Fired And Unfired Pressure
A pressure vessel is a vessel
in which pressure is obtained
from an external source, or
by the application of heat
from an indirect or direct
Vessels may gases, vapors,
and liquids at various
pressures and temperatures.
Fired And Unfired Pressure
Fired pressure
– External heat
Unfired pressure
– No external heat
Pressure Calculations
Stress versus
Hoop Stress
Design And Construction Of
Pressure Vessels
ASME – American Society of
Mechanical Engineers
 ASME Boiler and Pressure Vessel Code
– rules for the design, fabrication, and
inspection of boilers and pressure vessels
National Board of Boiler and
Pressure Vessel Inspectors
Composed of chief boiler and pressure
vessel inspectors representing states,
cities, and provinces enforcing pressure
equipment laws and regulations
National Board Inspection Code (NBIC)
is a consensus document
 Sets standards for the installation,
inspection, and repair and/or alteration
of boilers, pressure vessels, and
pressure relief devices
Electric Boilers
A power boiler,
heating boiler,
high or low
water boiler in
which the source
of heat is
High Temperature Water Boiler
A water boiler
intended for
operations at
pressures in
excess of 160
psig or
temperatures in
excess of 250
degrees F.
Hot Water Heating Boiler
A boiler in which no steam is
generated, from which hot water
is circulated for heating
purposes and then returned to
the boiler, and which operates
at a pressure not exceeding 160
psig or a temperature of 250
degrees F at the boiler outlet.
Process Steam Generator
A vessel or system
of vessels
comprised of one or
more drums and
one or more heat
exchange surfaces
as used in waste
heat or heat
recovery type steam
Unfired Steam Boiler
A vessel or system
of vessels intended
for operation at a
pressure in excess
of 15 psig for the
purpose of
producing and
controlling an output
of thermal energy.
Water Heater Supply Boiler
A closed vessel in which water is
heated by combustion of fuels,
electricity or any other source and
withdrawn for use external to the
system at pressure not exceeding 160
psig and should include all controls and
devices necessary to prevent water
temperatures from exceeding 210
degrees F.
External Inspection
As complete an examination as can be
reasonably made of the external
surfaces and safety devices while the
boiler or pressure vessel is in operation.
Internal Inspection
As complete an examination as can be reasonably made of the
internal and external surfaces of a boiler or pressure vessel
while it is shut down and while manhole plates, handhole plates
or other inspection opening closures are removed as required
by the inspector.
Safety Appliances
Include, but not be limited to:
– Rupture disk device
– Safety relief valve
– Temperature limit control
– Pressure limit control
– Major gas train controls
– Low water cutoffs
– Flame supervisory unit (igniter)
– High and low gas pressure switches
– Trial for ignition limiting timer (15 seconds)
Safety Appliances
Relief Valve
An automatic pressurerelieving device
actuated by a static
pressure upstream of
the valve which opens
further with the increase
in pressure over the
opening pressure.
 It is used primarily for
liquid service.
Rupture Disk Device
A nonreclosing pressure-relief device
actuated by inlet static pressure and
designed to function by the bursting of a
pressure-containing disk.
Safety Relief Valve
An automatic, pressure-actuated relieving
device suitable for use as a safety or relief
valve, depending on application.
Temperature/pressure Relief Valve
A valve set to relieve at a designated
temperature and pressure.
Common Failures Of Pressure Vessels
Error in design and construction
Improper operation
Failure to inspect properly
Lack of preventative maintenance
Boilers In Use
Majority are automatic or semi-automatic
 Operate unattended for long periods of time
Controlling Boiler Fires
Fully enclosed boiler room
 Fire rated doors and walls
 No combustible materials
Fire Protection
Provide clearance around
– Loss control strategies
Boiler explosions and fires
– Testing program
– Safety relief devices
Repair program
– Preventative
maintenance program
Keep a boiler log
Boiler Maintenance
Most of the boiler failures are due to
inadequate maintenance
Low Water Test
Should be tested with
the boiler operating, the
burner should shut off, if
it does not it should be
Tests should be made
daily on pressures>15
PSI and weekly for
Hydrostatic Test Applied to Existing Vessels
To determine tightness, the hydrostatic test
pressure need be no greater than the set
pressure of the safety valve having the lowest
 For safety tests, the pressure should be equal
to 2 times the maximum allowable working
pressure, less corrosion factor, as applicable.
 All major repairs and alterations should
require a safety test.
Blowoff Equipment
All materials used in the
fabrication of object blowoff
equipment should comply
with code.
All blowoff equipment should
be equipped with openings
to facilitate cleaning and
Open valves on each lowwater fuel cutoff valve, low
water alarm, tests the
switches and clears out
debris and obstructions.
Alterations, Retrofits and Repairs to Objects
Alterations, retrofits, and repairs should be
made so that the object should be at least as
safe as the original construction.
 Alterations, retrofits, and repairs should be
done as though new construction and should
comply with the applicable code or codes.
Repairs or alterations by
welding should be approved
beforehand by an authorized
All welding repairs or
alterations must be in
accordance with the “repairs
and alterations to boilers and
pressure vessels by welding,
of the NB code.
All welding should be done
by an organization holding a
national board “R” stamp.
All objects should be so located that
adequate space is provided for the proper
operation, inspection, and necessary
maintenance and repair of the boiler and its
Exit From Rooms Containing Objects
Rooms exceeding 500 square feet of floor
area and containing one or more boilers
having a fuel-burning capacity of 1 million
Btu’s should have two means of exit remotely
located from each other on each level.
Air and Ventilation
A permanent source of outside air should be
provided for each room to permit satisfactory
combustion of fuel and ventilation if
necessary under normal operations.
 The minimum ventilation for coal, gas, or oil
burners in rooms containing objects is based
on the Btu’s per hour, required air, and
louvered area.