A method for detecting finished product of steel structure fireproof coating

Abstract

The application discloses a kind of steel structure fireproof coating finished product detection methods, it is related to coating finished product detection technical field, by apparent expansion ratio reflects the overall expansion degree of steel structure fireproof coating after being fired, and by continuous carbon layer thickness proportion reflects the proportion of continuous connection part in carbon layer with steel plate, so that finished product detection result reflects carbon layer external thickness and internal connection state simultaneously, can identify the situation that carbon layer thickness is larger, but there is interface separation, through crack, interlayer continuous cavity or collapse area inside, simultaneously, uncut carbon layer and steel plate connection closed pore is counted into continuous carbon layer, reduce the possibility that normal porous structure is misjudged as carbon layer structure defect, improve the same model steel structure fireproof coating finished product batch fire performance screening ability to distinguish carbon layer actual state, provide reliable basis for factory detection and fire resistance performance before screening.

Description

Technical Field

[0001] This invention relates to the field of finished coating testing technology, specifically a method for testing finished fire-retardant coatings for steel structures. Background Technology

[0002] After being applied to the surface of steel components, fire-resistant coatings can delay the temperature rise of the steel components under fire conditions. The quality of the finished product usually needs to be tested through methods such as test panel preparation, fire test, and observation of the coating condition after fire to determine the formation of a char layer after the coating is heated.

[0003] Current testing methods typically evaluate the expansion performance of coatings based on changes in coating thickness before and after exposure to fire, expansion ratio, or morphology of the char layer. However, when the char layer is thick, there may still be large cavities, interlayer separation, through cracks, or loose structures near the steel plate. Using thickness or expansion ratio alone is insufficient to accurately reflect the actual state of the char layer.

[0004] When a carbon layer with the aforementioned defects is still judged to have good expansion performance, the test results may be inconsistent with the actual fire performance of the coating. This could lead to the use of coating products with discontinuous internal structures, local suspensions, or easy collapse, affecting the heat insulation and protection effect of steel components when exposed to fire. Summary of the Invention

[0005] This invention provides a method for testing finished fire-retardant coatings for steel structures, which solves the problems mentioned in the background art.

[0006] A method for testing finished fire-retardant coatings for steel structures includes the following steps: S1. Prepare multiple coating test panels using the finished fireproof coating for the steel structure to be tested, measure the coating thickness of each test panel before exposure to fire, and determine the average coating thickness before exposure to fire. S2. Each coating test plate is subjected to fire treatment and cooling under the same fire conditions. Multiple carbon layer sections perpendicular to the steel plate surface are formed on the carbon layer after fire treatment. The distance from the steel plate surface to the outer surface of the carbon layer is measured to determine the total average thickness of the carbon layer. S3. The carbon layer portion that is continuously connected to the steel plate surface through the carbon layer material is defined as the continuous carbon layer. The carbon layer portion that is separated from the steel plate by the interface, through cracks, interlayer continuous cavities or collapsed areas is excluded. The closed pores that have not severed the connection between the carbon layer and the steel plate are included in the continuous carbon layer, and the average thickness of the continuous carbon layer is determined. S4. Determine the apparent expansion ratio based on the total average thickness of the char layer and the average thickness of the coating before firing, determine the proportion of continuous char layer thickness based on the average thickness of the continuous char layer and the total average thickness of the char layer, and determine the finished product test result based on the apparent expansion ratio and the proportion of continuous char layer thickness.

[0007] Preferably, S1 includes S11 and S12; S11. Set up multiple thickness detection positions on each coating test plate and measure the vertical distance from the steel plate surface to the outer surface of the coating at each thickness detection position. S12. Calculate the arithmetic mean of the vertical distances corresponding to the thickness detection positions on the same coating test plate, and determine the calculation result as the average coating thickness of the coating test plate before fire exposure.

[0008] Preferably, S2 includes S21 and S22; S21. Each coating test plate is subjected to fire treatment according to the same test plate placement direction, flame action position, distance between flame and coating test plate and fire treatment time. After the fire treatment is completed, each coating test plate is cooled under the same conditions, and a carbon layer cross section perpendicular to the steel plate surface is formed at multiple positions of each coating test plate. S22. Set multiple carbon layer thickness detection positions at the same interval on each carbon layer cross section. Measure the vertical distance from the steel plate surface to the outer surface of the carbon layer at each carbon layer thickness detection position. Use the vertical distance as the total carbon layer thickness at the corresponding carbon layer thickness detection position. Calculate the arithmetic mean of the total carbon layer thickness at all carbon layer thickness detection positions on the same coating test plate. Determine the calculation result as the total average carbon layer thickness of the coating test plate.

[0009] Preferably, S3 includes S31 and S32; S31. In each carbon layer section, the part that forms a gap between the carbon layer and the steel plate surface and separates the carbon layer outside the gap from the steel plate surface is defined as interface separation. The cavity located inside the carbon layer and extending in a direction parallel to the steel plate surface and separating the carbon layer outside the cavity from the carbon layer near the steel plate is defined as interlayer continuous cavity. S32. A crack that connects one end to the outer surface of the carbon layer and extends to the surface of the steel plate, where the interface is separated or the interlayer continuous cavity is defined as a through crack. A region where the carbon layer sinks towards the steel plate and the connection between the carbon layer material on the outer side of the carbon layer and the carbon layer material on the side closer to the steel plate is interrupted is defined as a collapse region.

[0010] Preferably, S3 further includes S33 and S34; S33. Using the same steel plate edge as a reference, select carbon layer thickness detection positions at the same distance from the steel plate edge on adjacent carbon layer cross sections, and check whether the interface separation, the through crack, the interlayer continuous cavity, or the collapse area exists at the corresponding carbon layer thickness detection positions. When the same type of structure exists at the corresponding carbon layer thickness detection positions of adjacent carbon layer cross sections, and the structure of this type causes the carbon layer material connection to be interrupted, it is determined that the corresponding structure extends to the adjacent carbon layer cross section. S34. When the interface detachment, the through crack, the interlayer continuous cavity, or the collapse area that causes the interruption of the carbon layer material connection appears only at the corresponding carbon layer thickness detection position of a carbon layer cross section, carbon layer cross sections are added on both sides of the carbon layer cross section, and the corresponding carbon layer thickness detection position in the added carbon layer cross section is checked according to S33 to determine whether the corresponding structure extends to both sides of the carbon layer cross section.

[0011] Preferably, S3 further includes S35 and S36; S35. Taking the steel plate surface corresponding to each carbon layer thickness detection position as the starting position, determine the carbon layer portion that is continuously connected to the steel plate surface through the carbon layer material. Exclude the outer carbon layer that is separated from the steel plate surface by the interface separation, the through crack, the interlayer continuous cavity, or the collapse area. Include the closed pores that are surrounded by the carbon layer material and do not separate the outer carbon layer from the carbon layer near the steel plate side in the continuous carbon layer. S36. At each carbon layer thickness detection position, measure the distance from the steel plate surface to the outermost position of the continuous carbon layer in a direction perpendicular to the steel plate surface. Use the distance as the continuous carbon layer thickness at the corresponding carbon layer thickness detection position. Calculate the arithmetic mean of the continuous carbon layer thickness at all carbon layer thickness detection positions on the same coating test plate. Determine the calculation result as the average continuous carbon layer thickness of the coating test plate.

[0012] Preferably, S4 includes S41 and S42; S41. Calculate the ratio of the total average thickness of the char layer to the corresponding average thickness of the coating before fire exposure for each coating test panel. Determine the arithmetic mean of the corresponding ratios for each coating test panel as the apparent expansion factor of the finished fire-resistant coating for the steel structure to be tested. Calculate the ratio of the average thickness of the continuous char layer to the corresponding total average thickness of the char layer for each coating test panel. Determine the arithmetic mean of the corresponding ratios for each coating test panel as the percentage of the continuous char layer thickness in the finished fire-resistant coating for the steel structure to be tested. S42. Calculate the ratio of the continuous carbon layer thickness to the total carbon layer thickness corresponding to each carbon layer thickness detection position, and record each ratio according to the arrangement order of each carbon layer thickness detection position on the coating test plate.

