Hot water storage tank, method for manufacturing the same and hot water preparation

Abstract

A hot water storage tank consists of a body, a first part, and a weld seam formed by welding the body and the first part together. The body is made of a corrosion-resistant material other than austenitic stainless steel.

Description

Technical area

[0001] The present invention relates to a hot water storage tank, a method for manufacturing the hot water storage tank and a hot water heater with the hot water storage tank. Technical background

[0002] In the past, materials with corrosion resistance that does not deteriorate during welding were desired for hot water storage tanks containing chloride-containing water. For example, patent 1 discloses austenitic stainless steel as a material for a container that comes into contact with clean water or wastewater. The composition of the austenitic stainless steel described in patent 1 results in a weld seam with a solidification structure that prevents the easy formation of a dense packing of ferrite layers. Therefore, it is expected that the austenitic stainless steel described in patent 1 will prevent a deterioration in corrosion resistance caused by a chromium-deficient layer and thus maintain excellent corrosion resistance at the weld seam. List of citations from patent literature

[0003] Patent Literature 1: Japanese Patent Application Publication JP 2003 - 64 453 A Summary of the invention: Technical problem

[0004] From the perspective of manufacturing costs, it is sometimes desirable to use less expensive materials for hot water storage tanks. However, even when made from less expensive materials, hot water storage tanks must still exhibit a certain degree of corrosion resistance.

[0005] The present invention is applied to solve the above-mentioned problems and relates to a hot water storage tank that can maintain corrosion resistance at a weld seam while reducing manufacturing costs, a method for manufacturing the hot water storage tank, and a water heater that includes the hot water storage tank. Solution to the problem

[0006] A hot water storage tank according to an embodiment of the present invention comprises: a main body; a first part; and a weld seam formed by welding the main body and the first part together. The main body is made of a corrosion-resistant material other than austenitic stainless steel.

[0007] A method for manufacturing a hot water storage tank according to another embodiment of the present invention comprises the following: forming a main body of the hot water storage tank, which has a container body with a cylindrical shape, using a wound material of ferritic stainless steel or a wound material of duplex stainless steel, which is a mixture of ferritic stainless steel and austenitic stainless steel, wherein the ferritic stainless steel and the duplex stainless steel each have a pitting corrosion potential of more than or equal to 0.3 V against Ag / AgCl;and welding a pipe connection section to the main body, wherein the pipe connection section is made of ferritic stainless steel, austenitic stainless steel or stainless duplex steel which is a mixture of ferritic stainless steel and austenitic stainless steel, wherein the ferritic stainless steel, the austenitic stainless steel and the stainless duplex steel each have a pitting corrosion potential greater than or equal to 0.3 V against Ag / AgCl.

[0008] A water heater according to a further embodiment of the present invention comprises the above-mentioned hot water storage tank, a circulation water circuit in which water circulates as a heat transfer medium, and a tap water circuit in which tap water circulates as a heat transfer medium. Advantageous effects of the invention

[0009] The hot water storage tank according to the embodiment of the present invention has a weld seam formed by welding the main body and the first part together. The body is made of a corrosion-resistant material other than austenitic stainless steel. This makes it possible to maintain the corrosion resistance of the weld seam while simultaneously reducing the manufacturing costs of the hot water storage tank. Brief description of the drawings Fig. Figure 1 is a schematic configuration diagram of a water heater according to embodiment 1. Fig. Figure 2 is a schematic configuration diagram of a hot water storage tank according to embodiment 1. Fig. Figure 3 shows an example of a measurement result of the pitting corrosion potential. Fig. Figure 4 is a flowchart illustrating the manufacturing steps of the hot water storage tank according to embodiment 1. Fig. Figure 5 is an illustrative representation of a gap between a main body and a pipe connection at a main body weld seam of the hot water storage tank according to embodiment 1. Fig. Figure 6 is an illustrative representation of a leg section of a hot water storage tank according to embodiment 2. Fig. Figure 7 is an illustrative representation of another example of the leg part of the hot water storage tank according to embodiment 2. Fig. Figure 8 is an explanatory illustration of a further example for each of the leg parts of the hot water storage tank according to embodiment 2. Fig. Figure 9 shows another example of the leg part of the hot water storage tank according to embodiment 2. Description of the embodiments

[0010] A hot water storage tank, a method for manufacturing the hot water storage tank, and a hot water heater according to the embodiments of the present invention are described with reference to the drawings. The present invention is not limited to the embodiments described below. Various modifications can be made without departing from the core of the present invention. The present invention can encompass all possible combinations of configurations as described in the embodiments below. In the following descriptions, terms indicating directions (e.g., "upper," "lower," "right," and "left") are used appropriately to make the embodiments and modifications easier to understand and are not intended to limit the present invention.In each of the figures, components that are identical or equivalent to those in one or more preceding illustrations are marked with the same reference symbols. The same applies to the entire text of the description. It should be noted that in each of the figures, a relationship or relationships in relative dimensions between components or a shape or shapes thereof may differ from the actual ones. Design 1: Configuration of the water heater

[0011] Fig. Figure 1 is a schematic configuration diagram of a water heater 100 according to embodiment 1. Fig. 1. Solid lines indicate a circulating water circuit 102 and dashed dotted lines indicate a tap water circuit 103. Furthermore, the solid arrows in Fig. 1 the direction of flow of the tap water in the tap water circuit 103.

[0012] As in Fig. As shown in Figure 1, the water heater 100 comprises a hot water storage tank 101, the circulation water circuit 102, and the supply water circuit 103. The circulation water circuit 102 is configured such that an outdoor unit 140, an auxiliary heater 151, a radiator 152, a strainer 153, a circulation water circuit pump 154, a flow meter 155, an expansion vessel 156, a plate heat exchanger 170, and a first three-way valve 159 are connected by pipes. The auxiliary heater 151, the strainer 153, the circulation water circuit pump 154, the flow meter 155, the expansion vessel 156, the plate heat exchanger 170, and the first three-way valve 159 are located in an indoor unit 150.

