JPH0567762B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION BACKGROUND OF THE INVENTION Field of the Invention This invention relates to the welding repair of high pressure steam turbine rotors, and in particular to the welding of 9Cr-1Mo alloy steel (ASTM
It concerns the repair of rotors by ring welding using rings made from A182, grade F91).

DESCRIPTION OF RELATED TECHNOLOGY Recent technological advances have greatly improved high pressure steam turbine equipment, and in particular have proposed improved rotor structures to minimize the tendency for deterioration during use. Some, especially older units currently in service, sometimes experience deterioration due to general wear, external cracking, and other forms of wear and tear. Such wear-out phenomena have become more common as current trends result in longer service life and improved quality rather than replacement with new units.

Particularly in high pressure steam turbine rotors of chromium-molybdenum-vanadium alloy steel (Cr-Mo-V alloy steel), severe cracks often occur in the blade fixing region. If the cracking is sometimes too severe, the vanes in a particular row must be permanently removed or replaced with vanes having a different vane fixation device. A more practical solution was to completely remove the cracked vane fixation area and replace it with a forged ring welded to the rotor. Such a ring has a width and diameter greater than that of the original rotor anchorage area in order to increase the cross-sectional area, allow the use of different types of blade anchorage areas, and reduce stress on the rotor anchorage area. Both dimensions generally had to be increased. This is similar to the conventional Cr-Mo-V
Welding of alloy steels was necessary as the welding process creates low strength, heat affected areas.

SUMMARY OF THE INVENTION The present invention provides a rotor repair method that avoids the above-described problems encountered in the past in repairing high pressure steam turbine rotors made of chromium-molybdenum-vanadium alloy steel (Cr-Mo-V alloy steel). In particular, the present invention provides a method for repairing damaged Cr −
A method for repairing a Mo-V high pressure steam turbine rotor is provided.

In its broadest form, the invention involves machining an area of said rotor that has been damaged to form a surface profile suitable for receiving a replacement vane retaining ring; 9Cr-1Mo alloy steel) and
A pair of approximately semicircular ring forged parts each having a pair of ends is prepared, and the pair of ends of one of the ring forged parts are placed close to the corresponding end of the other ring forged part. and are shaped complementary to the corresponding end of said other ring forging so as to form said replacement vane retaining ring when welded together; arranging the pair of ring forged parts adjacent to the machined area of the rotor such that the corresponding ends are joined complementary to each other; completing the replacement blade fixing ring; to weld the corresponding ends of the pair of ring forgings together using narrow gap metal arc welding and 9Cr-1Mo alloy steel weld metal; A method for repairing a high pressure turbine rotor by welding a replacement blade fixing ring is provided. In a more preferred form of the invention, the replacement ring is welded to the rotor using narrow gap submerged arc welding or narrow gap gas metal arc welding. In a further preferred form of the invention, the replacement ring is 9Cr-
Welded to the rotor using 1Mo alloy steel. In a further preferred form of the invention, welding the replacement ring to the rotor comprises welding the replacement ring to the replacement area from a first side of the replacement ring and then removing it from the opposite side of the replacement ring. and welding a replacement ring to the replacement area. In a particularly preferred method, after the replacement ring is welded to the replacement area from a first side thereof and before welding the replacement ring to the replacement area from the opposite side of the replacement ring, the repair area is , the interior of the welded first side is machined from its opposite side to ensure 100% joint penetration.

In yet another particular form of the invention, the semicircular ring forging of the joined replacement ring is formed by first cutting the forged ring into approximately two halves. Ru.

DESCRIPTION OF THE PREFERRED EMBODIMENTS As outlined above, the present invention
- Concerns an excellent method for repairing high-pressure steam turbine rows made of Mo-V alloy steel, in which rings made of 9Cr-1Mo steel are attached to the rotor to replace damaged blade fixing areas. Including welding. The method of this invention is
In particular, the Cr-Mo-V alloy steels are welded together to provide the repair area with a vane fixation area with sufficient base material strength to counter the turbine's design stress limits and to To provide a vane fixation area that exceeds the strength of the affected normal repair area.

In accordance with the present invention, a new method is provided for repairing a damaged Cr-Mo-V alloy steel rotor. As is known to those skilled in the art, high pressure steam turbine rotors to which this invention pertains typically include a series of turbine blades attached to and extending radially outwardly from the outer circumferential surface of the rotor. ing. The vanes are conventionally attached to the rotor by tongue-and-groove means, with the tongues of the vane fitting into grooves in the rotor and pinned in place through pins through fastening holes in the rotor. It is in these areas that crack damage occurs and requires provision of new vane fixation areas on the rotor. As is clear, the replacement area must have a minimum design stress limit.