[0013] Preferably, S4 further includes S43 and S44; S43. Select multiple historical batches that are the same model as the finished fireproof coating for the steel structure to be tested and have been determined to be qualified by fire resistance performance testing. Determine the apparent expansion ratio, the proportion of continuous char layer thickness, and the ratio corresponding to each char layer thickness detection position for each historical batch. Based on the test results corresponding to each historical batch, determine the lower limit of the apparent expansion ratio, the lower limit of the proportion of continuous char layer thickness, and the lower limit of the char layer thickness detection position. S44. Compare the ratios corresponding to the finished steel structure fireproof coating to be tested with the lower limit of the qualified carbon layer thickness at the corresponding detection position, and combine the interface separation, through cracks, interlayer continuous cavities or the extension of the collapsed area to the adjacent carbon layer section determined by S33 and S34 to determine whether there is a local carbon layer structure defect in the finished steel structure fireproof coating to be tested.

[0014] Preferably, S4 further includes S45 and S46; S45. Compare the apparent expansion ratio of the finished fireproof coating of the steel structure to be tested with the lower limit of the apparent expansion ratio, compare the proportion of continuous carbon layer thickness with the lower limit of the proportion of continuous carbon layer thickness, and determine whether there is any unqualified local carbon layer structure according to S44. S46. When the apparent expansion ratio is less than the lower limit of the apparent expansion ratio, the finished product test result is determined to be insufficient expansion; when the apparent expansion ratio is not less than the lower limit of the apparent expansion ratio, and the proportion of continuous carbon layer thickness is less than the lower limit of the proportion of continuous carbon layer thickness, or when it is determined according to S44 that there is a local carbon layer structure defect, the finished product test result is determined to be a carbon layer structure defect; when the apparent expansion ratio is not less than the lower limit of the apparent expansion ratio, the proportion of continuous carbon layer thickness is not less than the lower limit of the proportion of continuous carbon layer thickness, and it is determined according to S44 that there is no local carbon layer structure defect, the finished product test result is determined to be qualified.

[0015] This invention provides a method for testing finished fire-retardant coatings for steel structures, which has the following advantages: By evaluating the apparent expansion ratio and the proportion of continuous char layer thickness together, the char layer condition of fire-retardant coatings for steel structures after being exposed to fire can be identified. This method can identify cases where the char layer is thick but contains interface separation, through cracks, continuous cavities between layers, or collapsed areas. Furthermore, closed pores that have not severed the connection between the char layer and the steel plate are included in the continuous char layer, thereby reducing misjudgments of the char layer structure and improving the accuracy and reliability of screening the fire performance of finished product batches. Attached Figure Description

[0016] Figure 1A schematic diagram showing the types of carbon layer defects and thickness measurements; Figure 2 This is a schematic diagram showing three cross-sections along the length of the plate and the detection locations. Detailed Implementation

[0017] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0018] Example 1 The method for testing finished steel structure fireproof coatings provided by this invention can be applied to batch testing of steel structure fireproof coatings, R&D verification after formula adjustment, batch verification after production process adjustment, internal screening before fire resistance performance testing, and quality re-inspection of retained samples. This embodiment takes the fire performance screening of the same model of finished product batch to be tested during the production process of steel structure fireproof coatings as the application scenario. After the finished product to be tested is completed and the test panel preparation conditions are met, multiple coating test panels are prepared from the batch of finished products. Under the same conditions, the coating thickness is measured, fire treatment and cooling are completed, and then the cross-section of the char layer formed after fire is tested. By comparing the overall expansion degree of the char layer after fire and the part of the char layer that is continuously connected to the steel plate, it is possible to identify cases where only the char layer thickness is large but there are interface separation, through cracks, continuous cavities between layers or collapsed areas. Based on the test results, the state of the char layer after fire of the batch of finished steel structure fireproof coatings is determined, providing a test basis for the quality judgment of the batch of finished products.

[0019] This invention provides a method for testing finished fire-retardant coatings for steel structures, comprising the following steps: S1. Prepare multiple coating test panels using the finished fireproof coating for the steel structure to be tested, measure the coating thickness of each test panel before exposure to fire, and determine the average coating thickness before exposure to fire. S2. Each coating test plate is subjected to fire treatment and cooling under the same fire conditions. Multiple carbon layer sections perpendicular to the steel plate surface are formed on the carbon layer after fire treatment. The distance from the steel plate surface to the outer surface of the carbon layer is measured to determine the total average thickness of the carbon layer. S3. The carbon layer portion that is continuously connected to the steel plate surface through the carbon layer material is defined as the continuous carbon layer. The carbon layer portion that is separated from the steel plate by the interface, through cracks, interlayer continuous cavities or collapsed areas is excluded. The closed pores that have not severed the connection between the carbon layer and the steel plate are included in the continuous carbon layer, and the average thickness of the continuous carbon layer is determined. S4. Determine the apparent expansion ratio based on the total average thickness of the char layer and the average thickness of the coating before firing, determine the proportion of continuous char layer thickness based on the average thickness of the continuous char layer and the total average thickness of the char layer, and determine the finished product test result based on the apparent expansion ratio and the proportion of continuous char layer thickness.

[0020] In this embodiment, the apparent expansion ratio reflects the overall expansion degree of the fire-retardant coating on the steel structure after being exposed to fire, and the proportion of continuous char layer thickness reflects the proportion of the char layer that maintains a continuous connection with the steel plate. This allows the finished product test results to simultaneously reflect the external thickness and internal connection status of the char layer. This avoids misjudging a char layer with internal interface separation, through cracks, continuous cavities between layers, or collapsed areas, but still maintaining a large external thickness, as having a good expansion state when relying solely on the char layer thickness or expansion ratio. At the same time, it preserves closed pores that have not severed the connection between the char layer and the steel plate in the continuous char layer, preventing the normal porous structure formed by the intumescent fire-retardant coating from being mistakenly identified as a char layer structural defect. This improves the ability of the batch screening of the fire performance of the same type of fire-retardant coating for steel structures to distinguish the actual state of the char layer, enabling the test results to more accurately reflect the integrity of the char layer formed after the finished product is exposed to fire. This provides a more reliable quality judgment basis for batch testing before leaving the factory and internal screening before submitting for fire resistance performance testing.

[0021] Example 2 Based on the fire performance screening scenario of the same type of fireproof coating for steel structures in Example 1, this example further illustrates the process of obtaining the average thickness of the coating before fire and the total average thickness of the char layer, so that the coating thickness before fire, the total thickness of the char layer after fire, and the thickness of the subsequent continuous char layer adopt the same position reference.

[0022] Please see Figure 2 Specifically: S1 includes S11 and S12; S11. Set up multiple thickness detection positions on each coating test plate and measure the vertical distance from the steel plate surface to the outer surface of the coating at each thickness detection position. Specifically: Samples are taken from the same batch of finished products to be tested. After stirring the samples, samples are taken from the top, middle and near the bottom of the container for inspection. When there are no visible lumps in any of the three locations, the samples are used to prepare coating test panels.

[0023] In this embodiment: three steel plates, each with dimensions of 300 mm × 150 mm × 2 mm and coated with the same matching anti-rust primer, are selected. Fire retardant coating, fiberglass mesh, fire retardant coating and topcoat are sequentially formed on the surface of the anti-rust primer. The target value of the total coating thickness before fire is 4.0 mm. The actual thickness after coating is completed is recorded according to the measurement results of S11.

[0024] It should be noted that: between two consecutive coatings, the surface of the previous coating layer should be checked 40 minutes after the coating is completed. When no paint transfers to the finger surface after lightly touching the coating with a clean glove, the next coating should be applied. If paint transfer still occurs, continue to place for 10 minutes and check again. After the last coating layer is completed, place the three coating test panels horizontally in an indoor environment with a temperature of 23℃±2℃ and a relative humidity of 50%±10% for 24 hours.