[0013] In the circulation water circuit 102, water circulates as a heat transfer medium. The circulation water pump 154 ​​circulates the water in the circulation water circuit 102. The outdoor unit 140 contains a refrigerant circuit (not shown) in which the refrigerant circulates. The water circulating in the circulation water circuit 102 is heated in the outdoor unit 140 by heat exchange with the refrigerant. The water circulating in the circulation water circuit 102 is also heated by the auxiliary heater 151. The water heated by the refrigerant and the auxiliary heater 151 flows into the first three-way valve 159.

[0014] The first three-way valve 159 switches a flow channel for the water circulating in the circulation water circuit 102 between several flow channels. More precisely, the water heated by the auxiliary heater 151 is directed through the first three-way valve 159 into the plate heat exchanger 170 and / or the radiator 152.

[0015] In the plate heat exchanger 170, the water flowing in the circulation water circuit 102 and the tap water flowing in the mains water circuit 103 exchange heat with each other. The mains water flowing in the mains water circuit 103 is heated by the water that has flowed from the first three-way valve 159 into the plate heat exchanger 170 in the circulation water circuit 102.

[0016] Radiator 152 is located outside the indoor unit 150 to heat the room. The water flowing from the first three-way valve 159 into radiator 152, and circulating in the circulation water circuit 102, transfers heat to the room air in radiator 152. It should be noted that the device provided outside the indoor unit 150 for heating the room can be a different device than radiator 152. For example, underfloor heating can be installed instead of radiator 152.

[0017] After heat transfer in the plate heat exchanger 170 or the radiator 152, the water circulating in the circulation water circuit 102 flows into the dirt trap 153. Iron rust particles and other foreign matter, which may originate in the radiator 152 and other areas, can sometimes enter the first three-way valve 159 along with the water circulating in the circulation water circuit 102. Such iron rust particles and other foreign matter can damage the first three-way valve 159. The dirt trap 153 serves to remove the iron rust particles and other foreign matter from the water circulating in the circulation water circuit 102.

[0018] The water flowing out of the dirt trap 153 passes through the flow meter 155 into the outdoor unit 140. In the circulation water circuit 102, the expansion vessel 156 can be located between the auxiliary heater 151 and the first three-way valve 159. The expansion vessel 156 receives the resulting expansion water.

[0019] The domestic hot water circuit 103 is configured such that the hot water storage tank 101, a domestic hot water circulation pump 164, the plate heat exchanger 170, a water softener 160, and a second three-way valve 169 are connected by pipes. The hot water storage tank 101 can be equipped with a pressure relief valve 50. The hot water storage tank 101, the domestic hot water circulation pump 164, the plate heat exchanger 170, and the water softener 160 are housed in the indoor unit 150.

[0020] In the mains water circuit 103, the mains water flows as a heat transfer medium. The mains water can either circulate in the mains water circuit 103 or flow from the water heater 100. Whether the mains water circulates in the mains water circuit 103 or flows from the water heater 100 depends on the state of the second three-way valve 169.

[0021] As indicated by the solid arrow A in Fig. As indicated in Figure 1, tap water flows from the outside into the tap water circuit 103. The tap water that has flowed into the tap water circuit 103 flows from the lower part of the hot water storage tank 101 into the hot water storage tank 101. The tap water that flowed into the hot water storage tank 101 flows out of the hot water storage tank 101 from a section of the lower part of the hot water storage tank 101 that differs from the section where the tap water flowed into the hot water storage tank 101, and is then directed by the pump 164 of the tap water circuit to the plate heat exchanger 170. The tap water that has been directed to the plate heat exchanger 170 and flows into the tap water circuit 103 is heated by heat exchange with the water flowing in the circulation water circuit 102.

[0022] The tap water heated in the plate heat exchanger 170 and flowing in the tap water circuit 103 passes through the descaling device 160 into the upper part of the hot water storage tank 101. The descaling device 160 removes scale ions such as calcium and magnesium ions, as well as ionic silica, which are contained in the tap water flowing into the tap water circuit 103. As the temperature of the tap water increases, the scale ions precipitate more easily. Therefore, when the tap water heated in the plate heat exchanger 170 passes through the descaling device 160, the scale ions are easily removed.

[0023] Furthermore, if boiler scale ions are deposited in the plate heat exchanger 170, they impair the heat exchange efficiency and block the flow path within the plate heat exchanger 170. However, the boiler scale ions are removed from the tap water that flows back into the hot water storage tank 101 after being heated in the plate heat exchanger 170. Therefore, it is possible to prevent the formation of deposit ions in the plate heat exchanger 170 if the tap water that has flowed back into the hot water storage tank 101 is recirculated into the plate heat exchanger 170 by the pump 164 of the tap water circuit. In this way, it is possible to protect the plate heat exchanger 170 by removing boiler scale ions, a process accomplished by the descaling device 160.

[0024] The heated tap water, which has flowed through the descaling device 160 into the upper part of the hot water storage tank 101, flows out of a section of the upper part of the hot water storage tank 101 that differs from the section through which the tap water flowed into the hot water storage tank 101. The heated tap water that has flowed out of the hot water storage tank 101 flows from the water heater 100 through the second three-way valve 169 to the outside. The tap water flowing out to the outside of the water heater 100 is supplied, for example, to a shower room, a toilet, and a kitchen.

[0025] The second three-way valve 169 switches the flow channel for the water circulating in the mains water circuit 103. More precisely, after the heated mains water flows out of the hot water storage tank 101, the second three-way valve 169 causes it to flow to the outside of the water heater 100 or to the mains water circuit 103.

[0026] If the second three-way valve 169 does not cause the flow channel for the tap water to be connected to the outside, the flow channel for the tap water is connected to the tap water circuit 103. In this case, the tap water heated in the hot water storage tank 101 circulates in the tap water circuit 103. Thus, after passing through the second three-way valve 169, the tap water heated in the hot water storage tank 101 meets tap water flowing into the tap water circuit 103 from the outside. The externally flowing tap water and the heated tap water then flow together into the hot water storage tank 101. Hot water storage tank configuration

[0027] The hot water storage tank 101 according to embodiment 1 is described with reference to Fig. 2 described. Fig. Figure 2 is a schematic configuration diagram of the hot water storage tank 101 according to embodiment 1. The hot water storage tank 101 comprises a main body 1, pipe connection sections 2 and main body welds 3, which are formed by welding the main body 1 and the pipe connection sections 2.

