JPS61249274A - Shot peening method for pipe - Google Patents

Abstract

PURPOSE:To regulate a shot peening condition in an extremely accurate manner, by attaching a C ring elastically to a pipe inner surface, while measuring a variation in a distance between the gauge marks put to this C ring before and after performing the shot peening to a pipe. CONSTITUTION:Each of three C rings 41-43 removing a part of an annular body having an outer diameter little larger than an inner diameter of a pipe 1 is elastically attached to an inner surface of the pipe 1. Next, a variation in a distance between a two-piece-set pair of gauge marks put to these C rings 41-43 before and after performing the shot peening to the pipe 1 is measured by an optical type displacement measuring instrument 7 being set outward a pipe end. On the basis of this measured value, a shot peening condition optimum to give the extent of depth of a compressed residual stress layer to be formed in and round a pipe outer end of a setting part of each of these C rings 41-43 of the pipe 1 is regulated, so that variations in quality of a product as the pipe being subject to the shot peening can be made smaller.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for shot peening a pipe material, such as a steel pipe, for applying shot peening to the outer surface of the pipe material.

Purpose of the invention In pipe materials with strict specifications such as steel pipes used in nuclear steam generators, shot peening is applied to the outer surface of the tube to generate compressive residual stress near the outer surface of the tube in order to prevent stress corrosion cracking even on the outer surface of the tube. It is being done. The compressive residual stress layer, which is the surface layer near the outer surface of the pipe that produces such compressive residual stress, is temporarily removed due to general corrosion over many years, so the pressure m residual stress at a depth of more than a certain amount is removed. It is necessary to apply sufficient shot peening to form a layer. However, if shot peening is applied excessively, the tensile residual stress simultaneously generated on the inner surface of the tube becomes excessive, and when a crack occurs due to intergranular corrosion, etc., the crack is likely to propagate. Therefore, it is important to perform direct shot peening to form a compressive residual stress layer of an appropriate depth in the surface layer near the outer surface of the tube. Shot peening of lI amount can be obtained by maximizing shot peening conditions such as shot projection pressure, tube feeding speed, shot particle size, etc.

Conventionally, when performing shot peening on a pipe, various shot peening pressures, test material feed speeds, shot particle diameters, etc. are used for the test material of the pipe to be shot peened. After performing shot peening in case i, the depth of the compressive residual stress layer formed near the outer surface of the shot peened tube is measured by Xn,
Alternatively, by estimating the amount of strain that occurs after removing the surface layer near the outer surface of the tube, find the optimal shot peening conditions to give the depth of the stress layer at a predetermined pressure tmlA, and apply the shot peening conditions to the tube using the optimal shot peening conditions. Shot peening was applied to the tube at a fixed setting throughout the process.

However, with this method of setting shot peening conditions in a fixed manner, shot peening is applied to a large number of pipes or long pipes, and the shot peening is used repeatedly, resulting in wear and tear. As the grain size gradually decreases, the depth of the compressive residual stress layer formed by shot peening applied to the tube tends to decrease gradually.

Furthermore, while shot peening is being applied to a large number of pipes or to a long pipe, other shot peening conditions such as shot jet pressure also vary. Therefore, it was unavoidable that variations would occur in the products of pipes subjected to shear W9 topi-lining. Therefore, the present inventors attached strain gauges to the inner surface of the tube in the patent application specification ml (name: residual stress application depth measurement method) filed on January 25, 1985 (Japanese Patent Application No. 80-12830). proposed a method for estimating the instantaneous depth of the compressive residual stress layer near the outer surface of the tube based on changes in the measured values of the strain gauge, and provided a means for obtaining a uniform compressive residual stress layer depth. did. However, in such a method, there is a problem in that a special jig is required for attaching the strain gauge to the inner surface of the tube in the case of a long, small diameter tube. The present invention aims to solve such problems.

Structure of the Invention The present invention achieves the above-mentioned object by providing one or more C-shaped elastic bodies (hereinafter referred to as C-rings), which are formed by cutting off a part of an annular body having an outer diameter slightly larger than the inner diameter of a tube. elastically attached to the inner surface of the tube, and measuring the amount of change in the distance between the gauge marks attached to the C-ring before and after subjecting the tube to shot peening with an optical displacement measuring device installed outside the tube end; This is a method for shot peening a tube, the gist of which is to vary the shot peening conditions into m sections based on the measurements.

