KR20120131118A - Method of manufacturing a weld-free apparatus for connection of dissimilar metals using functionally graded compositionally control powder metallurgy and hot isostatic processing methods - Google Patents

Abstract

PURPOSE: A method for manufacturing a weld-free apparatus for connecting different metal using functionally graded composition control powder metallurgy and hot isostatic processing methods is provided to enable flexible transition between tube thicknesses. CONSTITUTION: A method for manufacturing a weld-free apparatus for connecting different metal comprises the steps of: preparing a mold for reproducing a reverse mold, injecting first metal powder into a first portion of the mold, injecting second metal powder into a second portion of the mold, injecting third metal powder into a third portion of the mold, forming a transition portion out of the second metal powder between the first and third metal powder, forming a vacuum in the mold and sealing the mold for maintaining the vacuum condition, locating the mold in a High-Temperature Isostatic Pressing(HIP) furnace to melt and integrate the first through third metal powder, and cooling the mold to room temperature and removing a molded apparatus from the mold.

Description

METHOD OF MANUFACTURING A WELD-FREE APPARATUS FOR CONNECTION OF DISSIMILAR METALS USING FUNCTIONALLY GRADED COMPOSITIONALLY CONTROL POWDER METALLURGY AND HOT ISOSTATIC PROCESSING METHODS}

The present invention claims the benefit of Provisional Application No. 61 / 489,501, filed May 24, 2011.

The present invention relates to a method of manufacturing a weld-free device for use in the connection of dissimilar metals, in particular to a method for providing a weldless tube Dutchman for use in the connection of dissimilar metals in a power plant environment.

Conventional thermal power plants use thousands of dissimilar metal tube welds (DMWs) across economizers, superheaters, and reheat assemblies. DMWs are used to provide transitions between carbon, chromium-molybdenum (CrMo), or creep strength reinforced ferrite (CSEF) steel tubes and austenitic stainless steel or nickel based tubes. This transition is necessary when certain parts of the boiler are exposed to higher operating and / or corrosive conditions. DMWs are generally performed using nickel-based weld filler metal that provides a coefficient of thermal expansion that lies between the two tube materials to be joined. This reduces the overall stress in the weld joint area while providing good weldability.

Unfortunately due to exposure to high temperatures, most of these DMWs joints have a limited 7 to 12 years until the creep strength is replaced due to carbon free zones or carbon activity gradients that result in the formation of harmful Type I or II carbides. Have a lifetime. One option used by OEMs and maintenance companies is to use "Dutchman" to eliminate the need to implement DMWs in the field. Dutchmen are usually about 12 inches (304.8 mm) long and are DMW tube sections made in a shovel facility. Dutchman also includes dissimilar tube alloys and nickel-based welds between these alloys. However, Dutchman can be manufactured under controllable shovel conditions and when it starts to be used, welders only produce "similar" welds: ferrite-to-ferrite or austenite-to-austenite (not DMWs). The difference is that it requires. Welders no longer need to form difficult DMWs in the field. However, even Dutchman welded on a high quality shovel, failure can still occur too early due to the difference in coefficient of thermal expansion.

Accordingly, there is a need for a method of providing a welding-free device for use in connection of dissimilar metals in a power plant environment.

These and other disadvantages of the prior art are solved by the present invention which provides a method of providing a non-welding device such as Dutchman for use in connecting dissimilar metals.

According to one aspect of the invention, a method of providing a welding-free device for use in the connection of dissimilar metals comprises the steps of providing a mold designed to duplicate a reverse mold of the device, providing a first metal powder and Introducing a first metal powder into a first portion of the mold, providing a second metal powder and introducing the second metal powder into a second portion of the mold, and providing a third metal powder and Introducing a third metal powder into a third portion of the mold. The second metal powder forms a transition portion between the first metal and the third metal powder. The method includes sealing the mold to introduce a vacuum into the mold and to maintain a vacuum, and to mold the mold to a high temperature isostatic pressing (HIP) furnace to melt and integrate the first, second and third metal powders. Positioning therein, and cooling the mold to room temperature and removing the device from the mold.

According to another aspect of the invention, a method of providing a non-welding device for use in connection of dissimilar metals comprises the steps of providing a mold designed to replicate the reverse mold of the device, and a low alloy ferrite steel composition atomized powder into the mold Introducing a series of atomized powders into the second portion of the mold to form a transition region between the ferritic steel composition and the austenitic stainless steel composition; Introducing a stainless steel composition atomized powder into a third portion of the mold, and melting and integrating the atomized powder at high temperature, high pressure in an inert atmosphere to form the device.