[0028] The main body 1 comprises a cylindrical container body 10 and container heads 20, which cover both ends of the container body 10. The container heads 20 are a first container head 21, provided at one end of the container body 10, and a second container head 22, provided at the other end of the container body 10. In the following description, the first container head 21 and the second container head 22 may each be referred to as container head 20 if it is not necessary to distinguish between the first container head 21 and the second container head 22.

[0029] The vessel body 10 and the vessel head 20 are each made of a corrosion-resistant material that differs from austenitic stainless steel in its corrosion resistance. The corrosion-resistant material that differs from austenitic stainless steel in its corrosion resistance is ferritic stainless steel or stainless duplex steel, which is a mixture of ferritic and austenitic stainless steel, wherein the ferritic and stainless duplex steels each exhibit a pitting potential of 0.3 V against Ag / AgCl or more.

[0030] In the following description, ferritic stainless steel, austenitic stainless steel, and stainless duplex steel (a mixture of ferritic and austenitic stainless steel) can each be referred to as stainless steel when it is necessary to distinguish between them. Furthermore, stainless duplex steel, which is a mixture of ferritic and austenitic stainless steel, is sometimes also called stainless duplex steel.

[0031] The vessel body 10 is formed into a cylindrical shape by welding plate-shaped ferritic stainless steel or plate-shaped duplex stainless steel, the plate-shaped ferritic stainless steel and the plate-shaped duplex stainless steel each having a pitting corrosion potential of 0.3 V against Ag / AgCl or more. A portion of the vessel body 10 to which the plate-shaped stainless steel is welded is a vessel body weld 13. Furthermore, the vessel body 10 and the first vessel head 21 are welded together, and the vessel body 10 and the second vessel head 22 are also welded together. A weld seam where the container body 10 and the first container head 21 are welded together is a first container head weld seam 31, and a weld seam where the container body 10 and the second container head 22 are welded together is a second container head weld seam 32.

[0032] The vessel body weld 13 extends between the first vessel head 21 and the second vessel head 22 in a direction perpendicular to the circumferential direction of the cylindrical shape. The first vessel head weld 31 and the second vessel head weld 32 extend in the circumferential direction of the cylindrical shape. The entire vessel body 10, the first vessel head 21, and the second vessel head 22 can be made of the same stainless steel. Alternatively, one of these components can be made of ferritic stainless steel and the other components of duplex stainless steel.

[0033] The pipe connection sections 2 each consist of ferritic stainless steel, austenitic stainless steel, or stainless duplex steel, which is a mixture of ferritic and austenitic stainless steel, wherein the ferritic stainless steel, the austenitic stainless steel, and the stainless duplex steel each have a pitting corrosion potential of 0.3 V against Ag / AgCl or more. Pipes forming the mains water circuit 103 are connected to the pipe connection sections 2 (see Fig. 1) and through which the mains water flows, connected to the hot water storage tank 101. The pipe connection sections 2 can be part of the pipes in the mains water circuit 103, or they can be connections with which the pipes in the mains water circuit 103 are connected.

[0034] The pipe connection sections 2 can be part of pipes other than the pipes in the mains water circuit 103. The connection corresponding to each of the pipe connection sections 2 is, for example, a threaded connection or a clamping connection. The connection corresponding to the pipe connection section 2 can, for example, be connected to the pressure relief valve 50 (see Fig. 1) be connected.

[0035] Although in Fig. While five pipe connection sections 2 are shown as an example, the number of pipe connection sections 2 is not particularly limited. The number of pipe connection sections 2 can be one, five, or more. The pipe connection sections 2 can be arranged at any point on the main body 1. That is, the pipe connection sections 2 can be located on any part of the following components: the tank body 10, the first tank head 21, and the second tank head 22.

[0036] However, in the case where each of the pipe connection sections 2 is located on a part made of ferritic stainless steel, the pipe connection section 2 is manufactured from a material containing austenitic stainless steel. It should be noted that the material containing austenitic stainless steel corresponds to austenitic stainless steel and duplex stainless steel, which is a mixture of ferritic and austenitic stainless steel.

[0037] The main body welds 3 are formed by welding the main body 1 and the pipe connection sections 2. Each of the main body welds 3 will be described in detail later. Pitting corrosion potential of a hot water storage tank

[0038] Fig. Figure 3 shows an example of a measurement result of the pitting corrosion potential. Fig. Figure 3 shows an example of the change in the current value flowing during voltage sampling. Fig. Figure 3: The horizontal axis represents the potential obtained during sampling, and the vertical axis represents the common logarithm of the current value. In the example of the measurement result in Fig. 3. Silver and silver chloride (Ag / AgCl) are used as reference electrodes.

[0039] It is possible to measure the pitting corrosion potential of a metallic material using electrochemical measurements. To measure the potential dependence and reaction rate of oxidation-reduction reactions occurring at an electrode, the potential of the metallic material is scanned in either the positive or negative direction. The metallic material serves as the electrode during this process.

[0040] The pitting corrosion potential can be measured using methods that employ an electrochemical measuring device such as a potentiostat and that include the method described in “JIS G 0577:2014, Methods for measuring the pitting corrosion potential of stainless steels”, as well as under test conditions that take into account the operating specifications of a water heater including a hot water storage tank and the water quality at the installation site.

[0041] In Fig. At point P1, the current rises abruptly. Ferritic stainless steel, austenitic stainless steel, or duplex stainless steel (a mixture of ferritic and austenitic stainless steel) has formed a passive film on its surface. Although the passive film is initially intact, it is locally disrupted when the potential increases, leading to the formation of pits. In other words, pitting corrosion increases. The lower limiting potential at which pitting corrosion occurs and increases is called the pitting potential.

[0042] In Fig. Figure 3, “PP”, represents an example of the pitting corrosion potential. In embodiment 1, the pitting corrosion potential of the stainless steel from which the main body 1 is made is greater than or equal to 0.3 V vs. Ag / AgCl before welding. Furthermore, it is desirable that the pitting corrosion potential of the stainless steel forming the pipe connection section 2 be greater than or equal to 0.3 V vs. Ag / AgCl before welding.

