ASME BPVC.VIII.1-2025
SUBSECTION A
GENERAL REQUIREMENTS
PART UG
GENERAL REQUIREMENTS FOR ALL METHODS OF
CONSTRUCTION AND ALL MATERIALS
UG-1 SCOPE
The requirements of Part UG are applicable to all pressure
vessels and vessel parts and shall be used in conjunction
with the specific requirements in Subsections B, C,
and D and the Mandatory Appendices that pertain to
the method of fabrication and the material used.
MATERIALS
UG-4 GENERAL
(a) Material subject to stress due to pressure shall conform
to one of the specifications given in Section II, Part D,
Subpart 1, Tables 1A, 1B, and 3, including all applicable
notes in the tables, and shall be limited to those that are
permitted in the applicable Part of Subsection C, except
as otherwise permitted in UG-9; UG-10; UG-11; UG-15;
Part UCS; Subsection D, Part UIG; and the Mandatory Appendices.
Material may be identified as meeting more
than one material specification and/or grade, provided
the material meets all requirements of the identified material
specification(s) and/or grade(s) [see UG-23(a)].
(b) Material for nonpressure parts, such as skirts, supports,
baffles, lugs, clips, and extended heat transfer surfaces,
need not conform to the specifications for the
material to which they are attached or to a material specification
permitted in this Division, but if attached to the
vessel by welding shall be of weldable quality [see
UW-5(b)]. The allowable stress values for material not
identified in accordance with UG-93 shall not exceed
80% of the maximum allowable stress value permitted
for similar material in Subsection C.
(c) Material covered by specifications in Section II is
not restricted as to the method of production unless so
stated in the specification, and so long as the product
complies with the requirements of the specification.
(See UG-85.)
(d) Materials other than those allowed by the rules of
this Division shall not be used. Data for new materials
shall be submitted to and approved by the ASME Boiler
and Pressure Vessel Committee on Materials in accordance
with Section II, Part D, Mandatory Appendix 5.
(e) Materials outside the limits of size and/or thickness
given in the title or scope clause of the specifications given
in Section II, and permitted by the applicable Part of
Subsection C, may be used if the material is in compliance
with the other requirements of the specification,6 and no
size or thickness limitation is given in the stress tables. In
those specifications in which chemical composition or
mechanical properties vary with size or thickness, materials
outside the range shall be required to conform to
the composition and mechanical properties shown for
the nearest specified range.
(f) It is recommended that the user or the user’s designated
agent ensure that materials used for the construction
of the vessels will be suitable for the intended
service with respect to retention of satisfactory mechanical
properties, and resistance to corrosion, erosion, oxidation,
and other deterioration during their intended
service life. See also informative and nonmandatory guidance
regarding metallurgical phenomena in Section II,
Part D, Nonmandatory Appendix A.
(g) When specifications, grades, classes, and types are
referenced, and the material specification in Section II,
Part A or Part B is a dual‐unit specification (e.g.,
SA-516/SA-516M), the design values and rules shall be
applicable to either the U.S. Customary version of the material
specification or the SI unit version of the material
specification. For example, when SA-516M Grade 485 is
used in construction, the design values listed for its
equivalent, SA-516 Grade 70, in either the U.S. Customary
or metric Section II, Part D (as appropriate) shall be used.
(h) When the rules of this Division require the use of
material physical properties, these properties shall be
taken from the applicable tables in Section II, Part D,
UG-1 – UG-4 ASME BPVC.VIII.1-2025
8
Subpart 2. If the applicable tables in Section II, Part D,
Subpart 2 do not contain these properties for a permitted
material or do not list them within the required temperature
range, the Manufacturer may use other authoritative
sources for the needed information. The Manufacturer’s
Data Report shall note under “Remarks” the property values
obtained and their source.
NOTE: If material physical properties are not listed, the Manufacturer
is encouraged to bring the information to the attention of the
ASME Committee on Materials (BPV Section II) so that the data
can be added in Section II, Part D, Subpart 2.
UG-5 PLATE7
Plate used in the construction of pressure parts of pressure
vessels shall conform to one of the specifications in
Section II for which allowable stress values are given in
the tables referenced in UG-23, except as otherwise provided
in UG-4, UG-10, UG-11, and UG-15.
UG-6 FORGINGS
(a) Specifications and maximum allowable stress values
for acceptable forging materials are given in the
tables referenced in UG-23. (See Part UF for forged
vessels.)
(b) Bar [as defined in UG-14(a)] that is forged independent
of the material specification to which it is certified
may be used only within the limitations of UG-14.
(c) Forgings certified to SA-105, SA-181, SA-182,
SA-350, SA-403, and SA-420 may be used as tubesheets
and hollow cylindrical forgings for pressure vessel shells
that otherwise meet all the rules of this Division, provided
the following additional requirements are met:
(1) Forgings certified to SA-105 or SA-181 shall be
subject to one of the austenitizing heat treatments permitted
by these specifications.
(2) One tension test specimen shall be taken from
each forging weighing more than 5,000 lb (2 250 kg).
