JPS589811B2 - Management method for shot peening on the inner surface of pipes - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The method of the present invention relates to a method for managing shot peening treatment applied to the inner surface of a tube.

In order to prevent stress corrosion cracking or pickling from occurring on the inner surface of thin tubes, increasing the hardness and compressive residual stress of the inner surface is considered, and shot peening of the inner surface of the tube is being considered.

Shot peening can improve strength if applied under suitable conditions, but it can also have a negative effect, so the intensity and cove-rage of the peening, as well as the size and shape of the shot, must be carefully controlled. What you are required to do.

Usually shot peening is done using Almen cage (Alme
Shot peening on the inner surface of the pipe is performed by ejecting the shot from the nozzle at almost right angles and in a 360° circumferential direction, and the nozzle is rotated while the shot peening is performed. Move in a straight line.

Therefore, when Almen gauge is used, there is a strong possibility that uniform shot peening may not be possible since the gauge is in the form of a plate, and a separate construction management method is required.

In order to manage shot beaning on the inside of a tube, the following conditions must be met.

(1) A measurand that shows a meaningful value can be obtained.

(2) The measurement method is easy.

In view of the above circumstances, the method of the present invention was proposed for the purpose of providing a management method that satisfies the above conditions.The method of the present invention forms a slit in the longitudinal direction of a tube subjected to shot peening, and the outer diameter D of the tube before and after the slit formation, D' and the pipe thickness h are measured, and from these measured values, the average diameter of the pipe Dm = D - h and the change in the pipe outer diameter ΔD = D - D are calculated, and from these, ΔD/D2m is calculated. A method for managing shot peening construction on the inner surface of a pipe is provided, which is characterized in that the shot peening construction is managed based on this value.

Next, the method of the present invention will be explained in detail with reference to Examples.

FIG. 1 explains the procedure of the method of the present invention. In FIG. 1a, 1 is a thin tube, such as an Inconel 600 tube, before being subjected to shot peening treatment.

The method of the present invention employs the tube itself as a gauge, forms a slit in the longitudinal direction after shot peening, and measures the change in the outer diameter of the tube by cutting a portion of the tube.

In order to control the strength or density of peening, it is not necessary to insist on using Inconel 600 as the tube material, and any material that is sensitive to differences in shot peening conditions within the range of conditions to be controlled can be used.

First, the tube thickness h is measured in the state shown in FIG. 1, and then, as shown in FIG. 1b, peening treatment is performed using the tube inner surface shot peening device 2 as described above.

Next, the outer diameter D of the tube is measured as shown in FIG. 1C, and a slit 3 is formed in the longitudinal direction of the tube 1 as shown in FIG. 1D, and then the outer diameter D' of the tube is measured.

The outer diameter of the tube can be measured, for example, by pinching at 120° in the circumferential direction and taking the average at three points.

From these measured values h, D, D', the average diameter of the tube Dm=
D-h, and the tube outer diameter change ΔD=D'-D are determined, and ΔD/D2m is further calculated.

The residual stress σr in the circumferential direction on the inner surface of the tube is obtained by the following equation as a first-order approximation.

However, E: elastic constant ν: Poisson's ratio, ie, ΔD/D2m, is closely related to residual stress and is easy to measure.

Next, FIG. 2 shows the results of calculating ΔD/D2m using the method shown in FIG. 1 for tubes made of Inconel 600 that were actually peened under various shot peening conditions.

In the figure, the horizontal axis is the nozzle feed speed, ○ indicates the shot supply pressure is 6.1 kg/cm2, Δ indicates 5.4 kg/cm2, □ indicates 47 kg/cm2, and ◇ indicates 4.0 kg/cm2. The shot size is ≠32 to 42 mesh, and the black dots indicate X-ray residual stress measurements.

The feed rate is considered to be a quantity corresponding to the peening coverage.

The nozzle rotation speed is proportional to the feed rate.

As can be seen from FIG. 2, ΔD/D2m tends to have a higher value as the feed rate is slower and the shot pressure is higher.

Next, when applying it to an actual Inconel 600 pipe, the target values were to set the supply pressure to 5.0 kg/cm2 and the feed speed to 80 m.
It was set at m/min.

Therefore, we selected the sample indicated by the black dot in Figure 2 around the feed rate of 8 Qmm/rHin, made it into a strip, and determined the residual stress distribution using the X-ray residual stress measurement method. Based on the measurement results, we found the following. I tried to find various quantities.

a Circumferential residual stress σr on the pipe inner surface σr−σ′r+σrX (2) However, σ'r: Based on formula (1).

σr×: Measured value of X-ray residual stress on inner surface b Compressive residual stress layer thickness dc due to shot peening For convenience, it was determined from the depth direction distribution of circumferential force stress determined by X-ray residual stress measurement.

C σr×dc The results of plotting the above quantities against ΔD/D2m are shown in FIG.

As can be seen from the figure, each quantity is △D with the band width in the figure.
/D2m compatible.

In particular, the supply pressure was 4.7 kg/cm2, which was blurred in Figure 2.
, it is proven that the sample (marked with ■) at a feed rate of 70 mm/mih was not actually subjected to effective shot peening.

It is desirable that the depth of the compressive residual stress layer is sufficient to prevent corrosion cracking.

Further, the inner surface residual stress x compressed layer depth can be considered as a parameter indicating the effectiveness of shot peening.

As mentioned above, the method of the present invention is effective in controlling shot peening by D/D2m, and from Fig. 3,
Unless there is a major change in the sample used, the circumferential residual stress on the inner surface of the tube due to shot peening or the depth of the compressive residual stress layer can be approximately estimated by measuring ΔD/D2m.

In other words, by determining the target value of △D/D2m through a stress corrosion cracking test H, etc., and using that value as the control standard,
Shono Topi] You will be able to manage construction work.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram showing the procedure of the method of the present invention, Fig. 2 is a diagram showing the relationship between nozzle feed speed and △D/D2m value, and Fig. 3 is a diagram showing the relationship between △D/D2m and inner surface residual stress (σr ), an X-ray residual stress compression layer thickness (dc), and a diagram showing the relationship between σr×dc. 1... Pipe to be treated, 2... Pipe inner surface shot peening device, 3... Slit.

Claims (1)

[Claims] 1. Form a slit in the longitudinal direction of the shot-peened tube, measure the tube outer diameters D, D' and tube thickness h before and after forming the slit, and calculate the average diameter Dm of the tube from these measured values.
= D-h and the change in pipe outer diameter △D=D'-D are determined, △D/D2m is calculated from these values, and the shot peening process is managed based on this value. How to manage peening construction.