Medium-frequency simmering technology for A335P92 material bend pipe

Abstract

The invention provides a medium-frequency simmering technology for an A335P92 material bend pipe. The simmering technology is characterized by comprising the following steps of 1) determining a width (B) of an induction heating ring, 2) determining promoting speed during bend pipe medium-frequency simmering, 3) determining a technology section, 4) conducting medium-frequency simmering, 5) determining cooling temperature, 6)taking heat-insulating measures after formation of medium-frequency simmering, and 7) conducting thermal processing after formation of medium-frequency simmering. In the 1) step, induction heating coil width (B)=(2T1 to 50)mm is provided for a thick-wall bend pipe while simmering a main steam pipeline, so wrinkles in an arc position can be prevented when the bend pipe comes out of the induction ring during medium-frequency simmering. In the 2) step, prompting speed during medium-frequency bend pipe simmering is controlled between 10 to 15mm / min, so local excessive stress produced during the medium-frequency simmering can be controlled. In the 3) step, the technology section is formed by a transition section and top material; the transition section is made from low-chromium-molybdenum steel and the length L is no more than 500mm; the transition section can be re-used; and the top material is a carbon steel pipe.

Description

technical field [0001] The present invention relates to the manufacture of intermediate frequency bent pipes, specifically, it relates to the manufacturing process of intermediate frequency bent pipes used in supercritical and ultra-supercritical units such as 660MW and 1000MW supercritical and ultra-supercritical units with working temperatures exceeding 600°C and working pressures exceeding 25MPa in thermal power plants. An intermediate frequency simmering process for A335P92 material elbows. Background technique [0002] At this stage, supercritical and ultra-supercritical units are the main development direction of thermal power generation at present and in the future. In order to meet the needs of large-capacity and high-parameter operation of the unit, domestic ultra-supercritical unit main steam pipes, hot reheat steam pipes, high-pressure bypass valve pre-pipes, and low-pressure bypass valve pre-pipes adopt cost-effective, imported from abroad A335P92 steel. In mod...

AI Technical Summary

Problems solved by technology

Due to the particularity of the chemical composition of A335P92 steel (see the table below), the steel has extremely high requirements for the ambient temperature of the operation. In the low temperature environment in winter, if the A335P92 material elbow is simmered by the conventional intermediate frequency simmering process, there will be The following problems: First, the width of the intermediate frequency induction heating ring is relatively wide, and the arc starting section of the intermediate frequency elbow is prone to wrinkles; second, the process section is welded with the same material pipe and elbow material, and the weld hardness is high. The thickness of the wall, after hot simmering and forming, can not be cut by ordinary plasma cutting machine or oxyacetylene cutting machine, it needs to be transported outside to the machining workshop for cutting by band sawing machine, the heating temperature of A335P92 elbow is generally very high, in winter Under the condition of minus 20°C, heat and cold alternate, the temperature on the surface of the elbow cools down rapidly, but the temperature inside the elbow is still very high, and there is a large deviation between the temperature on the surface of the elbow and the temperature inside the elbow, resulting in Excessive stress, stress release, resulting in cracks on the surface of the bend; third, the pushing speed of the bend is controlled at ≥18mm / min. For the A335P92 material thick-walled bend, the pushing speed is too fast, and the inside of the bend will It is easy to produce local excessive stress and stress release, resulting in cracks on the surface of the elbow; fourth, there is no specific requirement for the cooling rate of the elbow after simmering. Since the wall of the elbow made of A335P92 is very thick, the temperature on the surface of the elbow is related to the temperature of the elbow. The temperature inside the tube has a large deviation, which leads to excessive stress in the bend, and the stress is released, resulting in cracks on the surface of the bend; There is a large deviation between the temperature of the elbow and the temperature inside the elbow, resulting in excessive stress in the elbow, stress release, and cracks on the surface of the elbow; Sixth, there is no specific time requirement for the heat treatment process after hot simmering, and the storage time is long , the temperature on the surface of the elbow has a large deviation from the temperature inside the elbow, resulting in excessive stress in the elbow, and the stress is released, resulting in cracks on the surface of the elbow

Wrinkled elbows should be ground under the premise of ensuring the wall thickness, and cracked elbows can only be scrapped, and raw materials must be repurchased and re-simmered. This will undoubtedly greatly increase the production cost of the product and greatly reduce the production of the product. Efficiency, which is contrary to the purpose of enterprises to reduce costs and improve production efficiency, and to improve market competitiveness

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