JB 3622-1984 Strength calculation of pressure components of shell boilers
Some standard content:
ICS27.060.30
National Standard of the People's Republic of China
GB/T 16508—1996
Strength calculation of pressure parts for shell boilers
boilers1996-09-03 Issued
State Administration of Technical Supervision
1996-12-01 Implementation
Subject content and scope of application
Referenced standards
Materials, allowable stresses and calculated pressures
Circular and simple components subject to internal pressure
Cylindrical furnaces, cupolas, smoke pipes and other components subject to external pressureConvex heads, furnace tops, hemispherical furnaces and convex tube sheetsSlabs and tube sheets with bracing (reinforcement)
Struts and reinforcements
Rectangular headers
Header end covers, built-in hole covers
Bottom rings·
Hole and hole reinforcement·||tt| |Pressure components of cast iron boilers (supplement)
Appendix A
Appendix B
Examples (reference)
Appendix C
Unit conversion (reference):
Electric aid
(12)
(22)
(27)
(34)
(39)
(43)
(46)
(47)
(56)
(58)
(97)
National Standard of the People's Republic of China
Strength calculation of pressure components of shell boilers
Strength Calculation of pressure parts for shell boilers1Subject content and scope of application
GB/T16508-1996
Replaces JB3622-84
1.1This standard specifies the strength calculation method and relevant structural provisions for the pressure components of fixed shell boilers with smoke pipes and (or) furnaces welded by low carbon steel or low carbon manganese steel and cast iron boilers. 1.2This standard is applicable to steam boilers with a rated steam pressure not greater than 2.5MPa and hot water boilers with a rated water outlet pressure not less than 0.1MPa, but hot water boilers with a rated water outlet pressure less than 0.1MPa can also be used as a reference. 1.3The design, manufacture, installation, use, repair and modification of boilers shall comply with the current national "Safety Technical Supervision Regulations for Steam Boilers", "Safety Technical Supervision Regulations for Hot Water Boilers", relevant boiler manufacturing technical conditions and other relevant national standards. 2 Reference standards
Technical conditions for high-quality carbon structural steel
Dimensions, shapes, weights and tolerances of hot-rolled copper plates and strips GB711
High-quality carbon structural steel hot-rolled thick plates and wide strips Carbon steel and low-alloy steel plates for boilers
Water quality standards for low-pressure boilers
GB1576
GB3087
GB3274
GB 8163
Seamless steel tubes for low and medium pressure boilers
Seamless steel tubes for hot-rolled thick steel plates and steel strips of carbon structural steel and low alloy structural steel for conveying fluids
Strength calculation of pressure components of water tube boilers
GB9222
3 Materials, allowable stresses and calculated pressures
3.1 Explanation of symbols
The meanings and units of the symbols used in this chapter are as follows: -Tensile strength at room temperature, MPa!
Suitable point at room temperature, MPa;
-Yield point at calculated wall temperature, MPa!
—elongation at room temperature, %,
—allowable stress, MPa;
Basic allowable stress, MPa:
Basic allowable stress correction factor:
thiCalculated wall temperature, C;
t)——medium saturation temperature under calculation pressure (absolute pressure) or rated outlet water temperature of hot water boiler, ℃: Approved by the State Bureau of Technical Supervision on September 3, 1996 and implemented on December 1, 1996
p--Calculation pressure (gauge pressure), MPa;
pe—Rated pressure (gauge pressure) of boiler, MPa;Ap—Additional pressure, MPa;
GB/T16508—1996
△p.-Pressure drop between calculation element and boiler outlet at maximum flow, MPa;Aps---Static pressure of water column on calculation element, MPa;Cp]-
Maximum allowable calculation pressure (gauge pressure), MPa: [p]. —Maximum allowable working pressure at boiler outlet, MPa. 3.2 Materials
3.2.1 Pressure components of shell boilers shall be made of low carbon steel or low carbon manganese steel for boilers in accordance with relevant national standards or industry standards. When using some steel grades of the above materials not listed in this standard, they shall comply with the relevant provisions of the current national "Regulations on Safety Technical Supervision of Steam Boilers" and "Regulations on Safety Technical Supervision of Hot Water Boilers". 3.2.2 The steel plates used to manufacture pressure components shall have good plasticity, and their elongation at room temperature shall not be less than 18%. 3.3 Allowable stress