[0043] The stainless steel from which the main body 1 and the pipe connection section 2 are made exhibits high corrosion resistance because a passive film forms on the metal's surface, consisting primarily of chromium (Cr). However, welding applies a significant amount of heat to the stainless steel. This heat input causes a phenomenon known as stainless steel sensitization. Sensitization is a phenomenon in which the concentration of chromium (Cr) in the stainless steel decreases along the grain boundaries, thus increasing its susceptibility to stress corrosion cracking.

[0044] When sensitization occurs, corrosion resistance decreases. In embodiment 1, the main body welds 3, the vessel body weld 13, the first vessel head weld 31, and the second vessel head weld 32 are parts produced by welding. Even if the pitting potential before welding is greater than or equal to 0.3 V against Ag / AgCl, the pitting potential may decrease after welding. In embodiment 1, it is advantageous that the main body weld 3, the vessel body weld 13, the first vessel head weld 31, and the second vessel head weld 32 each have a pitting potential of 0.3 V against Ag / AgCl or more.

[0045] More precisely, it is preferable that, for each of the main body weld 3, the vessel body weld 13, the first vessel head weld 31, and the second vessel head weld 32, the portion of each of these welds that comes into contact with the water stored in the main body 1 has a pitting corrosion potential of 0.3 V against Ag / AgCl or more. It should be noted that, for each of the aforementioned welds 3, 13, 31, and 32, a portion of the main body 1 located on an outer circumferential side of the main body 1 and not in contact with water may have a pitting corrosion potential of less than 0.3 V against Ag / AgCl.

[0046] Provided that the main body 1 and the pipe connection section 2 are each made of stainless steel having a pitting corrosion potential of at least 0.3 V vs. Ag / AgCl, and the main body weld 3, the tank body weld 13, the first tank head weld 31 and the second tank head weld 32 each have a pitting corrosion potential of at least 0.3 V vs. Ag / AgCl on a part of each of the above welds that comes into contact with water, it is possible to provide a hot water storage tank 101 that retains its corrosion resistance and a water heater 100 that includes such a hot water storage tank 101.

[0047] The welding process used to produce the main body weld 3, the vessel body weld 13, the first vessel head weld 31, and the second vessel head weld 32 is not particularly limited. A suitable welding process can be selected based on the shape of the part to be welded and the welding conditions applied. Laser welding, tungsten inert gas (TIG) welding, and cold metal transfer (CMT) welding are available as welding processes. A suitable one can be selected from these.

[0048] Regardless of the welding method chosen, an oxide, known as oxide scale or weld discoloration, can form on the surface of the resulting weld. The formation of such an oxide depends on the welding conditions. Therefore, after welding, a so-called tempering color adheres to the main body weld 3, the tank body weld 13, the first tank head weld 31, and the second tank head weld 32. Such an oxide can lead to a deterioration of the corrosion resistance of the hot water storage tank 101. Therefore, a pickling process is carried out in steps, from pickling step S16 for the tank body weld to pickling step S19 for the main body weld, which is described later, to remove the oxide from the welded part.

[0049] Under certain pickling conditions, however, the pitting potential of the weld can decrease. For example, the pitting potential of the weld can decrease if the pickling process is carried out over a longer period or if the concentration of the acid used in the pickling process is high. For this reason, in embodiment 1, it is preferable that the main body weld 3, the vessel body weld 13, the first vessel head weld 31, and the second vessel head weld 32 each have a pitting potential of 0.3 V against Ag / AgCl or more after pickling.

[0050] More specifically, it is preferred that after pickling, a portion of the main body weld 3, the vessel body weld 13, the first vessel head weld 31, and the second vessel head weld 32 exhibits a pitting corrosion potential of 0.3 V against Ag / AgCl or more, wherein the aforementioned portion is the part that comes into contact with the water stored in the main body 1. It should be noted that after pickling, a portion of the main body weld 3, the vessel body weld 13, the first vessel head weld 31, and the second vessel head weld 32 may exhibit a pitting corrosion potential of less than 0.3 V against Ag / AgCl, wherein the aforementioned portion is the part that does not come into contact with water. The outer circumferential surface of the main body 1 may be either pickled or not pickled. Method for manufacturing a hot water storage tank

[0051] A method for manufacturing the hot water storage tank 101 is described with reference to Fig. 4 described. Fig. Figure 4 is a flowchart showing the manufacturing steps of the hot water storage tank 101 according to embodiment 1. As shown in Fig. As shown in Figure 4, the method for manufacturing the hot water storage tank 101 comprises a step S11 for forming the tank body, a step S12 for welding the tank body, a step S13 for welding the pipe connection section, a step S14 for welding the first tank head, a step S15 for welding the second tank head, a step S16 for pickling the tank body weld, a step S17 for pickling the first tank head weld, a step S18 for pickling the second tank head weld and a step S19 for pickling the main body weld.

[0052] In step S11 of the vessel body formation process, a section is cut from a roll of stainless steel to serve as the vessel body 10, and holes are formed for connecting the pipe connection sections 2. The stainless steel forming the vessel body 10, i.e., ferritic stainless steel or duplex stainless steel, which is a mixture of ferritic and austenitic stainless steel, is stainless steel in sheet form. This stainless steel sheet is in the form of a coiled roll and is referred to as wound material. The ferritic stainless steel or duplex stainless steel from which the vessel body 10 is made has a pitting corrosion potential greater than or equal to 0.3 V against Ag / AgCl.

[0053] In step S11 of the container body formation process, the wound material is cut to a predetermined length to form a rectangular stainless steel plate, from which the container body 10 will be formed. Next, holes are drilled into the resulting stainless steel sheet for welding the pipe connection sections 2. The holes are created by cutting the stainless steel sheet. The method for cutting the wound material is not particularly limited. For example, the wound material can be cut with a laser.

[0054] In the vessel body welding step S12, the stainless steel sheet with the holes formed in the vessel body formation step S11 is rolled and bent to form it into a cylindrical shape, so that its elongated end sections are in contact with each other. These end sections of the cylindrically formed stainless steel sheet are then welded together, creating the vessel body 10 with the cylindrical shape. The portion of the stainless steel sheet that is welded corresponds to the vessel body weld 13. Preferably, the pitting corrosion potential of the vessel body weld 13 should be greater than or equal to 0.3 V against Ag / AgCl.

