Transcript Chapter 5 – Boilers and Unfired Pressure Vessels

Accident Prevention Manual
for Business & Industry:
Engineering & Technology
13th edition
National Safety Council
Compiled by
Dr. S.D. Allen Iske, Associate Professor
University of Central Missouri
CHAPTER 5
BOILERS AND UNFIRED
PRESSURE VESSELS
Definitions
• Boiler: A closed vessel in which water is heated by
combustion of fuels or heat from other sources.
Definitions (Cont.)
• Unfired pressure vessels: air tanks, steam-jacketed
kettles, digesters, vulcanizers, and other such vessels
Definitions (Cont.)
• High-temperature water: Water kept in closed systems
under a high pressure so that it remains a liquid rather
than turning into steam.
• Pressure parts: Any component of a vessel, boiler, or
water heater that retains steam, hot water, or other fluids
under pressure.
• ASME: American Society of Mechanical Engineers
• NBIC: National Board of Boiler and Pressure Vessel
Inspector’s Code
Potential Safety Hazards
• Boilers and unfired pressure vessels
• Found in workplaces—offices, hospitals, manufacturing plants,
hotels, garages, warehouses
• Contents within vessels—gases, vapors, liquids, solids
• Toxic and benign substances
• Pressures ranging from almost full vacuum to thousands of psi
• Temperatures ranging from hundreds of degrees below zero to well
over 1000°F
Safety Hazards
• Fires
• Burns
• Explosions
• Asbestos
Safety Hazards (Cont.)
• BLEVE: boiling liquid expanding vapor explosion
• This is a type of explosion that can occur when a vessel containing
a pressurized liquid is ruptured. Such explosions can be extremely
hazardous.
• A BLEVE results from the rupture of a vessel containing a liquid
substantially above its atmospheric boiling point. The substance is
stored partly in liquid form, with
a gaseous vapor above the
liquid filling the remainder of
the container.
Image source: Wikipedia, 2009
Failure Modes
• Boilers and high-temperature water heaters
• Pressure part ruptures
• Furnace explosions
• Unfired pressure vessels
• Pressure part ruptures
Boilers and Unfired Pressure
Vessels (UPV)
• Four elements for compliance with ASME
• design
• fabrication
• testing
• installation
Codes for Boilers and UPV
• ASME Boiler and Pressure Vessel Code
• National Board of Boiler and Pressure Vessel Inspectors
Code—governs inspection, repair, and alteration of boilers
and pressure vessels after placed in service
• Boilers and pressure vessel operations are strictly
regulated within jurisdiction of states, municipalities, or
Canadian provinces.
• Synopses of boiler and pressure vessel laws, rules, and
regulations are available from Uniform Boiler and
Pressure Vessel Laws Society.
• National Fire Protection Associations Boiler-Furnace
Standards (NFPA 85A–85E)
Code for Boilers and UPV (Cont.)
• Compliance with ASME is authorized by inspectors
commissioned by the National Board of Boiler & Pressure
Vessel Inspectors—licensed by state or provincial
governmental authority charged with enforcement.
• installation
• operation
• inspection
• repairs and alterations
• routine safety checks
ASME Boiler and
Pressure Vessel Code
• I Rules for Construction of Power Boilers
• II Material Specifications
• III Nuclear Power Facility Components
• IV Rules for Construction of Heating Boilers
• V Nondestructive Examination
• VI Recommended Rules for Care and Operation of
Heating Boilers
• VII Recommended Rules for Care of Power Boilers
ASME Boiler and
Pressure Vessel Code (Cont.)