3.3.1 The allowable stress of the material shall be calculated according to the following formula: [a] = nE],
3.3.2 The basic allowable stress [] of commonly used steel materials for shell boilers shall be the values listed in Table 1. For steel materials not listed in Table 1 but meeting the requirements of 3.2, the basic allowable stress [. } shall be calculated according to the following formula, and the smaller value of the two shall be taken. ra sa
When calculating, b, take the guaranteed value of the corresponding steel grade. When there is no guaranteed value, the minimum value obtained by the steel sampling test can be multiplied by 0.9 as the calculation value. The sampling test shall be carried out according to the relevant standards. If there is no data, the guaranteed value can be used. If there is no guaranteed value, the minimum value obtained by the steel sampling test can be multiplied by 0.9. Use the call/ratio values listed in Table 2 to convert. Table 1 Basic allowable stress of common steel materials []
Steel grade and standard number
Calculated wall temperature ℃
GB8163
GB3087
GB8163
GB3087
GB3274
GB/T 16508-
—1996
Note: ① The values of adjacent calculated wall temperature are determined by arithmetic interpolation. ② For 20g.16Mng steel plate, when the thickness is greater than 16mm, b., the value is determined according to GB713, but [. , is still taken according to the values listed in the table. Table 2 / Minimum value of low carbon steel or low carbon manganese steel Calculated wall temperature
/o Minimum value
Note: The values of adjacent values. / are determined by arithmetic interpolation. 3.3.3 The basic allowable stress correction factor 7 shall be determined according to Table 3. 300
Table 3 Basic allowable stress correction factor?
Component type and working conditions
Shell cylinder and nest cylinder subjected to internal pressure are not heated (outside the flue or reliably insulated) are heated (smoke temperature ≤ 600℃)
Heated (smoke temperature> 600℃)
Pipe (pipe joint) hole ring
Corrugated furnace
Convex head, furnace resistance top, hemispherical furnace, convex tube sheet Concave surface of vertical non-cupola boiler and dry steam chamber is under pressure Convex head of vertical non-cupola boiler Convex surface of hemispherical furnace Vertical non-cupola boiler Convex surface of furnace top Convex pressure furnace top of cupola boiler Vertical cupola boiler Convex pressure head Horizontal internal combustion boiler Concave pressure head Convex pressure tube sheet
Supported flat plate, smoke tube sheet
Supporting parts (tie rods, support tubes, gussets) Reinforced cross beams
Circular header cover
Rectangular header
Rectangular header cover
3.4 Calculated wall temperature
3.4.1 The calculated wall temperature used for strength calculation is the arithmetic average of the internal and external wall temperatures at the highest temperature of the component. In any case, the calculated wall temperature of the boiler pressure component shall not be less than 250℃. 3.4.2 Calculate the wall temperature tb according to Table 4.
(See Table 17)
Anti-coking box
GB/T16508-1996
Table 4 Calculate the wall temperature tbi
Types and working conditions of pressure-bearing components
Boiler shell, furnace, furnace top, flat plate, tube sheet, fire box plate, header directly exposed to flame radiation Boiler shell cylinder, reburner, flat plate, tube sheet, header in contact with flue gas with a temperature of more than 900℃ Boiler shell, reburner, flat plate, tube sheet, header in contact with flue gas with a temperature of 600-900℃ Boiler shell, reburner, flat plate, tube sheet, header in contact with flue gas with a temperature below 600℃ Water-cooled wall tubes
Convection tubes, tension tubes
Components not directly heated by flue gas or flame Note: The values listed in the table are only applicable to the case where the boiler feed water quality meets the GB1576 standard. 3.5 Calculation pressure
3.5.1 During design calculation, the calculation pressure is calculated as follows: e+Ap+Ap+Apz
Additional pressure A is determined according to the following principles:
When the rated pressure is less than 1.25MPa, Ap=0.02MPaWhen the rated pressure is not less than 1.25MPa, △b=0.04（pe+Ap,+△p）. When s<3%(++), it can be taken as zero.
