ex.
Ethanol Safety and HandlingProperties and Hazards• Different concentrations available
• Lower concentrations with water yield lower
combustion temperatures
• Highly flammable
• Avoid direct contact with skin
• Low volatility but vapors still present, don’t inhale
• Data Sheet
Incompatible Materials (degradation over time)• brass, lead, zinc and lead-based solder
• natural rubber, polyurethane, cork gasket material,
leather, polyvinyl chloride (PVC) polyamides, and
certain thermoplastic or thermoset polymers
Compatible Materials (resistance to degradation)• unplated steel, nickel-plated steel, stainless steel,
black iron and bronze
• reinforced fiberglass, Buna-N, Neoprene rubber,
polypropylene, nitrile rubber, Viton and Teflon
Ethanol Material Compatibility
Chart (google doc)
Personal Protective Equipment (PPE)When to use?
• Leak testing
• Pressure testing
• Hot fires
• Manufacturing
• Anytime when handling hazardous
chemicals, pressurized systems, or
dangerous equipment
• Check for proper PPE before testing!
Typical PPE
• Safety goggles
• Face shield
• Nitrile gloves
• Ear plugs
• Long pants
• Closed toe shoesVarious PPE
Oxidizer Cleaning• Oxygen rich environments need to be clean
of dirt, rust, organics, etc.• If not, then there’s a large fire hazard
• Use different solvent chemicals for
different materials or situations
• Ex: isopropyl alcohol, acetone,
trichloroethylene, simple green
• Basic Procedures• Pre-cleaning
• Deep cleaning
• Rinse in DI water
• Dry with nitrogen gas or in lab
convection oven
• Inspect visually with UV light and lint-
free wipes
• Bag in plastic zip-locks and label
• Standards• ASTM G93
• NASA Safety Standards for Oxygen
• Other team’s procedures
• Specifically for Nitrous Oxide• SpaceDev Report
• Youngblood Paper
Ultrasonic Cleaner
Lint-free Wipes
Pressure and Leak TestingLeak Testing• Ensure leak tight connections before using
propellants
Pressure Testing• Proof test tanks, engines, or other plumbing for
pressurized use
• Typically to 1.2-1.5 FOS, different standards and
requirements out there, so check before doing
• Pneumatic pressurization• Inert gas like nitrogen or helium, helium
molecules are small so it is very good at
finding cracks
• Compressible, so there can be danger of rapid
expansion of gases throwing loose fittings,
hoses, or fragmentation
• Depending on pressure range, can test in
person or far away by monitoring sensors
• Hydrostatic pressurization• Need hydrostatic pump and water
• Less hazardous since lower expansion
potential, incompressible
• At high pressures, possibility of water jet
cutting hazardHydrostatic Pumps
Hose Whip Arrestors
Pneumatic Leak Testing Procedures• Not bad idea to do hydrostatic proof test first
• Could also do hybrid test with nitrogen pressing on
water
• Connect nitrogen cylinder with pressure regulator to
pressurize system• Set regulator pressure before allowing gas to
flow through rest of plumbing
• Check each fitting by applying drops of leak detection
fluid, like Snoop (soapy water)
• Pressurize section, check fittings/monitor decaying
pressures, depressurize, tighten fittings where
needed, and repeat• Slowly go up to about 110% of nominal system
pressures, (not above MAWP)
• Use increments of 50-100 psi
• Only increase pressures when no leaks are
detected
• Never adjust fittings while pressurized
• Progressively test feed system in smaller sections to
isolate leaks
• Can torque stripe fittings after all leaks fixed
• This allows to keep track of fittings already
tested and easily show if any become un-
torqued
Snoop Bottle
Torque Stripping
Bubbles Indicate Leak
Cold Flows and Ignition TimingCold Flow Testing• Flow fluids through feed system and injector
without combustion• Use safe fluids with similar properties, like
water or CO2
• For calibrating system and evaluating
performance• Determining pressure drops, flow rates, flow
coefficients, injector atomization, any issues,
etc.
• Determine actual set pressure of regulators,
can use needle valves in place of engine to
simulate pressure drop
• Determine Cv or Cd coefficients for injector,
make sure to use desired pressure drop
Ignition Timing• Test timing of ignitor in relation to propellant flow
• Good ignition timing is needed to ensure
propellant ignition and avoid hard starts • Light ignitor before opening propellant valves
Fluid Impulse
Purdue Pintle Injector
BURPG Impinging Injector
Developing Testing Procedures• Plan out operating and contingency procedures in clear
lists to read off during test day• SOP – instructions to carry out testing operations
• COP – instructions to follow in case of off nominal
conditions, if stuff goes wrong
• Walk through step by step, and write down line by line
specific, concise operation instructions• Think through each step and what states each part
of the system will be in
• Safety should be most important priority
• Include the action, the component name, target values,
and expected results
• Make sure to include verification checks of valve
positioning, data collection, power supply, etc.
• Revisit and revise procedures many times to catch
errors and constantly improve• Make sure to keep track of edits and reasoning
• Practice running them in person without propellants to
nail down all steps and ingrain into memory• Make sure all test technicians and control operators
know these
• Get them reviewed by a professional if possible
Draft of NETS Operating Procedures
Risk and Hazard Analysis• Create a document or chart of the potential
hazards that could occur and how to mitigate them• Ex. Leaking propellant, ignition failure, etc.
• Could include danger level, likelihood,
preventative measures, possible causes, etc.
• MASA has a good example in their Spaceport
doc
• HAZOP – Hazard and Operability Study• Go through each plumbing component and
operating process
• Determine what the expected result would be if
each part fails
• If it poses a serious hazard then try to find a
design solution to fix it
• Very tedious but can easily help to find flaws Rocket Engine Diagram
Basic Hazard Analysis
TNT Equivalence and Safe Testing Distance• TNT Equivalence is a common measure of energy released
from an explosion• It compares the energy in a system to the energy per
weight of TNT• TNT Energy = 4850 kJ/kg
• Different models/equations for calculating stored gas
energy release, isentropic model is historically common
• Include all compressed gas cylinders, in case of rupture
• Include decomposition energy of nitrous present
• Safe Stand-off Distances• The TNT equivalence can then be used to determine safe
distances for testing
• Different for enclosed or open space, can lessen affected
area by enclosing test or using shielding
• Distances vary for dangers• Blast wave vs. Fragment throw
• Overpressure: Glass break (0.2 psig), Ear drum rupture
(2.4 psig), Lung hemorrhage (14.5 psig)
• Some Resources• DOE Stored Energy Risk Analysis
• Understanding Explosives• See Appendix B
• ASME Pneumatic Testing Distances• Safe distances for TNT weights
• ASME PCC-2 Mandatory Appendix 501-II, pg. 253-255
• Piping-World online summary
Compressed Gas Energy Release
(Isentropic Method)
Nitrous Decomposition
TNT Equivalent
Weight
Scaled Blast Radius
Additional Resources• Google Drive: Nitrous Safety and Handling Folder
• Doc with lists of safety and handling info and links to helpful sources!!!
• Material compatibility pdf’s
• Ox line cleaning and safety
• TNT equivalence calculations
• Aspirespace• Hybrid Safety
• Has info on nitrous as well as other oxidizers
• Purdue Video• Safety Procedures and Best Practices
• Mach 5 Low-Down • Rocket Test Stand and Testing Tips
• Gas Cylinders• Penn State Policies
***Please feel free to add information/slides for future presentations!!!