CONCLUSIONS i. Reconstruction of the radial gate of a spillway by installing an additional gate on the sill under the existing gate is an effective method of increasing the height of the gate, especially when the gate height is increased by 1.5-2 m and more. 2. The capacity of the gate hoisting gear can be increased by increasing the mechanical advantage of the block a n d t a c k l e with the installation of additional blocks and by increasing the capacity of the cable drum; such reconstruction increases the lifting capacity by 15-20%. 3. A sectional strut-braced flashboard permits even under winter conditions draining the spillway sill and reliably protecting the zone of works on the sill. 4. The use of hot water with a temperature of 50-60 ~ is an effective method of removing surface icing and fast ice on the perimeter of the gate if it is necessary to lift it in the winter, especially under conditions of the Far North. 5. When installing a sectional strut-braced flashboard in front of a radial gate at temperatures of minus 40-50 ~ it is necessary to heat the water in the intergate space (for example, by steam) to preclude the formation of a thick ice cover and ice attached to the gate.
SOP~ PROBLEMS OF THE DESIGN, MANUFACTURE, OPERATION OF ~ C H A N I C A L
INSTALLATION, AND
EQUIPMENT IN LOW-TEMPERATURE REGIONS
G. A. Polonskii
UDC 621.311.21.002.5
The widely launched construction of hydraulic structures in Siberia, Far North of the Soviet Union requires a considerable amount of mechanical tal structural elements of a "northern make." The requirements imposed on anical equipment and metal structural elements of such a specific purpose crease.
the Far East, and equipment and methe quality of mechshould steadily in-
The long-term experience in the design, manufacture, transport, installation, and operation of mechanical equipment and metal structural elements of Soviet hydroelectric stations and also the experience of foreign hydroelectric stations make it possible to take into account the operating characteristics of mechanical equipment of a "northern make." An analysis of brittle fractures of structural elements at negative temperatures shows t~at they are caused mainly by the following factors: use of steels with a high propensity for cold brittleness; inappropriate design shapes of the main structural elements and design imperfections of various unitizing articles; poor quality of manufacture and installation; violation of the rules of maintenance of the equipment and structural elements. When choosing the type of mechanical equipment it is necessary first of all to take into account the reliability and service life of the proposed structure. This requirement, mandatory in general for any structure, acquires special significance when dealing with equipment and structural elements of structures whose failure can lead to major disasters. An improvement of product quality promotes an increase of labor productivity, saving of material resources, acceleration of the pace of building the economy, and better use of fixed capital. The increasing importance of the problem of quality is a consequence of the objective development of productive forces, characterized primarily: by the rapid development of science and technology, which led to a considerable increase of the complexity of mechanical equipment being manufactured and of the requirements imposed on their technical and economic indices; by complication of production processes as a result of using modern equipment and means of mechanization and automation; by expansion of branch and interbranch cooperation; by an increase in the volume of production.
Translated from Gidrotekhnicheskoe
418
0018-8220/84/1809-0418508.50
Stroitel'stvo, No. 9, pp. 32-38, September, 1984.
~ 1985 Plenum Publishing Corporation
Fig. I. Structure of the fracture of lowalloy sheet steel at --60~ a) content of fiber 100%; b) content of fiber 65. i) Fibrous structure; 2) granular structure.
Fig. 2. Measurement of the thickness of ice formed on the skin plate of a vertical lift gate. With the current development of industrial relations and cooperation between enterprises and branches of industry, a considerable improvement of product quality by the efforts of individual enterprises or branches is practically impossible. The importance and complexity of the problem of providing quality of mechanical equipment and metal structural elements, especially of a "northern make," requires a fundamentally new approach to its solution. It is necessary to change from building individual enterprises to an efficient, scientifically founded and permanently acting system of providing quality at all levels of management, both within the framework of a single enterprise and on the scale of all enterprises associated with the creation of mechanical equipment of hydraulic structures. Problems of quality are inseparably related to problems of standardization. The main parameters and dimensions, technical characteristics, testing methods and means, indices of the reliability and life of articles, and requirements imposed on raw material and materials are determined by the USSR State Standards. A high level of quality of finished products can be obtained only provided that the raw material, materials, semifinished products, and unitizing articles meet the requirements of the standards. The principle of integrated standardization provides an optimal level of product quality, making it possible to control it from t h e very first stages of production.
