Ultrasonic thickness measurement

Ultrasonic thickness measurement is the process of analyzing a material or product for its thickness, hidden defects or structural disorders. Having been widely used in the middle of the XX century, today this method is the main method of non-destructive testing due to its versatility, accuracy, safety, and ease of operation. The main advantage of ultrasound is the ability to scan both surface and internal defects with results unattainable by other NC methods. In this article, we will consider the subtleties of UZT, which devices are used and what is its principle.

When and where it is used

The production and operation of aircraft engines, storage tanks for chemicals and gases, pipelines, nuclear and chemical reactors are accompanied by a thorough inspection at all stages. It is not difficult to identify external defects, but it will not be possible to detect hidden visual analysis. Therefore, ultrasonic thickness measurement is used to search for voids, cracks, and discontinuities in the material. It is used to determine the thickness of the object and other parameters necessary to study, eliminate the defect or replace the whole product.

The versatility of the UZK allows it to be used in all areas of industry, from the energy sector and mechanical engineering to construction and repair in Moscow and other Russian cities. Flaw detectors in various configurations with a set of suitable characteristics and functions are actively used in welding to assess the quality of seams and joints.

Devices for ultrasonic thickness measurement

The main device for ultrasonic thickness measurement is a thickness gauge or a flaw detector. Its task is to emit ultrasonic waves reflected from any foreign formations to compile a flaw diagram. In this way, the thickness of metallic and non-metallic products is examined, determining their strength characteristics and suitability for operation.

There are three types of flaw detectors:

• manual - a specialist or qualification is required to work with them. Manual models of flaw detectors provide a minimum of information on the basis of which the coordinates of the occurrence of defects in the thickness of the metal are calculated;
  
• mechanical - much easier to handle, since they perform part of the processes without the participation of an operator. However, they do not know how to interpret the results, so a specialist and special software are required to compile a flaw diagram.;
• automatic - the most common models that greatly simplify the procedure. They perform all tasks with built-in modules, providing a complete defect diagram at the output.

Flaw detectors differ in the number of channels. Single-channel ones have only one sensor that picks up ultrasonic waves, so it is compact and easy to carry. Two- and multi-channel connect several sensors at once. Despite the large dimensions, this speeds up the thickness measurement process, since a large area is scanned at the same time.

Types of thickness measurement

There are two methods of ultrasonic thickness measurement depending on the calculation method:

• resonant - pulsed or continuous radiation is used for it. The pulse frequency changes when the thickness of the product contains an integer number of half-waves - this moment is recorded by the flaw detector and measured until the next failure. The frequency difference shows the thickness, depth of the defects, their scale. The resonant method is used in automatic systems and is used to control mainly pipelines with thin walls;
  
• echo pulse - measures the interval between the first and second reference pulse. They are sounding and bottom echo pulses. The advantage of the method is high accuracy, but it can not be carried out in all conditions.

These methods are used to control products with certain characteristics.

How is the thickness measured

The work on measuring the thickness begins with familiarization with the documentation of the object, its characteristics, features of the external and bottom surface. It is marked up into sections depending on the area of operation of the flaw detector, then the surface is covered with a contact liquid. This is necessary to install the PEP in a minimally stable state. The screen is installed perpendicular to the pipe - this will help to get accurate information during the scanning process. If there are no results, the cause may be severe corrosion, poor contact, or defects at the measurement site.

By emitting and capturing reflected ultrasonic waves, the device converts them into electrical signals. On their basis, a calculation is subsequently built and a flaw diagram is compiled. Note that thickness measurement can be carried out both by a thickness gauge and a flaw detector, while the latter are more accurate and more versatile.