Some standard content:
Calculation method for strength of boiler fillet welds
JB/T6734-—1993
Subject content and scope of application
Mechanical Industry Standard of the People's Republic of China
Calculation method for strength of boiler fillet welds
This standard specifies the calculation method for strength of boiler fillet welds JB/T67341993
This standard is applicable to the connection welds of various pipe joints on the shells, headers and pipelines of fixed steam boilers with rated steam pressure greater than 2.5MPa, the connection welds welded to the load-bearing components on the boiler pressure elements, and the connection welds of the load-bearing components used in the manufacturing, installation and transportation processes.
Explanation of terms and symbols
Terms
Butt joint
A joint where the end faces of two weldments are relatively parallel.
2.1.2Fillet joint
A joint where the end faces of two weldments form an angle greater than 30° and less than 135°2.1.3T-joint
A joint where the end face of one weldment forms a right angle or a nearly right angle with the surface of another weldment:2.1.4Lap joint
A joint where two weldments partially overlap.
Round steel connection joint
A joint where two circular weldment surfaces are connected or where a circular weldment is connected to a non-circular weldment.Butt weld
A weld welded between the groove surfaces of weldments or between the groove surface of one weldment and the surface of another weldment. 2.1.7 Fillet weld
A weld welded along the intersection of two perpendicular or nearly perpendicular weldments. 2.1.8 Front fillet weld
A fillet weld whose weld axis is perpendicular to the stress direction of the weldment, see Figure 2-12.1.9
Side fillet weld
A fillet weld whose weld axis is parallel to the stress direction of the weldment, see Figure 2-2, 2.1.10
Longitudinal weld
A weld distributed along the length direction of the weldment.
Transverse weld
A weld perpendicular to the length direction of the weldment.
Approved by the Ministry of Machinery Industry on August 21, 1993
Implemented on October 1, 1993
Annular weld
A closed weld connected head to tail distributed along a simple weldment. Figure 2-1
Front fillet weld
Load-bearing weld
Welds used to bear loads on weldments,
2.1.14Non-bearing weld
Figure 2-2
Side fillet weld
Welds that do not directly bear loads on weldments and only serve as connections are usually called connection welds. 2.1.15
Groove depth
The dimension that is machined away from the end of the weldment along the thickness direction of the weldment when the weldment is grooved. 2.1.16
Weld leg size
The length of the right angle side of the largest right triangle drawn in the cross section of the fillet weld. 2.1.17Weld calculated thickness
The weld thickness used when designing welds.
2.1.18Weld calculated length
The weld length used when calculating weld strength. The calculated length of a closed weld is the actual length: the calculated length of an unclosed weld is the actual length minus 10mm for each weld. 2.1.19 Calculated thickness of weld
The product of the calculated thickness of weld and the calculated length of weld. 2.1.20 Full penetration weld
The weld is fully connected with molten metal over the full thickness of its connection, with no incomplete penetration, see Figure 2-3. If necessary, a full penetration weld can be reinforced with a fillet weld. 2.1.21 Partial penetration weld
The weldment is connected with molten metal over part of the thickness of its connection, with incomplete penetration, see Figure 2-4. If necessary, a partial penetration weld can be reinforced with a fillet weld. 2.2 Explanation of symbols
Calculated thickness of weld, mm;
A--calculated thickness of weld cross-sectional area, mm2: b--width of ear plate, mm;
h--transverse weld length of lap weld, mm;
b2--longitudinal weld length of lap weld, length of weld connecting round steel and steel plate, mm; b3, ba--elbow ear plate size, mm;
B, B, BzT-joint weld length, mm;1963
Figure 2-3
Full penetration weld
Figure 2.4 Partial penetration weld chain
--chord length of the arc part of the weld connecting the transverse ear plate and the header and the ear plate and the elbow, mm: d--pipe joint The diameter of the opening on the simplified body before assembly, mm: do-the outer diameter of the pipe joint, mm;
d-the inner diameter of the pipe joint, mn:
d, d2-the diameter of the large and small round steel, mm
D)-the inner diameter of the simplified body, mm;
