GB/T 16508.3-2022 PDF English
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Shell boilers - Part 3: Design and strength calculation
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GB/T 16508.3-2022: PDF in English (GBT 16508.3-2022) GB/T 16508.3-2022
GB
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 27.060.30
CCS J 98
Replacing GB/T 16508.3-2013
Shell boilers - Part 3: Design and strength calculation
ISSUED ON: JULY 11, 2022
IMPLEMENTED ON: FEBRUARY 01, 2023
Issued by: State Administration for Market Regulation;
Standardization Administration of the People's Republic of China.
Table of Contents
Foreword ... 3
Introduction ... 6
1 Scope ... 8
2 Normative references ... 8
3 Terms, definitions and symbols ... 9
4 Symbols ... 10
5 Design requirements ... 11
6 Cylindrical element subject to internal pressure ... 22
7 Cylindrical flues, cupolas, smoke tubes and other elements subjected to external
pressures ... 38
8 Convex head, flue roof, hemispherical flue and convex tube plate ... 54
9 Reinforced flat plates and tube plates with braces ... 63
10 Braces and reinforcements ... 75
11 Flat end covers and cover plates ... 85
12 Foot ring ... 91
13 Hole reinforcement ... 92
14 Welded tees ... 105
Annex A (normative) Test and finite element analysis verification method for
determining the maximum allowable working pressure of elements ... 110
Annex B (normative) Design calculation for water tube plate ... 117
Bibliography ... 120
Shell boilers - Part 3: Design and strength calculation
1 Scope
This document specifies the design requirements and strength calculation methods for
pressure elements of shell boilers. It also specifies the test and finite element analysis
verification methods for determining the maximum allowable working pressure of
elements.
This document is applicable to the design of pressure elements of shell boilers defined
in GB/T 16508.1 [including cylindrical elements bearing internal (external) pressure,
heads, tube plates, end covers, foot rings, etc.] and braces.
2 Normative references
The following referenced documents are indispensable for the application of this
document. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
GB/T 150.3, Pressure vessels - Part 3: Design
GB/T 985.1, Recommended joint preparation for gas welding, manual metal arc
welding, gas-shield arc welding and beam welding
GB/T 985.2, Recommended joint preparation for submerged arc welding
GB/T 1576, Water quality for industrial boilers
GB/T 2900.48, Electrotechnical terminology of boilers
GB/T 9252, Method for pressure cycling test of gas cylinders
GB/T 12145, Quality criterion of water and steam for power plant and steam-
generating equipment
GB/T 16507.3, Water-tube boilers - Part 3: Structure design
GB/T 16508.1, Shell boilers - Part 1: General requirements
GB/T 16508.2, Shell boilers - Part 2: Materials
GB/T 16508.4, Shell boilers - Part 4: Fabrication, inspection and acceptance
JB/T 6734, Calculation method of strength of boiler fillet welding seam
be considered:
1) Internal or external pressure of water or steam;
2) Liquid column static pressure;
3) Working fluid flow resistance;
4) Set pressure of safety valve;
5) The following loads shall also be considered when necessary:
• Self-weight load of pressure element and built-in self-weight load;
• Gravity load of attached equipment;
• Wind, snow loads and seismic loads;
• Other forces of connecting piping (thrust and moment of the piping, etc.);
• Forces caused by temperature gradients and differences in thermal expansion;
• Impact loads when the pressure fluctuates sharply;
• Forces during transport and lifting.
b) The following loads shall be considered when designing load-bearing non-
pressure elements:
1) Permanent loads, including supporting gravity, thermal expansion thrust;
2) Transient loads, including safety valve exhaust reaction force and other short-
term forces.
5.1.3 The design shall ensure that the wall temperature of the element does not exceed
the allowable temperature of the material used. Consider factors such as the temperature
difference between the inner and outer walls of the tube on the heating surface and the
inner wall's resistance to steam oxidation.