In the figures, the method of the invention is indicated by the numeral 10, so as to have a suitable shape to also receive a replacement ring, which is a replacement vane fixation ring, generally designated 12 in the drawings. The area of the rotor 11 that has been machined is first machined. Furthermore, although FIG. 1 shows a partial cross-section of the repair area after repair, those skilled in the art will appreciate that the replacement ring 1
2 extends fully 360 degrees around its rotor,
It will also be appreciated that the region 10 machined to receive the replacement ring extends 360 degrees around the rotor, so that the shape of the region 10 is generally annular.
The blades of the rotor are prepared by methods known to those skilled in the art.
It is fixed to the outer peripheral surface 12c of the replacement ring 12.

Preferably, the replacement ring 12 is initially provided as a complete ring-shaped forging. As you can see from Figure 2, such a ring is
The ring is cut into ring halves 12a and 12b, which are ring forged parts. Each is substantially semi-circular in shape and extends approximately around area 10 after the repair is completed.
It extends 180 degrees. In this regard, since the position of the fastening hole 13 changes from time to time and the weld groove 12d has to be located away from the fastening hole,
The ring half body 12a and the ring half body 12b are completely
It should be noted that it does not have to be a 180 degree segment. Furthermore, cutting the original replacement ring 12 into a pair of ring halves 12a and 12b that are substantially semicircular can be done by first positioning the replacement ring 12 adjacent to the area 10 to be repaired. It is pointed out that it is generally desirable to This is because the replacement ring is typically located at the center of the rotor, and the ends of the rotor are generally of a larger diameter than the center. As a result, it is impossible to slide a complete ring onto the rotor along the axial direction, and 12
The provision of a pair of semicircular ring halves, such as a and 12b, facilitates placement of the complete ring adjacent the area undergoing repair.

According to this invention, the semicircular annular rings, ie, the ring halves 12a and 12b, are made of 9Cr-1Mo alloy steel and are formed by cutting the original ring forging, respectively. The ring halves 12a, 12b have a pair of end portions 12a', 12
It has b′. The ends 12a', 12b' are particularly machined on the sides, leaving an area known as a weld groove 12d between the sides. As a result, the ends 12a',
12b' is shaped complementary to the corresponding end of the other ring half, and when the corresponding ends 12a', 12b' are placed closely together, as best seen in FIG. The replacement ring 12 has an adjacent end 1
A welding groove 12d is formed between the welding groove 2a' and the end 12b'.

The 9Cr-1Mo alloy steel used to make the replacement ring 12 in accordance with the present invention is known as a commercially available alloy;
It is listed in the standard as A182 and grade F91. This ASTM standard is set forth in Table 1 below.

Table 1, Detailed specifications for commercial ASTM standards for 9Cr-1Mo alloy steel ASTM A-182, Grade F91 Chemical composition elemental range (w/w) C 0.08-0.12 Mn 0.30-0.50 Si 0.2-0.5 P Maximum 0.02 S Max 0.01 Cr 8-9.5 Ni Max 0.4 Mo 0.85-1.05 Cu Max 0.1 V 0.18-0.25 Nb 0.06-0.10 N 0.3-0.07 Al Max 0.04 Required tensile and hardness Tensile strength, min 59.8Kg/mm ² ( 85ksi) Descending strength, min. 42.2Kg/mm ² (60ksi) Elongation, min. 20% Section reduction, min. 40 Brinell hardness number, max. 248 Heat treatment Normalizing temperature 1038~1093℃ (1900~2000〓) Tempering temperature Minimum 732° C. (1350°) Ring halves 12a and 12b are fitted around the region 10 of the rotor and are arranged essentially as shown in FIG. After that, ring half 1
2a and the corresponding end 12a' of the ring half 12b,
The ends 12b' are each welded together at a weld groove 12, as shown in FIG. At this time, the weld groove 12d is welded using narrow gap gas metal arc welding. Welding groove portion 1 of end portion 12a′ and end portion 12b′ of ring half body 12a and ring half body 12b
When welding at 2d is completed, the ring extends 360 degrees around the rotor. As shown in FIG. 1, the replacement rings 12 are arranged side by side in the area 10.

Ends 12a', 12b' of ring halves 12a and 12b are welded together using 9Cr-1Mo alloy steel weld metal to complete replacement ring 12. And, as mentioned above,
Welding in the weld groove 12d is suitably completed using narrow gap gas metal arc welding. Such narrow-gap welding is done so that the weld is located between the vane pins and away from the vane pins.
Make a weld seam 1.27cm (1/2in) wide. Such a pin is inserted into the fastening hole 13 in a manner known to those skilled in the art. Therefore, the weld will be away from areas of high stress. Furthermore, with respect to the present invention, welding of 9Cr-1Mo alloy steel using 9Cr-1Mo alloy steel welding consumables does not result in low-strength, heat-affected regions.

