The online inspection of the rolling process (Rolling Process Online Inspection)  refers to the continuous measurement of the rolling process parameters, the size of the rolling piece, and the internal and external quality in the rolling production line. Relying on these continuous detection signals and mathematical models, the rolling mill and the temperature of the rolling piece are adjusted to achieve comprehensive computer automatic control.

The automation, high speed, and continuous processing of modern rolling mills require online inspection of the rolling process, and modern testing instruments make online inspection of the rolling process possible. For example, the general horizontal wire rod mill has a low rolling speed and is lightweight of the finished coil. Therefore, the outer diameter of the wire is usually inspected manually after rolling. If there is a difference, the rolling mill is manually or electrically adjusted to adjust and control the diameter of the next wire rod.

For high-speed wire rod mills, the rolling speed is high (up to 130m/s) and the coil is heavy (up to 2t). Therefore, it is necessary to adopt the hot continuous online caliper method to adjust and control the full length of the same wire. Modern testing instruments, such as laser calipers and TV measuring instruments can be used for online testing.

The Rolling Process Online Inspection can generally achieve the rolling process parameters, the size of the rolled piece, and the internal and external quality. For example, online inspection of rolling force, strip thickness, plate crown, plate width, plate temperature, roll gap, etc. of strip and strip mill. The width of the continuous strip is an important part size. In the past, due to the limitation of the measuring instrument, the contact manual measurement was adopted. It has low precision, long reaction time and working condition is poor, especially the hot-rolled steel plate, the temperature is high, the heat dissipation area is large, and the measurement work is very difficult.

Photoelectric width gauges have been successfully used, which measure the width of the moving strip and the lateral position of the strip to the work rolls in a non-contact, continuous manner through the optical system, and indicate and record the deviation values while sending measurement signal to the computer. Another example is the modern wire rod rolling mill, which uses a digital speed measuring device, automatic caliper, loop monitor, pressure measuring element, etc. to automatically detect each rolling parameter, and uses a direct digital control computer to control the production process.

In the past, the surface quality inspection of rolled products was generally carried out by visual inspection, while the internal quality could only be detected by the broken method. At present, in order to facilitate the timely detection and elimination of defects, various non-destructive testing methods such as radiographic inspection are used on the production process line. Ultrasonic flaw detection, magnetic flaw detection, etc., directly check the internal and external defects of the rolled parts, and basically realize the mechanization and automation of the inspection of the rolled products or products.