CN112304863A - Method for evaluating adhesion of oxide skin on inner wall of superheater reheater pipe of thermal power plant - Google Patents
Method for evaluating adhesion of oxide skin on inner wall of superheater reheater pipe of thermal power plant Download PDFInfo
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Abstract
The invention discloses a method for evaluating the adhesion of an oxide skin on the inner wall of a superheater reheater tube of a thermal power plant, which is used for evaluating the adhesion of the oxide skin on the inner wall of the superheater reheater tube of the thermal power plant to obtain the risk of peeling of the oxide skin in the thermal power plant and practically prevent the problem caused by peeling of the oxide skin. The method comprises the steps of marking a spiral line in a pipe, measuring the ratio of pixels occupied by the peeled part of the oxide scale to pixels occupied by the whole cutting test area, calculating the oxide scale peeling rate, namely the percentage of the area of the oxide scale peeling area to the total area of the grid cutting area, and grading and evaluating the adhesive force of the oxide scale on the inner wall of the pipe sample to be tested. The method aims at the characteristics that the oxide scale on the inner wall of the superheater tube of the power plant is compact, hard and layered, and the attachment surface is a curved surface, so that the attachment degree of the oxide scale on the inner wall of the tube in actual application of the thermal power plant is truly reflected, the test result can guide the peeling risk judgment of the oxide scale of the power plant, and the economic and safe operation of the power plant is ensured.
Description
Technical Field
The invention relates to a method for testing the adhesion testing force of oxide skin in a metal tube, in particular to a method for evaluating the adhesion force of oxide skin on the inner wall of a superheater reheater tube of a thermal power plant.
Background
The oxidation corrosion of the high-temperature steam of the boiler of the supercritical (supercritical) generating set is one of the main reasons for accidents of a power plant, and is the direct reasons for accidents of scale falling, blockage, pipe explosion, solid particle erosion and the like of a superheater and a reheater, so that the economic loss is serious. For decades, the scale accidents caused by the high-temperature steam oxidation corrosion frequently occur and are not thoroughly solved, the high-temperature steam oxidation problem is still one of the major problems which are troubled and threaten the safe, reliable and economic operation of the power plant unit, the deep development of the flexibility peak shaving of the power plant unit is influenced by various factors such as temperature, pressure and stress fluctuation, and the scale problem caused by the high-temperature steam oxidation corrosion is further aggravated.
The low adhesion of the scale is a direct cause of its flaking, clogging, but there is currently no method for its adhesion testing and evaluation. The existing domestic and foreign standards related to the adhesion test are that a plane test piece is taken as a test object, the plane test piece cannot be used for the adhesion test and evaluation of products formed by the corrosion action of the inner wall of the circular pipeline, and the plane test piece is mainly used for the adhesion test of paint films, plating layers and the like and is not suitable for the test and evaluation method of the adhesion of the compact and hard oxide skin on the inner wall of the heat exchange pipeline.
At present, the method for evaluating the adhesion force of the oxide skin on the inner wall of the superheater reheater pipe of the thermal power plant is not needed temporarily, the power plant is difficult to evaluate the risk of scale peeling, and the problem caused by scale peeling is practically prevented. Therefore, the method for more accurately testing the adhesion force of the oxide skin according with the practical application method is provided aiming at the characteristics that the oxide skin formed by the high-temperature steam oxidation of the inner wall of the superheater reheater tube of the thermal power plant is compact, hard and layered and the inner wall of the tube is curved.
Disclosure of Invention
Aiming at the problems in the prior art, the invention provides the method for evaluating the adhesion force of the oxide skin on the inner wall of the pipe of the superheater or reheater of the thermal power plant, the method is reasonable in design and convenient to operate, the adhesion degree of the oxide skin on the inner wall of the pipe in the actual application of the thermal power plant is truly reflected, and the test result can guide the judgment of the peeling risk of the oxide skin of the thermal power plant.
