JPS61164154A - Detection of corrosion of steel structure - Google Patents

Abstract

PURPOSE:To make possible the quick detection of corrosion in a wide region by making incident an ultrasonic wave to a specimen at the angle at which the reflection is repeated back and forth on the front and rear of the specimen and comparing the received sound pressure of the transmitted wave thereof and the received sound pressure in a defectless part which is preliminarily measured. CONSTITUTION:The ultrasonic wave released from a probe T for signal transmission passes through water 3, a vinyl film 4 and a contact medium 5 between the vinyl film and the specimen in a locally water-immersing pot 2 and is thrown diagonally into the specimen 1. The ultrasonic wave arrives at the bottom end of a probe R for reception while repeating reflections on the front and rear of the specimen 1. The wave passes through the medium 5, the film 4 and the water 3 in the pot from the bottom end of the probe R and is converted to a voltage signal by the probe R. If there is corrosion LF on the ultrasonic wave reflection surface of the specimen, the ultrasonic wave is scattered at that point and finally the received sound pressure is smaller than the sound pressure when there is no corrosion on the reflection surface. The received sound pressure of the defectless part is therefore measured preliminarily and the case in which the measured value of the specimen is considerably smaller than the received sound pressure of the defectless part is judged to be the presence of the corroded part.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for detecting corrosion of steel structures using ultrasonic waves.

[Prior Art] Steel structures such as pressure vessels, storage tanks, and piping are often subject to corrosion over time, due to their contents, or due to outside air. For detecting corrosion or detecting the degree of corrosion,
Conventionally, residual wall thickness has been measured using visual inspection or an ultrasonic thickness gauge. In particular, methods using ultrasonic thickness gauges are generally widely used because they are highly accurate and can measure from one side of a steel structure, such as the outer surface. Edited by the 19th Committee [Ultrasonic Flaw Detection Method] Nikkan Kogyo Shimbun (July 30, 1972) P.
571] is also disclosed.

However, in conventional measurement using an ultrasonic thickness gauge, (a) 1
Only one point can be measured in each measurement, and it takes a huge amount of effort to measure the entire surface to be measured. There were large fish such as , which required pretreatment to remove residual paint and scale. On the other hand, in many cases, inspections are carried out at intervals when corrosion is less likely to occur, and the purpose of the inspection is to determine whether the thickness of the steel structure is greater than the allowable thickness. The reality was that it was within the permissible range.

[Problem that the invention seeks to solve]

The current method of detecting corrosion using an ultrasonic thickness gauge is extremely labor-intensive as it involves accurately measuring every point one by one, even though there are no abnormalities in most cases.

The present invention has been made in view of these conventional problems, and it is an object of the present invention to provide a method that can quickly detect corrosion over a wide area.

[Means for solving problems]

In the present invention, an ultrasonic transmitting probe T is placed on the surface of the object, and the ultrasonic waves are incident on the object at an angle that repeats the back and forth reflections on the front and back surfaces of the object. Corrosion on the front or back surface of the object is detected by receiving the transmitted ultrasonic waves with the receiving probe R and comparing the received sound pressure with the received sound pressure of the healthy part measured in advance. .

This invention will be explained in detail with reference to FIG.

In FIG. 1, T and R are an ultrasonic transmitting probe and an ultrasonic receiving probe, respectively, and 1 is an object having a thickness of t. Subject 1 has a plate shape.

It is cylindrical, etc.

The transmitting probe T and the receiving probe R are of a local water immersion type, in which water 3 is placed in a cup 2 and the vinyl membrane 4 is used to cover the water 3.
It has a structure that holds the

The probe 'r used is of a water immersion type, and is tilted to allow the ultrasonic waves to enter the subject obliquely.

L is the distance between the probes, ■, F is the length of the corrosion part between the probes.

(Function) The ultrasonic waves emitted from the transmitting probe T penetrate the water 3. in the local water immersion pot 2. It is introduced diagonally into the specimen 1 through the vinyl membrane 4 and the couplant 5 between the vinyl membrane and the specimen. As shown in FIG. 1, the ultrasonic waves reach the lower end of the receiving probe R while being repeatedly reflected on the front and back surfaces of the subject.

From the lower end of R, couplant 5. The signal passes through the vinyl membrane 4 and the water 3 in the pot and is converted into a voltage signal by the receiving probe R.

At this time, as shown in Figure 1, if there is corrosion (LP) on the ultrasound reflecting surface of the object, the ultrasound will be scattered, and the received sound pressure will eventually reach the reflecting surface. smaller than when there is no corrosion. Therefore, the received sound pressure of a healthy part is measured in advance, and if the measured value is significantly smaller than the received sound pressure of the healthy part, it is assumed that there is a corroded part.

With this method, it is known that there is a corroded part between the transmitting probe T and the receiving contact R, but the range (Lp in FIG. 1) and its degree cannot be measured. Therefore, when a corroded part is detected, the extent of corrosion and the amount of thinning of that part are measured using a conventional method using an ultrasonic thickness gauge.

By doing this, as mentioned above, since corrosion is not normally detected in most areas, the working time can be significantly reduced compared to the case where all inspections are performed using an ultrasonic thickness gauge alone.

〔Example〕

Using a water immersion probe with a frequency of 2 MHz, ultrasonic waves are transmitted to the object (large cylindrical body with a nominal thickness of 5.5+ am, made of metal tuning board)
A transverse wave was made incident at a refraction angle of 45°. The distance between the transmitting and receiving probes was 140 mm.

At this time, we obtained the following results.

It is indicated by the degree of amplification (gain) required to achieve this.

When the corroded area was re-inspected using an ultrasonic thickness gauge, the width was 1010 mm.
Thickness reduction (thickness amount 1-2 mm) was observed in 0-120.

[Other embodiments].

In the above embodiment, the local water immersion method was used, but a direct contact type bevel probe may of course be used.

In that case, it is preferable to use 100% glycerin as the probe material in order to reduce the influence of the surface condition of the subject. Furthermore, if the subject has a curvature, it is preferable to provide a shoe that matches the curvature.

〔Effect of the invention〕

According to the present invention, a wide area can be quickly inspected for corrosion, and inspection costs can be significantly reduced.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional view showing one embodiment of the present invention. 1: Test object with thickness t 2: Pot 3: Water 4: Vinyl membrane 5: Coupling agent
6: Propagation of ultrasound beam T: Transmission probe
R: Receiving probe ■,: Distance between both probes LF
: Corrosion area range - 7 = Procedural amendment band (March 11, 1985 3, Relationship with the case of the person making the amendment Patent applicant address 2-6-3 Otemachi, Chiyoda-ku, Tokyo Name (665) New Nippon Steel Corporation Representative Takeshi 1
) Yutaka 4, Agent 103 Telephone 03-864-6
052 Address: 2-27-6-5 Higashi Nihonbashi, Chuo-ku, Tokyo, Column 6 of the detailed explanation of the invention in the specification subject to amendment, Corrected the erroneous two lines on the following page of the specification of contents of the amendment. Correct the content.

Claims (1)

[Claims] An ultrasound transmitting probe is placed on the surface of the subject, the ultrasound emitted from the probe is incident obliquely into the subject, and an ultrasound receiving probe placed on the same surface of the subject is placed on the subject. By measuring the received sound pressure of the ultrasonic waves traveling while repeating back and forth reflections on the front and back surfaces of the A corrosion detection method for steel structures that detects corrosion on the front or back surface of a specimen.