Power Technology and Engineering
Vol. 41, No. 2, 2007
TECHNICAL CHARACTERISTICS OF THE DESIGN OF WELDED HYDRAULIC-ENGINEERING STRUCTURES AND EQUIPMENT V. N. Panin1 Translated from Gidrotekhnicheskoe Stroitel’stvo, No. 2, February, 2007, pp. 6 – 10.
Examples are cited and substantiation provided for use of certain non-standard welded joints.
The design of welded, for example, hydraulic-engineering, structures and equipment presumes analysis on the subject of the structure’s adaptability to production. This operation presents no difficulties when employed in the design of type structural solutions, and type production procedures (processes) for fabrication, consolidation, and assembly. In a number of cases, however, the situation demands use of non-standard solutions, for example, non-standard welded joints (Table 1). Production characteristics of the structures and equipment, i.e., the impossibility of employing standard welded joints in a number of cases, improvement in the reliability and longevity of the welded joints, enhancement of productivity in the fabrication of structures and equipment, etc., are basic reasons for the adoption of these solutions. A circular field joint in a pressure conduit at a hydroelectric power plant (HPP) (Table 1, alternate scheme No. 1) is a typical example of a non-standard welded joint adopted for reasons of fabrication. The basic reason is a small pipe space, and, as a result, assembly, welding, and defectoscopy can only be accomplished from the inside the conduit. Development of joints depicted as alternate scheme No. 6 (Table 1) pursue the goal of improvement in the reliability and longevity of the joints. Thus, the proposed alternate scheme of welded joint exceeds its analogy by more than 50% in terms of static strength, while retaining its longevity. When this alternate scheme is employed, moreover, the operation involving the bending of anchors is precluded due to improvement in the concrete’s adhesion to a deformed reinforcing bar. These joints have been recommended for use in fabricating the linings of water-passing courses at HPP. The purpose of developing joints corresponding to alternate schemes No. 2 – 4 (Table 1) is to lower labor outlays and raise the productivity of the fabrication and assembly of structures and equipment. In all cases where some non-standard solutions are used for welded joints, substantiation of their serviceability is re1
quired, as a minimum, at the level of their standard analogies. This problem is usually solved by experimental means, i.e., by comparative mechanical tests (static, dynamic, low-cycle — as a function of the operating conditions of these joints in structures of either standardized specimens, or full-scale joints. Figure 1 shows tabulated results of similar tests. In a number of cases, analytical-experimental methods are employed for these purposes. The familiar relationships [1] s sh =
sin b æ 1 ö ; s u y çç h + ÷÷ tan sin( + q ) sin q b b 3 è ø
2
(1)
where ósh is the shear stress, óu is the is the ultimate strength for uniform mechanical properties of the base and weld-on metal, ø is the relative cross-sectional area of the weld-on metal, ç is the relative depth of penetration of the adjoined plates, â is the angle of incline of the forming joint, è is the direction angle of the yield band, h is the depth of penetration, F is the area of the joint, B is the thickness of the metal of the vertical element, and l is the length of poor penetration, were therefore used to substantiate welded joints with poor process penetration in the wall of the support beam of a plain gate (alternate scheme No. 3 in Table 1). As a result, formula (1) can be represented as ósh = Kióu, where Ki is the shear-stress-intensity factor, which links the geometric dimensions of the welded joint and the ratio of the magnitude of poor penetration to the cross section of the weld and the thickness of the metal being welded. During the course of the experimental studies, this relationship was corrected for actual heterogeneous properties of the base and weld-on metal with allowance for different depths of fusion. This relationship permitted computed prediction of the serviceability of similar welded joints on the
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82
V. N. Panin
Number of cycles to failure N ´ 105
4.0 x ± 2s t = 0.3 < t 2 = 2.26 3.5 x 1 = x 2
80
A–A
P
G
70
3.0
60
2.5
50
2.0
40
T G
A
1.5
A
T
30
1.0
20
0.5
10
P
0
1
0
2
1
2
a
b
Fig. 1. Effect of profile of reinforcing bars on longevity (a), and static strength (b) of welded joints: 1, die-rolled profile; 2, smooth profile.