The invention is realized by the following technical scheme:
a thermal power plant superheater reheater pipe inner wall oxide skin adhesion evaluation method comprises the following steps:
cleaning and drying the tube sample to be detected with the oxide layer generated on the inner wall;
cutting a spiral line cutting groove which is coaxial with the pipe sample on the inner wall of the pipe sample to be measured by using a cutting tool;
cutting axial cutting grooves on the inner wall of the pipe sample to be measured along a pipe sample bus by using a cutting tool, wherein the axial cutting grooves and the spiral line cutting grooves are staggered to form a grid cutting groove area;
cutting the tube sample into two halves along the axial direction of the tube sample at the position avoiding the grid grooving area, and cleaning and drying the half tube sample in the grid grooving area;
and carrying out image processing on the cutting area of the oxide skin grid on the inner wall of the test tube sample, obtaining the peeling rate of the oxide skin by obtaining the ratio of the pixels occupied by the peeled oxide skin part to the pixels occupied by the whole cutting test area, and evaluating the adhesive force of the oxide skin on the inner wall of the tube sample to be tested according to a set evaluation standard.
Preferably, the washing and drying steps are immersing the tube sample in absolute ethyl alcohol, scrubbing the tube sample with absorbent cotton, placing the tube sample on clean filter paper, and drying the tube sample with cold air.
Preferably, the tube sample is obtained by the following steps,
cutting a superheater reheater metal pipe to be tested into a straight pipe section with the length of 50-100 mm as an experimental test pipe sample, turning end faces at two ends of the pipe section along the radial direction of the pipe sample, wherein the turning thickness is not more than 1mm, and the concentricity tolerance value is not more than 0.1 mm.
Preferably, the cutting step of the spiral cutting groove is as follows,
the cutting tool is perpendicular to the inner surface of the pipe sample, the width of the thread is controlled, the depth of the tool bit extending into the surface of the inner wall of the pipe sample is fixed, and the cutting tool cuts the inner wall of the pipe sample at a constant speed in a clockwise direction to form a spiral line cutting groove.
Further, specifically, the width of the thread is controlled to be 0.5-2 mm, the depth of the tool bit extending into the surface of the inner wall of the tube sample is 0.5-2 mm, and the speed is 50-300 r/min in the clockwise direction.
Preferably, the step of cutting the axial incision is as follows,
making the cutting tool vertical to the inner surface of the pipe sample, axially drawing a cutting groove by taking arc bottoms at two ends of the pipe orifice as an axis, and drawing the cutting groove from the pipe orifice at one end to the pipe orifice at the other end; the scribing line is used as a central axis, and the two sides of the scribing line are respectively and parallelly cut for a plurality of times at intervals which are equidistant with the cutting groove interval, so that all the axial cutting grooves form a plurality of cutting bands.
Preferably, the grooving depth is 0.5-2 mm, and grooving is carried out in parallel at intervals of 2-6 mm at equal intervals of the grooving interval.
Preferably, the formula for calculating the scale falling rate p is as follows,
p＝(A1/A2×100％)
wherein the scale-shedding area A1Area of grid cutting area A2。
Preferably, the evaluation criteria corresponding to the set scale adhesion force are as follows,
grade 0, the shedding rate p is equal to 0%;
level 1, the range of the shedding rate p is less than 0 and less than or equal to 20%;
level 2, the range of the shedding rate p is less than 20 and less than 40 percent;
grade 3, the range of the shedding rate p is less than 40 and less than 60 percent;
level 4, the range of the shedding rate p is less than 60 and less than 80 percent;
and level 5, wherein the range of the shedding rate p is less than 80 < p < 100%.
Compared with the prior art, the invention has the following beneficial technical effects:
according to the method for evaluating the adhesion of the oxide skin on the inner wall of the superheater reheater tube of the thermal power plant, aiming at the characteristics of compact, hard and layered structure of the oxide skin and curved surface of the adhesion surface, the oxide skin on the inner wall of the tube sample is cut and stripped, and the adhesion of the oxide skin is evaluated according to the peeling rate of the oxide skin. The method provides a qualitative test and evaluation method for the adhesion force of the oxide skin formed by the oxidation of high-temperature steam on the inner wall of the pipe in the thermal power plant, and the test result can judge the risk of the peeling of the oxide skin on the inner wall of the superheater pipe in the thermal power plant and guide the operation and maintenance of the power plant.
Drawings
Fig. 1a is a schematic view of a scale spiral grooving spiral as described in the examples of the present invention.
Fig. 1b is a schematic view of a helical groove for scale in the form of a tube according to an embodiment of the present invention.