The invention will be explained with reference to the figures. Figure ti1 is a diagram showing an example of the arrangement of equipment for implementing the present invention. The tube on which shotting is applied (feed rolls (21) (21)
>(22) (22>) is sent to the right in Figure 1, and the shot grain (3) is projected onto the outer surface of the tube (1) at the part separated by the single-point chain mA-A and the single-point chain m3-B. Tube (
One or more (three in this example) C-rings (41>(42)(43)) are elastically attached to appropriate positions on the inner surface of the C-ring (1). 41) (42)
(43), in which a part of the annular body having an outer diameter slightly larger than the inner diameter of the tube (summer) is cut out respectively, and the gap (43) is removed.
11) C-shaped shape with (421) (431),
It is formed into an elastic body made of a material such as spring steel, and is located at an appropriate position (preferably C
A pair of gauge points (412>(412>, (4,22>(422)
, (432) A mark indicating (432) is attached. The mark of the reference point may be anything that can be optically identified, such as a punch mark or a sticker/sill mark, and C-rings (41) (42) (
43) may be marked on each inner circumferential edge ridgeline.

The cross sections of the carbon plates (41), (42), and (43) may be square, rectangular, polygonal, round, or other shapes.

The respective thicknesses d, ) (d, ) (d, ) of the C rings (41), (42), and (43) are different from each other (d, < d, in the figure).
cd,) C ring (41) (42) (43) to tube (1)
When installing the
Place the thick one at the front in the direction of movement of the tube (1), that is, the right side in FIG. , k li (41)
, (42), (43)+7) attached to III), third
The figure is a clear view from the right side of Figure 1 of the inside of the tube with the C-rings (41), (42), and (43) attached to the inner surface of the tube. It is a diagram showing a state where the
(43) 572nd place* Shi? : Add a marking line to the outer surface corresponding to the position of the inner surface of the pipe (1), or mark the inside of the pipe (1) clearly at the front in the direction of movement of the pipe (1), that is, to the right in Figure 1. Install an optical displacement measuring device at the position where the As an optical displacement measuring device, it tracks the light beams from two targets,
An electro-optical measuring device in which the output of a photomultiplier tube changes according to changes in the distance between two targets is suitable. An optical sensor is located at the position indicated by the dashed line A-A in FIG.
(51), and an optical sensor (52) is placed at the position of the single-dot chain 11B-B (hereinafter referred to as the B position) and on the side of the path through which the tube (1) is sent. Optical sensor (
51) and (52) emit a signal when they sense the marked line attached to the outer surface of the tube (1). The signal is sent to a controller (6) electrically connected to the optical sensors (51) and (52). A controller (6) is electrically connected to the optical displacement measuring device (1), and starts target tracking or targets the optical displacement measuring device (a), respectively, based on the signals sent from the optical sensors (51) and (52). Command to end tracking.

Function: To perform shot peening on the pipe (1) using the device arrangement as described above, first the feed rolls (21) (21) (
22) With (22), ';t (1) is sent to the right in FIG. Pipe (1) with C-ring (41) attached to the inner surface
When the portion reaches the A position, that is, the shot peening application start position, the optical sensor (51) senses the marked line previously attached to the outer surface of the tube (1), and sends a signal to the control section (
6), and based on the signal, the control unit (6) instructs the optical displacement measuring device (2) to start tracking the target. The optical displacement measuring device ■, which was instructed to start tracking the target, uses a C ring (・41
) Tracking is started with reference points (442) and (412) attached to the side end faces of the vehicle as targets. Thereafter, the outer surface of the portion of the tube 0) on which the C-ring (41) is attached is seat-beaded together with the outer surface of the other portion of the tube (1), and is sent to the right, to the B position, i.e. When the sheet peening application end position is reached, the optical sensor detects the marked line on the outer surface of the tube.
(52) senses it and sends a signal to the control section (6), and based on the signal, the control section (6) instructs the optical displacement measuring instrument (2) to end target tracking. The optical displacement measuring device (2), which has been instructed to end the target tracking, finishes tracking the gauge points (412) (412), and detects the pair of gauge points (412) between the start of the target tracking and the end of the target tracking. (412), that is, the amount of change before and after shot peening the tube is measured and displayed. The amount of change in the gauge point (412) is the amount of change in the pipe (1
) Since there is a certain relationship with the depth of the compressive residual stress layer formed near the tube outer surface of the C-ring (41) attachment part, the change in the distance between the displayed gauge points (412) (412) In comparison with the above-mentioned constant relationship, which was determined in advance for the test material,
mwI to the optimum shot peening conditions to provide the depth of the compressive residual stress layer to be formed near the outer surface of the tube at the t section.
do. C-ring (42) or (43) mounting part tube (
The outer surface portion of step 1) is also subjected to optimal shot peening conditions in the same manner as the outer surface portion of the tube (1) of the C-ring (41) mounting portion. The C-rings (41) (42) (
No. 3) If the marking line attached to the outer surface of the tube (1) of the installation part is likely to disappear during peening, the feed roll (21) (21) (22) C-ring (41) (42) from the feeding speed of tube (1) according to 22)
(43), the time of passing through the A position and passing through the B position is estimated, and at the time, the target tracking is started and the target tracking is ended, respectively, for the optical displacement measuring device (■) via the controller (6). It may also be configured to issue a command.

