JP5433461B2 - Heat exchanger - Google Patents

Description

  TECHNICAL FIELD The present invention relates to a heat exchanger, particularly a heat exchanger used at a high temperature for a fluid containing a high concentration of sulfur, and a heat exchanger suitable for use as a heater for heavy oil containing a high concentration of sulfur. It is about.

2. Description of the Related Art Conventionally, a multi-tube heat exchanger having a heat transfer tube whose end is fixed to a tube plate and exchanging heat between a fluid flowing inside the heat transfer tube and a fluid flowing outside the heat transfer tube is known. It has been. Multi-tube heat exchangers are used in various fields because they can provide a large heat transfer area in a small space, can be designed to reduce the pressure loss of the fluid, and can be adapted to a wide range of temperature and pressure. Yes.
Examples of a multi-tube heat exchanger include a fixed tube plate type in which both ends of a straight tube are fixed to a tube plate, a U tube type in which both ends of a U-shaped bent tube are fixed to the same tube plate, A floating head type or the like in which one head is movable in the axial direction of the tube with respect to the other head is known.

  As a multi-tube heat exchanger, for example, Patent Document 1 includes a plurality of baffle plates (baffle plates) spaced across a plurality of heat transfer tubes mounted in parallel between the tube plates and spaced loosely into the heat transfer tubes. A multi-tube heat exchanger is disclosed in which the baffle plate is fixed to a baffle plate support rod extending in parallel with the heat transfer tube, and the support rod is supported so as to be movable and adjustable in the axial direction. Has been.

  Such a multi-tube heat exchanger may be used as a fuel heater for heavy oil such as VR. Note that VR is a vacuum distillation residue obtained by refining main fuels such as gasoline and heavy oil.

  Since heavy oil such as VR contains sulfur, when a multi-tube heat exchanger is used as a fuel heater for heavy oil such as VR, high-temperature sulfidation corrosion due to sulfur in heavy oil In consideration of the above, as the material of the heat transfer tube (heating tube), chromium molybdenum steel such as STBA22 (1Cr-0.5Mo) standardized by the Japanese Industrial Standard (JIS) having high-temperature sulfidation corrosion resistance is used.

Japanese Patent Laid-Open No. 59-131891

  However, in recent years, conventional heavy oil such as VR, such as petroleum residue (hereinafter referred to as SDA pitch) generated when extracting the raw material of light oil fraction such as kerosene and light oil from heavy oil fraction such as asphalt, etc. Heavy oil, which has higher viscosity than oil, is used as boiler fuel in, for example, thermal power plants. At that time, it is required to use a multi-tube heat exchanger as a fuel heater for heavy oil. Yes.

  Heavy oil such as SDA pitch is heated by a fuel heater for heavy oil, and then sprayed on a boiler by a burner and is sown by a boiler. Therefore, considering sprayability and combustibility when sprayed on a boiler with a burner and burned with a boiler, heavy oil such as SDA pitch is heated to a higher temperature than conventional heavy oil with a fuel heater for heavy oil. It is necessary to heat and reduce the viscosity to an appropriate value. Further, it is known that heavy oil such as SDA pitch has a higher sulfur concentration than conventional heavy oil.

  Therefore, for heavy oil such as SDA pitch, when a multi-tube heat exchanger is used as a fuel heater for heavy oil, it heats heavy oil at a higher temperature than before and a higher sulfur concentration than before. It will be. Therefore, in a portion where the heater and the heavy oil such as the SDA pitch come into contact with each other, an environment in which high-temperature sulfidation corrosion is more likely to occur than in the past.

Therefore, it is conceivable to use stainless steel as a countermeasure against the high temperature sulfide corrosion due to high concentration sulfur.
However, since heavy oil such as SDA pitch contains chlorine and water is expected to be mixed, austenitic stainless steel (such as SUS304 in JIS standard) causes stress corrosion cracking, so it is often used as a heavy oil fuel heater. It cannot be applied as a material for tubular heat exchangers.