FIG. 2 is a schematic diagram of a scale-division-grid-method notch cutting according to an embodiment of the present invention.
Fig. 3 a-3 f are schematic diagrams of scale spallation corresponding to the adhesion assessment scale described in the examples of the present invention.
Detailed Description
The present invention will now be described in further detail with reference to specific examples, which are intended to be illustrative, but not limiting, of the invention.
The invention discloses a method for evaluating the adhesion of an oxide skin on the inner wall of a superheater reheater tube of a thermal power plant, which is used for evaluating the adhesion of the oxide skin on the inner wall of the superheater reheater tube of the thermal power plant to obtain the risk of peeling of the oxide skin in the thermal power plant and practically prevent the problem caused by peeling of the oxide skin. The method comprises the steps of marking a spiral line in a pipe, measuring the ratio of pixels occupied by the peeled part of the oxide scale to pixels occupied by the whole cutting test area, calculating the oxide scale peeling rate, namely the percentage of the area of the oxide scale peeling area to the total area of the grid cutting area, and grading and evaluating the adhesive force of the oxide scale on the inner wall of the pipe sample to be tested. The method aims at the characteristics that the oxide scale on the inner wall of the superheater tube of the power plant is compact, hard and layered, and the attachment surface is a curved surface, so that the attachment degree of the oxide scale on the inner wall of the tube in actual application of the thermal power plant is truly reflected, the test result can guide the peeling risk judgment of the oxide scale of the power plant, and the economic and safe operation of the power plant is ensured.
Specifically, the invention discloses a method for evaluating the adhesion of oxide skin on the inner wall of a superheater reheater pipe of a thermal power plant, which comprises the following steps:
and S1, providing the metal pipe of the superheater and the reheater to be tested, wherein the inner wall of the metal pipe to be tested has a scale layer.
S2, cutting the pipe to be tested into a straight pipe section with the length of 50-100 mm as an experimental test pipe sample, turning the end faces of the two ends of the pipe section along the radial direction of the pipe sample, and turning the outer wall of the pipe sample, wherein the turning thickness is not more than 1mm, and the concentricity tolerance value is not more than 0.1 mm.
And S3, immersing the tube sample into absolute ethyl alcohol, scrubbing the tube sample with absorbent cotton, placing the tube sample on clean filter paper, drying the tube sample with cold air, wrapping the tube sample with the filter paper, and placing the tube sample in a dryer for storage to be tested.
And S4, horizontally fixing the tube sample in a lathe. And setting machine tool parameters to enable the cutting tool to be perpendicular to the inner surface of the pipe sample, controlling the thread width to be 5mm, enabling the depth of the tool bit extending into the inner wall surface of the pipe sample to be 2mm, and uniformly cutting the inner wall of the pipe sample at the speed of 200r/min in the clockwise direction to form a spiral line cutting groove.
S5, horizontally fixing the pipe sample on a machine tool fixture, setting machine tool parameters to enable the cutting tool to be perpendicular to the inner surface of the pipe sample, axially drawing a cutting groove by taking arc bottoms at two ends of the pipe orifice as an axis, wherein the depth of the cutting groove is 2mm, and the cutting groove is drawn from the pipe orifice at one end to the pipe orifice at the other end. With the scribe line as the central axis, 5 cuts were made in parallel on both sides at an interval equidistant from the cutting grooves (5mm), respectively, so that 10 cutting bands were formed in all the axial cuts.
And S6, cutting the tube sample into two halves along the axial direction at the position avoiding the grid grooving area.
S7, taking out the tube sample, slightly sweeping off scale grains peeled off from the surface by using a brush, immersing the tube sample in absolute ethyl alcohol, scrubbing the tube sample by using absorbent cotton, placing the tube sample on clean filter paper, and drying the tube sample by cold wind.
S8, performing image processing on the cutting area of the oxide skin grid on the inner wall of the test tube sample, and calculating the scale falling rate p, namely the area A of the scale falling area by obtaining the ratio of the pixels occupied by the scale falling part and the pixels occupied by the whole cutting test area1Occupying the total area A of the grid cutting zone2Percent of (A)1/A2X 100%), and evaluating the adhesion of the oxide skin on the inner wall of the tube sample to be tested according to the set evaluation standard.
