Manufacture of exhaust-heat boiler of steam-gas plant of 150 MW capacity for Alchevsk Iron & Steel Works allowed using the secondary metallurgical gases as alternative to the nature gas. Its modular design, high closeness of arrangement in heat-exchange blocks of thin-walled small-diameter pipes of heating surfaces decreased the dimensions of the plant and increased its efficiency factor up to 44.6 %. Due to a narrow gap between the pipes the butts of these pipes occurred to be hard-to-reach for welding and control. This caused the increase in the amount of inadmissible defects in welds, and also made the welded joints of pipes almost not suitable for the repair. The making of welded joints on different stands by applying methods of argon-arc and combined welding allowed improving the quality, gave an opportunity to perform repair and to realize their X-ray, ultrasonic and visual-optic control. The manufactured heat-exchange blocks withstood the hydraulic test without appearance of leakage in welded joints, were installed and put into service. Significant saving of fuel for industrial enterprises of the metallurgical industry is the application of secondary fuel gases, such as blast furnace, converter, coke gases, forming during the metallurgical processes. Their application as a fuel, alternative to natural gases, was feasible by using steam-gas plants (SGP) of a combination cycle. In these plants the gases are mixed to form the safe concentration and required heat-generating ability and are burnt out, and the generated heat is converted into mechanical and electric energy. At Alchevsk Iron & Steel Works (AMK) a complex of SGP of total power of 300 MW (two blocks of 150 MW) was manufactured. The designing of SGP was made by the Mitsubishi Heavy Industries Company (Japan) with participation of Industrial Union of Donbass [1]. Construction of steam-gas electric plant for utilization of blast furnace, converter and coke gases (similar to AMK) was planning at F.E. Dzerzhinsky Dneprovsky Iron & Steel Works. The Iron & Steel Works «Azovstal» also announced about implementation of two SGP [2]. At AMK the operation of two steam-gas blocks allows providing the almost full need in electric power, keeping the standards for harmful gas blow-outs, accepted in EU.One of the SGP main components is an exhaust-heat boiler, which was designed from heatexchange modules of the evaporator, steam superheater and economizer.The heat-exchange modules were assembled of header panels, each of them has inlet and outlet headers (Figure 1, a, b) with three rows of A, B and C holes on the lateral surface, in total 40 pcs in each one (Figure 2, a). Concentrically to these holes the connecting pipes are welded-on by fillet weld, which in turn are joined by butt weld to pipes of heating surfaces (Figure 2, b). The fillet joints of connecting pipes and butt joints of pipes of heating surfaces were made with a full penetration. Connecting pipes in the middle and edge row were bent at 25 and 50° angle, respectively. Diameter of pipes and connecti...