Membrane wall tube inner wall corrosion failure critical judging method

Abstract

The invention relates to a membrane wall tube inner wall corrosion failure critical judging method. The method includes the steps of firstly, building the finite element model of a membrane wall tube to obtain the horizontal relationship form of the defect morphology and defect depth and the partial equivalent stress of a tube; secondly, performing nondestructive testing on the corrosion degree of the inner wall of the to-be-judged membrane wall tube to obtain corrosion morphology and corrosion depth; thirdly, finding the partial equivalent stress corresponding to the tested corrosion morphology and corrosion depth according to the horizontal relationship form obtained at the first step; fourthly, comparing the partial equivalent stress obtained at the third step with the yield strength of the membrane wall tube at 400 DEG C, taking the safety coefficient as 1.5, and judging that the membrane wall tube is in a critical failure state when the obtained partial equivalent stress sigma is not smaller than the yield extreme sigma s / 1.5 of the membrane wall tube at 400 DEG C. The method is simple in field implementation and free of special equipment, membrane wall tube replacing number can be reduced greatly, and unit safety operation is guaranteed.

Description

technical field [0001] The invention relates to a judging method for judging whether a pipeline fails, in particular to a method for judging the critical failure criticality of the corrosion failure of the inner wall of a membrane water-cooled wall pipe. Background technique [0002] Under the action of high temperature and high pressure, the inner wall of the membrane water wall tube made of carbon steel and low alloy heat-resistant steel becomes more sensitive to the residual impurities in the boiler feed water. If the content of impurity ions in the feed water exceeds the allowable concentration, the boiler will accelerate Corrosion causes corrosion and thinning of the steam-water side of the water-cooled fireplace tube, and because of the raised threads on the inner wall of the furnace tube, ion aggregation and stress concentration are easily formed at the recessed position on the edge of the thread, which will cause stress corrosion and cause local strength of the tube. ...

AI Technical Summary

Problems solved by technology

Adopting this scheme will cause a large number of pipelines that are still safe to serve to be cut off, resulting in a waste of resources, and multiple new welds will be formed during the replacement process, which will bring new welding safety risks

[0004] There are raised threads on the inner wall of the membrane water wall tube, resulting in uneven inner wall structure and differences in wall thickness

Uneven distribution of equivalent stress in service state

However, during the corrosion process of the inner wall of the pipe, due to the different types of corrosion and the location of the corrosion, the local material thinning caused by inner wall corrosion has different effects on the strength of the pipe. The critical state of pipeline failure cannot be judged simply by whether the wall thickness is thinned.

Images