Welding technology of high-purity ferrite stainless steel heat exchanger

Abstract

The invention provides a welding technology of a high-purity ferrite stainless steel heat exchanger. The technology comprises two steps including overlaying welding of a tube plate and welding of thetube plate and a heat exchange tube, wherein the tube plate comprises a tube plate basic layer and a tube plate multiple layer; the tube plate basic layer is 64 mm thick and made of 16MnIII; the tubeplate multiple layer is S11972 with the thickness of 4 mm; a processing amount of 10 mm is preserved at an outer circular diameter is roughly lathed on a whole forge piece; a seal face is lathed on the tube plate multiple layer to a to-be-overlaid surface, and a baffle groove is dug to the to-be-overlaid surface; then, overlaying welding of nickel base alloy ENiCrMo-3 is conducted on the to-be-overlaid surface, and the heat exchange tube is made of an S11972 material; and during welding of the tube plate and the heat exchange tube, a welding joint is connected through strength welding and pasting expansion, welding is conducted on two layers, self-fluxing is conducted for the first time, and welding wires are added on the second layer. The welding technology provided by the invention has the beneficial effects that the feasible welding technology of the high-purity ferrite stainless steel heat exchanger is formulated, and layering welding of the tube plate, and welding of the tube plate and the heat exchange tube are successfully carried out, so that defects such as hot cracks, inter-granular corrosion and multilayer damage during welding are solved, and product quality is good after welding.

Description

technical field [0001] The invention relates to the field of welding, in particular to a welding process for a high-purity ferritic stainless steel heat exchanger. Background technique [0002] The heat exchanger is the main static equipment of the petrochemical plant. A considerable part of the plant uses circulating water as the heat exchange medium. Seawater desalination is an important source of circulating water. The concentration of chloride ions in it has been above 300ppm for a long time, resulting in the welding of heat exchange tubes and tube sheets. Chloride ion pitting and stress corrosion occurred in the joints and heat exchange tubes, which affected the service life of the heat exchange equipment and seriously affected the smooth operation and efficiency of the device. A large number of equipment in the refinery unit of a petrochemical company are in similar working conditions, facing the harsh environment of circulating water quality. After researching that f...

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Problems solved by technology

Chinese patent 201410290317.3 discloses a ferritic stainless steel for tubular heat exchangers and its manufacturing method, which adjusts the content of Cr and Mo in the ferritic stainless steel, and then controls the pitting equivalent PRE, so that the ferritic stainless steel Corrosion resistance is equivalent to that of austenitic stainless steel 316L, but it still has the tendency of hot and cold cracks, embrittlement of joints, and intergranular corrosion

There is no precedent for the use of this type of material in the petrochemical industry, insufficient understanding of the welding performance of this material, and no relevant experience in structural manufacturing, and the above-mentioned patents only disclose the material of the heat exchanger, and do not disclose the welding process

[0011] Prior to this, our company applied for several welding processes related to heat exchangers, including: the application number is 201110038817.4, which discloses a welding method for the welded joints of heat exchanger tube sheets and heat exchange tubes. The welding route when welding the plate and the heat exchange tube. This patent is applicable to the welding of ordinary materials and can avoid crevice corrosion. However, we used the S11972 material this time. This method is not suitable for this welding, and the traditional welding parameters are used. If there is no preheating, there may be a tendency for intergranular corrosion to cooperate with this welding route. This is because without preheating, the chromium in the S11972 material cannot diffuse to the chromium-poor area and eliminate the chromium-poor grain boundary, and the corrosion resistance of the joint is poor. The phenomenon of intergranular corrosion is serious; the above-mentioned welding process is also relatively cumbersome; we have also applied for a structure that facilitates welding between the super ferrite heat exchange tube and the tube sheet, the patent number is 201720056830. There is an annular groove, and by changing its structure, the heat exchange tube and the tube sheet are easily welded, but it does not disclose methods to solve problems such as intergranular corrosion, thermal crack defects, and surface defects during the welding process, and the material used is not S11972

[0012] The welding of the heat exchanger includes two aspects, one is the surfacing welding of the tube sheet, and the other is the welding of the tube sheet and the heat exchange tube. The traditional welding method is used because the welding process is not rigorous enough, and the temperature and method are not suitable. , resulting in cracks on the surface of the surfacing welding, pores on the sealing surface, slag inclusions, and damage to the cladding layer, which seriously affect the service life of the heat exchanger. Increase the difficulty of post-manufacturing and affect the welding effect. Therefore, it is necessary to develop a welding process for high-purity ferritic stainless steel heat exchangers that can meet the requirements of petrochemical companies' refining units and can also achieve economical, applicability, and reliability purposes.

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