TABLE 1. Examples of Non-Standard Type Structural Solutions for Welded Joints Used in Hydraulic-Engineering Sketch of welded joint
Number of alternate scheme
Usage non-standard
1/3
1 ä
ä
Annular non-swiveling field joint in penstock (reduced pipe space)
ä
ä
1
2/3 1/3
ä
°
2/3
Æ3000 + 6000 B±2
15
1
°+
1
12
3000 + 6000
50°
5–6
standard
2
Annual swivel joint in penstock, formed by molten-slag arcless electric welding
ä
ä
50 ± 60
60°
22 – 26 B = 30
â
F2
n=6
È = 45° F1
33.3
3
K1 = 12
S = 14...60
5
I
K1 = 12
È = 45° F1
I
t
K2
â
F2
Joint in wall of lined circular-support column (plain gates of regulated water-passing courses)
Lining
ä
Collar beam
4
Joint in lined collar beams (same) 45°
m
Shaft collar
Lining
5
45° m
Joint in lining with shaft collars (Y-tubes, penstock collectors)
m 45° 45° A–A
A–A
6
A
A
A
Class A-I; steel grade — St3; Æ 25 mm
Joint between reinforcing rod and lining stiffeners
A
Class A-II; steel grade — St3; Æ 25 mm
Technical Characteristics of the Design of Welded Hydraulic-Engineering Structures and Equipment
600
600
a
2
83
b 1
500
2 7
8
1
Stress, MPa
Stress, MPa
500
400 5 7
400
300
300
8
4 5
4 I 0.5
II 0.6
III 0.7 0.8 Factor Ki
0.9
II
I 0.5
0.6
III 0.7 0.8 Factor Ki
0.9
Fig. 2. Computed shear stresses in welded T-joint: a, steel 09G2S, sv-08G2S wire; b, steel St3sp, Sv-08G2S wire; 1, 2, ultimate strength; 4, 5, actual shear stress; 7, 8, computed shear stress; 1, 4, 7, weld metal; 2, 5, 8, base metal; I, II, III, edge scarf of 0, 5, and 10 mm, respectively.
basis of the criterion ósh, its establishment in factory standards, and its use for further design of similar joints (Fig. 2). The local nature of the thermal welding cycle leads to nonuniform distribution of welding-induced stresses in both the process of forming the welded joint, and residual stresses. These stresses, in turn, dictate a different level of residual deformations in welded structures, which occasionally extend beyond the limits of the requirements set forth in regulatory technical documents. In these cases, dressing is the only means of imparting design dimensions to the structure: mechanical dressing for simple structures, and flame dressing for more complex structures. These operations are extremely time-consuming, and costly. Moreover, they do not always impart the design dimensions to the structure. The level of residual deformations will depend on a whole series of structural and procedural parameters, and does not always agree with computed prediction with sufficient accuracy. When a design is completed, prediction of residual deformations is possible only from the process parameters (welding sequence, method and conditions of welding, etc.). When industrial engineers switch to the design stage, the arsenal of means available for regulating residual deformations increases markedly due to the possibility of varying the structural components. When a completed design exists, moreover, a welded structure within tolerances established for residual stresses will not always be achieved due to production procedures. And, this will lead either to rejection of the structures, or, as has already been noted, to their dressing. The above-indicated approaches to prediction of residual welding deformations are cited below in examples of type designs, to wit: only those due to production procedures (without preliminary analyses), an analytical-experimental approach in the developmental stage of production, and an analytical-experimental approach in the design stage of the structure. Regulation of residual deformations by optimization of individual production parameters (sequence of welded-joint
positioning, welding regimes, etc.) is indicated in an example of consolidation of a radial gate for an HPP (Fig. 3). The analytical-experimental approach in the stage of production development (in structural plan, the article is viewed from the end) is demonstrated in an example of molten-slag arcless electric welding of longitudinal joints in the linings of penstocks at HPP. The empirical relationship f = 49.2 ×10 -6
qn d
æLö ç ÷ èRø
0.11
(2)
is obtained on the basis of experimental investigations [2] with use of common analytical approaches [3], where f is the deflection of the longitudinal joint, qn is the linear welding energy, and ä, L, and R are, respectively, the thickness, length, and radius of the lining, which make it possible to predict the level of residual deformations in the lining of penstocks at HPP with allowance for variation in both production parameters, including parameters of the welding regime, and also structural parameters, including the stiffness of the structure (Fig. 4). The analytical-experimental approach in the design stage of a structure is presented in an example of the construction of the lining of mechanical equipment for the supply line to an HPP in the form of a new structural solution for linings in Fig. 5. This approach is implemented in accordance with the following algorithm: calculation of residual welding deformations using the familiar body of mathematics, followed by experimental studies to investigate actual deformations in prototype assemblies and segments, adjustment of appropriate coefficients, analysis, and finally, adjustment of the design in conformity with computational data. CONCLUSIONS 1. Examples are cited and substantiation is provided for use of certain non-standard welded joints dictated by adapt-
84
V. N. Panin From pressure-free side
From pressure side
IX A V
IV II I
VII B P3
P1
B=B VI-VII H2
K1 X
X
P1 K4
A-A
P2
XI
III B b
a I (2 pcs.)