-the length of the straight section of the welding seam connecting the ear plate and the elbow, mm; f-the groove depth of the pipe joint and T-joint, mm; F-concentrated force, N:
Fx, F, F-concentrated force in the
r, y, directions, N;
h-the distance from the center of the ear plate hole to the connecting weld along the ear plate height direction, mm; hl, h2-the maximum and minimum distances from the center of the ear plate hole to the connecting weld along the ear plate height direction, mm: H- - butt joint groove depth, mm;
-shell constant, 1/mm;
K-weld leg size of equal-leg fillet weld, mm; K1, K2-weld leg size of unequal-leg fillet weld, mm: I,-weld calculated length, mm;
M-moment, Nm
Ma-bending moment per unit circumference of the connection between the end cover and the cylinder, N·m/m; M, M, M-moment of rotation around r, y, axis, Nm; 1964
N-longitudinal force per unit circumference of the connection between the end cover and the cylinder, N/m; P-calculated pressure, MPa;
Q-transverse force per unit circumference of the connection between the end cover and the cylinder, N/m; Ro--simple The outer radius of the body, the radius of curvature of the outer arc of the elbow, mm: Rm—the average radius of the cylinder, mm;
s—the longitudinal distance from the center of the lifting ear plate hole of the boiler shell to the center of gravity of the boiler drum, mm; t-—the effective wall thickness of the cylinder, mm;
t, the theoretical calculated wall thickness of the cylinder without holes, mm; tn——the wall thickness of the pipe joint, mm;
W-the bending section coefficient of the weld, mm;
Wx, W, the bending section coefficient of the weld on the r and y axes, mmWk—the torsional section coefficient of the weld, mm; the effective reinforcement width of the cylinder opening, mm;
α—the groove angle of the V-shaped groove of the butt joint, degrees: β—the angle between the calculated thickness section of the weld and the weld leg size K2. degrees; - the angle between the direction of force and the height direction of the ear plate, the counterclockwise direction is positive, degrees; - plate thickness, mm;
31, 32 - the thickness of thicker and thinner plates, mm; △---unwelded dimensions in the thickness direction of the steel plate, mm; e - the distance from the common tangent of the two round steels to the surface of the connecting weld, mm; 7 - allowable stress correction factor;
9 - half of the central angle subtended by the arc part of the ear plate connecting weld, degrees; - Poisson's ratio:
a - normal stress, N/mm2;
a1 —Normal stress of the calculated thickness section perpendicular to the weld, N/mm2; SF—Normal stress caused by concentrated force, N/mm2; Om
—Normal stress caused by bending moment, N/mm?; Normal stress caused by uniformly distributed bending moment, N/mm2; OMu
OQ—Normal stress caused by transverse uniform force, N/mm2; CN—Normal stress caused by longitudinal uniform force, N/mm2; 0—Equivalent stress calculated according to the third strength theory, N/mm; Service point of weldment at room temperature, N/mm2; [. 】——Allowable stress of weldment at calculation temperature, selected according to relevant strength calculation standard, N/mm2; t shear stress, N/mm;
ti——shear stress in weld calculation thickness section and perpendicular to weld direction, N/mm2; t2——shear stress in weld calculation thickness section and parallel to weld direction, N/mm2; F—shear stress caused by concentrated force, N/mm2; TM—shear stress caused by moment, N/mm; 1965
TMu—shear stress caused by uniform bending moment, N/mm; TQ—shear stress caused by transverse uniform force, N/mm2; TN——shear stress caused by longitudinal uniform force, N/mm2; —angle between the line connecting the end points of ear plate weld and the cross section of ear plate, degrees; circumference——angle between the line connecting the two end points of straight section of elbow and the center of curvature of outer arc of elbow, degrees. 3 Technical requirements
3.1 Process requirements
The strength of welding materials shall not be lower than the lower strength of welded parts. 3.1.1
Welding and welding process assessment shall comply with the provisions of relevant standards. For fillet joints calculated according to this standard, the angle between the two weld legs shall not be less than 60\ and not more than 120°. 3.1.3
3.2 Structural requirements
3.2.1. The leg size of fillet welds shall meet the following requirements: For plates, when the thickness of the weld in contact with the leg is greater than 7mm, the leg size shall not be less than 1.5/a.
