1. Choice of thickness measurement method

There are many classification methods of thickness measurement technology. According to the different measurement methods, they are divided into contact and non-contact thickness measurement; according to different purposes, they are divided into coating thickness measurement and film thickness measurement; according to the different thickness measurement principles, and It can be divided into electromagnetic induction thickness measurement, energy attenuation thickness measurement, ultrasonic thickness measurement and photoelectric imaging thickness measurement. In the following, we will review the existing thickness measurement technology from the perspective of thickness measurement principle.

Different thickness measurement methods have their own advantages and disadvantages, and their applicable occasions are also different. Through comparative analysis, it is concluded that a single ultrasonic thickness measurement has its unique advantages in steel pipe thickness measurement due to its simple device, low price, no pollution to water sources, and no limitation of working conditions, especially for dredging steel pipes. Where the side can be touched, it can show its superiority even more. The application of ultrasonic thickness measurement technology to steel pipe wall thickness monitoring in the dredging field has great development prospects.

2. Problems in measuring steel pipe wall thickness

The difference between measuring the wall thickness of steel pipes and plate parts is that the steel pipe has a certain curvature, which has two problems: one is that the steel pipe has a radius of curvature, especially when measuring the thickness of a small diameter pipe, the plane probe and the curved surface are a line Contact, the sound transmission rate is low, and the coupling effect is poor. This effect increases significantly with the decrease of the radius of curvature. The second reason is that the detection surface of the pipe fitting is non-planar, and the slight scattering of the probe signal will make the echo difficult to receive, and the instrument has no indication. When measuring curved workpieces similar to steel pipes, it is necessary to use a curved probe sheath or a special probe for small pipe diameter (φ6mm), which can more accurately measure the wall thickness of the steel pipe and other curved materials.

3. Measurement problems under complicated conditions of dredging

The working conditions of dredged steel pipes are worse than other industries. The dredged steel pipes are filled with mixtures of sediment, water, sand, gravel, etc. The online thickness measurement of dredged steel pipes under many boundary conditions mainly has the following three problems.

(1) The dredged steel pipe is filled with a mixture of dredged soil and water. Due to changes in soil quality, speed, concentration, etc., deposits will occur at the bottom of the pipeline. The acoustic impedance of sediments of different soils is different. When the impedance is not much different, the ultrasonic measurement will misjudge the thickness of the deposit as the wall thickness of the steel pipe, which will cause errors. At this time, the inspector should comprehensively judge the inspection data based on the information previously consulted and the thickness of the deposits in the steel pipe, the corrosion and wear of the tested steel pipe. When an abnormal indication is found, the dredged steel pipe is prone to thinning and erosion during the transportation process. Accurate measurement method should be adopted for the eroded part, that is, increase the number of measurements around the measurement point, change the position of the probe, and build a measurement point model according to the state of the sediment.

(2) When the dredging steel pipe transports gravel, coral reef and other hard materials, in addition to the wear of the pipe, it will also have a greater impact on the pipe, causing the inner wall to be uneven, causing the sound wave to attenuate during the measurement, and the phenomenon of irregular changes in the readings will occur. At this time, the inspectors are required to cooperate with the ultrasonic flaw detector to assist in the judgment.

(3) During the conveying process, the inner wall of the dredged steel pipe is continuously worn by various dredging media. The wear conditions are different at different positions. The inner surface and the detection surface are not parallel. When the sound wave reaches the inner wall, scattering occurs and it is difficult to receive echo signals. The measurement of these parts is particularly important. You can choose to change the angle of the dividing plane for multiple measurements, and use an ultrasonic flaw detector to assist in detection when necessary.

4. Development trend of thickness measurement technology

Different thickness measuring instruments have different principles, so they have their own applications. Online thickness measurement technology has been widely used in production. Improving the intelligent level, anti-interference ability and measurement accuracy of thickness measurement equipment will be the next development direction of thickness measurement technology. Under special working conditions, how to improve the overall performance of the thickness measurement system composed of thickness measurement instruments and other facilities is the development trend of thickness measurement technology in the future.

As far as the dredging industry is concerned, with the development of dredging projects to further and deeper waters, the length of steel pipes filled by dredgers in the land area continues to increase, and the impact of transportation links on production is further increased. How to reduce the interference of water, silt, gravel and other sediments on wall thickness measurement, how to achieve continuous online thickness measurement of dredged steel pipes, how to implement remote monitoring and early warning mechanisms for operating pipelines, will be the ultrasonic thickness measurement technology in the field of dredging The applied research direction has a lot of room for development.