JPS6235178A - Method of seal welding valve seat and valve main unit steam chamber - Google Patents

Abstract

PURPOSE:To improve a steam seal function, by padding top parts in fitting parts of a valve seat and a steam chamber through preliminary welding there after seal welding the preliminary padding of the top part by a welding rod of the same alloy system at that of a pad welded material. CONSTITUTION:Prior to finishing a valve main unit steam chamber 1 and a valve seat 2, first a padding groove, provided in the vicinity of the top part in each fitting part 3, performs in a single article condition welding of pads 4, 5 by a welding rod of an Ni-radical alloy, subsequently executing stress removal annealing. Next the welded pads 4, 5 and their vicinity are cut to a predetermined dimension. Thereafter, the fitting part 3 is formed by inserting the value seat 2 into the steam chamber 1, and a part between the welded pads 4, 5, previously provided in the top parts of said fitting parts, is seal welded by a welding rod of Ni-radical alloy of the same system to that of the welded pad.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method for seal welding a valve seat and a steam chamber in a main steam stop valve for a steam turbine and other various valves.

[Technical Background of the Invention and Problems Therein] Conventionally, there is a method shown in FIG. 6 as a seal welding method for a steam chamber and a valve seat of a main steam stop valve or the like.

In the same figure, after the fitting part 3 provided on the valve seat 2 is inserted into the fitting part 3 provided in the steam chamber 1 by cold fit, the tops of the steam chamber and the valve seat at16, 71! 1 is sealed and welded 8 to prevent steam leakage from the fitting part 3.

At the top of each of the steam chamber and valve seat, there is a stress relief groove 11 to prevent weld cracking during seal welding and cracking during service.
．． 12, and seal welding is performed at the narrow portion of each shelf 13, 14 adjacent to the grooves.

In addition, the material of the steam chamber 1 and the valve seat 2 is Cr-Mo-
Since heat-resistant steel such as V steel or Cr-MO steel is used, preheating to 200° C. or higher is performed to prevent weld cracking during seal welding.

However, with the above-mentioned seal welding method, (a) it is difficult to set the welding position when welding a narrow part with a stress-relaxing groove, and it is difficult to set the welding position, and furthermore, it is necessary to minimize fluctuations in welding conditions (welding current, speed, etc.) Good welding is inevitably difficult because of the need to press the weld. (b) Due to the presence of stress relaxation grooves, it is difficult to perform non-destructive inspection of the seal weld, making it impossible to detect welding defects. (C) To perform preheating. There are disadvantages such as poor welding workability and a tendency to cause welding defects, and there are also problems in that the steam sealing function of the seal weld is degraded, causing steam leakage and making erosion more likely to occur.

[Object of the Invention] The present invention has been made to eliminate the above-mentioned drawbacks in the background art, and therefore, it is an object of the present invention to provide a highly sound seal welding method that does not require stress relaxation grooves and does not require preheating. This is the purpose.

[Summary of the Invention] The seal welding method of the present invention involves applying a Ni-based alloy welding rod to the seal welding range between the valve seat and the steam chamber in advance, and applying stress relief annealing to the seal welding range between the valve seat and the steam chamber. , finishing processing (
The valve seat is fitted into the steam chamber and welded together without preheating.

[Embodiment 1 of the invention Next, one embodiment of the present invention will be described with reference to the drawings.

In the method of the present invention, as shown in Fig. 2 and Fig. Groove 9.
1o as a single item (before assembling the valve body and valve seat)
Weld pad 64.5 is performed using a Ni-based alloy welding rod (for example, 67Ni-18Cr Inconel alloy), and then stress relief annealing is performed. If these weld build-up and stress relief annealing are carried out at the same time as other welding of each part, there is no need for stress relief annealing or other treatments.

Next, as shown in FIGS. 4 and 5, weld overlay 4
．． 5 and its vicinity are cut to predetermined dimensions. On this occasion,
Conventionally, as shown in Figure 6, there was a stress relief groove 1 at the top of the fitting part.
1.12, but in the present invention, these grooves are not required.

Thereafter, as shown in FIG. 1, the valve seat 2 is inserted into the steam chamber 1 to form a fitting part 3, and the welding padding 4.5 that has been previously provided on the top of this fitting part is Seal weld 8 with a welding rod of a Ni-based alloy similar to that of the weld overlay.

This seal welding can be performed without preheating, and since there is no groove for stress relaxation, workability is improved and stable and good welding is possible.

In the method of the present invention, each top of the fitting portion 3 between the steam chamber 1 and the valve seat 2 is welded overlay 4. with a Ni-based alloy welding rod.
5. Ni-based alloy materials are more ductile than other materials, and are less likely to cause weld cracks or cracks during service even without the provision of stress-relaxing grooves, and they do not require rapid cooling during seal welding. It is used because it does not cause weld cracks that occur with Cr-Mo-V steel or Cr-Mo steel, has a smaller coefficient of thermal expansion than austenitic stainless steel, and is less susceptible to thermal stress during high-temperature use. This is because cracks are less likely to occur in the weld, and furthermore, decarburization and carburization at the weld boundary are less likely to occur in dissimilar metal joints than with other overlay materials.

Therefore, if weld overlay is done using a Ni-based alloy welding rod, there is no need to provide stress relief grooves, and seal welding can be performed on wide areas rather than seal welding on narrow shelf areas as shown in Figure 6. This allows for stable welding. In addition, the absence of stress relaxation grooves and the ability to form a stable weld bead facilitate the non-destructive inspection after seal welding and improve the defect inspection ability.

Furthermore, if weld overlay is performed using a Ni-based alloy welding rod, welding preheating during seal welding becomes unnecessary. Therefore, even if the seal welding area is welded in a narrow place, if preheating is not necessary, welding workability will be improved and sound seal welding will be possible.

[Effects of the Invention] As described above, according to the method of the present invention, welding work in narrow areas is facilitated, sound welding is possible, and since there is no stress relaxation groove, stable welding is possible even if the welding position is slightly shifted. I can do it,
In addition, since non-destructive testing becomes easy, the quality of the seal weld is improved.

[Brief explanation of drawings]

FIG. 1 shows an embodiment of the present invention, in which a sectional view of a seal welded portion of a steam chamber and a valve seat, which are overlay welded using a Ni base metal alloy welding material and seal welded using a similar type of welding material; Second
Figures 3 and 3 are cross-sectional views of the steam chamber and valve seat in the raw state with welded overlays applied to the ends of the steam chamber and valve seat, and Figures 4 and 5 are sectional views of the steam chamber and valve seat. A cross-sectional view of the seat after finishing processing, and FIG. 6 is a cross-sectional view for explaining conventional seal welding. 1... Steam chamber 2... Valve seat 3... Fitting part 4.5... Weld overlay 6.7. ...Top 8...Seal weld 9.10...Build-up groove 11.12...Stress relaxation groove 13.14...Shelf Fig. 1 Fig. 2 Fig. 4 Figure 3 Figure 5

Claims (2)

[Claims] (1) When seal-welding the valve body steam chamber (hereinafter referred to as steam chamber) and the valve seat, while the valve seat and steam chamber are each in a separate state, the top of the fitting part of the valve seat and steam chamber is The method is characterized in that the weld overlay is applied in advance to the provided overlay groove, stress relief annealing is performed, and then seal welding is performed between the weld overlays using an alloy welding rod of the same type as the overlay welding material. Seal welding method between valve seat and valve body steam chamber. (2) A method of seal welding between a valve seat and a valve body steam chamber according to claim 1, characterized in that the weld build-up is performed using a Ni-based alloy welding material.