3 is the thickness of the weld in contact with the leg. This limitation is not required when the welding process is guaranteed. When the thickness of the weld in contact with the leg is not greater than 7mm, the leg size shall not be less than the smaller value of the thickness of the weld in contact with the leg and 4mm.
b. For pipe joints, the minimum leg size of fillet welds shall not be less than the smaller value of the wall thickness of the pipe joint and 6mm. e. The leg size of the outer fillet weld between the reinforcing plate and the cylinder shall not be less than 0.7 times the thickness of the thinner weld, and the leg size of the outer fillet weld with the pipe joint shall not be less than the smaller value of the thickness of the thinner weld and 6mm. d. For plates, the leg size of fillet welds should not be greater than 1.2 times the thickness of the weld in contact with the leg. For pipe joints, the leg size of fillet welds should not be greater than 2 times the wall thickness of the pipe joint. 3.2.2 The calculated length of the side or front fillet weld shall not be less than 8 times the average value of the two weld leg sizes and 40mm3.2.3 The calculated length of the side fillet weld shall not be greater than 60 times the average value of the two weld leg sizes. If it is greater than the above values, the excess portion will not be considered in the calculation. If the internal force is distributed along the entire length of the side fillet weld, its calculated length is not subject to this limit3.2.4 When the ends of the plate are connected only by two side fillet welds (Figure 3-1), the length of each side fillet weld should not be less than the distance b between the two side fillet welds; at the same time, when 32 is greater than 12mm, 6, should not be greater than 1692: when 82 is not greater than 12mm, b, should not be greater than 200mm
3.2.5 The connection welds between the rod and the node plate should generally adopt two-sided side welding, or other non-closed welds. All welds must be welded continuously at the corners.
3.2.6 In lap joints, the length of the lap weld shall not be less than 5 times the thickness of the thinner weldment, and shall not be less than 25mm. 3.2.7 The calculated thickness of the weld between round steel and round steel, and between round steel and steel plate shall not be less than 0.2 times the diameter of the round steel (when the diameters of the two round steels being welded are different, take the average diameter), and shall not be less than 3mm, and shall not be greater than 1.2 times the thickness of the steel plate. The calculated length of the weld shall not be less than 20mm.
3.2.8 For the weld of the supporting ear plate on the pressure-bearing component, when the thickness of the ear plate is not more than 12mm, a fillet weld without groove may be used; when the thickness of the ear plate is more than 12mm, a groove must be opened. 3.2.9 When welding the load-bearing ear plate to a pressure-bearing component with a wall thickness of not less than 100mm, measures shall be taken to prevent lamellar tearing of the parent material.
4 Calculation principles
4.1 Basic assumptions
Figure 3-1 Schematic diagram of the connection dimensions of fillet welds on both sides This standard does not consider the effects of residual stress, stress concentration, fatigue and end deformation. The strength of the welded joint is verified by the stress acting on the calculated thickness section of the weld. The stress generated by the concentrated force and uniform force on the calculated thickness section of the weld is calculated according to the average distribution. The stress generated by the moment on the calculated thickness section of the weld is calculated according to the linear distribution (Figure 4-1 (a)) or the average distribution (Figure 4-1 (b)) according to different situations.
Figure 4-1 Schematic diagram of stress distribution on the calculated section of the weld Weld size
The calculated thickness and weld size parameters of commonly used welds are calculated according to Table 4-1. (6)
The direction of the pipe joint weld is assumed to be circular. The calculated thickness of the weld is the average value of the values at the shoulder and the belly. The calculated thickness of the belly weld is calculated according to No. 9 in Table 4-1. Table 4-1
Weld calculation barrier
Weld size parameters
Weld calculation thickness
2-V+court
a = (k+ f)sin3
Weld pupil size parameters
sinp = -
cosp s
Calculation of weld K on belly of cylinder
Table (2)
is the weld leg size of the upper part of cylinder
V-shaped groove of partially welded butt joint
U-shaped groove of partially welded butt joint
Load calculation
Weld calculation thickness
Same as No. 7;
When>,
Same as No. 8.
When.60,
When<60\,
Weld size parameters
When ≤V,
Same as No. 7;
When>/k,
Same as No. 8.
The loads considered in this standard are: Gravity, internal pressure, safety valve recoil force, wind force, and equivalent force derived from the area reinforcement principle. 4.3.1
4.3.2 The gravity load and wind load borne by the weld are determined by the static analysis of the system. When there is no condition to conduct a static analysis of the system, it can be estimated based on experience. 4.4 Strength criterion
4.4.1 The strength calculation criterion adopts the third strength theory. Equivalent stress. . Calculate according to the following formula:
=+4(+）
The stress components of the same name calculated according to the components of each force should be added according to the algebraic value. To simplify the calculation, the stress components of the same name can also be conservatively added according to the absolute value.
