ASME BPVC 2023 Section IV

ENDNOTES
1 In order to ensure that a finished head is not less than the minimum thickness required, it is customary to use a
thicker plate to take care of possible thinning during the process of forming. The neck of an opening in a head with an
integrally flanged opening will thin out due to the fluing operation. This is permissible, provided the neck thickness
is not less than the minimum thickness specified in HG-301 or the thickness required for a cylindrical shell having a
diameter equal to the maximum diameter of the opening. See HG-323.
2 The formulas provide safe construction as far as stress is concerned. Greater thicknesses may be necessary if
deflection would cause leakage at threaded or gasketed joints.
3 The rules governing openings as given in this Code are based on the stress intensification created by the existence of
a hole in an otherwise symmetrical section. They are based on experience with vessels designed with a safety factor
of five applied to the specified minimum tensile strength of the shell material. External loadings such as those due to
thermal expansion or to unsupported weight of connecting piping have not been evaluated. These factors should be
given attention in unusual designs or under conditions of cyclic loading.
4 Typical examples of the application of these rules are given in Nonmandatory Appendix D.
5 The opening made by a pipe or a circular nozzle, the axis of which is not perpendicular to the boiler wall or head, may
be considered an elliptical opening for design purposes.
6 An obround opening is one that is formed by two parallel sides and semicircular ends.
7 Suggested installation practices for the secondary side of heat exchangers.
8 The foundry that casts the boiler parts or sections and that may shop assemble.
9 May be etched.
10 May be stamped.
11 See HG-515.4 for additional requirements applicable to multiple, duplicate pressure vessel fabrication.
12 Examples of these nationally recognized standards are:
American National Standard/CSA Standard Z21.13/CSA 4.9 for Gas-Fired Low Pressure Steam and Hot Water
Boilers.
American National Standard/CSA Standard Z21.17/CSA 2.7 for Domestic Gas Conversion Burners.
American National Standard/ASME CSD-1, Controls and Safety Devices for Automatically Fired Boilers.
National Fire Protection Association Code/NFPA 85, Boiler and Combustion Systems Hazards Code.
Underwriters Laboratories, Inc., UL 296, Standards for Safety, Oil Burners.
Underwriters Laboratories, Inc., UL 726, Standards for Safety, Oil Fired Boiler Assemblies.
Underwriters Laboratories, Inc., UL 795, Standards for Safety, CommercialIndustrial Gas-Heating Equipment.
Underwriters Laboratories, Inc., UL 834, Electric Heating, Water Supply and Power Boilers.
13 See Nonmandatory Appendix H.
14 A certifying organization is one that provides uniform testing, examination, and listing procedures under established,
nationally recognized standards and that is acceptable to the authorities having jurisdiction.
15 The top or side of the boiler shall mean the highest practicable part of the boiler proper but in no case shall the
pressure relief valve be located below the normal operating level and in no case shall the pressure relief valve be
located below the lowest permissible water level.
16 Guidance for the design of piping systems may be found in ASME B31.9, Building Services Piping.
17 Plumbing codes may require the installation of a reduced pressure principle backflow preventer on a boiler when
the makeup water source is from a potable water supply.
18 These are pressure parts that comply with some ASME product standard accepted by reference in
Mandatory Appendix 2. The ASME product standard establishes the basis for the pressuretemperature
rating and marking.
19 These are pressure parts that comply with an ASME product standard not referenced in Mandatory Appendix 2, or
in accordance with a parts Manufacturers or the Boiler Manufacturers standard that defines the pressure
temperature rating described in the part literature. The part literature shall specify, as a minimum, the material
specification and pressure-temperature rating. The Manufacturer of the completed vessel shall satisfy him/ herself
that all such parts used comply with the applicable rules of this Section and are suitable for the design conditions of
the completed vessel.