CN112305063A

CN112305063A - Method for judging magnetism of austenitic stainless steel matrix

Info

Publication number: CN112305063A
Application number: CN202011158627.1A
Authority: CN
Inventors: 何晓东; 刘雪峰; 杨分; 曹海涛; 王强; 李江; 李季; 李东江; 贾若飞
Original assignee: Xian Thermal Power Research Institute Co Ltd
Current assignee: Xian Thermal Power Research Institute Co Ltd
Priority date: 2020-10-26
Filing date: 2020-10-26
Publication date: 2021-02-02

Abstract

The invention discloses a method for judging the magnetism of an austenitic stainless steel matrix, which comprises the following steps: continuously measuring on an austenitic stainless steel substrate to be judged by a measuring instrument based on a magnetic method to obtain a plurality of magnetic signal values, and drawing a magnetic signal value envelope line according to all the obtained magnetic signal values; and judging whether the envelope curve of the magnetic signal has jump or sharp angle, and when the envelope curve of the magnetic signal has jump or sharp angle, indicating that the austenitic stainless steel matrix has magnetism.

Description

Method for judging magnetism of austenitic stainless steel matrix

Technical Field

The invention belongs to the technical field of nondestructive testing diagnosis, and relates to a method for judging the magnetism of an austenitic stainless steel matrix.

Background

When a thermal power station unit operates in a long-term high-temperature environment, the inner walls of a superheater on the heating surface of a boiler and a reheater tube generate oxidation corrosion under the action of water vapor and the like to generate oxides, the oxides formed on the tube wall can fall off under the influence of external factors, and the peeled oxide skin is accumulated on the lower elbow part of the tube under the action of gravity to cause blockage, reduce the steam flow in the boiler tube and cause the burst of the boiler tube when the blockage is serious.

The method is realized on the basis of the difference that the austenitic stainless steel belongs to paramagnetism and the formed oxide belongs to ferromagnetism, when the austenitic stainless steel is in service in a high-temperature and high-pressure environment for a long time, the variation and aging of a matrix structure can cause the local magnetism of an austenitic stainless steel matrix, the existence of the matrix magnetism can cause interference on a magnetic method detection result, the misjudgment of the result is caused, and the detection accuracy is reduced, so that a method is needed for analyzing the detection result to determine that the source of a magnetic method detection signal is caused by the oxide inside a pipe or the self magnetism of the austenitic stainless steel matrix.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provides a method for judging the magnetism of an austenitic stainless steel matrix, which can accurately detect whether the magnetism exists in part of the austenitic stainless steel matrix.

In order to achieve the above object, the method for judging the magnetism of the austenitic stainless steel matrix comprises the following steps:

continuously measuring on an austenitic stainless steel substrate to be judged by a measuring instrument based on a magnetic method to obtain a plurality of magnetic signal values, and drawing a magnetic signal value envelope line according to all the obtained magnetic signal values;

and judging whether the envelope curve of the magnetic signal has jump or sharp angle, and if so, indicating that the austenitic stainless steel matrix has magnetism.

When the magnetic method-based measuring instrument continuously measures on the austenitic stainless steel substrate to be judged, the interval between adjacent measuring positions is less than 1 cm.

The magnetic signal value envelope curve is a change curve of the magnetic signal value along with the measuring position.

The invention has the following beneficial effects:

according to the method for judging the magnetism of the austenitic stainless steel matrix, during specific operation, an envelope curve of the magnetic signal value is drawn according to all obtained magnetic signal values, then whether the envelope curve of the magnetic signal has jump and sharp corners or not is judged, and when the envelope curve of the magnetic signal has jump or sharp corners, the existence of magnetism of the austenitic stainless steel matrix is indicated, so that whether magnetism exists in the local part of the austenitic stainless steel matrix is accurately detected, the operation is convenient and simple, and misjudgment on the result is effectively reduced.

Drawings

FIG. 1 is a schematic diagram of a location of a measurement site of a standard sample tube;

FIG. 2 is an envelope plot of measured oxide values for 150 grams loaded into a sample tube 1;

FIG. 3 is an envelope plot of measured values of 300 grams of oxide loaded into a sample tube 1;

FIG. 4 is a graph showing the envelope of measured values of oxides charged to 150 g in a standard sample tube 2;

fig. 5 is a graph of the envelope of the oxide measurements taken with 300 grams of the sample tube 2.

Detailed Description

The invention is described in further detail below with reference to the accompanying drawings:

the method for judging the magnetism of the austenitic stainless steel matrix comprises the following steps:

Confirmatory experiment

When oxide accumulation is detected in austenitic stainless steel without matrix magnetism, when oxide accumulation exists in the pipe, an envelope curve formed by the measured value of a magnetism method near the bend of the pipe has the characteristics of stability and smooth transition, and the standard sample pipe 1 without the matrix magnetism is utilized, and the specification is as follows: phi 42 multiplied by 7mm and made of TP347H, different amounts of oxides are filled in a standard sample tube, values are continuously measured and recorded at intervals of 1cm, a schematic diagram of measuring point positions is shown in figure 1, measured values are shown in table 1, the measured values are drawn in a two-dimensional plane coordinate and form a signal envelope line in parallel, as shown in figures 2 and 3, 150 g of oxides are filled in the standard sample tube 2 shown in figure 2; the sample tube 2 shown in fig. 3 contains 300 grams of oxide.

TABLE 1

When the austenite stainless steel basal body exists magnetism, the envelope curve formed by the measurement value of the magnetism method near the elbow of the pipe has the characteristics of jump and sharp angle, as shown in figure 4 and figure 5, by using the standard pipe 2 with magnetism of the basal body at the elbow, the specification: phi 42 x 7mm, material TP347H, various amounts of oxide were loaded into the sample tube 2, the measured values are shown in table 2, the measured values are plotted in two-dimensional planar coordinates and form a envelope, as shown in fig. 4 and 5, the sample tube 2 shown in fig. 4 is loaded with 150 grams of oxide; the sample tube 2 shown in fig. 5 contains 300 grams of oxide.

TABLE 2

Whether the austenite stainless steel matrix has magnetism or not can be judged by the envelope shapes of the measured values corresponding to the standard sample tube 1 and the standard sample tube 2 according to whether the sharp corner kick characteristic exists or not so as to improve the detection accuracy, and therefore whether the matrix has magnetism or not can be judged according to the change of the envelope.

Claims

1. A method for judging the magnetism of an austenitic stainless steel matrix is characterized by comprising the following steps:

2. The method for magnetically judging an austenitic stainless steel substrate according to claim 1, wherein the interval between adjacent measurement positions is less than 1cm when the austenitic stainless steel substrate to be judged is continuously measured by a magnetic-method-based measuring instrument.

3. The method for judging the magnetism of the austenitic stainless steel substrate according to claim 1, wherein the envelope of the magnetic signal values is a variation curve of the magnetic signal values with the measurement position.