3.5.2 During verification calculation, the calculated maximum allowable calculation pressure of the component includes the sum of the four pressures of,, A, and, and the maximum allowable working pressure at the boiler outlet is the minimum value of each component. 4 Cylindrical components subjected to internal pressure
4.1 Explanation of symbols
The meanings and units of the symbols used in this chapter are as follows: f
Theoretical calculated thickness, mm
Minimum required thickness, mm;
Used thickness (referred to as "thickness"), actual measured thickness, mm Thickness of connected head or flange components, mm; Effective thickness, mm;
Additional thickness considering corrosion thinning, material thickness deviation (when negative) and process thinning, I1 Additional thickness considering corrosion thinning, mm
Additional thickness considering material thickness deviation (when negative), mm; Additional thickness considering process thinning , mm;
Inner diameter of boiler shell, inner diameter of large horizontal water pipe, mm; Outer diameter of header shell, mm
Calculated pressure (gauge pressure), MPa;
Maximum allowable calculated pressure (gauge pressure), MPa;[a]-—Allowable stress, MPa
—Weld reduction coefficient:
Longitudinal hole bridge reduction coefficient;
Transverse hole bridge reduction coefficient;
Oblique hole bridge reduction coefficient;
—Oblique hole bridge equivalent reduction coefficient;
Equivalent reduction coefficient of check position;
Minimum reduction coefficient:
Oblique hole bridge conversion coefficient:
GB/T 16508—1996
The projected length of the pitch of two obliquely adjacent holes according to the average diameter of the cylinder in the circumferential direction of the cylinder, mI; 6
The projected length of the pitch of two obliquely adjacent holes according to the average diameter of the cylinder in the longitudinal direction of the cylinder, mIm; -The ratio of b to a (6/a)
The angle at which the axis of the hole deviates from the radial direction of the cylinder, (\); The minimum pitch of two adjacent holes without considering the influence between holes, mm The pitch of two longitudinally (axially) adjacent holes, mm; The pitch of two transversely (circumferentially) adjacent holes according to the average diameter of the cylinder, mm; The pitch of two obliquely adjacent holes according to the average diameter of the cylinder, mm; The diameter of the hole, groove type fillet welded pipe The inner diameter of the pipe or hole ring, the inner diameter of the double-sided fillet welded pipe or hole ring in the non-heated part, mm,
equivalent diameter of the hole, mm,
average value of the diameters of two adjacent holes, mm;
outer diameter of the pipe, mm;
the absolute value of the percentage of the lower deviation of the pipe thickness (when it is a negative value) to the nominal thickness of the pipe, %: A—coefficient;
coefficient:
the ratio of the bending radius of the pipe to the outer diameter of the pipe. 4.2 Calculation formula
4.2.1 The theoretical thickness of the shell cylinder is calculated according to the following formula: th
The minimum required thickness of the shell cylinder is calculated according to the following formula: p,
29mn[a] p
tmin =t+c
4.2.2 The theoretical thickness of the header shell is calculated as follows: t
29mn[o]+ p
Its minimum required thickness tmi is calculated as follows (6). 4.2.3 During the verification calculation, the maximum allowable calculation pressure of the shell and header shell is calculated as follows: Shell
Header
Where: The effective thickness t is calculated as follows: [p]
29[aJt
（6）
When t is calculated as follows (10), it is taken as equal to t, or it can be taken as the actual measured thickness of the verification part minus the possible corrosion thinning amount in the future. At this time, the minimum value of the product of the corresponding 9 and , of each verification part should be substituted into formula (8) or formula (9). In addition, the maximum allowable calculated pressure calculated by formula (8) and (9) shall also meet the strengthening requirements of holes in Chapter 12. 4.2.4 The theoretical calculated thickness of the pipe subjected to internal pressure is calculated according to the following formula: pdwWww.bzxZ.net
2a]+ p
Its minimum required thickness tm is calculated according to formula (6). .( 11)
GB/T16508—1996
4.2.5 During the verification calculation, the maximum allowable calculated pressure of the pipe subjected to internal pressure is calculated according to the following formula: 2[aJty
4.2.6 The thickness and maximum allowable calculated pressure of the large horizontal water pipe of a vertical boiler are calculated according to the following formula: t>昀+3
[p = 44(t- 3)
The above formula is applicable to the case where the pipe inner diameter D is 102~300mm. 4.3 Attenuation coefficient
（12）
++++*+( 13 )
4.3.1 The minimum attenuation coefficient 9 in formula (5) and formula (7) is the minimum value of the longitudinal weld attenuation coefficient 9, the longitudinal hole bridge attenuation coefficient 9, the double transverse hole bridge attenuation coefficient 2g (when 20>1, take 2g-1.00) and the equivalent attenuation coefficient series of the oblique hole bridge (when 1, take 9=1.00). If the hole bridge is located on the weld, it should be handled in accordance with the relevant provisions of 4.6.2. 4.3.2 For welds that have passed the inspection according to the boiler manufacturing technical conditions, the attenuation coefficient 9 shall be selected according to Table 5. If there is no hole on the circumferential weld, the attenuation coefficient of the circumferential weld may not be considered.