The evaluation standards corresponding to the oxide skin adhesion are as follows:
grade 0, the shedding rate p is equal to 0%;
level 1, the range of the shedding rate p is less than 0 and less than or equal to 20%;
level 2, the range of the shedding rate p is less than 20 < p < 40%
Grade 3, the range of the shedding rate p is less than 40 < p < 60%
Level 4, the range of the shedding rate p is less than 60 < p < 80%
Grade 5, the range of the shedding rate p is less than 80 < p < 100%
Example 1
The test was carried out under test conditions of 20 ℃ to 25 ℃. At least three different pipe section tests are carried out on the inner wall of the sample pipe. If the three results are inconsistent and the difference exceeds a unit scale, the test is repeated at more than three different locations and all test results are recorded. The test procedure is as follows:
(1) during the overhaul of a thermal power plant, T91 material superheater tubes are cut, and the diameter phi of each superheater tube is 45 mm by 7mm, and each superheater tube is a straight tube section with the length of 1000 mm.
(2) And cutting three sections of pipe sections with the length of 50mm on the pipe sample to be used as parallel samples, and flattening the end faces of the two ends of each pipe section along the direction vertical to the cylindrical surface. The remaining tube sections were the original blanks. Turning the outer wall of the pipe sample (the turning thickness is less than or equal to 1mm), wherein the concentricity tolerance value is 0.02 mm;
(3) immersing the tube sample in absolute ethyl alcohol, scrubbing twice with absorbent cotton, placing on clean filter paper, drying with cold air, wrapping with filter paper, and placing in a dryer for storage to be tested. The tube sample shall record the name, number, sampling site, sampling date, name of the person who sampled, etc.
(4) The tube sample was fixed horizontally in a lathe. Before testing, the cutting edge of the tool was inspected and kept in good condition by sharpening or replacing the blade. And carrying out automatic cutting according to specified steps. The lathe cutting mode is as follows: the sample pipe section is subjected to automatic spiral line cutting by a machine tool, the screw pitch is 5mm, and the groove depth is 2 mm. And setting parameters of a machine tool to enable a cutting tool to be perpendicular to the inner surface of the pipe sample, controlling the width of the thread, and uniformly cutting the inner wall of the pipe sample at the speed of 200r/min in the clockwise direction to form the spiral line cutting groove shown in the figure 1a and the figure 1 b. The cutting depth of the spiral line should be cut through to the surface of the substrate. If the substrate is not cut through due to large tube eccentricity, the surface test is invalid and is faithfully recorded.
(5) The method comprises the steps of horizontally fixing a pipe sample with a scribed spiral line on a machine tool clamp, setting machine tool parameters to enable a cutting tool to be perpendicular to the inner surface of the pipe sample, axially scribing a cutting groove by taking arc bottoms at two ends of a pipe orifice as an axis, wherein the depth of the cutting groove is 2mm, and the length of the cutting groove is from the pipe orifice at one end to the pipe orifice at the other end. With the scribe line as the center axis, 5 cuts were made in parallel on both sides thereof at an interval equidistant from the cutting pitch (5mm), so that 10 cutting bands were formed for all the axial cuts. The effect is shown in figure 2.
(6) The tube sample is cut in half along its axial direction at a position avoiding the grid grooving region.
(7) Taking out the tube sample, slightly sweeping off scale particles peeled off from the surface by using a brush to ensure that any loose scale particles scratched out cannot be remained, soaking the tube sample in absolute ethyl alcohol, scrubbing the tube sample by using absorbent cotton, placing the tube sample on clean filter paper, and drying the tube sample by using cold air.
(8) Carrying out image processing on a cutting area of an oxide skin grid on the inner wall of the test tube sample, and calculating an oxide skin peeling rate p, namely the area A of the oxide skin peeling area by obtaining the ratio of pixels occupied by the peeled oxide skin part to pixels occupied by the whole cutting test area1Percentage of the total area A2 of the grid cutting zone (A)1/A2X 100%), and evaluating the adhesion of the oxide skin on the inner wall of the tube sample to be tested.
(9) Repeating the operations (1) to (8) to obtain three different samples of the same tube sample, and calculating the average value.