[0055] In step S13, for welding the pipe connection sections, the holes that were introduced into the vessel body 10 in step S11 to form the vessel body are enlarged by deburring. The pipe connection sections 2 are then welded into the respective enlarged holes. The pipe connection sections 2 consist of ferritic stainless steel, austenitic stainless steel, or duplex stainless steel, which is a mixture of ferritic and austenitic stainless steel. Preferably, the ferritic stainless steel, the austenitic stainless steel, and the duplex stainless steel should have a pitting corrosion potential of at least 0.3 V against Ag / AgCl.

[0056] If the vessel body 10 is made of ferritic stainless steel, the pipe connection sections 2, made of austenitic stainless steel or duplex stainless steel, are welded to the vessel body 10. The locations where the pipe connection sections 2 are welded into the holes formed in the vessel body 10 correspond to the main body welds 3. Preferably, the main body welds 3 should have a pitting corrosion potential of 0.3 V against Ag / AgCl or higher.

[0057] In the first vessel head welding step S14, the first vessel head 21 is welded circumferentially to one end of the cylindrical vessel body 10. The first vessel head 21 is made of ferritic stainless steel, austenitic stainless steel, or duplex stainless steel, which is a mixture of ferritic and austenitic stainless steel, wherein the ferritic stainless steel, the austenitic stainless steel, and the duplex stainless steel each have a pitting corrosion potential of 0.3 V against Ag / AgCl or more.

[0058] The point where the first container head 21 and the container body 10 are welded together corresponds to the first container head weld 31. Preferably, the pitting corrosion potential of the first container head weld 31 should be greater than or equal to 0.3 V against Ag / AgCl. The container body 10 and the first container head 21 can be made of the same type of stainless steel. Alternatively, the container body 10 and the first container head 21 can be made of ferritic stainless steel and the other of duplex stainless steel.

[0059] In the second container head welding step S15, the second container head 22 is welded circumferentially to the other end of the cylindrical container body 10. The second container head 22 is made of ferritic stainless steel, austenitic stainless steel, or duplex stainless steel, which is a mixture of ferritic and austenitic stainless steel, wherein the ferritic stainless steel, the austenitic stainless steel, and the duplex stainless steel each have a pitting corrosion potential of 0.3 V against Ag / AgCl or more.

[0060] The point where the second container head 22 and the container body 10 are welded together corresponds to the second container head weld 32. Preferably, the pitting corrosion potential of the second container head weld 32 should be greater than or equal to 0.3 V against Ag / AgCl. The container body 10 and the second container head 22 can be made of the same type of stainless steel. Alternatively, the container body 10 and the second container head 22 can be made of ferritic stainless steel and the other of duplex stainless steel.

[0061] In step S16 of the pickling process of the vessel body weld, the vessel body weld 13 is subjected to a pickling process. Tempering color is removed from the vessel body weld 13 after the pickling process. Preferably, the vessel body weld 13 after the pickling process should have a pitting corrosion potential of 0.3 V against Ag / AgCl or higher.

[0062] In the first pickling step of the vessel head weld S17, the first vessel head weld 31 is subjected to pickling. Tempering color is removed from the first vessel head weld 31 being pickled. Preferably, the pitting corrosion potential of the first vessel head weld 31 being pickled should be greater than or equal to 0.3 V against Ag / AgCl.

[0063] In the second pickling step of the vessel head weld S18, the second vessel head weld 32 is subjected to pickling. Tempering color is removed from the second vessel head weld 32 undergoing the pickling process. Preferably, the pitting corrosion potential of the second vessel head weld 32 undergoing pickling should be greater than or equal to 0.3 V against Ag / AgCl.

[0064] In step S19 of the pickling process for the main body weld, the main body weld 3 is subjected to pickling. Tempering color is removed from the pickled main body weld 3. Preferably, the pitting corrosion potential of the pickled main body weld 3 should be greater than or equal to 0.3 V against Ag / AgCl.

[0065] Although the steps described above do not include the step of connecting the pipe connection sections 2 to the first vessel head 21 and the second vessel head 22, the pipe connection sections 2 can be welded to the first vessel head 21 and the second vessel head 22. The step of welding the pipe connection sections 2 to the first vessel head 21 and the second vessel head 22 is not particularly restricted. During the first vessel head welding step S14 and the second vessel head welding step S15, the first vessel head 21 and the second vessel head 22, to which the pipe connection sections 2 have already been connected, can be welded to the vessel body 10.

[0066] In the first vessel head welding step S14 and the second vessel head welding step S15, the first vessel head 21 and the second vessel head 22 are welded with holes for connecting the pipe connection sections 2 to the vessel body 10. In this case, it is sufficient that in the first vessel head welding step S14 and the second vessel head welding step S15, the first vessel head 21 and the second vessel head 22 are welded to the vessel body 10, and the pipe connection sections 2 are then welded to the first vessel head 21 and the second vessel head 22. In any case, in step S19 of the pickling of the main body welds, all main body welds 3 are subjected to pickling.This means that not only the main body welds 3, where the pipe connection sections 2 are welded to the tank body 10, but also the main body welds 3, where the pipe connection sections 2 are welded to the first tank head 21, and the main body welds 3, where the pipe connection sections 2 are welded to the second tank head 22, are pickled.

[0067] It should be noted that the steps from pickling the tank body weld S16 to pickling the main body weld S19 can be reversed in order. Furthermore, the steps from pickling the tank body S16 to pickling the main body weld S19 can be performed as a single pickling step rather than as individual steps. This means that in a single pickling step, the tank body weld 13, the first tank head weld 31, the second tank head weld 32, and the main body weld 3 can be pickled simultaneously. For example, by filling the hot water storage tank 101 with a pickling solution, it is possible to pickle these welds all at once. Main body weld

[0068] The main body weld seam 3 is described with reference to Fig. 5 described. Fig. Figure 5 is an illustrative representation of a gap SP between the main body 1 and the pipe connection section 2 at the main body weld seam 3 of the hot water storage tank 101 according to embodiment 1. A gap SP is shown in Figure 5. Fig. 3. The area designated “inside” is an area located within the main body 1, and is contained within Fig. 3 The area designated as “outside” is an area that is located outside the main body 1.