The subject matter regarded as the present invention can be best understood with reference to the following detailed description which is described in connection with the accompanying drawings.

1 shows a modified Dutchman showing the transition from 2-1 / 4CR low alloy steel to 304H / 347H stainless steel,
2 is a flowchart illustrating a method according to an embodiment of the present invention.

Referring to the drawings, a modified device, such as Dutchman, formed in accordance with an embodiment of the present invention is shown in FIG. 1 and is generally shown at 10.

The present invention completely removes the DMW. To form the modified Dutchman 10, a functionally sorted composition controlled powder metallurgical / hot isostatic molding (HIP) method is used. In this process, the composition of the Dutchman tube 10 is the ferrite tube composition (carbon-, CrMo, or CSEF) over the range of 1 to 3 inches (25.4 to 76.2 mm) of the Dutchman tube 10 12 inches (304.8 mm) long. Gradually transition from the steel) to the austenite SS composition. The gradual transition results in a smooth transition of the Dutchman tube 10 CTE from one alloy to another.

All important, carbon transfer problems (and accompanying loss of creep strength) often associated with DMWs are all eliminated and a flexible transition between tube thicknesses is provided. The modified Dutchman 10 is processed (manufactured) in a HIP furnace to achieve fusion and properties. Once manufactured, it can be used in the field in a manner similar to current Dutchmen.

In block 11, the process begins with a mold (container) that duplicates the reverse mold of the final tube dimensions. In block 12, carbon, low alloy, or CSEF steel composition atomized powder is introduced into approximately one half of the tube container (about -1 inch or about 25.4 mm). The transition for low alloy steel-to-austenite SS (usually formed from 2-1 / 4Cr-1Mo to 304H) requires a smooth transition from 2-1 / 4Cr to 18Cr SS. The powder is added to the container in block 13, starting at 5Cr and then in increments of 8Cr, 11Cr, and 15Cr. This occurs throughout the transition region of 2-3 inches (50.8-76.2 mm). The remainder of the container is filled in block 14 with 18 Cr SS atomized powder that matches the composition of the 304H or 347H SS tube alloy. In block 15, a vacuum enters the container and the container is sealed at one end.

Next, at block 16, the entire assembly is placed inside the HIP furnace and hot and pressurized in an inert (argon) atmosphere to melt and consolidate the powder. After being maintained under high temperature / high pressure for a given time, at block 17 the entire Dutchman assembly is removed from the HIP furnace and cooled to room temperature. In block 17, additional heat treatment steps may also be needed to normalize and temper the low alloy steel region of the tube. The final modified Dutchman assembly will require pickling, boring, and / or grinding to remove the outer container / canister at block 18. At this point, the modified Dutchman assembly is ready for final machining on either end before being used in the field.

The manufacturing process of 9Cr-to-18Cr (CSEF to austenitic SS) shows that at block 13, a transition occurs by 12Cr, 14Cr and 16Cr alloy powders in the transition region (2 to 3 inches or 50.8 to 76.2 mm). Except for the above, it is similar to the manufacturing process of the low alloy steel-to-austenite SS described above. Thus, the process proceeds from 9Cr to 18Cr in the final configuration before the modified Dutchman assembly is introduced into the HIP furnace.

Although the above description has been discussed with respect to specific metals, it should be understood that the invention is not limited to only the metals described above or combinations of the aforementioned metals or materials of particular grades. Rather, the present invention relates generally to the formation of devices that remove DMWs. Furthermore, while the foregoing description relates to the formation of Dutchman, it should be understood that Dutchman is used only as an example and that the foregoing methodology is applicable to the manufacture or formation of other devices or devices with respect to the effect of removing DMWs. I understand that you can.

Above, a method for providing a welding-free device for connecting dissimilar metals in a power plant environment has been described. While specific embodiments of the invention have been described, it will be apparent to those skilled in the art that various modifications of the invention can be made without departing from the spirit and scope of the invention. Accordingly, the foregoing descriptions of the preferred embodiments of the present invention and the preferred forms for carrying out the present invention are provided for purposes of illustration only and not for purposes of limitation.