Table 5 Weakening coefficient of butt weld
Welding method
Manual electric welding
Automatic welding under flux layer
Weld type
Double-sided welding
Single-sided welding with backing plate at the root of weld
Single-sided welding
Double-sided welding
Single-sided welding
4.3.3 When the pitch of two adjacent holes (longitudinal, transverse or oblique) is not less than the value calculated by the following formula, the hole bridge weakening coefficient does not need to be calculated. S. =d+ 2 V(D+ t)i
Where: d. Determined according to formula (21).
（15）
4.3.4 When the pitch of two adjacent holes is less than the value of 5 determined by formula (15), and the diameters of both holes are less than the maximum allowable diameter of the unreinforced hole determined by 12.2.4, the hole bridge reduction coefficient shall be calculated in accordance with the provisions of 4.3.6~4.3.13. If the diameter of one of the two adjacent holes is greater than the maximum allowable diameter of the unreinforced hole determined by 12.2.4, it shall be strengthened in accordance with the provisions of 12.2.5~12.2.7 under the conditions required by 12.6.1, and treated as no hole after strengthening. 4.3.5 For the coal feeding holes, slag discharge holes, etc. on the vertical boiler shell, they shall be strengthened in accordance with the provisions of 12.2.5~12.2.7, and treated as no hole after strengthening. The minimum required thickness of the coal feeding hole ring, slag discharge hole ring, etc. shall be determined in accordance with 12.3.4. 4.3.6 The hole bridge attenuation coefficient of two longitudinally adjacent holes of equal diameter (Figure 1) is calculated as follows: sd
4.3.7 The hole bridge attenuation coefficient of two transversely adjacent holes of equal diameter (Figure 2) is calculated as follows: g
（16）
（17）
GB/T16508—1996
Steady body axis
Figure 1 Longitudinal hole bridge
4.3.8 The hole bridge equivalent attenuation coefficient of two obliquely adjacent holes of equal diameter (Figure 3) is calculated as follows: g=Kpr
Cylinder axis
Figure 3 Oblique hole bridge
The oblique hole bridge conversion coefficient K is calculated as follows: 1
(1+n)2
When n≥2.4, K=1 can be taken, at this time cry=9\. The reduction coefficient of the oblique hole bridge is calculated as follows: In the formula, s\=ai+n2
When>1, take 9=1.00. The
sheet can also be directly checked according to the line calculation diagram (Figure 4). Figure 2 Transverse hole bridge
(18)
....( 20)
GB/T16508—1996
Note: The whole line in the figure is the line connecting the minimum values of each curve. Simplified axis
N=di+d
Figure 4 Line calculation diagram for determining the value
4.3.9 If the diameters of two adjacent holes are different, when calculating the hole bridge reduction coefficient, the diameter d in formulas <16), (17) and (20) is taken as the average value d of the two adjacent holes. That is,
+( 21)
4.3.70 When calculating the hole bridge reduction coefficient of the recessed hole (Figure 5), the diameter d in formulas (16), (17) and (20) is replaced by the equivalent diameter d and calculated according to the following formula:
da=d+h
-(d,-d,)
(22)
4.3.11 If the holes in the hole row are non-radial holes (Figure 6), when calculating the hole bridge reduction coefficient, the diameter d in formulas (16), (17) and (20) is replaced by the equivalent diameter d and determined according to the following provisions:
Longitudinal hole bridge
Transverse hole bridge
Oblique hole bridge
α should not be greater than 45°
GB/T16508--1996
V n?-+cos*a
Non-radial holes should be machined or formed by profiling gas cutting. Figure 5 Hole with a recess
Business body axis
Figure 6 Non-radial hole
4.3.12 For elliptical holes, when calculating the hole bridge reduction coefficient, the hole diameter d is determined according to the size of the hole along the corresponding pitch direction. (23)
4.3.13 The hole bridge reduction coefficient can be improved by the reinforcement effect of the excess thickness of the pipe joint of the groove type fillet weld structure. Its application conditions, structural requirements and calculation methods are shown in 12.6.
4.4 Additional thickness
4.4.1 The additional thickness c of the boiler shell is calculated as follows:++3
(25)
The additional thickness c1 considering corrosion thinning is generally taken as 0.5mm. If the corrosion thinning exceeds 0.5mm, the actual possible corrosion thinning value is taken.