[0025] Specifically: Using one edge of the steel plate along its 300 mm length as a length reference, a carbon layer cross-section position is determined at a distance of 120 mm, 150 mm, and 180 mm from the length reference. Using one edge of the steel plate along its 150 mm width as a width reference, five thickness detection positions are set at each carbon layer cross-section position at a distance of 45 mm, 60 mm, 75 mm, 90 mm, and 105 mm from the width reference. Thus, each coating test plate has 15 thickness detection positions, and the corresponding positions are marked on the back of the steel plate.

[0026] Specifically: A coating thickness gauge with a range of not less than 5 mm and a resolution of not more than 0.01 mm is used for measurement. Before measurement, zero-point calibration is performed on an uncoated steel plate with the same material and thickness as the coating test plate. A standard plate with known thickness is used to check the measurement reading. Measurement begins when the difference between the nominal thickness of the standard plate and the equipment reading is not greater than the allowable error of the equipment. At each thickness detection position, the measuring probe is placed vertically on the coating surface. After the reading remains unchanged for 2 seconds, the vertical distance from the surface of the steel plate to the outer surface of the coating is recorded.

[0027] S12. Calculate the arithmetic mean of the vertical distances corresponding to the thickness detection positions on the same coating test plate, and determine the calculation result as the average coating thickness of the coating test plate before fire exposure.

[0028] Specifically: the vertical distances corresponding to the 15 thickness detection positions of each coating test plate are added together and then divided by 15 to obtain the average coating thickness of the corresponding coating test plate before fire exposure. The calculation is performed separately for each coating test plate, and the data of different coating test plates are not mixed.

[0029] For example, the vertical distances obtained from the 15 thickness measurement positions of the first coating test plate are 4.00 mm, 4.10 mm, 3.90 mm, 4.00 mm, 4.00 mm, 4.10 mm, 4.00 mm, 4.00 mm, 3.90 mm, 4.00 mm, 4.00 mm, 4.10 mm, 4.00 mm, 3.90 mm and 4.00 mm respectively. The sum of the 15 vertical distances is 60.00 mm. Therefore, the average coating thickness of the coating test plate before being exposed to fire is 4.00 mm.

[0030] S2 includes S21 and S22; S21. Each coating test plate is subjected to fire treatment according to the same test plate placement direction, flame action position, distance between flame and coating test plate and fire treatment time. After the fire treatment is completed, each coating test plate is cooled under the same conditions, and a carbon layer cross section perpendicular to the steel plate surface is formed at multiple positions of each coating test plate. Specifically: A propane gas torch fixed on a metal bracket is used as the heat source for ignition. The coating test plate is vertically fixed so that the 300 mm length direction is vertical and the 150 mm width direction is horizontal, with the coating surface facing the torch. The torch nozzle axis is perpendicular to the steel plate surface and passes through the center of the test plate, which is 150 mm from the length reference and 75 mm from the width reference. The vertical distance from the torch nozzle to the outer surface of the coating before ignition is fixed at 100 mm.

[0031] In this embodiment: the blowtorch is lit and the gas valve is adjusted so that the flame is maintained continuously for 30 seconds without extinguishing or backfire, and then the flame is started. The flame exposure time is fixed at 12 minutes. After 12 minutes, the gas is turned off. The same blowtorch position, 100mm flame exposure distance and 12-minute flame exposure time are used for the same batch to be tested and the same historical batch of the same model used to establish subsequent comparison benchmarks.

[0032] Specifically: After the fire exposure is completed, the coating test plate is kept vertical and placed in an indoor environment with a temperature of 23℃±2℃ for natural cooling. Starting 20 minutes after the fire exposure is stopped, the center temperature of the back of the steel plate and the indoor ambient temperature are read every 5 minutes. Cooling is stopped when the difference between the back temperature of the steel plate and the indoor ambient temperature measured twice is not greater than 2℃.

[0033] Specifically: After cooling, cut lines perpendicular to the steel plate surface are formed at the three carbon layer cross-section positions of 120 mm, 150 mm and 180 mm determined in S11. A thin-bladed cutting tool with a thickness of no more than 0.5 mm is used to cut from the outer surface of the carbon layer along the cut lines to the surface of the steel plate. An auxiliary cut line parallel to each cut line is formed 5 mm away from one side of the plate length direction. The strip-shaped carbon layer that has been completely cut between the two cut lines is removed, so that the carbon layer cross-section formed by the original cut lines is fully exposed.

[0034] During the cross-section preparation process: when removing the strip-shaped carbon layer, the carbon layer cross-section formed by the original cutting line is not pressed, and the carbon layer cross-section is not filled, compacted, polished, shaped or brushed, so that the interface detachment, through cracks, interlayer continuous cavities, collapsed areas and closed pores formed after being fired remain in their original state.

[0035] S22. Set multiple carbon layer thickness detection positions at the same interval on each carbon layer cross section. Measure the vertical distance from the steel plate surface to the outer surface of the carbon layer at each carbon layer thickness detection position. Use the vertical distance as the total carbon layer thickness at the corresponding carbon layer thickness detection position. Calculate the arithmetic mean of the total carbon layer thickness at all carbon layer thickness detection positions on the same coating test plate. Determine the calculation result as the total average carbon layer thickness of the coating test plate.

[0036] Specifically: On the three carbon layer cross sections of 120 mm, 150 mm and 180 mm, five carbon layer thickness detection positions are set at distances of 45 mm, 60 mm, 75 mm, 90 mm and 105 mm from the width position reference, respectively, according to the width position determined by S11. This makes each coating test plate have 15 carbon layer thickness detection positions, which correspond to the 15 thickness detection positions before being exposed to fire.

[0037] Specifically: Using the steel plate surface as the measurement reference, at each carbon layer thickness detection position, the distance from the steel plate surface to the outer surface of the carbon layer is measured along a direction perpendicular to the steel plate surface using a digital depth gauge with a range of not less than 150 mm and a resolution of not more than 0.1 mm. The distance is taken as the total carbon layer thickness at that carbon layer thickness detection position. During the measurement, closed pores, interface separation, through cracks, interlayer continuous cavities or collapsed areas passed through the measurement direction are not deducted.

[0038] It should be noted that the total thickness of the char layer is used to represent the overall vertical distance from the surface of the steel plate to the outer surface of the char layer after it has been fired. Whether the internal structure of the char layer causes an interruption in the connection between the char layer material and the steel plate will be determined separately in the subsequent process of determining the continuous char layer.

[0039] During data processing: the total thickness of 15 carbon layers on three carbon layer cross sections of the same coated test plate is added together and then divided by 15 to obtain the total average thickness of the carbon layers of the coated test plate. The same calculation weight is used for each carbon layer thickness detection position.

[0040] For example, the total carbon layer thicknesses at the 15 carbon layer thickness detection locations on the first coating test plate are 92.0 mm, 94.0 mm, 95.0 mm, 96.0 mm, 93.0 mm, 94.0 mm, 95.0 mm, 97.0 mm, 96.0 mm, 92.0 mm, 93.0 mm, 95.0 mm, 94.0 mm, 96.0 mm, and 94.0 mm, respectively. The sum of the total carbon layer thicknesses at the 15 locations is 1416.0 mm. Therefore, the total average carbon layer thickness of this coating test plate is 94.4 mm.

[0041] It should be noted that the average thickness of the coating on the first coating test plate before exposure to fire was 4.00 mm, and the total average thickness of the char layer was 94.4 mm. Both data came from the same coating test plate and used the same position reference, providing corresponding data for subsequent determination of the apparent expansion of the coating test plate and the state of the continuous char layer.

