JPS62153730A - Method for testing gap corrosion fatigue - Google Patents

Abstract

PURPOSE:To perform a dynamic gap corrosion test without generating mechanical damage, by mounting a nonmetal soft elastomer to a fatigue test piece to generate a local gap on the surface of said test piece and loading repeating stress to the local gap while corrosive water is injected in said gap. CONSTITUTION:Rotary shafts 12 are mounted to both ends of the test piece 10 of a member receiving repeating stress under an environment easy to generate local corrosion like the implanted member of the turbine blade of an exhaust gas energy recovery apparatus and rotated by a rotary machine. A wt. 16 is suspended from the shaft 12 through a bearing 14 and repeating compression and tensile stresses are applied to the test piece 10. An O-ring 30 comprising neoprene rubber is mounted to the test piece 10 repeating stress is loaded to said test piece 10 while corrosive water 18 from a tank 20 is heated by a heating part 24 and injected to the test piece 10. By this method, the evaluation of fatigue strength can be performed only with respect to the effect of gap corrosion on fatigue strength without generating the mechanical damage in the test piece.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a crevice corrosion fatigue testing method that can evaluate the influence of actual machine parts, particularly on crevice corrosion, used in an environment where corrosion and fatigue coexist.

[Prior art]

Conventionally, fatigue tests have been used to determine the strength of members that are subjected to repeated stress.Fatigue tests are performed by applying a constant stress or strain amplitude to a test piece and determining the relationship between the number of repetitions of stress or strain until failure. It is used to evaluate the allowable stress of materials used in

By the way, it has been recognized that fatigue strength is significantly lower under the coexistence of corrosion and fatigue than when there is no corrosion. Therefore, fatigue strength of test pieces is conducted in a corrosive environment to determine the strength of the material. It is also used for strength evaluation.

[Problem that the invention seeks to solve]

However, in the conventional test method, the parts used in the actual machine are subjected to repeated stress in an environment where local corrosion is likely to occur, such as the implanted part of the turbine blade of an exhaust gas energy recovery device. There was a problem that corrosion fatigue strength could not be evaluated. In other words, for local corrosion of materials, a static corrosion test method in which a metal is glued to the test piece to artificially introduce local gaps and immersed in a corrosive liquid can be adopted, but fatigue tests can also be performed at the same time. If you try to do so, it will cause other mechanical damage in addition to the local gap, and eventually
There was no other way than to conduct fatigue tests and local corrosion separately and make a comprehensive judgment based on the individual evaluation values. Therefore, since a fatigue test method that involves localized corrosion such as crevice corrosion has not been established, it has not been possible to evaluate fatigue strength based solely on the influence of crevice corrosion on fatigue strength.

The present inventor investigated cases of cracks occurring in the implanted parts of turbine blades of energy recovery equipment for exhaust gas containing salt, and found that a large number of corroded bits were observed in the gaps between the implanted parts incorporated into the rotor. It was recognized that the problem originated from the corroded bit of the
This new finding points to the need to establish a test method to evaluate the effect of crevice corrosion on fatigue strength.

[Means and effects for solving the problems] Focusing on the above-mentioned conventional problems, the crevice corrosion testing method of the present invention creates local gaps on the surface of the test piece by attaching a non-metallic soft elastic body to the fatigue test piece. The test piece was configured to evaluate fatigue strength accompanied by crevice corrosion by repeatedly applying stress while pouring corrosive water onto the test piece.

With such a configuration, without causing mechanical damage,
A dynamic crevice corrosion test can be performed in which gaps are created in the test piece and stress is applied repeatedly, and fatigue strength can be evaluated only with respect to the influence of crevice corrosion on fatigue strength.

〔Example〕

EMBODIMENT OF THE INVENTION Below, the Example of the crevice corrosion fatigue test method based on this invention is described in detail with reference to drawings.

FIG. 1 shows the equipment configuration for carrying out the crevice corrosion fatigue test method. The testing machine uses a rotating bending tester.
Rotating shafts 12 are attached to both ends of the test piece 10, and the test piece 10 is rotated by a rotating machine (not shown). A weight 16 is suspended from the rotating shaft 12 via a bearing 14 so as to apply a load, and the action of this weight 16 and the same rotation action are used.

The test piece 10 is subjected to repeated stress of compression and tension, both positive and negative, with large values.

Further, a corrosive water circulation device is provided to inject corrosive water into the test piece 10. The corrosive water]-8 is stored in a tank 20 and sent from the tank 20 to the heating section 2 via a pump 22.
4 and heated to the operating temperature in the actual machine. The heated corrosive water 18 is poured into the test piece 1o via the supply pipe 26.

The corrosive water 18 after being injected is returned to the tank 20 through a water collecting section 28.