The additional thickness c2 considering the material thickness deviation (when it is a negative value) shall be determined according to the relevant material standards. The additional thickness cs considering process thinning shall be determined according to the specific process conditions: Under normal circumstances, the shell cylinder after cold rolling and cold calibration can be taken as zero; the shell cylinder after cold rolling and hot calibration can be taken as 1mm; the shell cylinder after hot rolling and hot calibration can be taken as 2mm. 4.4.2 Additional thickness of straight header cylinder and straight water pipe 4.4.2.1 During design calculation, the additional thickness of the straight header cylinder and straight water pipe shall be calculated according to formula (25), where c1 is processed according to the principle of 4.4.1, c3 is taken as zero, and C2 is calculated according to the following formula:
Ge = At
Wherein: The coefficient A is calculated according to the following formula:
The value of A can also be selected according to Table 6.
100一m
（26)
GB/T16508—1996
Table 6 Coefficient A
4.4.2.2 During verification calculation, the additional thickness c of the straight header cylinder and straight water pipe shall be calculated as follows: At + G
4.4.3 The additional thickness of the annular header cylinder and the curved water pipe 5
..( 28)
4.4.3.1 During design calculation, the additional thickness of the annular header cylinder and the curved water pipe shall be calculated as follows: (25), where c is processed according to the principle of 4.4.1, and c2 + c3 is calculated as follows:
C+ C=Aitf
Where: Coefficient A is selected according to the following provisions: When a.ni<1.8. A1 is calculated as follows:
n(4n, + 1)
b. When 1.8≤n≤3.5, A, shall be selected according to Table 7. m.%
When coefficient A1
cnm>3.5, A, shall be selected according to A in Table 6. +m
4.4.3.2 During verification calculation, the additional thickness c of the annular header cylinder and the curved water pipe shall be calculated as follows: At+c
4.5 Thickness limit
（29）
+（31）
4.5.1 When the inner diameter D of the boiler shell is greater than 1000mm, the thickness of the boiler shell cylinder shall not be less than 6mm; when the inner diameter D of the boiler shell is not greater than 1000mm, the thickness of the boiler shell cylinder shall not be less than 4mm. 4.5.2 The thickness of the large horizontal water pipe of a vertical boiler shall not be less than 6mm. 4.5.3 When the non-insulated shell is placed in a flue or furnace with a smoke temperature of not less than 600℃, the thickness should not be greater than the values listed in Table 8. Table 8 Maximum allowable thickness of non-insulated shell
In flue or furnace with a smoke temperature greater than 900℃
In flue with a smoke temperature between 600℃ and 900℃ 4.6 Structural requirements
Maximum allowable thickness
4.6.1 For expansion tube holes, the hole bridge reduction coefficient 99 and?\ should not be less than 0.3 The distance between the center of the expansion tube hole and the edge of the weld should not be less than 0.8d, and not less than 0.5d+12mm; there shall be no expansion tube holes on the longitudinal weld. If expansion tube holes are required on the circumferential seam, they shall comply with the requirements of the "Regulations on Boiler Safety Technical Supervision" 4.6.2 The welded pipe hole should be avoided as far as possible on the main weld, and the net distance between the edge of the pipe hole weld and the edge of the adjacent main weld should not be less than 10mm. If it cannot be avoided, the following two requirements should be met: the main weld a
within the range of 1.5 times the pipe hole diameter (when the pipe hole diameter is less than 60mm, it is 0.5d+60mm) from the center of the pipe hole is qualified by radiographic flaw detection, and there should be no slag inclusions around the hole; b. After welding, the pipe or pipe joint is heat treated or partially heat treated to eliminate residual stress. At this time, the attenuation coefficient of this part is the product of the hole bridge attenuation coefficient and the weld attenuation coefficient. 10(28)
4.4.3.1 During design calculation, the additional thickness of the annular header cylinder and the water bend shall be calculated according to formula (25), where c is handled according to the principle of 4.4.1, and c2 + c3 is calculated according to the following formula:
C+ C=Aitf
Wherein: Coefficient A is selected according to the following provisions: a. When ni<1.8, A1 is calculated according to the following formula:
n(4n, + 1)
b. When 1.8≤n≤3.5, A, is selected according to Table 7. m.%
When coefficient A1
cnm>3.5, A, is selected according to A in Table 6. +m
4.4.3.2 During the verification calculation, the additional thickness c of the annular header cylinder and the curved water pipe is calculated as follows: At+c
4.5 Thickness limit
(29)
+(31)