[0069] As described above in relation to step S13 for welding the pipe connection sections, the pipe connection sections 2 are welded into the holes enlarged by deburring in the vessel body 10. Similarly, in the first vessel head 21 and the second vessel head 22, the pipe connection sections 2 are welded into the holes enlarged by deburring. The main body welds 3 are formed by inserting and welding the pipe connection sections 2 into the holes provided in the main body 1, i.e., the holes provided in the vessel body 10, the first vessel head 21, and the second vessel head 22.

[0070] At this point, when welding the main body 1 and the pipe connection sections 2 inserted into the hole of the main body 1, a gap SP may in some cases occur, as shown in Fig. Figure 5 shows a gap formed between the main body 1 and the pipe connection section 2. In embodiment 1, the main body 1 and the pipe connection section 2 are welded together such that the gap SP has a width W of more than 100 µm. The width W of the gap SP is, in this case, the length in the lateral direction in the plane of Fig. 5. Preferably, the width W of the gap SP should not be greater than the thickness of the main body 1. In any case, the width W of the gap SP is not greater than or equal to 10 mm. For example, the width W of the gap SP is greater than 100 µm but less than or equal to 2 mm.

[0071] If the width W of the gap SP between the main body 1 and the pipe connection section 2 is less than or equal to 100 µm, the supply of dissolved oxygen in the gap SP becomes insufficient compared to that in the external environment, resulting in a lower oxygen concentration. In this case, an oxygen concentration cell forms due to the difference in oxygen concentration, and the corrosion reaction of the stainless steel progresses. Consequently, crevice corrosion at the weld of the main body 3 can lead to the formation of a hole in the main body 1, potentially resulting in water leakage from the main body 1.

[0072] Therefore, in embodiment 1, the main body 1 and the pipe connection section 2 are welded such that the width W of the gap SP is not less than 100 µm. It should be noted that during the welding of the main body 1 and the pipe connection section 2, in some cases the stainless steel may melt and then solidify in such a way that it extends over the main body 1 and the pipe connection section 2. In other words, in some cases the gap SP is formed in a space that is located outside the main body 1 before welding. Therefore, in embodiment 1, the main body 1 and the pipe connection section 2 are welded such that the width W of the gap SP formed as described above is not less than 100 µm.

[0073] As described above, the hot water storage tank 101 according to embodiment 1 comprises the main body 1, the pipe connection sections 2, which serve as the first part, and welds formed by welding the main body 1 and the pipe connection sections 2. The main body 1 is made of a corrosion-resistant material other than austenitic stainless steel. Therefore, it is possible to maintain the corrosion resistance of the weld while simultaneously reducing the manufacturing costs of the hot water storage tank 101.

[0074] In the hot water storage tank 101 according to embodiment 1, the corrosion-resistant material has a pitting corrosion potential of 0.3 V against Ag / AgCl or more. Therefore, the hot water storage tank 101 can retain its corrosion resistance.

[0075] In the hot water storage tank 101 according to embodiment 1, the first part consists of the pipe connection sections 2, which connect pipes to the main body 1, and the welds are the main body welds 3, at which the pipe connection sections 2 and the main body 1 are welded together. The pipe connection sections 2 are each made of a corrosion-resistant material other than austenitic stainless steel. Therefore, it is possible to maintain the corrosion resistance of the main body welds 3 while simultaneously reducing the manufacturing costs of the hot water storage tank 101.

[0076] The hot water storage tank 101 according to embodiment 1 comprises the main body 1, the pipe connection sections 2, which connect pipes to the main body 1, and the main body welds 3, which are formed by welding the pipe connection sections 2 and the main body 1. At least one of the main bodies 1 and each of the pipe connection sections 2 is made of a material containing austenitic stainless steel. The main body 1 is made of ferritic stainless steel or of duplex stainless steel, which is a mixture of ferritic and austenitic stainless steel. The pipe connection sections 2 are made of ferritic stainless steel, austenitic stainless steel, or duplex stainless steel, which is a mixture of ferritic and austenitic stainless steel.

[0077] In the configuration above, where the main body 1 is made of ferritic stainless steel, the pipe connection sections 2 are made of a material including austenitic stainless steel. The material containing austenitic stainless steel is either austenitic stainless steel or duplex stainless steel. Therefore, in the case where the main body 1 is made of ferritic stainless steel, the pipe connection sections 2 are made of austenitic stainless steel or duplex stainless steel.

[0078] On the other hand, if the main body 1 is made of duplex stainless steel, the pipe connection sections 2 can be made of ferritic stainless steel. That is, if the main body 1 is made of duplex stainless steel, the pipe connection sections 2 are made of ferritic stainless steel, austenitic stainless steel, or duplex stainless steel. As described above, in the hot water storage tank 101, at least one of the main bodies 1 and each of the pipe connection sections 2 are made of a material that includes austenitic stainless steel, so that it is possible to maintain the corrosion resistance of the main body weld 3.

[0079] The water heater 100 according to embodiment 1 comprises the hot water storage tank 101, the circulation water circuit 102 in which water circulates as a heat transfer medium, and the mains water circuit 103 in which mains water circulates as a heat transfer medium. The water heater 100 includes the hot water storage tank 101, which is able to maintain its corrosion resistance, thus reducing the risk that damage to the hot water storage tank 101 could impair the performance and service life of the water heater 100.

[0080] In the hot water storage tank 101 according to embodiment 1, the main body weld 3 has a pitting corrosion potential of 0.3 V against Ag / AgCl or more. Therefore, it is possible to maintain the corrosion resistance of the main body weld 3, where the pipe connection section 2 is welded to the main body 1.

[0081] In the hot water storage tank 101 according to embodiment 1, the main body 1 comprises the cylindrical tank body 10, the first tank head 21, which is provided at one end of the tank body 10, and the second tank head 22, which is provided at the other end of the tank body 10. The tank body 10 is welded at the tank body weld 13, which extends between one end and the other end and in a direction perpendicular to the circumferential direction of the cylindrical shape. The tank body 10 and the first tank head 21 are welded at the first tank head weld 31, and the tank body 10 and the second tank head 22 are welded at the second tank head weld 32. The tank body weld 13, the first tank head weld 31, and the second tank head weld 32 each have a pitting corrosion potential of 0.3 V against Ag / AgCl or more.