(10) The scale adhesion evaluation was gradually increased from 0 to 5, as shown in table 1, indicating that the lower the scale adhesion on the inner wall of the pipe, the greater the risk of flaking.
TABLE 1 test result grading
Example 2
The power plant #3 boiler is a 600 MW-HG-1900/25.4-YM 4 type once-intermediate reheating once supercritical pressure variable-pressure operation once-through boiler with an internal recirculation pump starting system, and adopts single hearth, balanced ventilation, solid slag discharge, full steel frame, full suspension structure and pi type arrangement. And in 9 months in 2019, the #3 unit has a mode that the screen of the superheater of the boiler is abnormally shut down after the screen is exploded, the position of the explosion port is 1 st from the 4 th screen from the left of the screen superheater, and the specification material is phi 38 multiplied by 6.6 and SA-213TP 347H. The transverse axis of the explosion opening is 61mm, the longitudinal axis is 71mm, the wall edge of the explosion opening is not obviously thinned, the whole explosion opening is trumpet-shaped, and a large amount of oxide skin is accumulated on the explosion opening; the inspection shows that a part slightly expands and thickens before and after the explosion opening; longitudinal cracks are formed at the expansion positions; the endoscope inspects the upper part of the blast opening and the upper part of the nearby tube panel, and the phenomenon of scale peeling is found. By adopting the method for evaluating the adhesion force of the oxide skin on the inner wall of the superheater reheater tube of the thermal power plant, the adhesion force of the oxide skin on the inner wall of the tube section close to the explosion port is evaluated, and the method mainly comprises the following steps:
(1) the tube sample is cut 500mm at a distance of 200mm from the explosion port.
(2) Cutting a pipe to be tested into 3 sections of test pipe samples with the length of 60mm, flattening the end faces of the two ends of each pipe section along the direction vertical to the cylindrical surface, turning the outer wall (the turning thickness is less than or equal to 1mm), and setting the concentricity tolerance value to be 0.03 mm.
(3) Immersing the tube sample in absolute ethyl alcohol, scrubbing the tube sample by absorbent cotton, placing the tube sample on clean filter paper, drying the tube sample by cold air, wrapping the tube sample by the filter paper, and placing the tube sample in a dryer for storage to be tested.
(4) The tube sample was fixed horizontally in a lathe. And setting machine tool parameters to enable the cutting tool to be perpendicular to the inner surface of the pipe sample, controlling the thread width to be 5mm, enabling the depth of the tool bit extending into the inner wall surface of the pipe sample to be 2mm, and uniformly cutting the inner wall of the pipe sample at the speed of 200r/min in the clockwise direction to form a spiral line cutting groove.
(5) The pipe sample is horizontally fixed on a machine tool fixture, machine tool parameters are set to enable a cutting tool to be perpendicular to the inner surface of the pipe sample, a cutting groove is axially drawn by taking arc bottoms at two ends of a pipe orifice as an axis, the depth of the cutting groove is 2mm, and the cutting groove is drawn from the pipe orifice at one end to the pipe orifice at the other end. With the scribe line as the central axis, 5 cuts were made in parallel on both sides at an interval equidistant from the cutting grooves (5mm), respectively, so that 10 cutting bands were formed in all the axial cuts.
(6) The tube sample is cut in half along its axial direction, avoiding the grid grooving area.
(7) Taking out the tube sample, slightly sweeping off scale oxide particles peeled off from the surface by using a hairbrush, immersing the tube sample in absolute ethyl alcohol, scrubbing the tube sample by using absorbent cotton, placing the tube sample on clean filter paper, and drying the tube sample by using cold air.
(8) Image processing is carried out on the cutting area of the oxide skin grid on the inner wall of the test tube sample by using a camera, and the oxide skin falling rate p, namely the area A of the oxide skin falling area, is calculated by obtaining the ratio of the pixels occupied by the part of the peeled oxide skin and the pixels occupied by the whole cutting test area1Occupying the total area A of the grid cutting zone2Percent of (A)1/A2X 100%), and evaluating the adhesion of the oxide skin on the inner wall of the tube sample to be tested. According to the experimental result, the scale falling rate is 73.8%, and reaches 4 grades, which shows that the scale on the inner surface of the pipe wall falls seriously and the risk of falling is high.
