Service life evaluation method of ultra-supercritical boiler special steel pipe welding connector

Abstract

The invention relates to a service life evaluation method of an ultra-supercritical boiler special steel pipe welding connector. The method includes the steps of firstly: using an NSW-MOD theoretical model to determine mathematic relation between a creep damage accumulation process and crack growth rate on the basis of a crack tip creep damage accumulation process; secondly, using a polynomial to fit a da / dt-a curve to obtain a maximum curvature point, namely the turning point a of creep crack growth; thirdly, calculating to obtain the ratio a / (S-a0), namely the creep crack growth service life loss a / (S-a0) of the special steel pipe welding connector under high temperature and high pressure, of special steel pipe welding connector pipeline wall thickness S to the difference (S-a0) of S and initial crack length a0; acquiring the creep crack growth residual service life of the special steel pipe welding connector under high temperature and high pressure by numerical integration between the crack length a at the turning point and the pipe wall thickness S. The method has strict physical and theoretical basis, and service life predication is highly matched with actual service life.

Description

technical field [0001] The invention relates to a method for predicting the service life of creep crack expansion of a welded joint of dissimilar steel pipes of an ultra-supercritical boiler under high temperature and high pressure conditions. Background technique [0002] my country is a coal-based energy country. Thermal power generation will still occupy a dominant position in the entire power production at present and for a long time to come, and will remain the most important source of power. At present, the way to improve the efficiency of thermal power generation in various countries in the world is mainly by increasing the steam parameters, that is, increasing the steam pressure and temperature entering the steam turbine. Therefore, super (super) critical thermal power generation units have been vigorously developed. [0003] The steam parameters of the thermal power generation unit, such as temperature and pressure increase, put forward stricter requirements on the ...

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Problems solved by technology

The linear extrapolation method of the enduring strength isotherm is to obtain the relationship between the short-term stress, fracture time and temperature of the material by increasing the stress and temperature, and then extrapolate the relationship between the long-term stress, fracture time and temperature. The extrapolation method is currently the basic method for the design of high-temperature components. However, because the prediction technology is sensitive to the working stress, the relationship between creep life and stress is quite questionable. Therefore, there are many deficiencies in the life evaluation of this technology for high-temperature components.

[0008] Different heat-resistant steels are used in the high-temperature parts of ultra-supercritical thermal power generation units. During welding and use, the composition, structure and mechanical properties of the welded joints will vary greatly, and there will be relatively high stress concentration in the welded joints to resist creep. The performance of the creep hole is gradually weakened, the nucleation of creep holes is easy to form, and grows and aggregates into microcracks, which is easy to cause creep damage failure

Therefore, the prediction results of the above method for the creep crack growth life of dissimilar steel welded joints will have large discrepancies.

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