5.1.4 The design of the boiler structure shall be convenient for installation, operation,
maintenance and cleaning inside and outside.
5.1.5 The design shall be in accordance with the relevant strength calculation formula
or stress analysis calculation formula and regulations in this document. Determine the
minimum required thickness of the pressure element.
5.1.6 Special-shaped compression elements or structures that cannot be calculated
according to the provisions of Chapters 6 to 14 and Annex B within the scope of this
document can be according to the test and finite element analysis verification methods
specified in Annex A. Determine the maximum allowable working pressure of the
element.
5.1.7 The strength calculation of boiler fillet welds shall comply with the provisions of
JB/T 6734.
5.2 Structural requirements
5.2.1 General requirements
5.2.1.1 The main pressure elements of the shell boiler include boiler shell, header,
piping, centralized descending tube, flue, backfire chamber, tube plate (head), flue roof
and foot ring, etc.
5.2.1.2 Pressure elements shall have sufficient strength. The form of the structure of the
pressure elements, the layout of the openings and welds shall avoid or reduce the
combined stress and stress concentration as far as possible.
5.2.2 Wall thickness and length of boiler shell and flue
5.2.2.1 When the inner diameter of the boiler shell is greater than 1000 mm, the wall
thickness of the boiler shell cylinder shall not be less than 6 mm. When the inner
diameter of the boiler shell is not greater than 1000 mm, the wall thickness of the boiler
shell cylinder shall not be less than 4 mm.
5.2.2.2 The wall thickness of the boiler shell cylinder and tube plate connected by
expansion joints shall not be less than 12 mm. Tubes with an outer diameter greater
than 89 mm shall not be connected by expansion joints.
5.2.2.3 The inner diameter of the flue shall not exceed 1800 mm. The flue wall thickness
meets the following requirements:
a) When the flue inner diameter is less than or equal to 1800 mm and greater than
400 mm, its wall thickness shall not be less than 8 mm and not greater than 22
mm.
b) When the flue inner diameter is less than or equal to 400 mm, the wall thickness
shall not be less than 6 mm.
5.2.2.4 For the backfire chamber of a horizontal internal combustion boiler, the wall
thickness of the cylinder shall be not less than 10 mm and not more than 35 mm.
5.2.2.5 The calculated length of the horizontal flat flue shall not exceed 2000 mm. When
the two ends of the flue are connected to the flange of the tube plate, the calculated
length of the straight flue can be enlarged to 3000 mm.
5.2.3 Safe water level
5.2.3.1 The minimum and maximum safe water levels of boilers shall be indicated on
the boiler drawings.
5.2.3.2 The minimum safe water level of the boiler during normal operation shall be
100 mm higher than the highest fire line. For a horizontal shell boiler with an inner
diameter of the shell not greater than 1500 mm, the minimum safe water level shall be
75 mm higher than the highest fire line.
5.2.3.3 When the water supply to the boiler is stopped, it will continue to run under the
rated load of the boiler. The time for the boiler water level to drop from the lowest safe
water level to the highest fire line (safe precipitation time) shall not be less than 7 min.
For gas (liquid) boilers, it shall not be less than 5 min.
5.2.4 Welding structure
5.2.4.1 The main welds of the main pressure elements of the boiler (including the
longitudinal and circumferential welds of the boiler shell, flue, backfire chamber,
header, etc. and the spliced welds of the head, tube plate, flue roof and foot ring, etc.)
shall adopt full penetration structure. The braces shall not be spliced.
5.2.4.2 For horizontal internal combustion shell boilers with boiler rated pressure not
greater than 2.5 MPa, waste heat boilers including shell boiler elements and through-
flow boilers, except for the joints directly washed by flue gas, if the following
requirements are met, the tube plate, the flue and the boiler shell can be connected by
T-shaped joints. However, overlapping connections shall not be used.
a) Adopt full penetration joint type (see Figure 1). The groove is machined.
b) The connection between the tube plate and the cylinder adopts a plug-in structure
(except for the through-flow boiler).
c) The required thickness of the weld at the connection part of the T-joint shall not
be less than the wall thickness of the tube plate (cover plate). The parts that can
be sealed and welded on the back of the weld seam shall be sealed and welded.