Example 3
The boiler #1 of a certain power plant is an HG-1164/25.4-YM1 type bituminous coal boiler. The type is single-hearth balance ventilation, variable-pressure operation, primary intermediate reheating, front and rear wall opposite-impact cyclone burners, a medium-speed mill positive-pressure direct-fired pulverizing system and an n-shaped arrangement supercritical parameter direct-current boiler. The high-temperature reheater is arranged in 65 pieces along the width of the furnace, the transverse pitch is 230mm, each tube group adopts 8 tubes, the inlet section tube is phi 57 multiplied by 4.5 and is made of 12Cr1MoVG, the middle section tube is phi 51 multiplied by 4.5 and is made of SA-213T91, and the outlet section tube is phi 51 multiplied by 4.5 and is made of SA-213TP 347H. The power plant discovers that the oxide skin of the final-stage reheater is seriously peeled off in the process of stopping and overhauling at a certain time, and in order to avoid the pipe explosion accident caused by large-area peeling of the oxide skin again, the adhesion evaluation of the oxide skin on the inner wall of the reheater pipe needs to be carried out, and the method mainly comprises the following steps:
(1) and intercepting a straight pipe sample 500mm to be measured of the reheater.
(2) Cutting a pipe to be tested into 3 sections of test pipe samples with the length of 60mm, flattening the end faces of the two ends of each pipe section along the direction vertical to the cylindrical surface, turning the outer wall (the turning thickness is less than or equal to 1mm), and setting the concentricity tolerance value to be 0.03 mm.
(3) Immersing the tube sample in absolute ethyl alcohol, scrubbing the tube sample by absorbent cotton, placing the tube sample on clean filter paper, drying the tube sample by cold air, wrapping the tube sample by the filter paper, and placing the tube sample in a dryer for storage to be tested.
(4) The tube sample was fixed horizontally in a lathe. And setting machine tool parameters to enable the cutting tool to be perpendicular to the inner surface of the pipe sample, controlling the thread width to be 5mm, enabling the depth of the tool bit extending into the inner wall surface of the pipe sample to be 2mm, and uniformly cutting the inner wall of the pipe sample at the speed of 200r/min in the clockwise direction to form a spiral line cutting groove.
(5) The pipe sample is horizontally fixed on a machine tool fixture, machine tool parameters are set to enable a cutting tool to be perpendicular to the inner surface of the pipe sample, a cutting groove is axially drawn by taking arc bottoms at two ends of a pipe orifice as an axis, the depth of the cutting groove is 2mm, and the cutting groove is drawn from the pipe orifice at one end to the pipe orifice at the other end. With the scribe line as the central axis, 5 cuts were made in parallel on both sides at an interval equidistant from the cutting grooves (5mm), respectively, so that 10 cutting bands were formed in all the axial cuts.
(6) The tube sample is cut in half along its axial direction, avoiding the grid grooving area.
(7) Taking out the tube sample, slightly sweeping off scale oxide particles peeled off from the surface by using a hairbrush, immersing the tube sample in absolute ethyl alcohol, scrubbing the tube sample by using absorbent cotton, placing the tube sample on clean filter paper, and drying the tube sample by using cold air.
(8) Image processing is carried out on the cutting area of the oxide skin grid on the inner wall of the test tube sample by using a camera, and the oxide skin falling rate p, namely the area A of the oxide skin falling area, is calculated by obtaining the ratio of the pixels occupied by the part of the peeled oxide skin and the pixels occupied by the whole cutting test area1Occupying the total area A of the grid cutting zone2Percentage ofNumber (A)1/A2X 100%), and evaluating the adhesion of the oxide skin on the inner wall of the tube sample to be tested. According to the experimental result, the scale peeling rate is 42.3%, and reaches grade 3, which indicates that the inner wall surface of the reheater tube has the peeling risk, and the supervision is reinforced.