• VIII Rules of Construction for Pressure Vessels
• Division 1
• Division 2—Alternate rules
• Division 3—Alternate rules
• IX Welding and Brazing Qualifications
• X Fiberglass-Reinforced Plastic Pressure Vessels
• XI Rules for In-service Inspection of Nuclear Power Plant
Components
Inspections of Boilers and UPV
• ASME Code—covers design, fabrication, and inspection
requirements only during construction of boilers and
pressure vessels
• NBIC Code—standard governs after initial installation of
boiler or pressure vessels
• NBIC—guidelines for inspection, repair, alteration, rating,
and rerating for the remainder of boiler or pressure
vessel’s service life
• Manufacturer’s instructions—installation and maintenance
Workers Training
• Train operating personnel:
• to operate equipment properly
• to make routine safety checks
• to call qualified maintenance personnel if necessary or appropriate
• National Board
• Certificates of authorization to perform specific tasks
• NB stamps
Common Causes of Explosions
in Pressure Vessels
• Errors in design, construction, and installation
• Improper installation, human failure, and inadequate
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training of operators
Corrosion/erosion of construction materials
Failure or intentional defeat of safety devices; failure or
override of automatic control devices
Failure to inspect and test thoroughly, properly, and
frequently
Improper application of equipment; overfiring
Lack of planned preventive maintenance
Common Boiler Hazards
• Explosion hazards
• Fire hazards—leakage of fuel or gas
Prevention Measures for Boiler Fires
• Fully enclosed boiler rooms
• Large door openings on boiler rooms
• Noncombustible ceiling and automatic sprinklers
• Proper clearance around exterior walls
How to Minimize Fires and Explosions
• Establish testing and servicing program.
• Always test safety and relief valves under pressure.
• Have repairs made immediately.
• Check and service the boiler in and out of heating season.
• Keep a boiler log.
Boilers
• Boiler—a closed vessel in which water is heated and
steam is generated or superheated under pressure by the
direct application of heat
• Heat sources—combustion of fuel, most common; also
electricity and waste heat from chemical reaction
• Boilers—firetube or watertube
• Boilers registered and certified in accordance with state or
local agencies. Some states require operators to be
licensed.
Design and Construction
• Controls and instrumentation—monitor and control
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combustion and steam production
Economizers—transfer heat from flue gas to incoming
feed water
Super heaters—increase temperature of steam
Air repeaters—transfer heat from flue gas to incoming air
Chimneys—discharge products of combustions
Ash-disposal equipment—remove ash produced
Design and Construction (Cont.)
• Water treatment—remove dissolved O2 and CO2, control
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pH
Blow down pipes and valves—remove sludge and
impurities in boiler water
Safety valves and fusible plugs—safe operation, relieve
excess pressure or vacuum conditions
Steam pressure and water-level indicators/controls—
monitor safe and proper operation
Good piping practice—minimize maintenance work and
easy to reach
Placing boilers in and out of service—manufacturer’s
recommendations
Annual Inspection, Cleaning
and Maintenance
• Clean boilers promptly.
• Follow correct guidelines.
• Schedule maintenance guidelines.
• Follow general precautions for entrance.
• Wear proper attire when entering.
Boiler Rooms
• Safety precautions:
• floors—slippery and dirty
• lighting—source of emergency lighting; controls and gauges well lit;
spare flashlights; exits well lit and identified
• exits—two or more exits (remotely located from each other); proper
exits for each story to a fire escape or directly outside
• emergency shutdown buttons at exits
• stairs, ladders and runways—proper access to operate and service
boiler safely
Operator Training, Procedures
and Boiler Room Emergencies
• Operator error is a major contributing factor in boiler
accidents.
• Operators must understand the process and hazards with
the system, including the purpose and principles of the
control and safety devices installed.
• Procedures for start-up, shutdown and basic
troubleshooting must be developed with assistance from
the manufacturer or a qualified person. Emergency
procedure must be developed for operation.
• Train multiple operators as well as security personnel
patrolling premises and facility.
Safety of High-Temperature Water
• High-temperature water (HTW) vs. steam and cold
water—break in pipe/equipment
• HTW release—volume increases at high rate, energy released at
very low rate; no energy for rupturing equipment or imparting
energy to fragments, but high potential for scalding injuries
• Steam and cold water release—16 times more energy released
during expansion than HTW escape; energy left to produce
explosive effect
• Main causes of failure
• operating errors or mechanical forces (water hammer, thermal
expansion and thermal shock)
• faulty materials
Unfired Pressure Vessels (UPV)
• Vessels designed to contain fluids under internal pressure
or vacuum and not heated directly through the
combustion of fuels or other external heat sources.