419
Perfection of mechanical equipment and metal structural elements is determined by the specific consumption of metal per unit useful load. A decrease of the specific weight of a structural element, provided that it has the necessary service reliability, is one of the main problems being solved daily by the creators of mechanical equipment and metal structural elements. The successful solution Of this problem is to a considerable extent determined by the properties of the steel used for their manufacture. The demand for steels combining high strength with sufficient plasticity, ductility, fatigue strength, corrosion resistance, and weldability is increasing. The low-alloy steels with a yield point of 35-40 kgf/mm 2 (343-392 MPa) presently widely used for the manufacture of equipment and structural elements in many cases do not meet the increased requirements of Soviet hydrotechnical construction, which served as the impetus to develop the production of special low,alloysteels of increased and high strength. The required structure and set of mechanical and technological properties of these steels are obtained by combining a certain alloying composition and heat treatment. An increase of steel strength requires more thorough design studies of individual weldments and improvement of the quality of manufacture and control. The technology of treatment and welding for heat-treated steels and for the well-mastered ordinary carbon steels is different. The considerable experience gained in recent years in the USSR, USA, and other countries showed that the use of high-strength low-alloy steels, on meeting certain requirements in the design and manufacture of welded structures, substantially broadens the engineering possibilities in the manufacture of unique structural elements and mechanical equipment. In the northern regions of our country the temperature in the winter drops to minus 4060~ and therefore the reliability of mechanical equipment of hydraulic structures in the so-called northern make is determined to a considerable degree by the cold strength of t h e materials used. During transport, installation, and operation of mechanical equipment and structural elements under low-temperature conditions the materials in them to one extent or another change their physicochemical properties; the structure, strength characteristics, plasticity, ductility, magnetic and electrical properties of the metals change, the volume and linear dimensions of parts and of the entire equipment as a whole change, To ensure performance, reliability, and durability of the equipment and structural elements under low-temperature conditions, it is necessary to solve a number of problems related to the selection of materials, special methods of building the equipment, heat treatment, etc. A decrease of temperature causes deformations of parts, which depend on the nominal size, temperature drop, and coefficient of linear expansion of the material. In this case the coefficients of linear expansion themselves a r e n o t constant for the majority of metals and their alloys -- they decrease with decrease of temperature. In those cases when the materials of mating parts have different coefficients of linear expansion the different temperature deformations of theparts cause a change in the character of the fit, allowance, or interference in the connection. These changes can hinder or make impossible the operation of certain components of mechanical equipment under low-temperature conditions. They should be taken into account when building mechanical equipment. Ductility worsens with decrease of temperature, and in a certain temperature interval, which depends also on the loading conditions, steel can pass into a brittle state. In this case fracture occurs rapidly without preliminary plastic deformation with a crystalline surface appearance characteristic for brittle fractures. Consequently, one of the main requirements which should be met by the steel used for the manufacture of equipment and structural elements of hydraulic structures of "northern make" is small sensitivity to brittle fractures at negative temperatures. The main factors influencing the propensity of steel for brittle fracture are the grain size and character of the structure. Fine-grained steels are less sensitive to brittle fractures. One of the measures providing a fine grain, and still better a fibrous structure, is heat treatment of hot-rolled metal and the weld zone of welded joints. The propensity of steel for brittle fracture is usually judged on the basis of the threshold of cold brittleness, which is usually determined by the change in impact strength with change in temperature. In this case it is advisable to evaluate also the appearance of the
420
fracture surface. It seems to us that for high resistance of welded structures to brittle fractures it is necessary that at low temperatures the steel have sufficient impact strength and a satisfactory structure of the fracture, i.e., with a sufficient amount of fiber (Fig. i). High-strength hot-rolled steel T-I and T-I of type A with a yield point of 703 MPa (7030 kgf/cm 2) was used for reducing the cost of the penstocks and lining of the tunnel at the Tom Sauk pumped-storage station (USA). Such steel was used for a lining with design stresses of 281 MPa (2810 kgf/cm2), which in the given case corresponds to the maximum static head. For penstocks immediately adjacent to the powerhouse and more complex in design than the lining, a design stress up to 201 MPa (2010 kgf/cm 2) was taken. In the construction of the Tom Sauk pumped-storage station only 2090 tons of high-strength steel were used, i.e., half as much as in the case if construction had been carried out with the use of ordinary carbon steels, which reduced the cost of manufacturing the structural elements. In this case 25-mm-thick high-strength steel sheets were used for constructing the penstocks instead of 50-mm-thiek carbon steel sheets usually used for this purpose. The use of hard-surfaced metal was accordingly reduced fourfold. When