Construction of a high-strength steel penstock

Abstract

Since a pumped-storage plant operates briefly in a power generation regime its capacity can be increased by increasing the parameter P. D (product of the pressure and penstock diameter) of the penstocks with a comparatively small vohime of the reservoir. However, an increase in diameter and pressure leads to an increase in the thickness of the penstock walls and consequently to a decrease in the reliability of the structure and to complications in manufacture and assembly. The thickness of the penstock walls can be reduced by using higher strength steels. The experience of a number of countries shows that the most promising in hydropower construction are the low alloy steels and, in particular, high-strength, heat-treated low-alloy steels in the highest pressure parts of penstocks [1-3].The 200,000-kW Kiev pumped-storage plant, whose construction was completed in 1972, includes six penstocks with a diameter of 3800 mm and wall thickness of 14-30 mm made of steel Mt6CS (GOST 6713-53). The working pressure in the penstock is 6.4 arm. During construction of the sixth penstock two 10.5-m links of high-strengthsteel 14Kh2GMR (ChMTU-1-645-69) with a wall thickness of 20 mm were installed in place of steel M16$ with a wall thickness of 28 mm in the lower, most loaded section of the penstock. The links of steel Ivi168 were replaced by steel 14Kh2GMR for conducting experimental welding of large-diameter, high-strength steel penstocks and for studying the design strength of the experimental links during operation of the plant. Observation of the experimentalconstruction work during operation of the Kiev plant revealed no difficulties, since the penstock was laid on the ground surface.The high-strength, low-alloy steel 14Kh2GMR is one of the most promising, since it combines high strength characteristics with sufficient weldability, cold resistance, and comparatively low cost.The rolled sheet products for the experimental links of the Kiev plant penstock were hardened and tempered when delivered. The chemical composition and main mechanical properties of the 20-mm-thick steel sheet are presented in Table 1.In fabricating the cylindrical sections of steel 14Kh2GMR V, grooving for welding the circular joints was done mechanically. Gas cutting with subsequent dressing by an emery stone was used for X-grooving forwelding the longitudinal joints when assembling the cylinders into sections. Each section was made up of two cylinders, the length of the section was 1500 mm. Connection of the cylinders into sections and enlargement of the sections into ]inks were done by automatic submerged arc welding. Welding was done without preheating.The root welds during automatic welding were made with a 3-mm-diameter Svl0GA electrode (GOST 2246-70). FilLing of the grooves was done with a 3-mm-diameter high-strength Svl0KhGN2MYu electrode (TU 43-71). Flux AN17M was used during welding (TU IE5 26F-69). Electrodes UONI-13/45 (type 342A) and ANP-2 (type ET0) with a diameter of 4 mm were used for assembling the elements of the penstock and welding...