Therefore, it is conceivable to use ferritic stainless steel (SUS410S or the like) as a special material having both high-temperature sulfidation corrosion resistance and stress corrosion cracking resistance.
Since the heater is a pressure vessel, for example, when it is used in a boiler for a thermal power plant, it is necessary to weld a portion requiring strength welding by a welding method defined in the Electricity Business Act. However, the fact that ferritic stainless steel is a special material that is not normally used for pressure vessels, there are almost no welding contractors having this welding method.
When acquiring the welding method, it is necessary to obtain the certification specified in the Electricity Business Act after examining and verifying the validity of the method, and in the construction period of the heater Inevitably becomes a bottleneck. In particular, when a plurality of heaters are produced or when the production deadline is short, the welding work becomes a bottleneck, and there is a possibility that the production time will not be met.

  In order to solve the above problems, in the present invention, in a heat exchanger used for heating a fluid containing a high concentration of sulfur such as heavy oil, it has high-temperature sulfidation corrosion resistance and stress corrosion cracking resistance, and It aims at providing the heat exchanger which can be manufactured without using the special welding construction method prescribed | regulated to the electricity business law applied to a special material.

In order to solve the above problems, in the first invention (claim 1),
In a heat exchanger used for heat exchange of a fluid containing sulfur,
The heat exchanger includes a body through which the fluid flows, a tube plate provided at an end portion of the body, an end portion fixed to the tube plate and disposed in the body, and a heating medium. A multi-tube heat exchanger having a heating tube that circulates,
The fuselage and the tube sheet are made of clad steel made of carbon steel as a base material and clad with ferritic stainless steel, and the heating tube is made of high Cr-Ni steel or ferritic stainless steel. ,
The body is configured by joining a plurality of parts constituting the body by welding,
Between the said parts, while carbon steel of clad steel is welded, the surface of this carbon steel weld part is build-up welded using a ferritic stainless steel, It is characterized by the above-mentioned.
In the second invention (Claim 6),
In a heat exchanger used for heat exchange of a fluid containing sulfur,
The parts that require strength welding related to pressure vessels in the Electricity Business Law use clad steel clad with ferritic stainless steel with carbon steel as the base material,
The part that does not require the strength welding and is in contact with the fluid is formed using high Cr-Ni steel or ferritic stainless steel,
As for the welded portion in the portion requiring the strength welding, the carbon steel of the clad steel is welded by the strength welding related to the pressure vessel in the electric utility method, and the surface of the carbon steel welded portion is entirely made of ferritic stainless steel. It is characterized by being overlay welded.

  By using clad steel whose base material is carbon steel and whose surface material is ferritic stainless steel as a material for parts requiring strength welding for pressure vessels in the Electric Power Business Law, heavy oil, etc. Since the contact portion with the fluid containing sulfur is ferritic stainless steel, high-temperature sulfidation corrosion resistance and stress corrosion cracking resistance can be ensured. In addition, since the base material is carbon steel and not a special material, even if it is a part that requires strength welding related to the pressure vessel in the Electricity Business Law, it is usual in the welding method of carbon steel that the welder has Can be welded. In addition, since the surface material is treated as a corrosion allowance and the welded portion is not strength welding, a special welding method defined in the Electricity Business Law is not required.

  By using high Cr-Ni steel or ferritic stainless steel as the material of the part that does not require the strength welding and is in contact with the fluid such as heavy oil, high temperature sulfidation corrosion resistance and stress corrosion resistance Breakability can be secured.

  The heat exchanger includes a body through which the fluid flows, a tube plate provided at an end of the body, an end fixed to the tube sheet, and a heat exchanger disposed in the body. A multi-tube heat exchanger having a heating tube through which a medium flows, wherein the body and the tube plate are formed of clad steel in which carbon steel is used as a base material and ferritic stainless steel is clad, and the heating tube is It is good to form using high Cr-Ni steel or ferritic stainless steel.

  Thereby, the present invention can be applied to a multitubular heat exchanger having an advantage that a large heat transfer area can be obtained in a small space. For a multi-tube heat exchanger, the fuselage and the tube sheet correspond to a part that requires strength welding related to the pressure vessel in the Electric Power Business Act, and therefore are formed of the clad steel. Since it does not correspond to the site | part which requires the strength welding regarding a pressure vessel, and in order to contact the said fluids, such as heavy oil, it forms using high Cr-Ni steel or a ferritic stainless steel.