designing mechanical equipment in a "northernmake" it is necessary to subordinate everything to the operational requirements and to take into account the difficulties related to various types of ice formation and their effect on mechanical equipment. The operation of the equipment and structural elements of hydraulic structures under winter conditions can be divided according to this character into the following types: difficulties owing to ice within the water body (shuga) related to the fact that during intense shuga formation, shuga jams form in the river channel which can lead to winter floods in the case of their breakthrough, which requires immediate opening of the spillway gates; difficulties due to surface ice formations: a) static pressure of the ice field on the spillway gates; b) dynamic effect of the ice during an ice run on the gates and their elements; c) clogging of the racks with floating ice. Surface icing forms at seepage places in the winter, the gates freeze to the embedded parts, which prevents their operation. Measures to control the aforementioned difficulties were developed by Soviet planning and design organizations. The static pressure of ice on a gate is not taken into account, and therefore for safe operation it is necessary to provide heating, air blowing, stream formation, and, in the extreme case, chipping of the ice in front of the gates, which sufficiently ensures the maintenance of a nonfreezing strip along the gate. If these measures are not taken, the gates are severely frozen over in the winter (Fig. 2). The thickness of the frozen-over ice reaches 1 m and more with broadening of the surface icing toward the concrete abutments or piers in the upper part of the gate. On the sill freezing over decreases, since in the lower layers the water is warmer than in the upper layers. In addition to freezing over of ice on the skin plate, considerable surfacing icing in the presence of seepage occurs also in the grooves, on the horizontal beams, diaphragms, and iongitudinai braces (Fig. 3). On the Keokuk dam on the Mississippi River (USA) three gates were crushed simultaneously by ice because the necessary measures were not taken to prevent the static pressure of the ice field on the gates during its thermal expansion; on the dam of the Votkinsk hydrostation a double gate was crushed. An air blower and stream producer with an automatic operating cycle require minimum manpower for their operation and for this reason they are considered the main methods for maintaining an ice clearing. However, the layout of these devices should be issued before placing the concrete so that the system of air lines is laid in the concrete, since a positive temperature should be provided in the pipelines. Only in this case will it be possible to successfully adjust the operation of the air blower. Otherwise the pipelines and hoses will freeze through, owing to which the smooth operation of the device will be disturbed. In the case of the untimely issuance of the layout it will be necessary to perform considerable drilling works on the already constructed structures, which occasionally are difficult to perform. Stream producers have become widespread. They are simple in design, are easily installed practically in any place, and are readily automated. Their main shortcoming is the need to break the ice around the floats, and also certain difficulties during operation under conditions of variation of the water level of the upper pool. The air blower and stream producers can operate successfully if the water temperature at depth is within plus 0.5-0.3~ Stream 421
producers are operating successfully at the Bratsk hydrostations and an air blower at the Gorki~ Kegum, and a number of other hydrostations. The following methods are used to control freezing over: circulating and noncirculating heating; heating by the direct passage of a current through the embedded parts (busbar method); heating of the trash racks by direct passage of a current the bars; induction heating. Induction heating has the following advantages over the other heating methods: possibility of the more efficient use of the heat being spent on heating by directing it to where it is most needed; high efficiency, practically equal to unity; no need for special transformers; impossibility of short circuits. The cost effectiveness of this type of heating in many cases is considerably higher than other types of heating. However, in the case of induction heating it is required to create complex configurations of the embedded parts and rack bars, which complicates installation works. Therefore the use of this heating method for large surfaces is irrational. Successful control of freezing over of the gates should be accomplished not only by directly heating the gates and embedded parts but also by protecting the large concrete surfaces adjacent to the gates from freezing over. For uninterrupted operation of locks under conditions of an extended navigation season, in addition to heating the heel and ~iter posts of miter gates and also of the embedded parts of falling gates, it is necessary to install stream producers for driving the floatingice from the gate recess, for which perforated pipes having air outlets are laid along the seals. The compressed air delivered periodically from a compressor--receiver plant, emerging through the air outlets, rises upward and entrains the warmer deep water. The water "floats" the ice forming on the gates and walls of the recesses. Partial breaking of the ice occurs also from the mechanical action of the air bubbles on it. Ice is driven from the recesses by the concentrated release of air through the 25-mm-diameter holes in the pipes led up to the gate posts and middle part of the recesses. For normal operation of the floating mooring rings at negative temperatures, they are heated by electric infrared heaters which are fastened above the grooves of the rings and maintain a positive temperature of the surface of the rings and linings. Furthermore, compressed air is fed to the