The largest obtainable tension test specimen as specified
by the test methods referenced in the applicable specification
shall be used. Except for upset-disk forgings, the longitudinal
axis of the test specimen shall be taken parallel
to the direction of major working of the forging. For
upset-disk forgings, the longitudinal axis of the test specimen
shall be taken in the tangential direction. When
agreed to by the Manufacturer, and when not prohibited
by the material specification, test specimens may be machined
from specially forged test blocks meeting the provisions
provided in SA-266 or other similar specifications
for large forgings.
(3) For quenched and tempered forgings weighing
more than 10,000 lb (4 500 kg) at the time of heat treatment,
two tension test specimens shall be taken from
each forging. These shall be offset 180 deg from each
other, except that if the length of the forging, excluding
test prolongations, exceeds 12 ft (3.7 m), then one specimen
shall be taken from each end of the forging.
UG-7 CASTINGS
Cast material may be used in the construction of pressure
vessels and vessel parts. Specifications and maximum
allowable stress values for acceptable casting
materials are given in the tables referenced in UG-23.
These allowable stress values shall be multiplied by the
applicable casting quality factor given in UG-24 for all materials
except cast iron.
UG-8 PIPE AND TUBES
(a) Pipe and tubes of seamless or welded8 construction
conforming to one of the specifications given in Section II
may be used for shells and other parts of pressure vessels.
Allowable stress values for the materials used in pipe and
tubes are given in the tables referenced in UG-23.
(b) Integrally finned tubes may be made from tubes
that conform in every respect with one of the specifications
given in Section II. The requirements of (1), (2),
(3), and (5) do not apply to tubes produced in accordance
with a Section II integrally-finned material specification.
These tubes may be used under the following conditions:
(1) The tubes, after finning, shall have a temper or
condition that conforms to one of those provided in the
governing specifications, or, when specified, they may
be furnished in the “as‐fabricated condition” where the
finned portions of the tube are in the cold worked temper
(as‐finned) resulting from the finning operation, and the
unfinned portions in the temper of the tube prior to
finning.
(2) The maximum allowable stress value for the
finned tube shall be that given in the tables referenced
in UG-23 for the tube before finning except as permitted
in (3) below.
(3) The maximum allowable stress value for a temper
or condition that has a higher stress value than that
of the tube before finning may be used, provided that qualifying
mechanical property tests demonstrate that such a
temper or condition is obtained and conforms to one of
those provided in the governing specifications in Section
II, and provided that allowable stress values have been established
in the tables referenced in UG-23 for the tube
material used. The qualifying mechanical property tests
shall be made on specimens of finned tube from which
the fins have been removed by machining. The frequency
of tests shall be as required in the unfinned tube
specification.
(4) The maximum allowable internal or external
working pressure of the tube shall be based on the root
diameter and the minimum wall of the finned section,
or the outside diameter and wall of the unfinned section
together with appropriate stress values, whichever results
in the lower maximum allowable working pressure.
Alternatively, the maximum allowable external pressure
for tubes with integral fins may be established under
the rules of Mandatory Appendix 23.
ASME BPVC.VIII.1-2025 UG-4 – UG-8
9with such other markings as will serve to identify the particular
parts with accompanying material identification.
The Manufacturer of the completed vessel shall be satisfied
that the part is suitable for the design conditions specified
for the completed vessel in accordance with the
rules of this Division.
(c) Cast, Forged, Rolled, or Die Formed Standard Pressure
Parts That Comply With an ASME Product Standard,
Either Welded or Nonwelded
(1) These are pressure parts that comply with an
ASME product standard accepted by reference in
UG-44(a). The ASME product standard establishes the basis
for the pressure–temperature rating and marking unless
modified in UG-44(a).
(2) Flanges and flanged fittings may be used at the
pressure–temperature ratings specified in the appropriate
standard listed in this Division.
(3) Materials for standard pressure parts shall be as
follows:
(-a) as permitted by this Division or
(-b) as specifically listed in the ASME product
standard
(4) When welding is performed it shall meet the
following:
(-a) the requirements of UW-26(a), UW-26(b),
and UW-26(c) and UW-27 through UW-40, or;
(-b) the welding requirements of ASME specification
SA-234.
(5) Standard pressure parts as identified in UG-11(c)
do not require inspection, identification in accordance
with UG-93.1 or UG-93.2, or Partial Data Reports, provided
the requirements of UG-11(c) are met.
(6) If postweld heat treatment is required by the
rules of this Division, it may be performed either in the location
of the parts manufacturer or in the location of the
Manufacturer of the vessel to be marked with the Certification
Mark.
(7) If radiography or other volumetric examination is
required by the rules of this Division, it may be performed
at one of the following locations:
(-a) the location of the Manufacturer of the completed
vessel
(-b) t h e l o c a t i o n of the pressure p a r t s
manufacturer
(8) Parts made to an ASME product standard shall be
marked as required by the ASME product standard.
(9) The Manufacturer of the completed vessels shall
have the following responsibilities when using standard
pressure parts that comply with an ASME product
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