[0042] In this embodiment, by using the same thickness detection position, fire-exposed position, fire-exposed distance, fire-exposed time, and cooling endpoint for multiple coating test plates, and by ensuring that the thickness detection position before fire-exposed corresponds to the carbon layer thickness detection position after fire-exposed, the average thickness of the coating before fire-exposed and the total average thickness of the carbon layer have the same position and fire-exposed condition basis. At the same time, the total thickness of the carbon layer is measured according to the complete distance from the surface of the steel plate to the outer surface of the carbon layer, providing corresponding detection data for subsequently distinguishing the overall expansion degree of the carbon layer and the internal connection state of the carbon layer.

[0043] Example 3 Based on the fire performance screening scenario of the same type of fireproof coating for steel structures set in Example 1 and the fire-exposed coating test plate formed in Example 2, this example further illustrates the process of determining the continuous char layer. It continues to use three char layer cross sections formed at distances of 120 mm, 150 mm and 180 mm from the steel plate length reference. On each char layer cross section, five char layer thickness detection positions are set at distances of 45 mm, 60 mm, 75 mm, 90 mm and 105 mm from the steel plate width reference, so that the continuous char layer thickness corresponds one-to-one with the total char layer thickness at the corresponding position in Example 2.

[0044] Please see Figure 1 and Figure 2 Specifically: S3 includes S31 and S32; S31. In each carbon layer section, the part that forms a gap between the carbon layer and the steel plate surface and separates the carbon layer outside the gap from the steel plate surface is defined as interface separation. The cavity located inside the carbon layer and extending in a direction parallel to the steel plate surface and separating the carbon layer outside the cavity from the carbon layer near the steel plate is defined as interlayer continuous cavity. Specifically: The cross-section of each carbon layer is checked sequentially at five carbon layer thickness detection positions of 45 mm, 60 mm, 75 mm, 90 mm and 105 mm. When there is a continuous gap between the steel plate surface and the carbon layer adjacent to the steel plate, and the gap causes no carbon layer material connection between the outer carbon layer at the corresponding position and the steel plate surface, it is determined that there is interface detachment at that position. When there is still carbon layer material connection between the steel plate surface and the carbon layer, it is not determined to be interface detachment.

[0045] Specifically: when there is a cavity extending parallel to the surface of the steel plate inside the carbon layer, and the cavity passes through the corresponding carbon layer thickness detection position and there is no carbon layer material connection between the carbon layer outside the cavity and the carbon layer near the steel plate, the cavity is defined as a continuous interlayer cavity. When there is still carbon layer material around the cavity so that the carbon layer outside the cavity is connected to the carbon layer near the steel plate, it is treated as a closed pore.

[0046] For example, the total thickness of the carbon layer at the 90 mm carbon layer thickness detection position of the 150 mm carbon layer section of the first coated test plate is 96.0 mm. There is a cavity passing through the carbon layer thickness detection position at a distance of 61.0 mm to 67.0 mm from the steel plate surface, and the cavity interrupts the connection between the carbon layer materials on both sides. Therefore, this cavity is identified as an interlayer continuous cavity.

[0047] S32. A crack that connects one end to the outer surface of the carbon layer and extends to the surface of the steel plate, where the interface is separated or the interlayer continuous cavity is defined as a through crack. A region where the carbon layer sinks towards the steel plate and the connection between the carbon layer material on the outer side of the carbon layer and the carbon layer material on the side closer to the steel plate is interrupted is defined as a collapse region.

[0048] Specifically: From the crack entrance on the outer surface of the carbon layer, inspect along the crack towards the steel plate. When the crack extends continuously to the surface of the steel plate, or separates from the already determined interface or connects with the interlayer continuous cavity, the crack is identified as a through crack. When the crack terminates before reaching the surface of the steel plate, separating from the interface or interlayer continuous cavity, and there is still carbon layer material connecting the crack termination position to the steel plate, it is not determined as a through crack.

[0049] Specifically: When the carbon layer sinks towards the steel plate, and there is no carbon layer material connection between the carbon layer on the outer side of the sinking position and the carbon layer on the side closer to the steel plate, the corresponding area is identified as a collapse area. When there is only a depression on the surface of the carbon layer but the carbon layer material below remains continuously connected, it is not determined to be a collapse area.

[0050] S3 also includes S33 and S34; S33. Using the same steel plate edge as a reference, select carbon layer thickness detection positions at the same distance from the steel plate edge on adjacent carbon layer cross sections, and check whether the interface separation, the through crack, the interlayer continuous cavity, or the collapse area exists at the corresponding carbon layer thickness detection positions. When the same type of structure exists at the corresponding carbon layer thickness detection positions of adjacent carbon layer cross sections, and the structure of this type causes the carbon layer material connection to be interrupted, it is determined that the corresponding structure extends to the adjacent carbon layer cross section. Specifically: the 120 mm and 150 mm carbon layer cross sections are taken as one group of adjacent carbon layer cross sections, and the 150 mm and 180 mm carbon layer cross sections are taken as another group of adjacent carbon layer cross sections. The corresponding carbon layer thickness detection positions of 45 mm, 60 mm, 75 mm, 90 mm and 105 mm in the adjacent carbon layer cross sections are compared respectively. The same type of structure means that the corresponding positions are all determined to be the same structural category in the interface separation, through crack, interlayer continuous cavity or collapse area. The length, width or shape of the corresponding structure is not required to be the same.

[0051] For example, in the first coated test plate, there is a continuous interlayer cavity at the 90 mm position of the 150 mm carbon layer cross section, and there is also a continuous interlayer cavity at the 90 mm position of the 180 mm carbon layer cross section. The total thickness of the carbon layer at this position is 96.0 mm. The cavity extends from 63.0 mm to 69.0 mm from the surface of the steel plate and causes an interruption in the connection of the carbon layer material. Therefore, it is determined that the continuous interlayer cavity extends from the 150 mm carbon layer cross section to the 180 mm carbon layer cross section.

[0052] S34. When the interface detachment, the through crack, the interlayer continuous cavity, or the collapse area that causes the interruption of the carbon layer material connection appears only at the corresponding carbon layer thickness detection position of a carbon layer cross section, carbon layer cross sections are added on both sides of the carbon layer cross section, and the corresponding carbon layer thickness detection position in the added carbon layer cross section is checked according to S33 to determine whether the corresponding structure extends to both sides of the carbon layer cross section.

[0053] Specifically: When the corresponding structure appears only in one original carbon layer cross section, take the original carbon layer cross section as the reference, and add a carbon layer cross section at intervals of 15 mm on both sides along the length of the steel plate. The carbon layer cross sections are added using the same cross section preparation method as in Example 2, and check whether there is a structure of the same type at the same width position. For example, a 150 mm original carbon layer cross section corresponds to adding 135 mm and 165 mm carbon layer cross sections, a 120 mm original carbon layer cross section corresponds to adding 105 mm and 135 mm carbon layer cross sections, and a 180 mm original carbon layer cross section corresponds to adding 165 mm and 195 mm carbon layer cross sections.

[0054] For example, the first coated test plate showed interface detachment at the 60 mm position of the 150 mm carbon layer cross section, while there was no interface detachment at the 60 mm position of the 120 mm and 180 mm carbon layer cross sections. Therefore, carbon layer cross sections were added at positions 135 mm and 165 mm away from the reference position of the steel plate length, respectively, and the 60 mm position of the two added carbon layer cross sections was checked.

[0055] Specifically: when there is no interface detachment at the 60 mm position of the two increased carbon layer cross sections of 135 mm and 165 mm, it is determined that the interface detachment at the 60 mm position of the 150 mm carbon layer cross section has not extended to both sides. When there is interface detachment at the corresponding position of any increased carbon layer cross section, it is determined that the interface detachment extends to the side where the increased carbon layer cross section is located. The inspection results of the increased carbon layer cross section are only used to determine the structural extension situation and do not change the structural type that has already been determined for the original carbon layer cross section.