Argon arc welding or other gas-shielded welding shall be used for backing the
parts that cannot be sealed and welded. Guarantee penetration.
d) The welding seam of the T-joint connection part shall be ultrasonically tested
according to the requirements of NB/T 47013.3.
5.2.6.1 The requirements for expansion tube holes are as follows.
a) The net distance between the expansion tube holes shall not be less than 19 mm,
and not less than 6 times the wall thickness of the tube.
b) The distance between the center of the expansion tube hole and the edge of the
weld seam and the starting point of the flange of the tube plate shall not be less
than 0.8d and shall not be less than 0.5d + 12 mm.
c) The expansion tube holes shall not be arranged on the longitudinal weld of the
boiler shell. Also try to avoid the arrangement on the circumferential weld seam.
If the structural design cannot avoid being located in the circumferential weld
seam, the weld seams within 60 mm (if the tube hole diameter is greater than 60
mm, take the hole diameter value) around the tube hole are qualified by
radiographic or ultrasonic testing. There is no slag inclusion defect in the weld
seam on the edge of the tube hole. At the same time, after grinding the inner and
outer surfaces of the weld seam at the tube hole and heat-treating the entire
pressure element, the expansion tube hole can be arranged on the circumferential
weld.
5.2.6.2 Welded tube holes shall meet the following requirements:
a) The tube holes of the centralized descending tube shall not be arranged on the
weld and its heat-affected zone.
b) Other welded tube holes shall not be arranged on the weld seam and its heat-
affected zone.
c) When the structural design cannot be avoided, the weld seams within 60 mm
around the tube hole (if the diameter of the tube hole is greater than 60 mm, take
the value of the hole diameter) shall pass the radiographic or ultrasonic inspection.
There is no slag inclusion defect in the weld seam on the edge of the tube hole. If
the tube joints undergo heat treatment after welding (except for hot water boilers
with a rated outlet water temperature of less than 120°C) to relieve stress, welded
tube holes can be arranged on the weld seam and its heat-affected zone.
5.2.6.3 The clear distance between the edges of welded seams of adjacent welded tube
holes shall not be less than 6 mm. If heat treatment or local heat treatment is done after
welding (except for hot water boilers with rated outlet water temperature less than
120°C), it is not subject to this restriction.
5.2.6.4 The number and position of manholes, head holes, hand holes, cleaning holes,
inspection holes and observation holes opened on boiler pressure elements shall meet
the needs of installation, inspection, maintenance, operation monitoring and cleaning
(clearing). For boilers with smoke tubes in the shell, the arrangement of manholes and
head holes shall consider the maintenance requirements of the upper and lower parts of
the shell. Specific requirements are as follows:
a) For boiler shells with an inner diameter greater than 1000 mm, at least one
manhole shall be opened on the cylinder or head (tube plate). When personnel
cannot enter the boiler due to structural restrictions, only the head hole may be
opened.
b) For boiler shells with an inner diameter of 800 mm ~ 1000 mm, at least one head
hole shall be opened on the cylinder or head (tube plate).
c) At least 3 hand holes shall be provided in the lower part of vertical shell boilers
(except electric heating boilers).
5.3 Corrosion allowance thickness
The corrosion allowance thickness shall be determined according to the following
requirements:
a) For elements with δ >20 mm, take C1≥0 mm;
b) For elements with δ≤20 mm, take C1≥0.5 mm;
c) In the case that severe corrosion may occur, the corrosion allowance thickness
shall be increased accordingly.
5.4 Weld joint coefficient
5.4.1 The quality of weld joints shall comply with the relevant provisions of GB/T
16508.4.
5.4.2 The weld joint coefficient (φw) shall be determined according to the weld type of
the butt joint and the proportion of non-destructive testing.
