Abstract: In this paper the main problems concerning the quality of flash butt welding of boiler tubes from a technological point of view are discussed.It is emphasized that the prevailing explanation for the mechanism of forming low plasticity structures like the "grey fish eyes" remains to be made perfect with further investigations.The "grey fish eyes" defects could be best put under control by technological means.The practical methods of improving welding technology are stated;and the selection of welding parameters analyzed.The paper also introduces the principle of the technique of preheat energy auto-control.In flash welding with preheating,the "heat level" of joints can be monitored by varying the degree of preheating,thus making the regulating process of welding parameters much more simplified.The said improvements have been put into practice and proven to be reliable and satisfactory in production.