[0056] S3 also includes S35 and S36; S35. Taking the steel plate surface corresponding to each carbon layer thickness detection position as the starting position, determine the carbon layer portion that is continuously connected to the steel plate surface through the carbon layer material. Exclude the outer carbon layer that is separated from the steel plate surface by the interface separation, the through crack, the interlayer continuous cavity, or the collapse area. Include the closed pores that are surrounded by the carbon layer material and do not separate the outer carbon layer from the carbon layer near the steel plate side in the continuous carbon layer. Specifically: At each carbon layer thickness detection position, starting from the steel plate surface, check towards the outer surface of the carbon layer in a direction perpendicular to the steel plate surface. When there is a continuous carbon layer material between the steel plate surface and the outer surface of the carbon layer, or only through the closed pores connected by the carbon layer material on the periphery, the carbon layer from the steel plate surface to the outer surface of the carbon layer at the corresponding position is counted as a continuous carbon layer.

[0057] Specifically: when the interface separation, through crack, interlayer continuous cavity or collapse area that causes the connection of carbon layer material to be interrupted is first encountered along the direction, the boundary of the connection interruption structure near the steel plate is taken as the termination position of the continuous carbon layer at that position, and the carbon layer located outside the termination position is not counted as a continuous carbon layer.

[0058] For example, the total thickness of the carbon layer at the 90 mm position of the 150 mm carbon layer cross section is 96.0 mm. The continuous cavity between layers starts from the position 61.0 mm away from the surface of the steel plate. Therefore, the carbon layer within the range from the surface of the steel plate to 61.0 mm at this position is included in the continuous carbon layer, and the carbon layer outside it is no longer included in the continuous carbon layer.

[0059] For example, the total thickness of the carbon layer at the 60 mm position of the 150 mm carbon layer cross section is 95.0 mm. Since the interface is directly located between the steel plate surface and the carbon layer, there is no carbon layer material that maintains a continuous connection from the steel plate surface at this position. Therefore, the thickness of the continuous carbon layer at this position is recorded as 0 mm.

[0060] S36. At each carbon layer thickness detection position, measure the distance from the steel plate surface to the outermost position of the continuous carbon layer in a direction perpendicular to the steel plate surface. Use the distance as the continuous carbon layer thickness at the corresponding carbon layer thickness detection position. Calculate the arithmetic mean of the continuous carbon layer thickness at all carbon layer thickness detection positions on the same coating test plate. Determine the calculation result as the average continuous carbon layer thickness of the coating test plate.

[0061] Specifically: taking the steel plate surface as the starting point of 0 mm, when there is no interruption in the connection of carbon layer material at the corresponding carbon layer thickness detection position, the continuous carbon layer thickness is the same as the total carbon layer thickness at that position. When there is an interruption in the connection of carbon layer material, the continuous carbon layer thickness is the vertical distance from the steel plate surface to the boundary of the first connection interruption position near the steel plate side.

[0062] In this embodiment: there is no interruption in the connection of carbon layer material at any of the five positions of the 120 mm carbon layer cross section of the first coated test plate, and the corresponding continuous carbon layer thicknesses are 92.0 mm, 94.0 mm, 95.0 mm, 96.0 mm and 93.0 mm, respectively; The continuous carbon layer thicknesses at positions of 45 mm, 60 mm, 75 mm, 90 mm and 105 mm in the 150 mm carbon layer section are 94.0 mm, 0 mm, 97.0 mm, 61.0 mm and 92.0 mm, respectively. The continuous carbon layer thicknesses at positions of 45 mm, 60 mm, 75 mm, 90 mm and 105 mm in the 180 mm carbon layer section are 93.0 mm, 95.0 mm, 94.0 mm, 63.0 mm and 94.0 mm, respectively.

[0063] During data processing: the thickness of the 15 consecutive carbon layers is added together to obtain 1253.0 mm, and then divided by 15 to obtain the average thickness of the continuous carbon layer of the first coating test plate as 83.53 mm. In Example 2, the average thickness of the coating before fire on the coating test plate is 4.00 mm and the total average thickness of the carbon layer is 94.4 mm. Therefore, the three thickness results all correspond to the same coating test plate and the same detection location system.

[0064] In this embodiment, the interface separation, through cracks, interlayer continuous cavities, collapsed areas, and closed pores are distinguished according to whether the carbon layer material maintains a continuous connection with the steel plate. The extension of the connection interruption structure is determined by the cross-section of adjacent carbon layers and the cross-section of additional carbon layers. This ensures that the average thickness of the continuous carbon layer reflects the portion of the carbon layer that still maintains a continuous connection with the steel plate after being exposed to fire. At the same time, it avoids excluding closed pores that have not severed the connection of the carbon layer as structures that need to be excluded. This provides a detection basis for judging the internal connection status of the carbon layer based on the difference between the total thickness of the carbon layer and the thickness of the continuous carbon layer.

[0065] Example 4 Based on the fire performance screening scenario of the same type of fireproof coating for steel structures set in Example 1, the coating thickness and total char layer thickness before fire determined in Example 2, and the continuous char layer determined in Example 3, this example further illustrates the specific determination process of apparent expansion ratio, continuous char layer thickness ratio, corresponding ratio of each char layer thickness detection position, lower limit of each item, and finished product test results. Among them, the same 3 coating test plates, 3 original char layer cross sections, and 5 char layer thickness detection positions on each original char layer cross section are still used in Examples 2 and 3.

[0066] Specifically: S4 includes S41 and S42; S41. Calculate the ratio of the total average thickness of the char layer to the corresponding average thickness of the coating before fire exposure for each coating test panel. Determine the arithmetic mean of the corresponding ratios for each coating test panel as the apparent expansion factor of the finished fire-resistant coating for the steel structure to be tested. Calculate the ratio of the average thickness of the continuous char layer to the corresponding total average thickness of the char layer for each coating test panel. Determine the arithmetic mean of the corresponding ratios for each coating test panel as the percentage of the continuous char layer thickness in the finished fire-resistant coating for the steel structure to be tested. Specifically: For each coating test panel, the average thickness of the coating before fire, the total average thickness of the char layer, and the average thickness of the continuous char layer of the coating test panel itself are calculated separately. Data before and after fire from different coating test panels are not used interchangeably.

[0067] In this embodiment: the first coating test plate continues to use the data obtained in Examples 2 and 3. Its average coating thickness before fire is 4.00 mm, the total average thickness of the char layer is 94.4 mm, and the average thickness of the continuous char layer is 83.53 mm. Therefore, the ratio of the total average thickness of the char layer to the average thickness of the coating before fire is 23.600, and the ratio of the average thickness of the continuous char layer to the total average thickness of the char layer is 0.8849.

[0068] Specifically: The second coating test plate was prepared, fired, cooled, had its cross-section formed, and measured in the same way as the first coating test plate. Before firing, its average coating thickness was 4.02 mm, the total average thickness of the char layer was 94.0 mm, and the average thickness of the continuous char layer was 91.8 mm. Thus, the ratio of the total average thickness of the char layer to the average thickness of the coating before firing was 23.383, and the ratio of the average thickness of the continuous char layer to the total average thickness of the char layer was 0.9766.

[0069] Specifically: the average thickness of the coating before fire on the third coating test plate was 3.99 mm, the total average thickness of the char layer was 94.6 mm, and the average thickness of the continuous char layer was 92.0 mm. Thus, the ratio of the total average thickness of the char layer to the average thickness of the coating before fire was 23.709, and the ratio of the average thickness of the continuous char layer to the total average thickness of the char layer was 0.9725.

[0070] During data processing: the values ​​of 23.600, 23.383, and 23.709 corresponding to the first, second, and third coating test plates were added together and divided by 3 to obtain 23.564. 23.564 was determined as the apparent expansion ratio of the finished steel structure fireproof coating to be tested in this batch. 0.8849, 0.9766, and 0.9725 were added together and divided by 3 to obtain 0.9447. 0.9447 was determined as the percentage of continuous char layer thickness of the finished steel structure fireproof coating to be tested in this batch.

[0071] It should be noted that the above calculations first establish the correspondence between the data before and after the fire exposure for each coating test panel, and then calculate the arithmetic mean of the calculation results for the three coating test panels. Therefore, the difference in the initial coating thickness of each coating test panel is calculated within its own data range.