The body has an outlet nozzle at an outlet portion of the fluid flowing through the inside, and the outlet nozzle is formed of a carbon forged product, and the inner surface through which the fluid flows is entirely made of ferritic stainless steel. It is good to be overlay welding.
About the said exit nozzle, the high temperature heavy oil after a heating passes the inside. Therefore, for the outlet nozzle, the main body is a forged carbon steel, and the inner surface through which the fluid such as heavy oil passes is subjected to overlay welding using ferritic stainless steel, so that heavy oil, etc. Since the inner surface in contact with the fluid is made entirely of ferritic stainless steel, high-temperature sulfidation corrosion resistance and stress corrosion cracking resistance can be ensured.
Further, when the temperature of the heavy oil flowing into the heater is high, it is preferable that the inner surface of the inlet nozzle is welded with ferritic stainless steel as in the case of the outlet nozzle.

The body may include a plurality of baffle plates that partition the axial direction of the body in parallel, and the baffle plates may be formed using high Cr-Ni steel or ferritic stainless steel.
Heat exchange efficiency can be improved by providing the baffle plate. In addition, the baffle plate does not correspond to a portion requiring strength welding related to the pressure vessel in the Electric Power Business Act and is made of high Cr-Ni steel or ferritic stainless steel because it contacts heavy oil. Therefore, high-temperature sulfidation corrosion resistance and stress corrosion cracking resistance can be ensured.

In addition, a tie rod that supports the baffle plate and a spacer that determines a distance between the baffle plates, and the tie rod and the spacer are formed using high Cr-Ni steel or ferritic stainless steel. Good.
Neither the tie rods nor the spacers correspond to parts requiring strength welding for pressure vessels in the Electric Power Business Law, and contact with heavy oil, so use high Cr-Ni steel or ferritic stainless steel. By forming it, high-temperature sulfidation corrosion resistance and stress corrosion cracking resistance can be ensured.

The tie rod and spacer may be formed using the same material as the heating tube.
Thereby, the thermal expansion coefficients of the tie rod and spacer and the heating tube are the same, and it is possible to prevent the function of the heating tube, tie rod or spacer from being impaired by the thermal expansion of the heating tube, tie rod or spacer due to heat exchange.

Moreover, the said fuselage | body is comprised from a some part, and the carbon steel welding part surface between the said parts is good to be build-up welded using ferritic stainless steel.
Thus, even when the multi-tube heat exchanger has a large body and it is difficult to manufacture it as an integral body, it is possible to cope with it. In addition, since the body is formed of the clad steel, a special welding method defined in the Electric Power Business Act applied to special materials at the time of overlay welding is not required. Furthermore, high temperature sulfidation corrosion resistance and stress corrosion cracking resistance can be ensured for welded parts by overlay welding using ferritic stainless steel.

  According to the present invention, a heat exchanger used for heating a fluid containing a high concentration of sulfur, such as heavy oil, has high-temperature sulfidation corrosion resistance and stress corrosion cracking resistance, and is applied to a special material. It is possible to provide a heat exchanger that can be manufactured without using a special welding method defined in the Electric Business Law.

It is a whole lineblock diagram showing the U tube type heat exchanger concerning an example. It is a block diagram which shows the welding part vicinity of the heating pipe and tube sheet which concern on an Example. It is a side view which shows the U tube type heat exchanger which concerns on an Example. It is the schematic which shows the welding seam of the trunk | drum which concerns on an Example.

  Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention unless otherwise specified, but are merely illustrative examples. Not too much.

FIG. 1 is an overall configuration diagram illustrating a U-tube heat exchanger according to an embodiment.
A U-tube heat exchanger 1 shown in FIG. 1 is a horizontal U-tube heat exchanger.
First, the outline of the configuration and operation of the heat exchanger according to the present invention will be described with reference to FIG.

  The body 2 constituting the U-tube type heat exchanger 1 is horizontally arranged, one end side is closed by the end plate 4, and the other end side is fixed to the tube plate 6. The tube plate 6 and the body 2 form a heat exchange chamber 8 in which heat exchange is performed inside the body. Further, an end plate 10 is provided on the opposite side of the tube plate 6 from the body 2, and an inlet chamber 14 and a high temperature fluid outlet for high-temperature fluid such as steam partitioned by the partition plate 12 between the end plate 10 and the tube plate 6. A chamber 16 is formed, and the hot fluid inlet chamber 14 and the hot fluid outlet chamber 16 are provided with a hot fluid inlet nozzle 18 and a hot fluid outlet nozzle 20, respectively.

