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GB 26640-2011: [GB/T 26640-2011] Specification for minimal thickness of the shell of valves
GB 26640-2011
NATIONAL STANDARD OF THE
PEOPLE?€?S REPUBLIC OF CHINA
ICS 23.060.01
J 16
Specification for minimal thickness of the shell of valves
ISSUED ON: JUNE 16, 2011
IMPLEMENTED ON: SEPTEMBER 01, 2012
Issued by: General Administration of Quality Supervision, Inspection and
Quarantine of the PRC;
Standardization Administration of the PRC.
Table of Contents
Foreword ... 3??
1 Scope ... 4??
2 Normative references ... 4??
3 Minimal thickness of steel valves ... 4??
4 Minimal thickness of iron valves ... 17??
Appendix A (Informative) Relationship between the nominal dimension of steel valve
and the basic inside diameter of the end of the valve body... 26??
Specification for minimal thickness of the shell of valves
1 Scope
This Standard specifies the wall thickness requirements for iron and steel valves such
as ball valves, butterfly valves, gate valves, globe valves, check valves, plug valves and
diaphragm valves.
The parameter ranges of the valves to which this Standard applies are:
a) Steel valves with nominal pressure PN 10~PN 760. Nominal pressure PN 760 is
only suitable for welded end valves;
b) Flange connection, wafer connection, and butt-welding connection end steel
valves with nominal dimension not greater than DN 1250;
c) Socket-welded end and threaded connection end steel valves with nominal
dimension not greater than DN 100;
d) Iron valves with nominal pressure PN 1.0~PN 25;
e) Iron valves with nominal dimension not greater than DN 3000.
2 Normative references
The following documents contain the provisions which, through reference in this
Standard, constitute the provisions of this Standard. For the dated references, their
subsequent amendments (excluding corrections) or revisions do not apply to this
Standard. However, the parties who enter into agreement based on this Standard are
encouraged to investigate whether the latest editions of these documents are applicable.
For undated reference documents, the latest editions apply to this Standard.
GB/T 12224-2005 General requirements for industrial steel valves (ASTM
B16.34a:1998, NEQ)
GB/T 14976 Stainless steel seamless tubes for fluid transport (GB/T 14976-2002,
ASTM A269:2000, NEQ)
3 Minimal thickness of steel valves
3.1 General requirements
3.1.1 Look up table to determine minimal thickness
The thickness tm of the steel valve body shall not be less than that specified in Table 1;
except for the end dimensions specified in 3.1.3~3.1.6, 3.1.8, as well as in 6.2 and 6.7
of GB/T 12224-2005.
When using Table 1, the values in the middle of the listed values can be obtained by
linear interpolation.
Unlined valve body thickness is measured from the inner surface in contact with the
fluid. The minimal thickness shall not include the thickness of the liner, insert or
bushing.
3.1.2 Calculation of minimal thickness
When the thickness value cannot be found from Table 1, it can be calculated by formula
(1). The minimal thickness values in Table 1 are larger than those calculated using
formula (1).
Where:
tm - Calculated shell thickness, in millimeters (mm);
Pc - The value is 0.1 times the nominal pressure, in megapascals (MPa);
d - The inside diameter of the end of valve body, in accordance with the provisions of
Appendix A, in millimeters (mm);
n - Coefficient. When Pc???2.5 MPa, n=3.8; when Pc >2.5 MPa, n=4.8;
S - Stress coefficient. S=48.3 MPa.
Formula (1) does not apply to valves with nominal pressure greater than PN 760.
The actual value in Table 1 is about 3 mm~5 mm thicker than the value obtained by
formula (1). Additional thickness is required to account for assembly stress, valve
opening-closing stress, non-circular shape, and stress concentration. Therefore, the
manufacturer shall add a certain thickness allowance to the calculated thickness value,
to ensure that the valve meets the strength requirements.
intermediate pressure ratings
The minimal thickness of the shell at the intermediate pressure level is determined by
the linear insertion method by formulas (4) and (5):
Where:
Prd - Nominal pressure of intermediate pressure level;
tm - The minimal thickness of the shell for the intermediate pressure level, in millimeters
(mm);
Pd - Working pressure at design temperature, in megapascals (MPa);
P1 - The low value of pressure adjacent to Pd, in megapascals (MPa);
P2 - The high value of pressure adjacent to Pd, in megapascals (MPa);
Pr1 - Nominal pressure PN corresponding to P1;
Pr2 - Nominal pressure PN corresponding to P2;
t1 - The minimal thickness of the nominal pressure Pr1, in millimeters (mm);
t2 - The minimal thickness of the nominal pressure Pr2, in millimeters (mm).