5.4.3 Double-welded butt joints and full-penetration butt joints equivalent to double-
sided welding are determined as follows:
a) 100% non-destructive testing, φw=1.00;
b) Partial non-destructive testing, φw=0.90.
5.4.4 Single-sided welded butt joints are determined as follows:
a) 100% non-destructive testing, φw=0.90;
b) Partial non-destructive testing, φw=0.80.
5.5 Allowable stress
5.5.1 According to the structural characteristics and working conditions of the elements,
the allowable stress ([σ]) of the material is calculated according to the formula (1)
during the design calculation.
sided fillet welded tube joint (or hole ring), the size of the elliptical hole in the direction
of the corresponding pitch, in millimeters (mm);
NOTE: Plug-in double-sided fillet welding is limited to boilers with pr ≤ 2.5 MPa and non-heated
tube joints (or hole rings).
de - The equivalent diameter of the hole, in millimeters (mm);
dm - The average value of the diameters of two adjacent holes, in millimeters (mm);
do - The outer diameter of the tube, in millimeters (mm);
[d] - The maximum allowable diameter of unreinforced holes, in millimeters (mm);
K - The conversion factor of inclined hole bridge;
K1 - The factor of bent tube shape;
m - The absolute value of the percentage of the lower deviation of the tube thickness
(when it is a negative value) and the nominal thickness of the tube, expressed as a
percentage (%);
n - The ratio of the distance b between the two holes in the direction of the axis of the
cylinder to the arc length α between the two holes in the direction of the circumference
of the cylinder's average diameter;
n1 - The ratio of the radius R of the centerline of the bent tube to the outer diameter of
the tube;
[p]w - The maximum allowable working pressure calculated by bent tube check, in
megapascals (MPa);
R - The radius of the centerline of the bent tube or the radius of the centerline of the arc
header, in millimeters (mm);
s0 - The minimum pitch between two adjacent holes that does not consider the influence
between holes, in millimeters (mm);
s - The pitch between two adjacent holes in the longitudinal direction (axial direction),
or the inner wall spacing of the fire box tube plate, in millimeters (mm);
s' - The pitch of two adjacent holes in the horizontal (circumferential) direction, in
millimeters (mm);
s'' - The pitch of two adjacent holes obliquely, in millimeters (mm);
α' - The angle that the axis of the hole deviates from the radial direction of the cylinder,
in degrees (°);
steel of the cylinder, the d in the calculation of the weakening coefficient shall be taken
as the sum of the inner diameter of the connecting tube (or hole ring) and 2δ1[1-
([σ]1/[σ])] (δ1 is the nominal thickness of the reinforced tube joint or the reinforced ring).
6.6.4 When the pitch of two adjacent holes is less than the s0 value determined
according to the formula (23), and the diameter of the two holes is not greater than the
maximum allowable diameter ([d]) of the unreinforced hole determined according to
13.3.6, the weakening coefficient of the hole bridge shall be calculated according to the
provisions of 6.6.6.
If one of two adjacent holes is larger than the maximum permissible diameter ([d]) of
an unreinforced hole determined in accordance with 13.3.6, under the condition of
meeting the requirements of 13.7.2, the large hole shall be reinforced as a single hole
according to the provisions of 13.3.7~13.3.9. After reinforcement, treat as non-hole.
If two adjacent holes need to be reinforced, the pitch shall not be less than 1.5 times
their average diameter. After reinforcement, treat as non-hole.
When reinforcement is required for both adjacent holes, the reinforcement calculation
shall meet the following requirements in addition to the requirements in 13.3.7~13.3.9:
a) The height of the thickened tube joint is 2.5 times the thickness.
b) The weld leg size of the thickened tube joint is equal to the thickness of the
thickened tube joint.
c) If the pitch of the two holes is less than the sum of the diameters of the two holes,
causing their effective reinforcement ranges to overlap, the reinforcement shall
be carried out in such a way that the total reinforcement area of the two holes is
not less than the sum of the individual reinforcement areas required by each hole.
