JP2012255208A - Method of using powder metallurgy fabrication for manufacturing integral header and tube replacement section - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing integral header and tube replacement sections that is cost-effective, requires shorter lead-times, and can eliminate a number of attachment welds.SOLUTION: The method of manufacturing the integral header and tube replacement sections includes the steps of: providing a reverse mold of a head and tube replacement section; providing atomized steel powder; and filling the reverse mold with the atomized steel powder. The method further includes the step of inserting the mold into a hot isostatic processing (HIP) furnace to consolidate and sinter the powder into the shape of the head and tube replacement section.

Description

This application claims priority from US provisional application 61/499505 (filing date: May 24, 2011).
The present application relates to a method for manufacturing an integral header and tube replacement part.

  Many fossil fuel plants have been built for continuous load operation and now important cycle operations are beginning to emerge. Heavy loads on components such as headers and hot pipes are generally accompanied by cyclical operations that often result in component degradation, cracking and failure. Furthermore, cycling can cause thermal gradients at various locations along the length of the header, which can lead to overheating and damage to these locations. When damage occurs, you are faced with the choice of replacing the entire header or removing a short section of the header (usually about 3 feet long (about 91 cm) to 8 feet long (about 244 cm)).

  Carbon steel or low alloy steel headers and stainless steel headers are typically made using either roll weld (R & W) plate portions or extruded pipe portions. A penetration (or hole) is machined into the header with a specific orientation along a specific length around the diameter of the header, after which a stub tube is connected to the member. The stub tube is connected to the header by various welding methods selected by the manufacturer. Because of the stub shape (or placement) relative to the header to be welded, welding is often done manually (manual) and is very difficult to inspect. Therefore, welding failure and pipe crevice cracks between penetrations are common failure mechanisms.

  Obtaining replacement parts often requires a long lead time of 12 months or more, resulting in manufacturers shutting down the plant or losing revenue until replacement parts or new headers are available.

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  These disadvantages of the prior art are overcome by the present invention which provides a method for manufacturing an integral header and tube replacement. This method provides a cost-effective alternative to the traditional manufacturing process used to manufacture header replacement parts, allows for short lead times and eliminates many mounting welds (many tubes for the header). Can improve the overall quality of the header replacement part.

  According to one aspect of the present invention, an integrated header and tube replacement portion manufacturing method provides a reverse mold of the header and tube replacement portion, and provides atomized steel powder. Step, filling the reverse mold with atomized steel powder, inserting the mold into a hot isostatic press (HIP) furnace, solidifying and sintering the powder into the shape of the header and tube replacement part Steps.

  The technical subject matter regarded as the invention is best understood by referring to the following description in conjunction with the accompanying drawings.

FIG. 1 shows an integrated header and tube fitting according to one embodiment of the present invention. FIG. 2 is a flowchart of a method of manufacturing an integrated header / pipe attachment.

  Detailed Description of the Invention

  Referring to the drawings, an integrated header and tube mounting portion formed in accordance with one embodiment of the present invention is indicated by "10" in FIG.

  The present invention provides an alternative to conventional manufacturing processes that provide even shorter lead times and improved overall quality of replacement parts. This is to make a replacement part, which is an approximate molded body with a stub tube manufactured as part of the overall PM / HIP, so that powder metallurgy (PM) and hot isostatic pressure (HIP) Use a combination. No welding is required to connect the stub tube to the header. This process eliminates troublesome weld joints and results in a one-piece header assembly with significantly increased life. This technology can be applied to headers used in petroleum plants that handle headers and header replacements, HRSG plants, and other uses (chemical, petrochemical, pulp and paper).

  HIP / PM technology eliminates roll welding or extrusion manufacturing steps because the header portion can be manufactured as one complete system. More importantly, since the stub tube and header are manufactured in one continuous PM / HIP process, the step of joining the stub tube to the header is eliminated. Referring to FIG. 2, the process involves the design of an exact duplicate of the damaged header portion (block 11), including the short tube portion of FIG. 1 derived from the header diagram. Next, a reverse mold (ie, a forming container) of the header portion is formed by two halves (or more divisions) from a carbon steel material that establishes the final shape of the header portion (block 12). The mold is assembled and filled with atomized low alloy steel powder to fill the mold (block 13). The mold is then evacuated using a vacuum to remove potential air pockets and sealed by welding (block 14).

  The entire assembly is then inserted into a HIP furnace, subjected to high temperature and pressure (usually under an inert argon atmosphere), and the powder is consolidated and sintered to the final shape of the header (block 16). The assembly is maintained at the sintering temperature for a set time and then cooled to room temperature (block 17 and block 18). Additional heat treatment will be required to normalize and temper the header (block 19). This final heat treatment is performed inside or outside the mold. When the header returns to room temperature, the mold must be removed (block 20).

  At this point, the header is in an approximate shape (almost final shape). Some cleaning and polishing will be required to remove the residue to obtain the final (finished) surface (block 21). At this point, two additional steps are also required. That is, (1) boring (piercing) the stub tube to create an internal through hole (block 22) and (2) chamfering the inner diameter of the cavity region (block 23). These steps can be easily accomplished using CNC milling / drilling.

  This makes the stub tube an integral part of the header and eliminates the need for a weld transition between the header and the stub tube, which was a major problem in the past. The removal of the weld eliminates thermal expansion problems, metal fatigue and creep damage problems, and often the wedging (wedge cracks) associated with stub tube weld fittings. Because it is an integral stub tube, only welding to attach the stub tube to an existing boiler tube is required, greatly reducing the possibility of future damage. Since the shape is carefully managed, a repeatable smooth transition between the stub and header can be achieved, reducing the possibility of stress concentration formation.

  The manufacturing method of the integrated header and pipe replacement part was explained. While specific embodiments of the present invention have been described, it will be apparent to those skilled in the art that various modifications can be made without departing from the spirit and scope of the invention. Accordingly, the foregoing description of the preferred embodiment of the invention and the best mode for carrying out the invention are exemplary and are not intended to limit the invention.

Claims (12)

A method of manufacturing an integrated header and tube replacement part,
(A) providing a reverse mold of the header and tube replacement part;
(B) providing a atomized steel powder;
(C) filling the reverse mold with the atomized steel powder;
(D) inserting the mold into a hot isostatic pressing (HIP) furnace, solidifying and sintering the powder to form a header and tube replacement part;
A method characterized by comprising.   The method of claim 1, further comprising the step of evacuating the mold to eliminate air pockets.   The method of claim 2, further comprising sealing the mold to maintain a vacuum.   The method of claim 1, further comprising the step of bringing the HIP furnace to high pressure and high temperature to consolidate and sinter the powder.   5. The method of claim 4, wherein the HIP furnace is brought to a high temperature and pressure under an inert gas atmosphere.   5. The method of claim 4, further comprising maintaining the HIP furnace at a high temperature and pressure for a predetermined time.   The method of claim 1, further comprising cooling the mold and the sintered powder to room temperature.   The method of claim 1, further comprising heat treating the header and tube replacement portion.   The method of claim 1, further comprising finishing the header and tube replacement portion to a final shape.   The method of claim 9, wherein the finishing step includes polishing the outer surface of the header and tube replacement portion to remove residue and obtain a final surface.   The method of claim 9, wherein the finishing step includes drilling a stub tube in the header and tube replacement portion to form an inner penetration.   The method of claim 9, wherein the finishing step includes chamfering the inside of the cavity region of the header and tube replacement portion.

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