[0082] In the configuration above, the welded part of the main body 1 has a pitting corrosion potential of 0.3 V or more against Ag / AgCl. It is therefore possible to maintain the corrosion resistance of the welded part.

[0083] In the hot water storage tank 101 according to embodiment 1, each of the main body weld 3, the tank body weld 13, the first tank head weld 31 and the second tank head weld 32 is in a pickled condition and exhibits a pitting corrosion potential of more than or equal to 0.3 V against Ag / AgCl. Therefore, it is possible to maintain the corrosion resistance of the welded part that is pickled.

[0084] In the hot water storage tank 101 according to embodiment 1, a gap SP of more than 100 µm is provided at the main body weld 3 between the main body 1 and the pipe connection section 2. Therefore, it is possible to reduce the occurrence of crevice corrosion and to maintain the corrosion resistance of the main body weld 3.

[0085] The method for manufacturing the hot water storage tank 101 according to embodiment 1 comprises step S11 of forming the main body 1 with the cylindrical storage body 10 using a wound material of ferritic stainless steel or a wound material of duplex stainless steel, which is a mixture of ferritic stainless steel and austenitic stainless steel, wherein the ferritic stainless steel and the duplex stainless steel each have a pitting corrosion potential of 0.3 V against Ag / AgCl or more.

[0086] The process also includes step S13 of welding each of the pipe connection sections 2 to the main body 1. The pipe connection section 2 consists of ferritic stainless steel, austenitic stainless steel or stainless duplex steel, which is a mixture of ferritic stainless steel and austenitic stainless steel, wherein the ferritic stainless steel, the austenitic stainless steel and the stainless duplex steel each have a pitting corrosion potential of 0.3 V against Ag / AgCl or more.

[0087] In the above configuration, the hot water storage tank 101 is made of stainless steel with a pitting corrosion potential of 0.3 V against Ag / AgCl or more, making it possible to manufacture the hot water storage tank 101 with high corrosion resistance, even if fluctuations occur in production, e.g. in welding conditions.

[0088] The method for manufacturing the hot water storage tank 101 according to embodiment 1 further comprises step S16 of pickling the tank body weld 13 of the tank body 10, which is the weld where the wound material is welded and which has a pitting corrosion potential of greater than or equal to 0.3 V vs. Ag / AgCl; step S17 of pickling the first tank head weld 31, which is the weld between the tank body 10 and the first tank head 21 provided at one end of the tank body 10 and which has a pitting corrosion potential of greater than or equal to 0.3 V vs. Ag / AgCl; and step S18 of pickling the second container head weld 32, which is the weld between the container body 10 and the second container head 22, which is provided at the other end of the container body 10, and which has a pitting corrosion potential of greater than or equal to 0.3 V against Ag / AgCl.

[0089] In the configuration described above, the tank body weld 13, the first tank head weld 31, and the second tank head weld 32, each exhibiting a pitting corrosion potential of greater than or equal to 0.3 V against Ag / AgCl after welding, are subjected to pickling. Since the tank body weld 13, the first tank head weld 31, and the second tank head weld 32 each exhibit a pitting corrosion potential of at least 0.3 V against Ag / AgCl before pickling, it is possible to maintain the corrosion resistance of these welds after pickling. Therefore, it is possible to manufacture the hot water storage tank 101 with high corrosion resistance. Design 2

[0090] The following description of embodiment 2 relates mainly to the differences between embodiments 1 and 2. In embodiment 2, the hot water storage tank 101 includes a leg section 40, which is provided on the main body 1. In this respect, embodiment 2 differs from embodiment 1. The other

[0091] Configurations of embodiment 2 are the same as those of embodiment 1, and their descriptions are therefore omitted.

[0092] The leg section 40 according to embodiment 2 is described with reference to the Fig. 6 to 9 described. Fig. Figure 6 is an illustrative view of the leg section 40 of the hot water storage tank 101 according to embodiment 2. Fig. Figure 7 is an illustrative view of another example of the leg part 40 of the hot water storage tank 101 according to embodiment 2. Fig. Figure 8 is an illustrative view for a further example of each of the leg parts 40 of the hot water storage tank 101 according to embodiment 2. Fig. Figure 9 is an illustrative view for a further example of each of the leg parts 40 of the hot water storage tank 101 according to embodiment 2.

[0093] As in the Fig. As shown in Figures 6 to 9, the hot water storage tank 101 comprises the leg section 40 or leg sections 40 provided on the main body 1. The leg section or each of the leg sections 40 is made of ferritic stainless steel, austenitic stainless steel, or duplex stainless steel, which is a mixture of ferritic and austenitic stainless steel. The leg section 40 serves to enable the main body 1 to stand independently. Therefore, the leg section 40 is provided on the tank head 20, which, in the direction of gravity, is the lower of the two tank heads 21 and 22. As long as the leg section 40 is attached to the tank head 20 by the fastening method, the fastening method is not particularly restricted.

[0094] However, it is preferable that the leg section 40 be attached to the container head 20 by welding. When welding the leg section 40 to the container head 20, preferably at least one of the two parts, the container head 20 or the leg section 40, should be made of stainless steel, including austenitic stainless steel. If either the container head 20 or the leg section 40 is made of austenitic stainless steel, it is possible to attach the leg section 40 to the main body 1 without impairing the corrosion resistance of the hot water storage tank 101.

[0095] The leg part 40 can have a pitting corrosion potential of less than 0.3 V against Ag / AgCl. However, if an area where the leg part 40 is welded is exposed on an inner circumferential side of the main body 1 to come into contact with water stored therein, it is preferable that the pitting corrosion potential of the area where the leg part 40 is welded is higher than or equal to 0.3 V against Ag / AgCl.