The area of reinforcement in overlapping parts shall not be counted repeatedly.
6.6.5 For the coal feeding holes and slag outlet holes on the vertical boiler shell, the
holes shall be reinforced according to the provisions of 13.3.7~13.3.9. After
reinforcement, treat as non-hole. The minimum required thickness of coal feeding hole
circle and slag discharge hole circle shall be determined according to 13.4.4.
6.6.6 The hole-bridge weakening coefficients of two adjacent holes are calculated
according to the following method.
a) The hole bridge weakening coefficient of two longitudinally adjacent holes of
equal diameter (see Figure 2) is calculated according to formula (24):
Figure 8 -- Connection between the boiler shell cylinder and the flanged flat tube
plate or convex head
7 Cylindrical flues, cupolas, smoke tubes and other elements
subjected to external pressures
7.1 Overview
This chapter specifies the design calculation methods and structural requirements for
the following cylindrical elements subjected to external pressure:
a) Flue, cupola and smoke tube of vertical shell boilers with rated working pressure
not greater than 2.5 MPa;
b) Flue and backfire chamber of horizontal shell boiler with rated working pressure
not greater than 3.8 MPa;
c) Smoke tubes of horizontal shell boilers with rated working pressure less than 5.3
MPa.
7.2 Symbols
This chapter uses the following symbols:
a - The distance between the neutral axis X-X and the axis X0-X0 passing through the
center of the circle, in millimeters (mm);
Di - The inner diameter of the flue, in millimeters (mm);
Dm - The average diameter of the flue, the average diameter of the straight part of the
corrugated flue, in millimeters (mm);
Do - The outer diameter of the flue, in millimeters (mm);
Et - The elastic modulus at the calculating temperature, in megapascals (MPa);
hJ - The height of the reinforcing ring, in millimeters (mm);
ho - The outer height of the flue roof, in millimeters (mm);
I1 - The moment of inertia of the corrugated section to its own neutral axis, in the fourth
power millimeter (mm4);
I2 - The moment of inertia of the reinforcing ring on its own neutral axis, in the fourth
power millimeter (mm4);
I3 - The moment of inertia of the expansion ring to its own neutral axis, in fourth power
millimeter (mm4);
I', I″, I‴ - The required moment of inertia, in the fourth power millimeter (mm4);
l - The length of the straight section of the edge element, in millimeters (mm);
L - The calculating length of the flue, in millimeters (mm);
n1 - The strength safety factor;
n2 - The stability safety factor;
Ro - The outer radius of the corrugation of the corrugated flue, in millimeters (mm);
R - The center radius of the corrugation of the corrugated flue, in millimeters (mm);
r - The inner radius of the corrugation of the corrugated flue, in millimeters (mm);
s - The corrugation pitch of the corrugated flue, in millimeters (mm);
u - The percentage of roundness of horizontal flat flue;
W - The corrugation depth of the corrugated flue, in millimeters (mm);
X - The added value of calculated length of the flat flue;
α' - The included angle, semi-included angle, in degrees (°);
δ - The nominal thickness of the pressure element, in millimeters (mm);
δc - The calculated thickness of the pressure element, in millimeters (mm);
δJ - The thickness of the reinforcing ring, in millimeters (mm);
δmin - the minimum required thickness of the pressure element, in millimeters (mm);
δs - The design thickness of pressure element, in millimeters (mm);
δe - The effective thickness of the pressure element, in millimeters (mm);
φmin - The minimum weakening coefficient.
7.3 Cylindrical flue
7.3.1 Flat flue
7.3.1.1 The design thickness of the horizontal flat flue is calculated according to
formula (46) and formula (48), whichever is larger.
......
Source: Above contents are excerpted from the PDF -- translated/reviewed by: www.chinesestandard.net / Wayne Zheng et al.
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