Use the design temperature and working pressure Pd to check the pressure-temperature
rating specified in 3.1.1 of GB/T 12224-2005. Then determine the low value P1 of rated
pressure adjacent to Pd and the adjacent high value P2. P1 and P2 are rated values
equivalent to pressure levels Pr1 and Pr2. Determine the intermediate pressure level Prd
corresponding to the design condition and use formula (4) to calculate.
Use the appropriate inside diameter d in Table 1, to determine the minimal thicknesses
t1 and t2 for the nominal pressures Pr1 and Pr2, respectively. Determine the minimal
thickness corresponding to the design condition and use formula (5) to calculate.
3.1.6 Wall thickness of valve body ends
a) Butt-welding end
The shell thickness of the flow passage part of the valve body welding groove
shall not be less than the required value tm in 3.1.1 or 3.1.4. The thickness at a
distance of 1.33 tm from the welding end shall not be less than 0.77 tm.
b) Socket-welded end and threaded connection end
The distance FROM the centerline of the basic cylindrical flow passage TO the
outer surface of the valve body flow passage shall not be less than 0.5 times the
nominal outside diameter of the tube listed in GB/T 14976.
3.1.7 Local area
When the thickness of the shell in the local area is less than the minimal thickness, it is
acceptable when all the following constraints are met.
a) Areas less than the minimal thickness can be enclosed by a circle with a diameter
not greater than 0.35 . For the valve body neck, d0=d?€? and t0=t?€? (see 3.1.3).
For all other local areas, d0=d (see 3.1.2) and t0=tm (see corresponding 3.1.1 or
3.1.4);
b) The measured thickness is not less than 0.75 t0;
c) The distance between the edges of the surrounding circles is not less than
1.75 .
3.1.8 Additional thickness allowance
Due to the influence of factors such as piping system load, operation (closing and
opening) load, non-circular shape, and stress concentration, additional thickness
allowance is required for the shell thickness checked according to Table 1. Because
there are many factors to be considered for the additional thickness allowance, the
additional thickness allowance is determined by the manufacturer's design and
calculation.
For inclined stem steel valves (which enlarge the intersecting surfaces and openings of
the valve body cavity) and assembly-welded body steel valves, additional
reinforcement may be required, to ensure adequate strength and rigidity.
3.1.9 Wafer-type steel valves
For wafer-type steel valves (such as butterfly valves), the wall thickness shall meet the
requirements of flange connection steel valves and the following requirements (see
Figure 2).
a) The required minimal thickness tm of the valve body shall be the minimum
distance measured outward FROM the inner circumference of the valve body TO
the outer circumference of the valve body; or the distance FROM the inner
circumference of the valve body TO the tangent to the inside of the flange bolt
hole.
b) The inside thickness (e in Figure 2) of the through hole or threaded blind hole
near the valve stem passage shall not be less than 0.25 times the required wall
thickness of the valve body neck; but not less than 2.5 mm.
c) The inside thickness (f in Figure 2) of the hole parallel to the valve body passage
shall not be less than 0.25 tm; but not less than 2.5 mm. The sum of the inside
thickness and the outside thickness shall not be less than the valve body thickness
tm.
d) The minimal thickness (j in Figure 2) of the valve body between two adjacent
holes in the valve body wall shall not be less than 0.25 tm; but not less than 2.5
mm.
e) The inside thickness (c in Figure 2) of radial blind hole is not less than 0.75 tm.
3.2 Requirements for minimal thickness of the shell of various types of steel valves
3.2.1 Petroleum and chemical steel valves
The minimal thickness of the shell of steel gate valve, globe valve, plug valve, lift check
valve, swing check valve, and wafer check valve for petroleum, chemical and related
industries SHALL be in accordance with Table 2. The minimal thickness of the shell of
steel ball valve for petroleum, chemical and related industries SHALL be in accordance
with Table 1.