  A heating tube 22 bent in a U-shape is provided in the heat exchange chamber 8, and both ends of the heating tube 22 are fixed to the same tube plate 6. At this time, the heating tube 22 is fixed to the tube plate 6 so that the inside of the heating tube 22 is in communication with the inside of the high-temperature fluid inlet chamber 14 and the inside of the high-temperature fluid outlet chamber 16.

  In addition, a plurality of baffle plates 24 for partitioning the axial direction of the body in parallel are provided in the heat exchange chamber 8, and the plurality of baffle plates 24 are supported on the tube plate 6 side via tie rods as support members, respectively. Yes. The baffle plate 24 is provided to improve heat exchange efficiency. Spacers are inserted between the baffle plates 24. The spacer is inserted between the baffle plates 24 to determine the distance between the baffle plates 24.

An inlet nozzle 26 for heavy oil containing high-concentration sulfur such as SDA pitch to be heated is provided at the lower end position of the heat exchange chamber 8, and the heated heavy oil is provided at the upper end position. The outlet nozzle 28 is provided.
Reference numeral 30 is a support leg, and 32 is a relief valve nozzle.

In the above configuration, a high-temperature fluid such as steam is introduced into the U-shaped heating pipe 22 through the high-temperature fluid inlet nozzle 18 and the high-temperature fluid inlet chamber 14, and a heavy oil such as SDA pitch is introduced from the heavy oil inlet nozzle 26. A quality oil is introduced into the heat exchange material 8.
Thereby, the heavy oil in the heat exchange chamber 8 and the high-temperature fluid in the heating pipe 22 are heat-exchanged, and the heavy oil heated by the heat exchange is led out from the outlet nozzle 28 and cooled. Steam is drained and discharged from the hot fluid outlet nozzle 20 through the hot fluid outlet chamber 16.

  The material which forms each component in the U tube type heat exchanger 1 of such a structure and operation | movement is demonstrated.

(1) About the heating pipe 22 Although the inside of the heating pipe 22 is not in contact with heavy oil through which a high-temperature fluid such as steam flows, the outside of the heating pipe 22 is located in the heat exchange chamber 8 where heavy oil exists. Contact heavy oil. In addition, as a welded portion with other parts, there is a welded portion with the tube sheet 6, but this portion is not strength welding but seal welding. Therefore, regardless of the material of the heating tube 22, a special welding method defined in the Electric Power Business Law applied to strength welding is not required, and welding by pipe expansion seal welding is possible.

Accordingly, regarding the material of the heating tube 22, high Cr-Ni steel (such as NCF825 (22Cr-42Ni) standardized by JIS) or ferritic stainless steel considering high-temperature sulfidation corrosion resistance and stress corrosion cracking resistance. (SUS410S (13Cr) standardized by JIS) is used. By using high Cr—Ni steel or ferritic stainless steel as the material of the heating tube 22, the high-temperature sulfidation corrosion resistance and stress corrosion cracking resistance of the heating tube 22 can be ensured.
In addition, when high Cr-Ni steel is used, if Cr-Ni steel containing 19.5 to 23.5% Cr and 38.0 to 46.0% Ni is used, heavy oil such as SDA pitch is also used. High temperature sulfidation corrosion resistance and stress corrosion cracking resistance can be ensured.

A welded portion between the heating tube 22 and the tube sheet 6 will be described with reference to FIG.
FIG. 2 is a configuration diagram showing the vicinity of a welded portion between the heating tube 22 and the tube sheet 6 according to the embodiment, and corresponds to an enlarged view of a portion C in FIG. In FIG. 2, 34 is the above-mentioned tie rod, and 36 is the above-mentioned spacer.
The heating tube 22 has a tube expansion portion 38 at a welded portion with the tube plate 6, and a tip B portion thereof is joined to the tube plate 6 by welding by seal welding.

(2) Tube plate The tube plate 6 is in contact with heavy oil on the heat exchange chamber 8 side, and corresponds to a part that requires strength welding related to the pressure vessel in the Electric Power Business Act. In the case of a special material specified in the Business Law, a special welding method specified in the Electricity Business Law applied to the special material is required.

  Therefore, the tube plate 6 is a clad steel whose base material is carbon steel (for example, SFVAF11A standardized by JIS) and whose surface material is ferritic stainless steel (for example, SUS410S standardized by JIS). At this time, the tube sheet 6 is manufactured and arranged so that the surface material comes into contact with the heavy oil.