• Found in commercial and industrial facilities.
• Heat can be generated from chemical reactions within
vessel or by applying a heating medium within the vessel
or circulating it around the vessel (jacket).
• Examples: compressed air tanks, propane tanks,
deaerators and condensate tanks, steam-jacketed kettles,
pulp mill digesters, rubber vulcanizers
UPV Design
• ASME Code UPV exceptions:
• vessels subject to federal regulations
• vessels with a nominal capacity of 120 gal (450 l) or less of water
under pressure, in which any trapped air serves only as a cushion
• vessels having an internal or external operating pressure not
exceeding 15 psi (103 kPa), with no limitation on size
• vessels with an inside diameter not exceeding 6 in. (15 cm), and no
limitation on pressure
• hot-water storage tanks heated by steam or other indirect means—
heat input of 200,000 Btu (59,000 J/s) or less, water temperature of
200ºF (93ºC) or less, and nominal capacity of 120 gal (450 l) or
less
UPV—Code Divisions
• Design: ASME Code, Section VIII
• Division I—normally covers vessels with ratings of 3,000 psi or
less.
• Division II—normally covers vessels used at pressures exceeding
3,000 psi.
• Other Codes—American Petroleum Institute’s code or state and
local codes may be enforced. Codes may impose size or service
limits more restrictive than ASME Code.
• Secondhand vessels
• Prior to purchase, written report that equipment meets requirements of
jurisdiction where it is to be installed.
• Have the equipment inspected by a NB licensed inspector.
UPV—Internal Inspection
• Internal inspection
• Periodic internal inspections to evaluate integrity of equipment.
• Inspections should be carried out by NB licensed inspectors to
ensure compliance with jurisdictional or insurance requirements.
• Preventive maintenance
UFP—Vessel History Documents
• Inspection or maintenance department should keep file or
log of original design documents, records of inspections,
and vessel history documents.
• blueprints
• manufacturer’s data reports and instructions
• design data, including location of dimensional checkpoints
• installation information
• records of process changes
• vessel’s historical profile, including records of all repairs and
conditions found during inspections
UPV—Entry
• Develop safe policy and procedure for entering tanks
• Confined space with permit and lockout/tagout safety
procedures required by OSHA
• Potential hazards of confined spaces:
• toxic materials including inert gases
• flammable vapors which may be ignited
• insufficient oxygen
• heat or smoke from fire inside vessel
• introduction of hot gases or fluids from external sources
• start up of agitators or putting confined space in motion
UPV Entry (Cont.)
• Prior to entry into pressure vessel:
• Ensure it is properly drained, ventilated, and cleaned
• Test atmosphere for oxygen content, explosiveness, and toxic
levels
• Disconnect and blank all connecting pipelines, or close, lock out,
and tag valves on the line
• All power-driven devices—disconnected, locked out, and tagged
• Confined-space permit issued
• Provide access for safe entry and exit from vessel
• Use safety harnesses and lifelines
• Put on proper PPE
UPV—Cleaning and Purging
• Clean and purge the vessel’s internal surfaces prior to
entry.
• Use specific methods based on the substance contained
inside the vessel.
• Forced ventilation is required to ensure all potentially
harmful or dangerous gases and vapors have been
removed.
• Test atmosphere prior to entry as well as routinely
throughout work processes inside a vessel.
UPV—Testing
• Hydrostatic tests
• Can be used for vessels constructed without access for an
internal inspection to ensure the vessel is fit for continued service.
• Targeted for the maximum allowable working pressure, the set
pressure of the lowest installed safety valve, or the normal
operating pressure of the boiler or pressure vessel at discretion of
the authorized inspector.
• Testing should follow ASME Code and NBIC Codes.
• Minimize hazards to personnel during testing, isolate test area
from operations, and provide suitable barricades.
UPV—Testing (Cont.)
