Method for calculating thickness of oxide film of martensite heat-resistant steel under supercritical high-temperature steam

Abstract

The invention relates to a method for calculating the thickness of an oxide film of martensitic heat-resistant steel under supercritical high-temperature steam. The method is particularly suitable for9% Cr martensitic heat-resistant steel. According to the method, a parabola model of metal oxidation kinetics is utilized; mathematical correction is carried out on the Arrhenius equation on the basis of the parabola model; a large number of actual operation results of a power plant and simulation experiment data are comprehensively taken into consideration; an oxide film thickness calculation formula of the 9% Cr martensitic heat-resistant steel in a high-temperature steam environment with a temperature of 23-35MPa is obtained by using a step-by-step linear fitting method and a function curve fitting method; and according to the formula, the influence of time and temperature on the thickness of the oxide film is comprehensively taken into consideration, and the thickness of the oxide film of the 9% Cr martensite heat-resistant steel under the condition can be calculated by substituting steam temperature and running time into the formula. The formula breaks through the limitation thatmost oxidation kinetic models only consider the influence of a single factor, and overcomes the defects that traditional oxide skin thickness measurement method is long in test period, high in cost,complex in operation and unstable in precision, or need to cut a steel pipe and the like.

Description

technical field [0001] The invention relates to a method for calculating the oxide film thickness of martensitic heat-resistant steel under supercritical high-temperature steam, in particular to the oxidation of 9% Cr martensitic heat-resistant steel under supercritical or ultra-supercritical high-temperature steam environment Calculation method of film thickness. Background technique [0002] 9% Cr martensitic heat-resistant steel mainly includes martensitic heat-resistant steels such as T / P91, T / P92, E911 and G115 (9Cr3W3Co), which are widely used in ultra-supercritical boiler main steam pipes, headers, superheaters, High temperature components such as reheaters. In order to improve thermal efficiency, reduce coal consumption and emissions, the steam pressure and temperature of thermal power units continue to increase, and the problem of high-temperature oxidation of key components of the unit has also become serious. Oxidation and corrosion caused by high temperature st...

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Problems solved by technology

The main concern in engineering is the thickness of the oxide scale formed by the material in the high-temperature steam. As the temperature rises, the growth rate of the oxide film accelerates, and the oxide scale formed within a certain period of time becomes thicker, which will lead to the following problems: First, the oxide film Thickening reduces the effective pipe wall, increasing the pressure on the pipe wall, and even destroying it due to creep; second, the low thermal conductivity of the oxide film will cause the pipe wall to heat up, further accelerating oxidation corrosion and failure; 3. When the oxide scale reaches a certain thickness or the oxide scale is heated unevenly due to overheating of the pipeline or frequent start-up and shutdown, part of the oxide scale will peel off due to stress, and the peeled oxide debris may block the pipeline or enter the steam turbine to cause damage to the steam turbine. blade erosion etc.

At present, domestic and foreign studies on the high-temperature steam oxidation kinetics of 9Cr% heat-resistant steel mainly use the method of oxidation weight gain, and the research on oxide scale thickness is often limited to the influence of a single variable (steam temperature or time).

However, the operating temperature of different units is often different, and the growth rate of oxide scale is also different at different temperatures. The oxidation kinetic model obtained from a single working condition cannot be applied to other temperature conditions. It is not suitable for calculating the thickness of oxide film in actual situations universal

Commonly used methods for measuring scale thickness in industry include cleaning method, sampling electron microscope measurement, micro-area analysis method and ultrasonic detection method, etc., but the above methods have high cost, long cycle, unstable accuracy, complicated operation and need to cut the tube, etc. Inadequacies

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