4.4.3 Calculation of stress The signs of the components of positive stress are determined according to the following rules: the one that is consistent with the external normal of the section with the retained portion of the weld calculated thickness is positive and is called tensile stress; the other is negative and is called compressive stress.
Shear stress: the one that is consistent with the direction of the coordinate axis is positive, otherwise it is negative. In addition, based on the section with the retained portion of the weld calculated thickness, the shear stress direction is positive if it is consistent with the clockwise direction of the external normal of the section with the weld calculated thickness, otherwise it is negative. 4.4.4 Regardless of the form of the weld, the strength of the fillet joint weld shall be verified according to the following formula: a,≤0.74[o]/m
1g1≤0.74g]
Where n value:
When the standard value c==240N/mm2 When t=0.7; when the standard value s=36.3N/mm2, n=0.85; other cases are determined by the following formula:
7=0.00122g,+0.4073
4.4.5 The strength calculation method of the weld of the full penetration butt joint is the same as that of the weldment. When the weld cannot ensure the same strength as the weldment, the weld reduction coefficient less than 1 should be considered. The weld of the partial penetration butt joint should be calculated as the fillet joint weld. 4.4.6 The full penetration weld of the plug-in pipe joint (Figure 4-2). When t is not greater than , there is no need to strengthen the fillet weld or calculate the strength of the weld. When it is greater than , double-sided groove welding is used. And both sides have symmetrical additions of 8mm, whichever is greater: In the case of a single-sided slope i reinforced fillet weld, the weld leg size of the reinforced fillet weld shall not be less than 3.6
, and in the case of only one side having a reinforced fillet weld, the weld leg size of the reinforced fillet weld shall not be less than the larger value of 1 and 8mm, and strength calculation may not be performed.
Figure 4-2 Full penetration weld of plug-in pipe joint
4.4.7 For the full penetration weld of saddle-type pipe joint (Figure 4-3), the weld leg size K of the reinforced fillet weld on the body shall not be less than 0.61., and the weld leg size K on the pipe joint shall not be less than 1.21s; strength calculation may not be performed. 5
Pipe joint connection weld
5.1 Load analysis
The total load borne by the pipe joint weld is shown in Figure 5-1: 5.1.2
The equivalent force derived from the area reinforcement principle is borne by the calculated thickness cross-sectional area of the entire weld and is determined by the following formula: F=2[dt.-(Xd)(tt)Jo)
X is the larger value of 2d, and d, +2(t+t,). For hole bridges, it shall not be greater than the distance between the centers of the two openings. When F is a negative value: F=0.
In the formula:
t,=2[ap
The value calculated by formula (5-1) is combined with other external forces according to 5.1.5.
Figure 4-3
Fully penetrated weld of shrouded pipe joint
Figure 5-1
Schematic diagram of total
load borne by pipe joint weld
The force exerted by the pipe joint on the weld under the action of internal pressure is determined by the following formula: Saddle type pipe joint:
Plug-in pipe joint:
Fa = Px(do-2)2
The mechanical force components exerted on the weld by the pipeline system are: Fx, Fy, F,, Mx, 5.1.4
M,, MWhen calculating the load components, the following formula can be used for the conversion: Fx = Fcos(t,ro) + Fcos(rye) + Fcos(,2u)F,= Fyocos(y,ro)+Focos(y,ye)+Fmcos(y,zo)F, = Fcos(2,r) + Fcos(,yo) + Facos(2,20)Mx= Mxocos(r,r)+ Myocos(r,y)+Mwcos(r,z)M,=Mxocas(y,T)+Mucosy,ye)+Mucos(y,ze)M,=Mxpcos(z,t。)+Mocos(z,yu)+Mcos(,ze)(5-5)
(5-10)
Wherein: brackets represent angles, Fu, Fso, Fz, Mxo, Myo, Mz are the components of force on the r。, y。, r。 axes respectively. 5.1.5
The strength of the weld is verified according to the following two force systems: a.
F,F=F+Fyl,F,=Fa+F2,Mx,My.Mz
(5-11)
b.Fx,F=Fl,F,=F+Fz+Fz+M,My,Mz(5-12)wwW.bzxz.Net
In which, in formula (5-11), the direction of F is the same as that of F, and in formula (5-12), the direction of F is the same as that of Fa+Fz.
The direction of F, Fy, F, Mx, My, M, is the same as that of Figure 5-1. 1971
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