Example 1 Using the shot peening conditions shown in Table 2 and the equipment arrangement for carrying out the present invention shown in Table 3, test shot peening was first applied to the tube shown in Table 1, and a pair of C-rings were prepared. Figures 4(a) and 4(b) show the results of measuring the amount of change in the distance between the points and measuring the depth of the compressive residual stress layer formed near the outer surface of the tube using X*. Figure 4 (a)
is a diagram showing the relationship between the amount of change in the distance between the two C-rings and the depth of the pressure 1ia residual stress layer formed near the outer surface of the tube. There is a substantially linear relationship in both the relationship between the amount of change in gauge distance and the depth of the compressive residual stress layer, and the relationship between the pipe feed speed and the amount of change in gauge distance between two pairs of C rings. I understand. Also, from the m4 diagram (a), there is a compressive residual stress layer depth of 25 mm near the outer surface of the tube.
The amount of change in gauge distance between two C-rings to form 0 μm is 8 μm, and from Figure 4 (b), the tube that gives a change in gauge distance of 8 μm between two C-rings is 8 μm. It can be seen that the feed rate is 300 sn/m+n in the case of Noa 1, G grain and shot projection pressure in Table 2. The tube feeding speed was fixedly set as the shot peening condition along with the shift grain and the shot projection pressure shown in Table 2 while the tubes were being shot peened, and the shots were applied to the 10 tubes shown in Table 1. After applying the two-tone treatment,
The depth of the pressure va8 residual stress layer formed near the outer surface of the tube is Xa
The measurement results are shown in the tJS diagram as white circles and dashed lines. Measure the amount of change in gauge distance between two pairs of C-rings attached to the pipe, adjust the tube feed speed so that the amount of change in gauge distance is always 8 μm, and After applying shot peening to 10 pieces,
The depth of the compressive residual stress layer formed near the outer surface of the tube was measured using X-rays, and the results are shown in FIG. 5, Table 1, Table 2, and Table 3 using black circles and solid lines. The horizontal axis in Figure 5 is
The vertical axis shows the depth of the compressive residual stress layer. As shown in Figure 5, when a large number of tubes are shot peened using the conventional method in which the shot peening conditions are fixed during shot peening, a compression residue is formed near the outer surface of the tube. The depth of the stress layer gradually decreases as the number of shot peened tubes increases and the wear of the shot peened particles increases. When performing spot peening on a large number of pipes using the method of the present invention, which measures the amount of change in the gauge distance of the steel/gage, changes the pipe feed speed based on the measurement, and adjusts the shot peening conditions. It can be seen that the depth of the compressive residual stress layer formed on the tube surface is always maintained constant.

Effects of the Invention As described above, the present invention provides a simple means for performing shot peening on a pipe, which does not involve the complicated work of attaching a strain gauge to the inner surface of the pipe and inserting a large number of lead wires into the pipe. Since the shot peening conditions can be determined extremely accurately by using the method, it is possible to easily reduce the variation in quality of pipes subjected to shot peening.

[Brief explanation of the drawing]

A diagram showing an example of an apparatus for carrying out the present invention in FIG. 1,
Figures 2 (A), (B), and (C) are diagrams showing a C-ring, Figure 3 is a diagram showing a bellows with a C-ring attached to the inner surface of the tube, and Figure 4 (
A) is a diagram of the relationship between the change in the gauge distance of two pairs of C-rings and the depth of the compressive residual stress layer, and Figure 4 (b) is a diagram of the relationship between the pipe feed speed and the gauges of two pairs of C-rings. Relationship diagram with Q distance change amount, j
The ffS diagram shows the number of tubes subjected to shot peening and the pressure m
It is a relationship diagram with residual stress. 1...tube 2! ...Feed roll 22...
・Feed roll 3-...7214 grains 4t...C-ring 4! G... Gap 412... Gauge
42...C ring 421...Fl 4
22... Gauge 43... C ring 431... Gap 432... Gauge 51... Optical sensor 5
2... Optical sensor - 6... Controller 7... Optical displacement measuring device Application Person: Sumitomo Metal Industries, Ltd. Figure 1 Bong Station Souda

Claims (1)

[Claims] One or more C-shaped elastic bodies having an outer diameter slightly larger than the inner diameter of the tube with a part cut out are elastically attached to the inner surface of the tube, and the C-shaped elastic body is elastically attached to the inner surface of the tube before and after shot peening the tube. The amount of change in the distance between two gauge marks attached to a shaped elastic body is measured using an optical displacement measuring device installed outside the tube end.
A method for shot peening a pipe, comprising adjusting shot peening conditions based on the measurement.