After the ring halves 12a and 12b are simultaneously welded in the welding groove 12d, the completed replacement ring 12 is juxtaposed in the area 40. after that,
The replacement ring 12 is welded to the surface of the region 10 of the rotor 11 using a narrow gap submerged welding process or a narrow gap gas metal arc welding process.

Regarding the welding of the replacement ring 12 to the rotor 11, the replacement ring has a welded portion 14, as can be seen in the figure.
is welded to the rotor 11 from one side of the replacement ring. The weld is then processed in such a way that processing from the opposite side of the replacement ring extends to the weld 14 to ensure 100% joint penetration.
It should be processed. This means that the weld 14
is indicated by the innermost concave region 14a. Then another weld 16 is made from the opposite side of the replacement ring. Preferably, the welds 14 and 16 are formed using a 9Cr-1Mo alloy steel weld metal in both cases, using a narrow-gap submerged arc welding method or a narrow-gap gas metal arc welding method. It is made by Additionally, although the welding procedure was described starting at weld 14 on one side and ending at the opposite side, it is clear to those skilled in the art that the first weld is performed at weld 16 and subsequent welds are performed at weld 14. It is clear that the welding operation of welding the replacement ring 12 to the rotor 11 can be reversed to do so. In this case, the machining between welds is carried out from the opposite side, and the machining extends to the weld 16, again to ensure 100% joint penetration.

As a result, the present invention solves the fundamental problem that often occurs when welding rotors of Cr-Mo-V alloy steel, namely, the problem of low strength and generation of heat-affected zone in Cr-Mo-V alloy steel rotors. Solve. According to this invention, such problems can be solved by 9Cr−1Mo
Eliminated through the use of replacement rings made from alloy steel (ASTMA182, grade F91). It is also used for the replacement ring 12 and the end 12
a', the 9Cr-1Mo alloy steel used as the weld metal for welding the ends 12b' together is the same as the original Cr
- has creep properties at least equal to the rotor material of Mo-V alloy steel; Furthermore, 9Cr−
When ring halves of 1Mo alloy steel are welded together with the same weld metal, the ring halves are Cr-
It has surprisingly been discovered that Mo-V alloy steel has low strength and no heat affected zone exhibiting the same poor creep properties as those produced when welded. As a result, narrow gap gas metal arm welding is performed on the ends 12a' of the ring halves 12a, 12b;
The ends 12b' are joined together by the weld groove 12d, and the area of the replacement ring 12 adjacent thereto has sufficient high temperature strength.

With respect to the narrow gap submerged arc welds or narrow gap gas metal arc welds used to form welds 14 and 16, a low strength, heat affected zone may occur on the rotor side of such welds. While this is true, such heat-affected zones are located in low-stress regions that allow all structural members to meet design allowable stress limits.

As will be apparent to those skilled in the art, the weld groove 12d and the welds 14, 16 are subjected to certain tests to ensure that they have the required quality before welding, after welding, and after weld heat treatment. Subjected to non-destructive testing. In this same regard, post-weld heat treatment is performed to minimize welding stresses after welding.
These procedures are conventional and well known to those skilled in the art. Therefore, there is no need to describe such procedures in detail.

[Brief explanation of the drawing]

FIG. 1 is a partially cutaway sectional perspective view schematically showing the weld repair area and the repair procedure of the present invention;
The figure is a plan view of the replacement ring shown in FIG. 1. 10: region, 11: rotor, 12: replacement ring (replacement blade fixing ring), 12a, 12b: ring half (ring forged part), 12a', 12b': end.

Claims (1)

[Scope of Claims] 1. By replacing a damaged blade fixing area of a chromium-molybdenum-vanadium alloy steel (Cr-Mo-V alloy steel) high-pressure turbine rotor with a replacement blade fixing ring, the high pressure A method of repairing a steam turbine rotor, the method comprising: a. machining a damaged area of the rotor to form a surface profile suitable for receiving the replacement vane retaining ring; b. a 9 chromium-1 molybdenum alloy. Steel (9Cr−1Mo
A pair of approximately semicircular ring forged parts each having a pair of ends are prepared, and the pair of ends of one of the ring forged parts are made from the other ring forged part. the corresponding ends of the other ring forging are shaped complementary to the corresponding ends of the other ring forging such that when the corresponding ends of the parts are closely spaced and welded together, they form the replacement vane retaining ring. c. disposing the pair of ring forged parts adjacent to the machined region of the rotor, such that the corresponding ends are joined complementary to each other to form the replacement blade fixing ring; d welding the corresponding ends of the pair of ring forgings together using narrow gap metal arc welding and 9Cr-1Mo alloy steel weld metal to complete the replacement vane retaining ring; e. A method for repairing a high-pressure turbine rotor, comprising welding the completed replacement blade fixing ring to the area of the rotor.