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Terms in this set (25)
pressure at which the relief device begins to activate
maximum allowable working pressure. max gauge pressure permissible at the top of a vessel for designated temperature.
gauge pressure during normal service, usually 10% below the MAWP
pressure increase over the MAWP during the relief process
pressure increase over the set pressure during the relief process
pressure at the outlet of the relief device during the relief process resulting from pressure in the discharge system.
maximum allowable accumulated pressure (MAAP)
sum of the MAWP and the allowable accumulation
which gov agency maintains CAMEO chemicals and what does it do
NOAA- National Oceanic and Atmospheric Administration
a tool designed for people who are involved in hazardous material incident response and planning.
difference between a tempered and non tempered system when considering pressure relief systems
tempered- reactor contains a volatile liquid that vaporizes or flashes during the relieving process. removes energy by means of the heat of vaporization and tempers the rate of temperature rise resulting from the exothermic rxn. COOLED BY PRODUCTION OF VAPOR DURING RELIEVING PROCESS (PRODUCES A VAPOR OR NONCONDENSING) AND MORE SELF REGULATION
NON TEMPERED- NOT COOLED BY PRODCUTION OF VAPOR (NO VAPOR, NON CONDENSABLE)
what distinguishes a hybrid or gassy system when considering pressure relief systems
gassy & hybrid- both produce non condensable vapors
gassy- non tempered
hybrid- can be tempered or non tempered
main considerations which would typically indicate a rupture disk should be used as opposed to spring operated
relief devices are chosen for specific applications, such as for liquids, gases, liquids and gases, solids and corrosive materials. may be vented to atmosphere or vented to containment systems.
rupture discs- used in corrosive service, can provide absolute isolation, can be used to protect spring-loaded devices, can be used to relieve slurries
5 guidelines which are used to identify the need for a relief device
1. all vessels need reliefs, including reactors, storage tanks, towers, and drums.
2. blocked-in sections of cool liquid-filled lines that are exposed to heat (such as the sun) or refrigeration need reliefs
3. positive displacement pumps, compressors, and turbines need reliefs on the discharge side
4. storage vessels need pressure and vacuum reliefs to protect against pumping in or out of a blocked-in vessel or against the generation of a vacuum by condensation
5. vessel steam jackets are often rated for low-pressure steam. reliefs are installed in jackets to prevent excessive steam pressures due to operator error or regulator failre
explain why a pressure gauge is often put between a rupture disk and a relief valve where the rupture disk is exposed to process conditions
the pressure gauge allows you to determine whether the rupture disk has ruptured, exposing process directly to the relief valve. if the pressure gauge shows a pressure increase, the rupture disk has ruptured and needs to be changed out.
important aspects of rupture disk
1 time use, lower cost, premature rupture can occur due to flexing, can be installed upside down, once open/always open
important aspects of spring operated valve
opens based on pressure drop across the valve seat, set pressure screw, all internals are exposed, reusable, back pressure can prevent relief at set pressure
important aspects of balanced bellows
bellows on the backside of the valve seat ensures that the pressure eon that side of the seat is always atmospheric, back pressure can still decreases flow rate but valve will always open at the desired set pressure, all internals are exposed (not for corrosive service), more expensive then spring operated
important aspects of pilot operated valves
more complex/expensive, high level control for set pressures (Delta P ~ 5%), used for accuracy, when the pilot valve reaches the set pressure it opens and releases the pressure above the main valve. the large valve piston then opens and exhausts the system fluid. the pilot and main valve reseat when the inlet pressure drops below the set pressure, commonly used in clean services.
buckling pin valve
rupture pin set to pressure, pin buckles at precise pressure, 1 time use, internals not exposed, full open (similar to disk) where other valves can have "whisping"
advantages and disadvantages of using a conventional spring operated relief valve compared to a balanced bellows relief valve
spring operated conv adv = very reliable, used in many services, reseats at pressures 4 % below set pressure/ disadvantages = relief pressure affected by back pressure, can chatter with high back pressures, don't use if corrosive
spring operated bal bellows adv = relief pressure not affected by back pressure, handles higher buildup back pressures, protects spring from corrosion/ disadvantages = bellows may fatigue/rupture, flow is function of back pressure, may release flammables/toxics to atmosphere
example of checklist important
peter pronovost, ICU, checklist for putting in patient lines- line infection rate went from 11 to 0%
brief overview of HAZOP study
multiple person, multiple discipline
PFD, P&ID and process info
identify items and scenarios
apply guide words and move through PFD
write/follow up action items
common mode failure
single event that affects a number of pieces of hardware simultaneously
example power outage, losing air, losing steam
layer of protection analysis- semi quantitative tool for analyzing and assessing risk. various layers of protection are added to a process to lower the frequency of the undesired consequences- may include inherently safer concepts, passive devices, active devices, etc.
probability of failure on demand. ex: flat spare in addition to a flat tire, turn light switch on and power doesn't work
what is typically assumed to be true for each LOPA layer
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