[0072] S42. Calculate the ratio of the continuous carbon layer thickness to the total carbon layer thickness corresponding to each carbon layer thickness detection position, and record each ratio according to the arrangement order of each carbon layer thickness detection position on the coating test plate.

[0073] Specifically: the ratio corresponding to each carbon layer thickness detection position is calculated by dividing the continuous carbon layer thickness at the same position by the total carbon layer thickness. The total carbon layer thickness is based on the data obtained in Example 2, and the continuous carbon layer thickness is based on the data obtained in Example 3. The two thicknesses correspond to the same coating test plate, the same carbon layer cross section, and the same width position.

[0074] In this embodiment: 15 ratios of the first coated test plate were recorded in a fixed order at positions of 45 mm, 60 mm, 75 mm, 90 mm and 105 mm of the 120 mm carbon layer cross section, positions of 45 mm, 60 mm, 75 mm, 90 mm and 105 mm of the 150 mm carbon layer cross section, and positions of 45 mm, 60 mm, 75 mm, 90 mm and 105 mm of the 180 mm carbon layer cross section. These ratios were 1.0000, 1.0000, 1.0000, 1.0000, 1.0000, 1.0000, 0, 1.0000, 0.6354, 1.0000, 1.0000, 1.0000, 1.0000, 0.6563 and 1.0000.

[0075] For example, on the first coated test plate, the continuous carbon layer thickness at the 90 mm position of the 150 mm carbon layer cross section is 61.0 mm, and the total carbon layer thickness is 96.0 mm, corresponding to the ratio of 0.6354. The continuous carbon layer thickness at the 90 mm position of the 180 mm carbon layer cross section is 63.0 mm, and the total carbon layer thickness is 96.0 mm, corresponding to the ratio of 0.6563. Due to interface separation at the 60 mm position of the 150 mm carbon layer cross section, the continuous carbon layer thickness is 0 mm, and the total carbon layer thickness is 95.0 mm, therefore the corresponding ratio is 0.

[0076] Specifically, the 15 ratios obtained from the second coating test plate in the same position as described above are 0.9785, 0.9787, 0.9789, 0.9787, 0.9787, 0.9785, 0.9789, 0.9681, 0.9688, 0.9785, 0.9787, 0.9789, 0.9785, 0.9789 and 0.9674.

[0077] Specifically, the 15 ratios obtained from the third coating test plate in the same position sequence are 0.9787, 0.9684, 0.9789, 0.9681, 0.9792, 0.9681, 0.9789, 0.9684, 0.9792, 0.9681, 0.9789, 0.9681, 0.9789, 0.9684 and 0.9565.

[0078] It should be noted that the ratio represents the proportion of the continuous carbon layer thickness to the total carbon layer thickness at the corresponding carbon layer thickness detection position. When the continuous carbon layer thickness is the same as the total carbon layer thickness, the ratio is 1. When the continuous carbon layer thickness is less than the total carbon layer thickness, the ratio is less than 1. When there is no continuous carbon layer starting from the surface of the steel plate at this position, the continuous carbon layer thickness is 0 mm and the ratio is 0.

[0079] S4 also includes S43 and S44; S43. Select multiple historical batches that are the same model as the finished fireproof coating for the steel structure to be tested and have been determined to be qualified by fire resistance performance testing. Determine the apparent expansion ratio, the proportion of continuous char layer thickness, and the ratio corresponding to each char layer thickness detection position for each historical batch. Based on the test results corresponding to each historical batch, determine the lower limit of the apparent expansion ratio, the lower limit of the proportion of continuous char layer thickness, and the lower limit of the char layer thickness detection position. Specifically: When establishing the testing benchmark for the same type of fireproof coating for steel structures, five batches are selected consecutively from the historical production batches of this type that have completed fire resistance performance testing and whose test results are qualified, in order of production time from most recent to oldest. The selected historical batches are tested using the same steel plate specifications, coating structure, plate making method, 12-minute fire exposure time, 100-mm spray distance, three original char layer cross-section positions, and 15 char layer thickness detection positions as in this embodiment.

[0080] Specifically: For each historical batch, the ratios corresponding to three coating test plates are obtained at each carbon layer thickness detection position, and the minimum value among the three ratios is taken as the ratio corresponding to the carbon layer thickness detection position for that historical batch. Then, the ratios corresponding to the same carbon layer thickness detection position for five historical batches are compared, and the minimum value is taken as the lower limit of acceptance for that carbon layer thickness detection position.

[0081] It should be noted that: the five historical qualified batches are selected consecutively according to the production time. After the establishment of the testing benchmark for the same model of product, the determined lower limit of each qualified batch is used without changing the steel plate specifications, coating structure, fire exposure time, fire spray distance, and carbon layer thickness testing position. The historical batches are not reselected or the lower limit of qualified batches is not adjusted based on the data of the current batch to be tested.

[0082] In this embodiment, the apparent expansion ratios corresponding to the five historical qualified batches are 22.80, 23.10, 22.90, 23.30 and 22.60, respectively, and the corresponding continuous carbon layer thickness ratios are 0.920, 0.930, 0.925, 0.940 and 0.910, respectively.

[0083] Specifically: the minimum apparent expansion ratio of 22.60 among the above 5 historical qualified batches is determined as the lower limit of the apparent expansion ratio, and the minimum continuous carbon layer thickness ratio of 0.910 is determined as the lower limit of the continuous carbon layer thickness ratio.

[0084] Specifically: For each of the 15 carbon layer thickness detection locations, a corresponding lower limit for acceptance is independently established. Following the positional order specified in S42, the minimum value among the ratios corresponding to each carbon layer thickness detection location for the five historical qualified batches is taken as the lower limit for acceptance at that location. Thus, the lower limits for acceptance for the 15 carbon layer thickness detection locations are, in order: 0.92, 0.91, 0.92, 0.90, 0.91, 0.90, 0.92, 0.91, 0.90, 0.91, and 0.92.

[0085] For example, the ratios for the five historical batches corresponding to the detection position of 90 mm carbon layer thickness at the 150 mm carbon layer cross section are 0.94, 0.93, 0.92, 0.95 and 0.91, respectively. Therefore, 0.91 is determined as the lower limit of acceptance for this position. The lower limit of acceptance of 0.91 for the 90 mm position at the 180 mm carbon layer cross section is obtained using the same method.

[0086] It should be noted that when the steel plate specifications, coating structure, fire exposure time, spray distance, or carbon layer thickness detection location change, the original lower limit of compliance will not continue to be used under the changed testing conditions. Instead, historical qualified batch data will be re-obtained according to the changed testing conditions to determine the corresponding lower limit of compliance.

[0087] S44. Compare the ratios corresponding to the finished steel structure fireproof coating to be tested with the lower limit of the qualified carbon layer thickness at the corresponding detection position, and combine the interface separation, through cracks, interlayer continuous cavities or the extension of the collapsed area to the adjacent carbon layer section determined by S33 and S34 to determine whether there is a local carbon layer structure defect in the finished steel structure fireproof coating to be tested.

[0088] Specifically: For the three coating test plates, according to the positional order specified in S42, the ratio of each carbon layer thickness detection position is compared with the lower limit of acceptance corresponding to the same carbon layer cross section and the same width position determined in S43. When the ratio is less than the corresponding lower limit of acceptance, the extension of the carbon layer material connection interruption structure in the length direction of the test plate is further judged in conjunction with the extension of the carbon layer material connection interruption structure determined in S33 and S34.

[0089] In this embodiment: the ratio at the 60 mm position of the 150 mm carbon layer cross section of the first coated test plate is 0, which is less than the lower limit of 0.90 for that position. However, in Example 3, the interface separation at that position has not extended to both sides by increasing the carbon layer cross section by 135 mm and 165 mm. Therefore, the verification is performed according to a single isolated position, and it is not directly determined from this position that there is a local carbon layer structure defect in the entire batch to be tested.