lower part of the grooves of the rings to prevent freezing over of the grooves when the water level in the chamber changes during locking. The most reliable gate for operating at negative temperatures is the radial gate with a heat-insulating cover and heating of the embedded parts, since a radial gate does not have recesses. This is confirmed by long-term operation of the radial gates of the spillway of the Rajakoski hydrostation (Fig. 4). Two openings are covered by 18 x 4.5-m radial gates. The cavities of the radial gates are heated by electric furnaces (six l-kW furnaces per gate) with three power positions. The embedded parts and concrete are heated from two 16.5~kVA transform~ ers. The end parts of the gate to which the seals are fastened have oil-filled cavities. Heaters supplied from two 5-kVA transformers are built-in in their lower part. Circulation of the oil is natural. In cases of closing surface outlets by vertical lift gates, both in the construction period and during permanent operation it is necessary to use slide gates with two skin plates, forming together with the walls of the horizontal beams a closed internal cavity. Such a gate design maximally corresponds to the operating conditions in regions of the Far North, since it permits winterizing the gate (for example, by coating the outer surface on the downstream side with a layer of polyurethane foam) and heating all compartments of the gate. The experience of operating the mechanical equipment of the Bratsk hydrostation showed, that deep gates located at the exit of the outlets in a closed position strongly freeze over. The linings of the curtain walls and recesses, being subjected to the effect of seeping water (along the contact between the concrete and lining) freezing at negative temperatures, bulge. As a result wedging of the gate occurs. To eliminate this phenomenon, heating of the outlets in the winter immediately after closing them by gates was provided for at the Ust'-llim hydrostation. For this purpose the outlet at the exit is covered by a wooden winterizing panel, a winterizing cover is placed above the recesses, and electric calorifiers are installed in the isolated space formed.
422
Fig. 3. Considerable surface icing on horizontal beams, diaphragms, and longitudinal braces of a vertical lift gate.
Fig. 4. Radial gates of the spillway of the Rajakoski hydrostation. View from downstream. At the Ust'-llim hydrostations the gantry cranes with grab beams servicing the gates have been adapted to operate at very low temperatures. The cranes have winterized and heated rooms of the mechanisms and grab beams. At negative outside air temperatures the electric calorifiers are turned on before operating the crane and the beams and mechanisms are heated. The rooms underneath are closed by shutters. The shutters automatically open when the sling of the crane with tile grab beam is lowered. The grab beam with an electric drive of high reliability with a large torque on the grab element can also split off the ice in the recesses. The gate chambers of the water intakes of hydrostations located in the north of our country should be of the closed type with an upper heated room, analogous to the Upper Tuloma or Khantaika hydrostation (Fig. 5). The existing intakes of the open type but embedded in the high wall of the upstream face should be protected from the penetration Of cold air and have special heating. To provide reliability and performance of the mechanical equipment and metal structural elements in a "northern make," additional measures should be taken (special designs, increase of strength and wear resistance, correction of the system of allowances and fits, use of frost-resistant materials, special technology of assembly and welding, heat treatment, and protective coatings). Mechanical equipment and metal structural elements in a "northern make" should be manufactured only under factory conditions with the use of the most progressive and technically perfect method with maximum possible automation and mechanization of the works according to a thoroughly developed technological process. In addition to planing parts to obtain more accurate dimensions, edges should be planed to remove zones of cold working after cutting on shears and zones of hardening or loss of strength after oxygen or plasma-arc cutting. It is recommended to design the cross section of welded elements symmetric and composed of a minimum number of parts so that the number of connecting joints is minimum, As an illustration we will give the design of a deep vertical lift gate (Fig. 6), where the flanges of
423
Fig. 5. Mechanical equipment of the intake of the Khantaika hydrostation: i) emergency gate; 2) cable mechanism; 3) trash rack; 4) clamshell; 5) bridge crane; 6) closed heated and ventilated room. the diaphragms and flanges of the horizontal beams are made as a unit without welds between them. Welds are made only for connecting the flanges to the webs of the diaphragms and beams. Rounding of the flanges of the diaphragms and beams where they intersect reduces stress concentration and increases the dynamic strength of the structure. Welding of structures or individual components should be done only after checking the correctness of their assembly and acceptance by the technical inspection department. Marked changes in cross sections and other factors causing stress concentration or nonuniform flow should not be allowed in welded elements. It is necessary to select joints with minimum stress concentration (butt joints, butt connection with a smooth transition, lap joints with welding around the contour, etc.). It is necessary also to take into account the harmful effect of welding stresses and strains and to provide for appropriate measures to reduce them (preliminary bending, optimal order of assembling and welding the elements, preliminary heating, etc.). With an increase of the requirements imposed on the geometry of welds and joints a change in the dimensions under the effect of a redistribution of residual Stresses is not allowed.