  Since the base material is carbon steel and the surface material is clad steel, which is ferritic stainless steel, the contact part with heavy oil is ferritic stainless steel. In addition, it is possible to ensure resistance to stress corrosion cracking, and because the base material is carbon steel, it does not correspond to the special material specified in the Electricity Business Law, and the part that requires strength welding related to the pressure vessel in the Electricity Business Law Even so, it does not require a special welding method specified in the Electricity Business Act applicable to special materials, so it is possible to perform normal welding with the carbon steel welding method possessed by the welder. .

(3) Fuselage The fuselage 2 is in contact with heavy oil on the inside, that is, the heat exchange chamber 8 side, and corresponds to a part that requires strength welding related to the pressure vessel in the Electric Power Business Act. The material of the fuselage 2 is a special material. In this case, a special welding method specified in the Electricity Business Law applied to special materials is required.

  Therefore, for the body 2, similarly to the tube plate 6, the base material is carbon steel (for example, SB480 standardized by JIS) and the surface material is ferritic stainless steel (for example, SUS410S standardized by JIS). Clad steel. At this time, the body 2 is manufactured so that the surface material is in contact with the heavy oil, that is, the inside is the surface material.

  As the material of the fuselage 2, the base material is carbon steel and the surface material is clad steel, which is ferritic stainless steel, and the contact portion with heavy oil is ferritic stainless steel. Because it can ensure stress corrosion cracking resistance and the base material is carbon steel, special welding work applied to special materials even in parts that require strength welding related to pressure vessels in the Electricity Business Act Since the method is not required, a normal welding process by the welding method of carbon steel possessed by the welder is possible.

Moreover, the trunk | drum 2 is comprised by joining several components.
FIG. 3 is a side view showing the U-tube heat exchanger according to the embodiment.
As shown in FIG. 3, the body 2 constituting the heat exchanger 1 is composed of four portions 2a, 2b, 2c, and 2d. In the present embodiment, the body 2 is composed of four parts, but may be composed of three or less parts or five or more parts depending on the size of the heat exchanger.

The parts 2a, 2b, 2c and 2d constituting the body 2 are joined by welding.
A welded portion of the portions 2a, 2b, 2c, and 2d constituting the body 2 will be described with reference to FIG.

FIG. 4 is a schematic view showing a weld seam of the fuselage according to the embodiment, and corresponds to an enlarged schematic view of a portion A in FIG. 3.
The portion 2b constituting the body 2 is formed of clad steel made of carbon steel 201b as a base material and ferritic stainless steel 202b as a surface material. Similarly, a portion 2c constituting the body 2 is formed of clad steel made of carbon steel 201c as a base material and ferritic stainless steel 202c as a surface material.

  The parts 2b and 2c constituting the body 2 are joined by overlay welding using SUS430, which is a ferritic stainless steel. The same applies between the parts 2a and 2b constituting the body 2 and between 2c and 2d.

  Since the clad steel, whose base material is carbon steel and whose surface material is ferritic stainless steel, is adopted as the material of the fuselage 2, the electric business method in which welding between the parts constituting the fuselage 2 is also applied to special materials The special welding construction method prescribed in Section 1 is not required, and the normal welding process by the carbon steel welding construction method possessed by the welder is possible. Moreover, since overlay welding is not strength welding, it does not require a special welding method applied to special materials specified in the Electricity Business Law, and normal overlay welding is possible.

(4) Heavy oil outlet nozzle The heavy oil outlet nozzle 28 passes through the inside thereof.
Therefore, for the heavy oil outlet nozzle 28, the main body is a forged carbon steel (for example, SF490A standardized by JIS), and the inner surface through which the heavy oil passes is ferritic stainless steel (for example, SUS430 standardized by JIS). Etc.) is used to carry out overall overlay welding. Thereby, since the inner surface which contacts heavy oil becomes a whole surface ferritic stainless steel, high temperature sulfidation corrosion resistance and stress corrosion cracking resistance can be secured.

(5) Baffle plate Since the baffle plate 24 exists in the heat exchange chamber 8, it contacts with heavy oil. Moreover, since no welded part is required, the welding method defined in the Electricity Business Law is not required regardless of the material.