Claims (17)

As a method of providing a welding-free device for use in connecting dissimilar metals,
(a) providing a mold designed to duplicate the reverse mold of the apparatus,
(b) providing a first metal powder and introducing the first metal powder into a first portion of the mold;
(c) providing a second metal powder and introducing the second metal powder into a second portion of the mold;
(d) providing a third metal powder and introducing the third metal powder into a third portion of the mold, wherein the second metal powder forms a transition between the first metal and the third metal powder, Steps,
(e) sealing the mold to introduce and maintain a vacuum in the mold,
(f) placing the mold inside a high temperature isostatic molding (HIP) furnace to melt and integrate the first, second and third metal powders, and
(g) cooling the mold to room temperature and removing the device from the mold,
A method of providing a welding-free device for use in connecting dissimilar metals.
The method of claim 1,
Wherein the first metal powder is a low alloy ferrite steel composition atomized powder,
A method of providing a welding-free device for use in connecting dissimilar metals.
The method of claim 1,
Wherein the third metal powder is an austenitic stainless steel composition atomized powder,
A method of providing a welding-free device for use in connecting dissimilar metals.
The method of claim 1,
The mold is maintained at high temperature and high pressure in an inert gas atmosphere in a HIP furnace,
A method of providing a welding-free device for use in connecting dissimilar metals.
The method of claim 1,
Further comprising heat-treating the device,
A method of providing a welding-free device for use in connecting dissimilar metals.
The method of claim 1,
Further comprising pickling, boring, and grinding steps for removing the mold from the device,
A method of providing a welding-free device for use in connecting dissimilar metals.
The method of claim 1,
Further machining the device to final dimensions,
A method of providing a welding-free device for use in connecting dissimilar metals.
As a method of providing a welding-free device for use in connecting dissimilar metals,
(a) providing a mold designed to duplicate the reverse mold of the apparatus,
(b) introducing a low alloy ferrite steel composition atomized powder into the first portion of the mold;
(c) gradually introducing a series of atomized powder into the second portion of the mold to form a transition region between the austenitic stainless steel composition and the ferritic steel composition;
(d) introducing an austenitic stainless steel composition atomized powder into a third portion of the mold, and
(e) melting and integrating said atomized powder at high temperature, high pressure in an inert gas atmosphere to form said device,
A method of providing a welding-free device for use in connecting dissimilar metals.
The method of claim 8,
Wherein the series of atomized powders forming the transition zone begins with a low alloyed steel powder and each series of atomized powders is increased to a high alloyed steel powder,
A method of providing a welding-free device for use in connecting dissimilar metals.
The method of claim 8,
The transition zone comprises four series of atomized powders, wherein the first atomized powder is a 5Cr steel powder, the second atomized powder is an 8Cr steel powder, the third atomized powder is an 11Cr steel powder, and The fourth atomized powder is a 15Cr steel powder,
A method of providing a welding-free device for use in connecting dissimilar metals.
11. The method of claim 10,
Wherein the ferritic steel composition atomized powder is 2-1 / 4Cr steel powder and the austenitic stainless steel composition atomized powder is 18Cr steel powder,
A method of providing a welding-free device for use in connecting dissimilar metals.
The method of claim 8,
The transition zone comprises three series of atomized powders, wherein the first atomized powder is a 12Cr steel powder, the second atomized powder is a 14Cr steel powder, and the third atomized powder is a 16Cr steel powder,
A method of providing a welding-free device for use in connecting dissimilar metals.
13. The method of claim 12,
Wherein the ferritic steel composition atomized powder is 9Cr steel powder and the austenitic stainless steel composition atomized powder is 18Cr steel powder,
A method of providing a welding-free device for use in connecting dissimilar metals.
The method of claim 8,
Wherein the first and third portions of the mold comprise about three quarters of the mold and the second portion of the mold comprises about one quarter of the mold
A method of providing a welding-free device for use in connecting dissimilar metals.
The method of claim 8,
Further comprising heat treating the device to normalize and temper the low alloy section of the device,
A method of providing a welding-free device for use in connecting dissimilar metals.
The method of claim 8,
Further comprising removing the mold from the device,
A method of providing a welding-free device for use in connecting dissimilar metals.
The method of claim 8,
Further comprising machining the device to final dimensions,
A method of providing a welding-free device for use in connecting dissimilar metals.

Images