424
View from free side
View from pressure side
6"700 4120
-i
-7-
7- ....
Ir
D I + + + +
q __
//
}
+ + + + +
~+
++
§ 2 4 7 2 4 7 +
i
L
7II
7
' II
II \- ,\ \ - , . ~ - ' q ~ \ \ \ \ \ \ \ \ Fig. 6.
\
Deep vertical lift gate: i) beam flanges; 2) diaphragm flanges.
Impartment to corner joints of a concave form and smooth transition to the base metal and the making of butt welds without reinforcement (if this is specified by the drawings) are done by selecting the welding conditions and by appropriate arrangement of the parts being welded. It is necessary to check the quality of welds by ultrasonic flaw detection. Butt joints of elongated elements, the results of checking which by ultrasonic flaw detection are in need of refinement, are additionally checked by roentgenography or gammagraphy methods. Organic coatings for mechanical equipment and metal structural elements operating under low-temperature conditions t o - 6 0 ~ should be subjected to a special c h e c k f o r strength, stability weatherproofness, and to a determination of adhesion by the lattice notch method. The character of installation works on hydraulic structures located in regions of the Far North has a number of specific features compared with analogous works when constructing hydraulic structures in regions of a temperate climate. The complex character of the equipment and structural elements of hydraulic structures requires special methods of installation, during which, along with assembling and welding the
425
structural elements, it is necessary to carefully assemble, adjust, and test the seals, ensuring complete sealing, embedded parts of the oil-heating system, embedded parts of the induction-heating system, and parts of the aeration pipes. When installing the embedded parts of the oil-heating system the necessary processes are preparation of the pipes and oil-pressure tank, cleaning, pickling, flushing, and lubricating, and also the installation, checking, and testing of the oil lines. The pipes should be protected from clogging. Certain requirements should also be fulfilled when concreting the oil lines. During installation of the embedded parts of the heating devices examination of the embedded parts and a check of the quality of the welds are required. The housings of the embedded pants should undergo hydraulic testing. During installation of the aeration pipes the quality of assembling and welding should be high, and also the welds should be strong and leakproof to keep cement grout out during grouting of the concrete. Before concreting the aeration pipes the impenetrability and strength of the welds should be checked by hydraulic testing. CONCLUSIONS i. The most important direction in works to increase the efficiency of producing mechanical equipment and metal structural elements intended for serviceat minus temperatures is a substantial improvement of the quality of products being manufactured. 2. The choice of materials for mechanical equipment of hydraulic structures in a "northern make" can be made only by a comprehensive approachwith consideration of the characteristics of their production and operation of the mechanical equipment. 3. When choosing the grade of steel it is necessary to attach particular importance to the structure of the fracture, on the quantity of fibers of which at low temperatures depends the resistance of highly loaded structural elements and mechanical equipment. 4. Designing of deep high-head gates requires consideration of problems which must be solved only with reference to the particular structure and with complete satisfaction of the temporary and permanent operating conditions. 5. The gate chambers of intakes located in low-temperature regions must have a closed heated room. 6. It is completely impermissible to put into operation mechanical equipment intended for operating at low temperatures without having completed the installation of various types of heating systems, insulation, and air-blowing devices and without having checked their reliable operation. LITERATURE CITED i. 2. 3. 4. 5.
426
Hydropower and Multipurpose Use of Water Resources of the USSR [in Russian], Energiya, Moscow (1982). G.A. Polonskii, Mechanical Equipment of Hydraulic Structures [in Russian], Energiya, Moscow (1982). G . F . Pisanko and V. L. Gerasimovich, "Mechanical equipment in the dam of the Ust'-llim hydroelectric station," Gidrotekh. Stroit., No. 3 (1978). E. Rudolph, "Tom Sauk pumped-storage station," Civil Eng., No. i (1963). A . R . Freishist, I. D. Rozina, and A. L. Rakhmanova, "From the experience of operating vertical lift gates under winter conditions," Gidrotekh. Stroit., No. 4 (1976).
