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ASME BPVC 2023 Section VI
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ARTICLE 3
TYPES OF BOILERS
3.1 CLASSIFICATION
Section VI classifies heating boilers by the ASME Certification,
method of manufacture, category, method of heat
input, and other design characteristics.
3.2 ASME CERTIFICATION MARK
Section IV provides requirements for using the Certification
Mark with H or HLW designator.
ð23 3.2.1 Boilers Marked With the Certification Mark
With H Designator
Boilers marked with the Certification Mark with H
designator may be steam heating boilers, hot water
heating boilers, or hot water supply boilers.
3.2.1.1 Steam heating boilers may be used in open or
closed systems in accordance with Manufacturers
instructions and jurisdictional requirements and shall
operate at 15 psi 100 kPa or less.
3.2.1.2 Hot water heating boilers are intended for use in
closed-loop systems with limited potential for corrosion of
the boiler. Hot water heating boilers are limited to operation
at 160 psi 1 100 kPa or less and water temperatures
not exceeding 250°F 120°C at or near the boiler outlet.
3.2.1.3 Hot water supply boilers may be used for
purposes other than space heating. They may be installed
in open- or closed-loop systems. Hot water supply boilers
are limited to operation at 160 psi 1 100 kPa or less and
water temperatures not exceeding 250°F 120°C at or
near the boiler outlet.
ð23 3.2.2 Potable Water Heaters Marked With the
Certification Mark With H or HLW Designator
Potable water heaters marked with the Certification
Mark with H or HLW designator may be used in openloop
systems and shall be constructed from corrosionresistant
materials or with a corrosion-resistant lining.
Water heaters are limited to operation at 160 psi
1 100 kPa or less and water temperatures not exceeding
210°F 99°C at or near the water outlet.
3.3 METHOD OF MANUFACTURE
3.3.1 Fabricated Boilers
Fabricated boilers may be steel, stainless steel, copper,
and less commonly, other metals or alloys. Some boilers
use polymer or composite materials in the boiler pressure
vessel and are generally classified as fabricated boilers
within Section VI.
3.3.1.1 Firetube Boilers. In firetube boilers, the gases of
combustion pass through the tubes and the water circulates
around them.
3.3.1.1.1 Horizontal Return Tube HRT. In an HRT,
the boiler is often in a refractory or brick setting and the
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products of combustion flow under the boiler and return
through the firetubes. The furnace may also be
constructed of steel. See Figure 3.3.1.1.1-1.
3.3.1.1.2 Scotch-Type Boilers. The scotch boilers
used in modern heating systems are similar to those
originally designed for shipboard installation and are
sometimes called scotch marine boilers. The furnace is
a cylinder completely surrounded by water. Most
scotch boilers are of the dry-back or partial wet-back
design and are arranged for multiple gas passes. See
Figure 3.3.1.1.2-1.
3.3.1.1.3 Firebox Boilers. Firebox boilers have the
firebox integral with the boiler, such as in the oil field
or locomotive type, and may be single or multiple
pass. The furnace of this type of boiler is usually enclosed
in a water-cooled upper sheet, called a crown sheet.
Various tube and shell configurations, characterizing
different Manufacturers designs, complete the boilers.
See Figures 3.3.1.1.3-1 and 3.3.1.1.3-2.
3.3.1.1.4 Vertical Firetube Boilers. In vertical firetube
boilers, the products of combustion pass up or
down through the tubes that are surrounded by water.
See Figure 3.3.1.1.4-1.
3.3.1.2 Watertube Boilers
3.3.1.2.1 In watertube boilers, the water passes
through the tube and the combustion gases pass
around them. Refer to the Manufacturers instructions
for minimum water flow rate requirements.
ASME BPVC.VI-2023
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