MANDATORY APPENDIX V
REQUIREMENTS FOR LIMITED CLASS VALVES
V-1 GENERAL
This Appendix covers alternative requirements for
valves having either threaded or welding ends and is
specifically restricted to NPS 2
1
∕
2
and smaller. Valves
complying with the requirements of this Appendix may
be designated as Limited Class. There is no provision
for this designation for flanged end valves.
V-1.2 Applicability
The paragraphs of this Appendix are numbered corre-
sponding with those of the body of this Standard. All re-
quirements for Standard Class valves are applicable to
Limited Class except as otherwise modified by this Appen-
dix.
V-2.1 General
Valves conforming to the requirements of this Appendix
and identified as Limited Class shall be suitable for pres-
sure–temperature ratings determined in accordance with
para. V-2.1.3. Threaded-end valves rated above Class 2500
and socket-weld-end valves rated above Class 4500 are
not within the scope of this Standard.
V-2.1.3 Limited Class Rating Method. Pressure–
temperature ratings for Limited Class valves are estab-
lished for Groups 1 and 2 materials of Table V-1 by
the equation
=p
y P
p
7000
7000 ( 0.4)
ld
r
sp
where
P
r
= pressure class rating index. For all designations
Class 300 through 4500, P
r
is equal to the Class
designation number (e.g., for Class 300, P
r
= 300).
For Class 150, P
r
= 115. For a rating designation
between Class 150 and Class 300, the interpola-
tion shall be made using P
r
= 115 for Class 150.
The equation is not valid for P
r
greater than 4500.
p
ld
= Limited Class rated working pressure for the
specified material at temperature T
p
sp
= Special Class rated working pressure for the
specified material at temperature T as deter-
mined by the method of Nonmandatory
Appendix B. These Special Class working pres-
sures are tabulated in Tables 2-1.1 through
2-3.19 (Tables 2-1.1C through 2-3.19C) having a
designation of “Special Class.” The tabulated
values shall be used for establishing Limited
Class ratings.
y = a material coefficient having values as listed in
Table V-1
In no case shall the working pressure increase with
increasing temperature. This shall be verified by the
manufacturer for all rating points greater than 480°C
(900°F) for ferritic steels and 565°C (1,050°F) for austen-
itic steels.
V-2.1.6 Fabrication by Welding. Fabricated valves that
are identified as Limited Class shall conform with the re-
quirements of para. 2.1.6(c)(2) for Special Class.
V-4.2.3 Rating. Valves shall be marked on the valve
body with the number for the appropriate pressure
rating class designation except that Limited Class and
Intermediate Rating Limited Class may instead be
marked on the valve body with a specific rated pressure
and temperature. For all valves in Limited Class, the iden-
tification plate shall show the applicable pressure rating at
38°C (100°F) and other markings required by MSS SP-25.
Valves conforming to Limited Class requirements, and
acknowledged as such, shall include the designation
“B16.34LTD” on the identification plate.
V-6.1 Body Dimensions
Limited Class is restricted in application to valve body
geometries that have internal wetted pressure boundary
surfaces that are generally characterized by cylindrical
passages, cylindrical or spherical chambers, and intersec-
tions thereof.
V-6.1.1 Wall Thickness. For inspection purposes, the
minimum thickness of the wall surrounding the body run
flow passage shall be as shown in Table 3A or Table 3B as
applicable.
V-6.1.2 Inside Diameter. For the purpose of deter-
mining flow passageway wall thickness, the inside
diameter, d (see Figure V-1), is the diameter of the cylin-
drical flow passage.
ASME B16.34-2020
192
V-6.1.3 Valve Body Necks. The minimum thickness of
the wall for the body neck shall be that shown in Table 3A
or Table 3B with d for this determination taken as two-
thirds of d′ where d′ is the inside diameter of the body neck.
In no case shall the body neck thickness be less than the
minimum value determined for the flow passage in para.
V-6.1.1. For values of body neck inside diameter not shown
in Table 3A or Table 3B as applicable, interpolation is
permitted.
V-6.1.5 Contours for Body Run Transitions. The re-
quirements of para. 6.1.5 are not applicable to Limited
Class.
V-6.1.8 Additional Metal Thickness. For Limited
Class, it is required that metal thickness reinforcement
be provided to satisfy the following:
+
i
k
j
j
j
j
j
y
{
z
z
z
z
z
S p
A
A
0.5
o
o
f
m
where
A
f
= fluid area (see Figure V-1)
A
m
= metal area (see Figure V-1)
p
o
= rated working pressure at 38°C (100°F)
S
o
= the lesser value of either two-thirds of the yield
strength, one quarter of the ultimate tensile
strength, or the allowable stress of the body
material at 38°C (100°F) as listed in ASME
BPVC, Section II, Part D, for either Section I or
Section VIII, Division 1
The fluid area and metal area are determined from a
drawing of the valve body crotch region in the mutual
plane of the bonnet and flow passage center lines (see
Figure V-1).
1
The fluid and metal areas are to be based
on the most adverse combination of dimensions permitted
Table V-1 Material Coefficient, y
Material
Applicable Temperature
480°C
(900°F)
and
Below
510°C
(950°F)
538°C
(1,000°F)
565°C
(1,050°F) 595°C (1,100°F)
620°C
(1,150°F)
and
Above
Ferritic steels 0.4 0.5 0.7 0.7 0.7 0.7
Austenitic steels 0.4 0.4 0.4 0.4 0.5 0.7
Other ductile materials 0.4 0.4 0.4 0.4 0.4 0.4
Figure V-1 Limited Class Stress Area Limits
d
L
A
T
r
L
N
r
d9
A
f
A
m
T
b
1
For guidance in regard to other valve configurations, see ASME BPVC,
Section III, Subsection NB, NB-3545.
ASME B16.34-2020
193
by tolerances. In Figure V-1, the distances L
N
and L
A
that
define fluid and metal area boundaries are determined as
= + +L r T d T0.5 0.354 ( )
N b b
and L
A
as the larger of
=L d T0.5
A b
or
=L T
A r
where
d′ = body neck inside diameter at crotch region
r = external fillet radius at crotch
T
b
= neck wall thickness at crotch region
T
r
= body run wall thickness at crotch region
If a calculated boundary lies beyond the body run end or
neck end, the sections to be used for area determination
shall terminate at the body run end or neck end.
ASME B16.34-2020
194