Claims (9)
1. A method for evaluating the adhesion of oxide skin on the inner wall of a superheater reheater pipe of a thermal power plant is characterized by comprising the following steps of:
cleaning and drying the tube sample to be detected with the oxide layer generated on the inner wall;
cutting a spiral line cutting groove which is coaxial with the pipe sample on the inner wall of the pipe sample to be measured by using a cutting tool;
cutting axial cutting grooves on the inner wall of the pipe sample to be measured along a pipe sample bus by using a cutting tool, wherein the axial cutting grooves and the spiral line cutting grooves are staggered to form a grid cutting groove area;
cutting the tube sample into two halves along the axial direction of the tube sample at the position avoiding the grid grooving area, and cleaning and drying the half tube sample in the grid grooving area;
and carrying out image processing on the cutting area of the oxide skin grid on the inner wall of the test tube sample, obtaining the peeling rate of the oxide skin by obtaining the ratio of the pixels occupied by the peeled oxide skin part to the pixels occupied by the whole cutting test area, and evaluating the adhesive force of the oxide skin on the inner wall of the tube sample to be tested according to a set evaluation standard.
2. The method for evaluating the adhesion of the oxide skin on the inner wall of the superheater or reheater tube of the thermal power plant as claimed in claim 1, wherein the cleaning and drying steps comprise immersing the tube sample in absolute ethanol, scrubbing the tube sample with absorbent cotton, placing the tube sample on clean filter paper, and drying the tube sample with cold air.
3. The method for evaluating the adhesion of the oxide skin on the inner wall of the superheater or reheater tube of the thermal power plant as claimed in claim 1, wherein the tube sample is obtained by the steps of,
cutting a superheater reheater metal pipe to be tested into a straight pipe section with the length of 50-100 mm as an experimental test pipe sample, turning end faces at two ends of the pipe section along the radial direction of the pipe sample, wherein the turning thickness is not more than 1mm, and the concentricity tolerance value is not more than 0.1 mm.
4. The method for evaluating the adhesion of the oxide skin on the inner wall of the superheater reheater tube of the thermal power plant as claimed in claim 1, wherein the cutting step of the spiral cutting groove is as follows,
the cutting tool is perpendicular to the inner surface of the pipe sample, the width of the thread is controlled, the depth of the tool bit extending into the surface of the inner wall of the pipe sample is fixed, and the cutting tool cuts the inner wall of the pipe sample at a constant speed in a clockwise direction to form a spiral line cutting groove.
5. The method for evaluating the adhesion of the oxide skin on the inner wall of the superheater or reheater tube of the thermal power plant as claimed in claim 4, wherein the thread width is controlled to be 0.5-2 mm, the depth of the cutter head extending into the inner wall surface of the tube sample is 0.5-2 mm, and the speed is 50-300 r/min in the clockwise direction.
6. The method for evaluating the adhesion of the oxide skin on the inner wall of the superheater reheater tube of the thermal power plant as claimed in claim 1, wherein the step of cutting the axial cutting groove comprises the following steps,
making the cutting tool vertical to the inner surface of the pipe sample, axially drawing a cutting groove by taking arc bottoms at two ends of the pipe orifice as an axis, and drawing the cutting groove from the pipe orifice at one end to the pipe orifice at the other end; the scribing line is used as a central axis, and the two sides of the scribing line are respectively and parallelly cut for a plurality of times at intervals which are equidistant with the cutting groove interval, so that all the axial cutting grooves form a plurality of cutting bands.
7. The method for evaluating the adhesion of the oxide skin on the inner wall of the superheater or reheater tube of the thermal power plant as claimed in claim 6, wherein the cutting grooves are formed in parallel at intervals of 0.5-2 mm in depth and 2-6 mm in equidistant spacing.
8. The method for evaluating the adhesion of the oxide skin on the inner wall of the superheater or reheater tube of the thermal power plant as claimed in claim 1, wherein the scale peeling rate p is calculated by the following formula,
p＝(A1/A2×100％)
wherein the scale-shedding area A1Area of grid cutting area A2。
9. The method for evaluating the adhesion of the oxide skin on the inner wall of the superheater or reheater tube of the thermal power plant as claimed in claim 1, wherein the evaluation criteria corresponding to the set adhesion of the oxide skin are as follows,
grade 0, the shedding rate p is equal to 0%;
level 1, the range of the shedding rate p is less than 0 and less than or equal to 20%;
level 2, the range of the shedding rate p is less than 20 and less than 40 percent;
grade 3, the range of the shedding rate p is less than 40 and less than 60 percent;
level 4, the range of the shedding rate p is less than 60 and less than 80 percent;
and level 5, wherein the range of the shedding rate p is less than 80 < p < 100%.
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