Method for preparing U-shaped seamless steel pipe of high-pressure feedwater heater

Abstract

The invention provides a method for preparing a U-shaped seamless steel pipe of a high-pressure feed water heater, relating to the high-pressure feed water heater. The method comprises the steps: the preparation of raw material pipes; the raw material pipes are unceasingly colddrawn by a cold drawing device to form middle parison pipes with the external diameter of 38 plus and minus 0.40mm and the thickness of 2.95 plus and minus 0.3mm; the middle parison pipes are further colddrawn by the cold drawing device to form middle semi-finished products pipes with the external diameter of 30-32mm and the thickness of 3.00-3.80mm; the middle semi-finished products pipes are colddrawn by a ring hole pattern mold and the cold drawing device to form finished products with the external diameter of 16-19mm, the thickness of 1.7-3.0mm and the length of 12-35mm; the finished products are bended into U-shaped pipes by a bent pipe mold; stressrelieving is carried out on the elbow parts of the U-shaped pipes; rust prevention treatment is carried out on the U-shaped pipes, and then U-shaped pipes are packed. The average yield stress of the high tension test of a gawga pipe prepared by the invention is 340MPa; the average tensile strength is 530MPa; the average unit extension is 36.7%; the invention totally meets the use demand of a high-pressure feed water heater and has the advantages of low cost, high performance.

Description

technical field [0001] The present invention relates to a high-pressure feed water heater, more specifically, to a material mainly used for preparing a U-shaped seamless steel pipe of a high-pressure feed water heater, and a high-pressure pipe prepared from the material, as well as its preparation and packaging methods. Background technique [0002] The high-pressure feed water heater is an indispensable key equipment in the steam-water circulation system of large-scale thermal power generating units. Its function is to use the steam after work to heat the feed water entering the boiler, so as to improve the efficiency of the unit, reduce energy consumption, reduce emissions, and protect the environment. The U-shaped tube is the pressure boundary for heat exchange and the core component that determines the performance of the high-pressure feed water heater. With the country's increasing requirements for energy saving, emission reduction, and environmental protection, and the...

AI Technical Summary

Problems solved by technology

At present, this kind of U-shaped high-pressure pipe is monopolized by a few companies, which is expensive and has low production capacity. At the same time, imported products have problems such as long lead times, which seriously restricts the development scale and speed of my country's thermal power industry.

[0003] For this reason, manufacturers of high-pressure feed water heaters intend to use domestically produced U-shaped seamless pipes to replace imported products. However, the commonly used material for preparing U-shaped seamless pipes is SA556 C2, which has a wide range of C and Mn contents (C≤0.30%) , Mn:0.29~1.06%), there are disadvantages of unstable mechanical properties

When C ≤ 0.15%, the strength of the U-shaped tube is too low to meet the requirements for use; when C ≥ 0.27%, the strength of the material is too high, the plasticity is poor, and processing and welding are difficult

At the same time, the content range of Mn is too wide, which will also bring similar consequences

In addition, most of the current high-plus U-shaped pipes adopt the cold drawing process in the straight pipe manufacturing process. Since this process applies simple longitudinal tensile stress to the pipe fittings, various defects are prone to occur in the pipe fittings during the deformation process. The dimensional accuracy and surface quality Both are not high, and the length of the straight pipe is also limited

Therefore, most of the high-strength U-shaped tubes made of SA556 C2 material through cold drawing process have shortcomings such as too thick tube wall, thick tube diameter, insufficient length, inaccurate size of U-shaped arc parts, and poor surface quality. How to provide a super-long, ultra-thin and high-plus U-shaped seamless steel pipe with a semi-circular bend whose mechanical properties meet the requirements of use and have stable performance is the motivation of the creators of this invention.

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