[0090] Specifically: If the ratio at only one location is lower than the corresponding lower limit of acceptance and S34 determines that the connection interruption has not extended to both sides, another verification coating test plate is prepared from the same batch to be tested. The same location is checked according to the same plate preparation, firing, cooling, cross-section formation and measurement methods as in Examples 2 and 3. When the ratio at the same location of the verification coating test plate is still lower than the corresponding lower limit of acceptance or the same type of structure that causes the connection interruption of the carbon layer material reappears, it is determined that there is a local carbon layer structure failure. When the ratio at the same location of the verification coating test plate is not lower than the corresponding lower limit of acceptance and there is no structure that causes the connection interruption of the carbon layer material, it is not determined that there is a local carbon layer structure failure in the entire batch to be tested based on the first single isolated location.

[0091] In this embodiment: the ratio of the verification coating test plate corresponding to the 60 mm position of the 150 mm carbon layer section of the first coating test plate is 0.96, which is not less than the corresponding lower limit of 0.90. Moreover, no interface separation, through cracks, interlayer continuous cavities or collapsed areas appear at this position. Therefore, the isolated interface separation that appears at this position in the first test is not used as the sole basis for judging the local carbon layer structure as unqualified in this batch of products.

[0092] Specifically: the ratio at the 90 mm position of the 150 mm carbon layer section on the first coating test plate is 0.6354, which is less than the corresponding lower limit of acceptance of 0.91. The ratio at the 90 mm position of the 180 mm carbon layer section is 0.6563, which is also less than the corresponding lower limit of acceptance of 0.91. Furthermore, Example 3 has determined that the interlayer continuous cavity extends from the 150 mm carbon layer section to the 180 mm carbon layer section. Therefore, it is determined that the finished fireproof coating for the steel structure to be tested has a local carbon layer structure that is unqualified.

[0093] It should be noted that when the ratio of the thickness of two adjacent carbon layers in the same carbon layer cross section is less than their respective lower limit of acceptance, it is determined that the situation of being lower than the corresponding lower limit of acceptance occurs continuously at the two adjacent carbon layer thickness detection positions, and it is determined that there is a local carbon layer structure that is unqualified. The distance between the two adjacent carbon layer thickness detection positions is 15 mm. When multiple locations below the corresponding lower limit of acceptance are not adjacent to each other and the corresponding carbon layer material connection interruption structure does not extend to the adjacent carbon layer cross section, they are checked separately according to the single isolated location check method. As long as any corresponding location is below the corresponding lower limit of acceptance again or the carbon layer material connection interruption occurs again in the checked coating test plate, it is determined that there is a local carbon layer structure that is unqualified.

[0094] It should be noted that: when there are interface separation, through cracks, interlayer continuous cavities, or collapsed areas that have been determined to extend to adjacent carbon layer sections according to S33 or S34, even if the ratio at the corresponding position is not less than the corresponding lower limit of acceptance, it is determined that there is a local carbon layer structure that is unqualified; after completing the comparison of all carbon layer thickness detection positions and the necessary verification, if there is no interruption in the connection of carbon layer material extending to adjacent carbon layer sections, no ratio at two adjacent carbon layer thickness detection positions at the same carbon layer section that is lower than the corresponding lower limit of acceptance, and no interruption in the connection of carbon layer material at the corresponding position of the verified coating test plate again, it is determined that there is no local carbon layer structure that is unqualified.

[0095] S4 also includes S45 and S46; S45. Compare the apparent expansion ratio of the finished fireproof coating of the steel structure to be tested with the lower limit of the apparent expansion ratio, compare the proportion of continuous carbon layer thickness with the lower limit of the proportion of continuous carbon layer thickness, and determine whether there is any unqualified local carbon layer structure according to S44. In this embodiment: the apparent expansion ratio of the finished fireproof coating for the steel structure to be tested is 23.564, which is not less than the lower limit of the apparent expansion ratio of 22.60; the proportion of continuous carbon layer thickness is 0.9447, which is not less than the lower limit of the continuous carbon layer thickness of 0.910; and according to S44, it has been determined that there is a local carbon layer structure that is unqualified.

[0096] It should be noted that although the apparent expansion ratio and the proportion of continuous carbon layer thickness both meet the corresponding lower limit of qualification, the ratios of the 90 mm position of the 150 mm carbon layer section and the 90 mm position of the 180 mm carbon layer section on the first coated test plate are 0.6354 and 0.6563, respectively, and the corresponding interlayer continuous cavity has been determined to extend from the 150 mm carbon layer section to the 180 mm carbon layer section. Therefore, the overall average result cannot replace S44's judgment on the local carbon layer structure.

[0097] S46. When the apparent expansion ratio is less than the lower limit of the apparent expansion ratio, the finished product test result is determined to be insufficient expansion. When the apparent expansion ratio is not less than the lower limit of the apparent expansion ratio, and the proportion of the continuous carbon layer thickness is less than the lower limit of the proportion of the continuous carbon layer thickness, or when it is determined according to S44 that there is a local carbon layer structure that is unqualified, the finished product test result is determined to be unqualified carbon layer structure. When the apparent expansion ratio is not less than the lower limit of the apparent expansion ratio, the proportion of the continuous carbon layer thickness is not less than the lower limit of the proportion of the continuous carbon layer thickness, and it is determined according to S44 that there is no unqualified local carbon layer structure, the finished product test result is determined to be qualified.

[0098] Specifically: following the judgment order of S46, the apparent expansion ratio is first compared. If it is less than the corresponding lower limit of acceptance, it is determined to be insufficient expansion. If it is not less than the corresponding lower limit of acceptance, the finished product test result is determined by combining the continuous carbon layer thickness ratio and the local carbon layer structure judgment result determined in S44. Thus, the same batch to be tested corresponds to a unique finished product test result.

[0099] In this embodiment: 23.564 is not less than 22.60, and 0.9447 is not less than 0.910. However, according to S44, it has been determined that there are local carbon layer structures that are unqualified. Therefore, the finished product test results of this batch of fireproof coatings for steel structures to be tested are determined to be unqualified in terms of carbon layer structure.

[0100] It should be noted that when the detected value is equal to the corresponding lower limit of acceptance, it shall be treated as not being less than the corresponding lower limit of acceptance. For example, when the apparent expansion ratio is 21.90, it is determined to be insufficient expansion; when the apparent expansion ratio is 23.20 and the continuous carbon layer thickness ratio is 0.88, it is determined to be unqualified carbon layer structure; when the apparent expansion ratio is 23.20, the continuous carbon layer thickness ratio is 0.95, and S44 determines that there is no local unqualified carbon layer structure, it is determined to be qualified.

[0101] In this embodiment, the apparent expansion ratio reflects the overall expansion degree of the fireproof coating product on the steel structure to be tested, and the continuous carbon layer thickness ratio reflects the proportion of the part of the overall carbon layer that is continuously connected to the steel plate. By combining the ratio corresponding to each carbon layer thickness detection position and the extension of interface separation, through cracks, interlayer continuous cavities or collapsed areas, local carbon layer structural problems are identified. At the same time, the qualified batches of the same model are used to establish the lower limit of each qualification, so that the finished product test results can simultaneously reflect the overall expansion state, the overall carbon layer continuity, and the local carbon layer structural state.

[0102] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended technical solutions and their equivalents.

