Vacuum furnace remelting method of boiler membrane wall anti-corrosion coating

Abstract

The invention belongs to the technical field of membrane wall coating remelting, and discloses a vacuum furnace remelting method of a boiler membrane wall anti-corrosion coating. The method comprisesthe steps that the surfaces of tube bundles are subjected to sand blasting roughening treatment by using an automatic sand blasting machine, and the coating is prepared by adopting flame spraying nickel-based self-fusion gold powder; a remelting system is formulated for a coating material and the thickness, heating, heat preservation and cooling curves of a vacuum furnace are designed, and the heating temperature is strictly controlled; a high-temperature alloy steel is made into a tube bundle conveying vehicle with rollers, the tube bundles are vertically placed on a support of the tube bundle conveying vehicle in a side direction by a truss crane one by one, finally, a rack vehicle is pushed into the furnace along a rail, and a furnace door is closed; a vacuum pump of the vacuum furnaceis started for vacuumizing; the remelting temperature is controlled; after the remelting of the tube bundles is completed, the tube bundle conveying vehicle is pulled out of the furnace; and the remelting effect of the coating on the surfaces of the tube bundles is tested. With the method, the inner temperature of the furnace is uniform and accurately adjustable, the defect of high-frequency induction remelting is eliminated, the preparation quality of the coating can be remarkably improved, and the high-temperature anti-corrosion performance and the service life of the water-cooled wall of aboiler are effectively improved.

Description

technical field [0001] The invention belongs to the technical field of membrane wall coating remelting, in particular to a vacuum furnace remelting method for a boiler membrane wall anticorrosion coating. Background technique [0002] At present, the closest existing technology: the current bottleneck problem restricting the technical development of waste incineration power generation is that the membrane water wall of the boiler is severely corroded due to high temperature, and tube bursts occur frequently. In recent years, the International Center for Cancer Research has listed dioxin as a first-class human carcinogen. In order to prevent the secondary pollution of dioxin at low temperature during the waste incineration process, the newly designed national standard for biomass boilers has now made the boiler tube row temperature resistant The requirement is raised to 700°C, and the service life reaches more than 6 years. At present, although some TP347 stainless steel is ...

AI Technical Summary

Problems solved by technology

[0004] (1) Since the heating surface of the water-cooled wall tube row is an irregular curved surface welded by the tube and the fin, when heating with a high-frequency coil, there are errors in the thickness of the coating, the width of the fin, the size of the weld, etc., resulting in The distance between the coil and the surface of the coating is difficult to be consistent, and the height difference can reach 3cm, so that the depth of heating of the coating is different. The distant parts such as the chip have not yet started to melt, so the unevenness of the coating remelting is more serious

Even if it is made into a profiling coil, the superposition of profiling manufacturing error and tube row structure error will make the gap size different, and the effect is still unsatisfactory

[0005] (2) Since the pipe row is naturally cooled in the air after remelting and heating, the faster cooling rate causes the residual tensile stress in the coating to be larger, thus laying the root of the cracks.

[0006] (3) Thousands of degrees of high temperature for coating remelting cause serious oxidation inside and on the back of the tube

The oxide skin in the pipe is very harmful, because there is a difference in the thermal expansion system of the pipe matrix and the oxide skin, so the oxide skin is easy to fall off under the cyclical pull of the base body's thermal expansion and contraction, and is washed to the elbow by high-pressure steam to deposit and accumulate. After reaching a certain level, the local temperature rise will intensify, resulting in the risk of tube explosion

[0007] (4) The heating temperature of the high-frequency induction coil is difficult to precisely control, which undoubtedly makes the uneven heating of the coating and the plight of oxide skin growth worse.

[0008] (5) For the tube row several meters long, high-frequency induction remelting belongs to local heating, and with the feeding movement of the tube row in the coil, the local high temperature causes serious bending deformation of the tube row, and special tooling must be used Perform deformation correction

[0011] (1) The high-grade stainless steel thickened pipes used in the prior art are expensive; the ordinary stainless steel used has a limited service life at high temperatures; when the 625 alloy is used, the temperature will reach 550 ° C and sensitization will occur, and the corrosion resistance of the material will decline rapidly. Once the service temperature exceeds 700°C, its actual service life is only 50% of the design life, and the coating will fail in less than three years

[0012] (2) The distance between the coil and the surface of the coating in the high-frequency induction remelting method is difficult to be consistent, so that the coating is heated to a different depth; The size is different, the top of the tube close to the coil is melted first, and when the root of the tube that is melted after waiting is also melted, the coating on the top of the tube has melted and flowed, resulting in uneven remelting quality of each part

[0013] (3) Since the pipe row is naturally cooled in the air after remelting and heating, the faster cooling rate results in greater residual tensile stress in the coating, which is prone to cracks

[0014] (4) The heating temperature of the high-frequency induction coil is difficult to precisely control, which aggravates the problem of uneven heating of the coating and the growth of oxide skin

[0015] (5) High-frequency induction remelting belongs to local heating, and the local high temperature causes serious bending deformation of the pipe row, and special tooling must be used for deformation correction

[0017] Other methods in the prior art are difficult to effectively improve the high-temperature anti-corrosion performance and service life of the boiler membrane wall

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