  Therefore, the baffle plate 24 is made of high Cr-Ni steel (such as NCF825 (22Cr-42Ni) standardized by JIS) or ferritic stainless steel (JIS) in consideration of high-temperature sulfidation corrosion resistance and stress corrosion cracking resistance. SUS410S (13Cr) or the like standardized by By using high Cr—Ni steel or ferritic stainless steel as the material of the baffle plate 24, the baffle plate 24 can be secured with high-temperature sulfidation corrosion resistance and stress corrosion cracking resistance.

(6) Tie rods and spacers Since the tie rods 34 and the spacers 36 are present in the heat exchange chamber 8, they are in contact with heavy oil. Moreover, since no welded part is required, the welding method defined in the Electricity Business Law is not required regardless of the material.

  Therefore, the tie rod 34 and the spacer 36 are made of high Cr-Ni steel (such as NCF825 (22Cr-42Ni) standardized by JIS) or ferritic stainless steel (high temperature sulfidation corrosion resistance and stress corrosion cracking resistance). SUS410S (13Cr) standardized by JIS) is used as a material. By using high Cr—Ni steel or ferritic stainless steel as the material of the tie rod 34 and the spacer 36, the high temperature sulfidation corrosion resistance and the stress corrosion cracking resistance can be secured for the tie rod 34 and the spacer 36.

  Furthermore, the tie rod 34 and the spacer 36 are preferably formed of the same material as the heating tube 22. Thereby, the thermal expansion coefficients of the tie rod 34 and the spacer 36 and the heating tube 22 are the same, and the function of the heating tube 22, the tie rod 34 or the spacer 36 is prevented from being impaired by the thermal expansion of the heating tube, tie rod or spacer due to heat exchange. it can.

  The present invention relates to a heat exchanger used for heating a fluid containing a high concentration of sulfur, such as heavy oil, and has high-temperature sulfidation corrosion resistance and stress corrosion cracking resistance and is applied to a special material. It can be used as a heat exchanger that can be manufactured without using a special welding method defined in the Business Law.

1 Heat Exchanger 2 Body 6 Tube Plate 22 Heating Tube 24 Baffle Plate 26 Heavy Oil Inlet Nozzle 28 Heavy Oil Outlet Nozzle 34 Tie Rod 36 Spacer

Claims (6)

In a heat exchanger used for heat exchange of a fluid containing sulfur,
The heat exchanger includes a body through which the fluid flows, a tube plate provided at an end portion of the body, an end portion fixed to the tube plate and disposed in the body, and a heating medium. A multi-tube heat exchanger having a heating tube that circulates,
The fuselage and the tube sheet are made of clad steel made of carbon steel as a base material and clad with ferritic stainless steel, and the heating tube is made of high Cr-Ni steel or ferritic stainless steel. ,
The body is configured by joining a plurality of parts constituting the body by welding,
Between the said parts, while the carbon steel of clad steel is welded, the surface of this carbon steel weld part is build-up welded using ferritic stainless steel, The heat exchanger characterized by the above-mentioned. The fuselage has an outlet nozzle at the outlet of the fluid flowing through the interior,
2. The heat exchanger according to claim 1, wherein the outlet nozzle is formed of a carbon forged product, and an internal surface through which the fluid flows is welded over the entire surface with ferritic stainless steel. A plurality of baffle plates in the body to partition the axial direction of the body in parallel;
The heat exchanger according to claim 1 or 2, wherein the baffle plate is formed using high Cr-Ni steel or ferritic stainless steel. A tie rod that supports the baffle plate, and a spacer that determines a distance between the baffle plates,
4. The heat exchanger according to claim 3, wherein the tie rod and the spacer are formed using high Cr-Ni steel or ferritic stainless steel.   The heat exchanger according to claim 4, wherein the tie rod and the spacer are formed using the same material as the heating tube. In a heat exchanger used for heat exchange of a fluid containing sulfur,
The parts that require strength welding related to pressure vessels in the Electricity Business Law use clad steel clad with ferritic stainless steel with carbon steel as the base material,
The part that does not require the strength welding and is in contact with the fluid is formed using high Cr-Ni steel or ferritic stainless steel,
As for the welded portion in the portion requiring the strength welding, the carbon steel of the clad steel is welded by the strength welding related to the pressure vessel in the electric utility method , and the surface of the carbon steel welded portion is entirely made of ferritic stainless steel . A heat exchanger characterized by overlay welding.

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