[0096] The shape and number of leg parts 40 are not particularly limited, as long as the leg part or leg parts 40 are able to support the main body 1 in such a way that the main body 1 can stand independently. As in Fig. As shown in Figure 6, the leg part 40 can have the form of a plate with a flat surface that can be placed on the ground. Fig. Figure 6 shows an example where a single plate-shaped leg section 40 is attached to the middle part of the container head 20. As in Fig. As shown in Figure 7, a surface of the leg part 40, which is attached to the container head 20, can have a shape that conforms to the curved surface of the container head 20.

[0097] Furthermore, the leg section 40 is not necessarily single; several leg sections 40 may also be provided, as shown in the Fig. 8 and Fig. 9 shown. Fig. Figure 8 shows an example in which two leg parts 40, which are L-shaped when viewed from the side, are attached to the container head 20. Fig. Figure 9 shows an example where three leg sections 40 are attached to the container head 20. As in Fig. As shown in Figure 9, not all leg parts 40 need to have the same shape or size. The leg part or parts 40 can also be made of materials other than ferritic stainless steel, austenitic stainless steel, and duplex stainless steel. Reference symbol list 1 main body, 2 pipe connection section, 3 Main body weld seam, 10 container bodies, 13 Container body weld seam, 20 container head, 21 first container head, 22 second container head, 31 first container head weld, 32 second container head weld, 40 Leg section, 50 Overpressure valve, 100 water heaters, 101 hot water storage tanks, 102 Circulating water circuit, 103 Mains water circuit, 140 outdoor unit, 150 indoor unit, 151 Auxiliary heater, 152 radiators, 153 mud flaps, 154 Circulating water pump, 155 flow meters, 156 Expansion vessel, 159 first three-way valve, 1 60 Descaling device, 164 Mains water circulation pump, 169 second three-way valve, 170 plate heat exchangers, P1 point PP pitting corrosion example SP gap, W width. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] JP 2003 - 64 453 A

[0003] Cited non-patent literature

[0000] JIS G 0577:2014

[0040]

Claims

[1] Hot water storage tank comprising the following features: a main body; a first part; and a weld seam formed by welding the main body and the first part together, the main body is made of a different corrosion-resistant material than austenitic stainless steel. [2] Hot water storage tank according to claim 1, wherein the corrosion-resistant material has a pitting corrosion potential of 0.3 V or more against Ag / AgCl. [3] Hot water storage tank according to claim 1 or 2 wherein the first part is a pipe connection section that connects a pipe to the main body, the weld is a main body weld formed by welding the pipe connection section and the main body together, and The pipe connection section is made of corrosion-resistant material. [4] Hot water storage tank comprising the following features: a main body; a pipe connection section that connects a pipe to the main body; and a main body weld formed by welding the pipe joint section and the main body, where at least one of the main body and pipe connection section is made of a material including austenitic stainless steel, the main body is made of ferritic stainless steel or of duplex stainless steel, which is a mixture of ferritic stainless steel and austenitic stainless steel, and the pipe connection section is made of ferritic stainless steel, austenitic stainless steel or duplex stainless steel, which is a mixture of ferritic and austenitic stainless steel. [5] Hot water storage tank according to claim 3 or 4, wherein the main body weld seam has a pitting corrosion potential of at least 0.3 V against Ag / AgCl. [6] Hot water storage tank according to one of claims 3 to 5, wherein the main body weld seam is in a pickled state and has a pitting corrosion potential of at least 0.3 V against Ag / AgCl. [7] Hot water storage tank according to any one of claims 3 to 6, the main body has the following features a container body with a cylindrical shape, a first container head formed at one end of the container body, and a second container head formed at another end of the container body, wherein the container body is welded at a container body weld seam which extends between one end and the other end of the container body and in a direction perpendicular to a circumferential direction of the cylindrical shape, wherein the container body and the first container head are welded together at a first container head weld, wherein the container body and the second container head are welded together at a second container head weld seam, and wherein the container body weld, the first container body weld and the second container body weld each exhibit a pitting corrosion potential of 0.3 V against Ag / AgCl or more. [8] Hot water storage tank according to claim 7, wherein the tank body weld, the first tank head weld and the second tank head weld are in a pickled state, and The container body weld, the first container body weld and the second container body weld each have a pitting corrosion potential of at least 0.3 V against Ag / AgCl. [9] Hot water storage tank according to one of claims 3 to 8, wherein a gap of more than 100 µm is provided at the main body weld seam between the main body and the pipe connection section. [10] Hot water storage tank according to any one of claims 3 to 9, further comprising a leg section formed on the main body, wherein the leg part is made of ferritic stainless steel, austenitic stainless steel or duplex stainless steel, which is a mixture of ferritic stainless steel and austenitic stainless steel. [11] Method for manufacturing a hot water storage tank, the method comprising: Forming a main body of the hot water storage tank, which has a vessel body with a cylindrical shape, using a wound material of ferritic stainless steel or a wound material of duplex stainless steel, which is a mixture of ferritic stainless steel and austenitic stainless steel, wherein the ferritic stainless steel and the duplex stainless steel each have a pitting corrosion potential of more than or equal to 0.3 V against Ag / AgCl; and Welding a pipe connection section to the main body, wherein the pipe connection section is made of ferritic stainless steel, austenitic stainless steel or stainless duplex steel, which is a mixture of ferritic stainless steel and austenitic stainless steel, wherein the ferritic stainless steel, the austenitic stainless steel and the stainless duplex steel each have a pitting corrosion potential of more than or equal to 0.3 V against Ag / AgCl. [12] Method according to claim 11 for manufacturing a hot water storage tank, wherein the method comprises: Pickling of a container body weld seam of the container body, which is a weld seam to which the wound material is welded, wherein the container body weld seam has a pitting corrosion potential of greater than or equal to 0.3 V against Ag / AgCl; Pickling of a first container head weld between the container body and a first container head formed at one end of the container body, wherein the first container head weld has a pitting corrosion potential of more than or equal to 0.3 V against Ag / AgCl; and Pickling of a second container head weld between the container body and a second container head formed at a different end of the container body, wherein the second container head weld has a pitting corrosion potential of more than or equal to 0.3 V against Ag / AgCl. [13] Water heater comprising the following features: the hot water storage tank according to any one of claims 1 to 10; a circulating water circuit in which water circulates as a heat transfer medium, and a tap water circuit in which tap water circulates as a heat transfer medium.

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