• Detecting cracks/measuring thickness
• Ammonia released inside vessel and compressed air applied to a
maximum pressure 50% of working pressure is obtained; swab
soaked in hydrochloric acid passed over all seams and suspect
areas; presence of white vapor (ammonium chloride) indicates
leakage
• Burning sulfur stick
• Non-destructive methods (NDE)—radiography (RT) and ultrasonic
examination (UT)—detect cracks, wastage, and other adverse
conditions
• Lacquer method—apply lacquer to clean system, then conduct
hydrostatic test, and examine for cracking of lacquer
UPV—Operator Training
and Supervision
• Thoroughly train employees working with pressure
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vessels in routine duties and emergency procedures.
Supervisors should be qualified and knowledgeable.
Review potential hazards of processes and systems.
Written detailed procedures should be reviewed
periodically and made available to personnel.
Use a checklist in the training process for start-up,
shutdown, or routine processing cycle.
Communication between all staff and personnel is
critical.
Proper labeling of valves, piping systems, and control
equipment prevents accidents caused by operator error.
UFP—Safety Devices
• UFP vessels used in processes with various materials and
chemicals, equip each vessel with appropriate safety
devices for the type of vessel and work performed.
• Safety devices are installed for a purpose:
• protect against overpressure
• chemical reactions
• abnormal conditions
Safety Devices UPV
• Types of safety devices:
• safety valves
• rupture disks
• vacuum breakers
• water seal
• vents
• regulating or reducing valves
Autoclaves and Other Vessels
with Quick-Opening Doors
• Pressure interlocks should be installed on autoclaves and
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other pressure vessels containing large volumes of steam
equipped with quick-open doors or reclosing devices.
Pressure interlock will prevent the opening of the door
until all pressure is relieved and prevent introduction of
steam until the door is closed.
Opening the door with chamber under pressure will
release extreme force and may cause accidents. Interior
items may be released like projectiles.
Most critical system of these vessels is the closure system
and its components.
Operators routinely inspect as well as licensed inspectors.
UPV-Autoclaves Safety Procedures
• Specific pressure vessel safety procedures:
• Do not weld to any part of the vessel.
• Do not cut, drill, or fasten to any part of the vessel.
• Assume vessel is pressurized any time the door is closed.
• Check for sufficient oxygen.
• Leave no flammable materials, debris, or plastics in autoclave.
• Closure alignment/inspect vessel
• Schedule periodic maintenance.
UPV Steam-Jacketed Vessels
• Used to heat liquid mixtures to moderate temperature
• Steam circulated between the outer and inner shells of
vessel and heat transferred through the inner shell to the
contents of vessel
• Use safety valves
• Operating procedures for safety:
• Thoroughly drain the steam space prior to adding steam to jacket.
• Admit steam to cold vessels slowly to allow for parts to heat and
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expand uniformly.
Unless automatic protection, open vents only when steam is shut off.
Where agitators are used, paddles must not strike the interior
surfaces of the vessel.
Vessels with large openings must have adequate safety measures to
prevent falls by personnel into the vessel.
Fill only to the point where specified and do not create undue
splashing.
Evaporating Pans
• Shallow pans containing steam coils
• Operational rules to avoid accidents:
• Attend to the pans continuously during operation.
• After each use, thoroughly clean the pans and coils.
• After shutting off steam in the coils, drain them to prevent the
product from being drawn into lines when steam condenses and
creates a vacuum. Installing a vacuum breaker would also prevent
this.
High-Pressure Systems
• Hazards of high-pressure systems result from failures due
to leaks, pulsation, vibration, and overpressure.
• Injuries are possible to employees from the high-pressure
release of steam or gas as well as projectiles thrown from
ruptures or unrestrained
sections of piping, tubing,
or hoses.
• Potential for injury and
damage is very high.
Pressure Gauges
• Pressure gauges used at 1800 psi or more should have
these properties:
• full size
• blowout backs
• integral sides
• front designed to withstand internal explosion
• have multi-ply plastic or double-laminated safety glass cover for
gauge faces
• install substantial shield in front of high-pressure gauges