K5(K6) 4 34
1
A
VIII K1
K3 P3 K6
K4 P3(P2) 4
III (2 pcs.)
III (4 pcs.) 7 P3(P2) 1
4 K6(K4) 3 34 1 5 5 5
B1 2
5
5
6
P1(P3) A-A
4
3
3
1
P1(P3) P1(P2) IV (12 pcs.)
2
V (2 pcs.)
P1(P2-P3)
VI (2 pcs.) 2
2 P1(P2)
H1(H2)
2 1
1 4 3
1
1
4 K5(K6) K4(K5-K6)
2
P1(P2) VII (4 pcs.) M1(M2)
H1(H2) VIII (2 pcs.) 1 K2(K3)
2
IX (16 pcs.) 32
2
K3(K)
1 5
K1(K2;K3)
1
4 3 1
2
2
P1(P2)
1 2
4 K1-K3
X (2 pcs.)
XI (2 pcs.) 2
P1-P3 1
1
P1-P3 K4-K6
1
2 321 123 321 123 321123
V IV III II I I II III IV V Length of weld 1(2)
2
Fig. 3. Welding sequence for assembled joints in radial gate: a, general appearance; b, layout of production assemblies; I-XI, production assemblies with respect to welding sequence; 1 – 7, sequence of weld superposition within assembly; K1 – K6, P1 – P3, B1, M1, M2, H1, H2, 32, 34, gate-assembly marks.
Technical Characteristics of the Design of Welded Hydraulic-Engineering Structures and Equipment f, mm
a
150 O 16
200
2.0 1.6 1.2 0.8 0.4 0.2
25
T3-8
L/R 20
70 100
30
1200
85
T3-6
12
15 10
40
100
70
KÄ
O 16
T3-8 T3-6
1.5
12
20
20 30 40 60 3 (qn/d ) ´ 10 , cal/cm2
150 200
200
10
1200
100 70
b
5
100
100
1
60
22 26 30 Ä
80 100 504540363230 25 22 20 dn, mm
Fig. 4. Nomogram for determination of maximum deflection f during molten-slag arcless electric welding of longitudinal joint in lining of pipeline section: ä, thickness of metal being welded; Ä, weld gap.
ability to production of hydraulic-engineering structures and equipment, and the basis of proof of their serviceability is also presented. 2. Basic approaches are given for regulation of residual welding-induced deformations of hydraulic-engineering structures, which ensure their assigned accuracy. These approaches are illustrated in specific examples (structures).
Fig. 5. Segments of lining structures for HPP supply lines: a, type structural variant; b, proposed variant.
3. Results of investigations relative to the above-cited trends have been introduced to regulatory instruction manuals, and design and procedural documents, and are incorporated in specific hydraulic-engineering weldments (pipelines, gates, tunnel linings, etc.). REFERENCES 1. M. V. Shakhmatov, V. V. Erofeev, and L. I. Khmarova, “Effect of geometric parameters of welded joints with ring butt welds on their bearing capacity and resistance to brittle failure,” Avtomat. Svarka, No. 5 (1986). 2. V. N. Panin, “Residual welding-induced deformations of penstock linings at HPP,” Gidrotekh. Stroit., No. 5 (2006). 3. S. A. Kuz’minov, Welding-Induced Deformations of Ship Hulls [in Russian], Sudostroenie, Leningrad (1974).