4.5.1 When the inner diameter D of the boiler shell is greater than 1000mm, the thickness of the boiler shell cylinder should not be less than 6mm; when the inner diameter D of the boiler shell is not greater than 1000mm, the thickness of the boiler shell cylinder should not be less than 4mm. 4.5.2 The thickness of the large horizontal water pipe of a vertical boiler should not be less than 6mm. 4.5.3 When the non-insulated boiler shell is placed in a flue or furnace with a smoke temperature of not less than 600℃, the thickness should not be greater than the values listed in Table 8. Table 8 Maximum allowable thickness of non-insulated boiler shell
In flue or furnace belly with smoke temperature greater than 900℃
In flue with smoke temperature between 600℃~~900℃ 4.6 Structural requirements
Maximum allowable thickness
4.6.1 For expansion tube holes, the hole bridge reduction coefficient 99 and?\ shall not be less than 0.3 The distance between the center of the expansion tube hole and the edge of the weld shall not be less than 0.8d, and not less than 0.5d+12mm; there shall be no expansion tube holes on the longitudinal weld. If expansion tube holes are required on the circumferential seam, they shall comply with the requirements of the "Regulations on Boiler Safety Technical Supervision" 4.6.2 The welded pipe hole should be avoided as far as possible on the main weld, and the net distance between the edge of the pipe hole weld and the edge of the adjacent main weld should not be less than 10mm. If it cannot be avoided, the following two requirements should be met: the main weld a
within the range of 1.5 times the pipe hole diameter (when the pipe hole diameter is less than 60mm, it is 0.5d+60mm) from the center of the pipe hole is qualified by radiographic flaw detection, and there should be no slag inclusions around the hole; b. After welding, the pipe or pipe joint is heat treated or partially heat treated to eliminate residual stress. At this time, the attenuation coefficient of this part is the product of the hole bridge attenuation coefficient and the weld attenuation coefficient. 10(28)
4.4.3.1 During design calculation, the additional thickness of the annular header cylinder and the water bend shall be calculated according to formula (25), where c is handled according to the principle of 4.4.1, and c2 + c3 is calculated according to the following formula:
C+ C=Aitf
Wherein: Coefficient A is selected according to the following provisions: a. When ni<1.8, A1 is calculated according to the following formula:
n(4n, + 1)
b. When 1.8≤n≤3.5, A, is selected according to Table 7. m.%
When coefficient A1
cnm>3.5, A, is selected according to A in Table 6. +m
4.4.3.2 During the verification calculation, the additional thickness c of the annular header cylinder and the curved water pipe is calculated as follows: At+c
4.5 Thickness limit
(29)
+(31)
4.5.1 When the inner diameter D of the boiler shell is greater than 1000mm, the thickness of the boiler shell cylinder should not be less than 6mm; when the inner diameter D of the boiler shell is not greater than 1000mm, the thickness of the boiler shell cylinder should not be less than 4mm. 4.5.2 The thickness of the large horizontal water pipe of a vertical boiler should not be less than 6mm. 4.5.3 When the non-insulated boiler shell is placed in a flue or furnace with a smoke temperature of not less than 600℃, the thickness should not be greater than the values listed in Table 8. Table 8 Maximum allowable thickness of non-insulated boiler shell
In flue or furnace belly with smoke temperature greater than 900℃
In flue with smoke temperature between 600℃~~900℃ 4.6 Structural requirements
Maximum allowable thickness
4.6.1 For expansion tube holes, the hole bridge reduction coefficient 99 and?\ shall not be less than 0.3 The distance between the center of the expansion tube hole and the edge of the weld shall not be less than 0.8d, and not less than 0.5d+12mm; there shall be no expansion tube holes on the longitudinal weld. If expansion tube holes are required on the circumferential seam, they shall comply with the requirements of the "Regulations on Boiler Safety Technical Supervision" 4.6.2 The welded pipe hole should be avoided as far as possible on the main weld, and the net distance between the edge of the pipe hole weld and the edge of the adjacent main weld should not be less than 10mm. If it cannot be avoided, the following two requirements should be met: the main weld a
within the range of 1.5 times the pipe hole diameter (when the pipe hole diameter is less than 60mm, it is 0.5d+60mm) from the center of the pipe hole is qualified by radiographic flaw detection, and there should be no slag inclusions around the hole; b. After welding, the pipe or pipe joint is heat treated or partially heat treated to eliminate residual stress. At this time, the attenuation coefficient of this part is the product of the hole bridge attenuation coefficient and the weld attenuation coefficient. 10
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