Here, in order to form a local gap in the test piece 1o,
In the embodiment, an O-ring 30 made of neoprene rubber as a non-metallic soft elastic body is attached. As shown in FIG. 2, by attaching the O-ring 30 to the test piece 10, a small gap 32 is created between the outer surface of the test piece 10 and the inner peripheral surface of the O-ring 30 in the circumferential direction. formed along the

Therefore, test piece 1 equipped with such O-ring 3Q
By injecting corrosive water 18 into 0, ttj2I?
T! 32 can cause local corrosion. Even when repeated stress is applied to the test piece 10 itself, the ○-ring 3o does not separate from the test piece 10 and the position of the gap 32 does not change, so the fatigue test is carried out. This makes it possible to cause local corrosion at the same time.

Next, a specific experimental example will be explained.

As the test piece 10, 5US630, 12Cr-5N i, 13 used in an exhaust gas energy recovery device was used.
Adopts Cr-3, 5N i, test part diameter φ14nw
A JIS No. 14 test piece of m was used. Also, O-ring 3
0 is inner diameter d=1.3.8no, thickness W=2.4m
A material made of neoprene rubber having a diameter of 1.5 m was used and was attached to the test piece 10 to form a gap 32.

Capacity 98. as a fatigue tester. Using an IN-m rotary bending tester, the repetition rate was set to 3400 cpI11. Two types of solutions A and B having the components shown in Table 1 were used as the corrosive liquid to be injected into the test piece 10, and the water was continuously injected using the corrosive liquid circulation device shown in FIG.

S in corrosive liquids A and B at 50°C with the above specifications.
US 630, 12Cr-5Ni,
The fatigue test results for 13Cr-3,5Ni are shown in Figures 3-8. These are shown simultaneously in comparison with the case in the atmosphere and the case without the O-ring 30 attached.

From Figures 3 and 4, if the 0-ring 30 is not installed, 5
Similar to the results in the atmosphere, a clear fatigue limit was observed in US630 (Liquid A: 549 MPa.

B liquid: 441 MPa), when an O-ring 30 is attached and a gap 32 is artificially introduced, the fatigue strength of 5US630 is significantly reduced although there are variations, and the repeated stress T a = 294 MPa in B liquid (=0.54σW
), the number of broken number repetitions Nf = 4, 8 x 1
It was 0'cycles. 0-ring mounting test piece 10
There were corroded bits in the crack propagation area.

Next, from FIGS. 5 and 6, when the O-ring 30 is not installed, 12Cr-5
Although the fatigue strength of Ni decreased, fatigue limits were observed in both cases (Liquid A: 392 MPa.

B liquid: 177 MPa). The fatigue strength of the ◯-ring attached test piece 10 decreased as in the case of 5US630, and corroded bits were present at the crack starting point.

From Figures 7 and 8, when O-ring 30 is not installed, A
Although the fatigue strength of 13Cr-3,5Ni in liquid B was significantly lower than that in liquid B, fatigue limits were observed in both cases (liquid A: 363 MPa, liquid B: 127 MPa). The fatigue limit of the 0-ring attached test piece 10 was significantly lowered in liquid A, and 5
As in the case of US630°12Cr-5Ni, corroded bits were present at all crack starting points.

Comparison results for these three types of test pieces are shown in Table 2. Note that "smooth" refers to the case where no O-ring is attached.

-: No data *As is clear from the extrapolated value, the O-ring 30 is attached to form a local gap 32 on the outer surface of the test piece 10, and the corrosive liquid 18
If a fatigue test is performed while causing local corrosion by injecting water, it can be seen that the fatigue strength decreases significantly, and it is possible to judge and evaluate the effect of only local corrosion on fatigue strength. Therefore, although there are various sources of local corrosion such as stress concentration areas, defects, and gaps in actual parts, when the actual parts are susceptible to local corrosion under the actual operating environment.

By using the method described above, it is possible to carry out tests that take into account the occurrence of crevice corrosion, and to achieve a practical evaluation of fatigue strength.

In addition, although the above-mentioned example explained the case where a rotary bending fatigue test was performed, it goes without saying that it can be applied to other pull-out compression fatigue tests.

〔Effect of the invention〕

As explained above, according to the present invention, the test piece 10 has
- It is possible to artificially introduce a gap by attaching a non-metallic soft elastic member such as a ring, and then perform a fatigue test while pouring corrosive liquid into the gap, thereby preventing crevice corrosion without causing mechanical damage. This has the effect of being able to evaluate only the impact.

[Brief explanation of drawings]

Figure 1 is a diagram of the equipment for performing a crevice corrosion fatigue test, Figure 2 is a side view of the test piece, Figures 3 to 8 are 5US630,
FIG. 3 is a diagram showing the results of fatigue tests conducted in different corrosive liquids on test pieces made of 12Cr-5Ni and 13Cr-3,5Ni. 10...Test piece, 18...Corrosion liquid, 30...
・・O-ring, 32・・Gap.

Claims (1)

[Claims] (1) By attaching a nonmetallic soft elastic body to a fatigue test piece, local gaps are generated on the surface of the test piece, and by repeatedly applying stress while pouring corrosive water to the test piece, crevice corrosion occurs. A crevice corrosion fatigue test method characterized by evaluating fatigue strength.