Claims

1. A method for testing finished fire-retardant coatings for steel structures, characterized in that, Includes the following steps: S1. Prepare multiple coating test panels using the finished fireproof coating for the steel structure to be tested, measure the coating thickness of each test panel before exposure to fire, and determine the average coating thickness before exposure to fire. S2. Each coating test plate is subjected to fire treatment and cooling under the same fire conditions. Multiple carbon layer sections perpendicular to the steel plate surface are formed on the carbon layer after fire treatment. The distance from the steel plate surface to the outer surface of the carbon layer is measured to determine the total average thickness of the carbon layer. S3. The carbon layer portion that is continuously connected to the steel plate surface through the carbon layer material is defined as the continuous carbon layer. The carbon layer portion that is separated from the steel plate by the interface, through cracks, interlayer continuous cavities or collapsed areas is excluded. The closed pores that have not severed the connection between the carbon layer and the steel plate are included in the continuous carbon layer, and the average thickness of the continuous carbon layer is determined. S4. Determine the apparent expansion ratio based on the total average thickness of the char layer and the average thickness of the coating before firing, determine the proportion of continuous char layer thickness based on the average thickness of the continuous char layer and the total average thickness of the char layer, and determine the finished product test result based on the apparent expansion ratio and the proportion of continuous char layer thickness.

2. The method for testing finished steel structure fireproof coatings according to claim 1, characterized in that, S1 includes S11 and S12; S11. Set up multiple thickness detection positions on each coating test plate and measure the vertical distance from the steel plate surface to the outer surface of the coating at each thickness detection position. S12. Calculate the arithmetic mean of the vertical distances corresponding to the thickness detection positions on the same coating test plate, and determine the calculation result as the average coating thickness of the coating test plate before fire exposure.

3. The method for testing finished steel structure fireproof coatings according to claim 2, characterized in that, S2 includes S21 and S22; S21. Each coating test plate is subjected to fire treatment according to the same test plate placement direction, flame action position, distance between flame and coating test plate and fire treatment time. After the fire treatment is completed, each coating test plate is cooled under the same conditions, and a carbon layer cross section perpendicular to the steel plate surface is formed at multiple positions of each coating test plate. S22. Set multiple carbon layer thickness detection positions at the same interval on each carbon layer cross section. Measure the vertical distance from the steel plate surface to the outer surface of the carbon layer at each carbon layer thickness detection position. Use the vertical distance as the total carbon layer thickness at the corresponding carbon layer thickness detection position. Calculate the arithmetic mean of the total carbon layer thickness at all carbon layer thickness detection positions on the same coating test plate. Determine the calculation result as the total average carbon layer thickness of the coating test plate.

4. The method for testing finished steel structure fireproof coatings according to claim 3, characterized in that, S3 includes S31 and S32; S31. In each carbon layer section, the part that forms a gap between the carbon layer and the steel plate surface and separates the carbon layer outside the gap from the steel plate surface is defined as interface separation. The cavity located inside the carbon layer and extending in a direction parallel to the steel plate surface and separating the carbon layer outside the cavity from the carbon layer near the steel plate is defined as interlayer continuous cavity. S32. A crack that connects one end to the outer surface of the carbon layer and extends to the surface of the steel plate, where the interface is separated or the interlayer continuous cavity is defined as a through crack. A region where the carbon layer sinks towards the steel plate and the connection between the carbon layer material on the outer side of the carbon layer and the carbon layer material on the side closer to the steel plate is interrupted is defined as a collapse region.

5. The method for testing finished steel structure fireproof coatings according to claim 4, characterized in that, S3 also includes S33 and S34; S33. Using the same steel plate edge as a reference, select carbon layer thickness detection positions at the same distance from the steel plate edge on adjacent carbon layer cross sections, and check whether the interface separation, the through crack, the interlayer continuous cavity, or the collapse area exists at the corresponding carbon layer thickness detection positions. When the same type of structure exists at the corresponding carbon layer thickness detection positions of adjacent carbon layer cross sections, and the structure of this type causes the carbon layer material connection to be interrupted, it is determined that the corresponding structure extends to the adjacent carbon layer cross section. S34. When the interface detachment, the through crack, the interlayer continuous cavity, or the collapse area that causes the interruption of the carbon layer material connection appears only at the corresponding carbon layer thickness detection position of a carbon layer cross section, carbon layer cross sections are added on both sides of the carbon layer cross section, and the corresponding carbon layer thickness detection position in the added carbon layer cross section is checked according to S33 to determine whether the corresponding structure extends to both sides of the carbon layer cross section.

6. The method for testing finished steel structure fireproof coatings according to claim 5, characterized in that, S3 also includes S35 and S36; S35. Taking the steel plate surface corresponding to each carbon layer thickness detection position as the starting position, determine the carbon layer portion that is continuously connected to the steel plate surface through the carbon layer material. Exclude the outer carbon layer that is separated from the steel plate surface by the interface separation, the through crack, the interlayer continuous cavity, or the collapse area. Include the closed pores that are surrounded by the carbon layer material and do not separate the outer carbon layer from the carbon layer near the steel plate side in the continuous carbon layer. S36. At each carbon layer thickness detection position, measure the distance from the steel plate surface to the outermost position of the continuous carbon layer in a direction perpendicular to the steel plate surface. Use the distance as the continuous carbon layer thickness at the corresponding carbon layer thickness detection position. Calculate the arithmetic mean of the continuous carbon layer thickness at all carbon layer thickness detection positions on the same coating test plate. Determine the calculation result as the average continuous carbon layer thickness of the coating test plate.

7. The method for testing finished steel structure fireproof coatings according to claim 6, characterized in that, S4 includes S41 and S42; S41. Calculate the ratio of the total average thickness of the char layer to the corresponding average thickness of the coating before fire exposure for each coating test panel. Determine the arithmetic mean of the corresponding ratios for each coating test panel as the apparent expansion factor of the finished fire-resistant coating for the steel structure to be tested. Calculate the ratio of the average thickness of the continuous char layer to the corresponding total average thickness of the char layer for each coating test panel. Determine the arithmetic mean of the corresponding ratios for each coating test panel as the percentage of the continuous char layer thickness in the finished fire-resistant coating for the steel structure to be tested. S42. Calculate the ratio of the continuous carbon layer thickness to the total carbon layer thickness corresponding to each carbon layer thickness detection position, and record each ratio according to the arrangement order of each carbon layer thickness detection position on the coating test plate.

8. The method for testing finished steel structure fireproof coatings according to claim 7, characterized in that, S4 also includes S43 and S44; S43. Select multiple historical batches that are the same model as the finished fireproof coating for the steel structure to be tested and have been determined to be qualified by fire resistance performance testing. Determine the apparent expansion ratio, the proportion of continuous char layer thickness, and the ratio corresponding to each char layer thickness detection position for each historical batch. Based on the test results corresponding to each historical batch, determine the lower limit of the apparent expansion ratio, the lower limit of the proportion of continuous char layer thickness, and the lower limit of the char layer thickness detection position. S44. Compare the ratios corresponding to the finished steel structure fireproof coating to be tested with the lower limit of the qualified carbon layer thickness at the corresponding detection position, and combine the interface separation, through cracks, interlayer continuous cavities or the extension of the collapsed area to the adjacent carbon layer section determined by S33 and S34 to determine whether there is a local carbon layer structure defect in the finished steel structure fireproof coating to be tested.

9. The method for testing finished steel structure fireproof coatings according to claim 8, characterized in that, S4 also includes S45 and S46; S45. Compare the apparent expansion ratio of the finished fireproof coating of the steel structure to be tested with the lower limit of the apparent expansion ratio, compare the proportion of continuous carbon layer thickness with the lower limit of the proportion of continuous carbon layer thickness, and determine whether there is any unqualified local carbon layer structure according to S44. S46. When the apparent expansion ratio is less than the lower limit of the apparent expansion ratio, the finished product test result is determined to be insufficient expansion; when the apparent expansion ratio is not less than the lower limit of the apparent expansion ratio, and the proportion of continuous carbon layer thickness is less than the lower limit of the proportion of continuous carbon layer thickness, or when it is determined according to S44 that there is a local carbon layer structure defect, the finished product test result is determined to be a carbon layer structure defect; when the apparent expansion ratio is not less than the lower limit of the apparent expansion ratio, the proportion of continuous carbon layer thickness is not less than the lower limit of the proportion of continuous carbon layer thickness, and it is determined according to S44 that there is no local carbon layer structure defect, the finished product test result is determined to be qualified.

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