30 September 2004
STEAM BOILER SYSTEMS
STEAM BOILER SYSTEM DEFINED. A steam boiler is an enclosed
vessel that holds water and is heated by an external source that converts the water to
steam. All steam boilers contain tubes that separate the water from the heat source.
Steam boilers are described in this Chapter; hot water boilers are addressed in Chapter
Types of Steam Boilers. Boilers are classified by two criteria: 1)
operating pressure (i.e., the amount of internal pressure generated by the steam that is
produced); and 2) the operational design (i.e., whether the water [water tube boiler] or
the heat source [fire tube boiler]) passes through the inside of the tubes of the boiler
Pressure Classification. A boiler that operates at pressures below 103
kilopascals (15 pounds per square inch gauge) is defined as a low-pressure boiler. A
boiler operating pressure greater than 103 kilopascals (15 pounds per square inch
gauge) is defined as high pressure. High-pressure boilers can operate at pressures
reaching thousands of kilopascals (thousands of pounds per square inch gauge).
through the interior of the boiler tubes to heat the water that surrounds the tubes (see
Figure 3-1). This type of boiler design is commonly used for factory-assembled
(package) boilers, which are low pressure.