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On the tandem cold-rolling tube mills [1, 2, etc.] developed at the All-Union Research Institute of the Pipe Industry (in Dnepropetrovsk) under the direction of M. V. Popov, the tube is deformed simultaneously by two successive pairs of rolls of the same size. This scheme makes it possible to increase the draft during the rolling operation by a factor of 1.5-2. The first pair of rolls, which initiates the deformation of the incoming semifinished product, is usually referred to as the breakdown pair. The second pair of rolls is called the sizing pair. These mills are difficult to operate because of the complicated adjustments that must be made to their equipment and the distinctive features of the process of deformation in two pairs of rolls simultaneously. These features should be reflected in the design of the equipment. Tandem cold-rolling tube mills are being used with success in Ukraine, but problems have been encountered with the mills at plants in the Urals. Most of these problems are related to the fact that the specific features of the rolling operation on these mills have not been adequately taken into account.This article examines certain aspects of the rolling conditions on tandem cold-rolling tube mills. Allowing for these conditions will facilitate the practical use of such mills.One of the most important features of the type of mill being discussed is that rotation is transferred from the breakdown pair of rolls to the sizing pair through a unilateral diagonal transmission with the gear ratio D g2 /D g1 = 1.03-1.06. As on a conventional mill, the rolls of the breakdown pair are brought into rotation by drive pinions with a pitch-circle diameter D p1 . The nominal diameter of the drive pinion of the second (sizing) roll pair is determined by the gear ratio

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The evaluation quality rating of hot-rolled pipes using complex quality indicators is considered. The weighted averages of arithmetic and geometric complex indicators as well as with probabilistic indicators of access to allowable intervals on the example of oil-grade pipes are compared. It is shown that all the indicators have similar values. A complex rating of the properties of pipes manufactured by current and improved technologies was conducted. The impact of individual indicators on the quality of pipes as a whole was estimated. A comparison of complex indicators of the quality of pipes rolled on two technologies made on the scale of Harrington's desires: the current technology indicator corresponds to a sufficient level of quality in accordance with the normative documents. The indicator of the improved technology corresponds to an acceptable and good level of quality.

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