Inspection of welds is difficult and it takes time to train inspectors. If you increase the number of inspectors in order to train them, inspection results will vary and quality will not be stable. In addition, a lot of time is required for inspection, and production cannot keep up.
Therefore, if welding inspection equipment is introduced, quality inspections can be performed faster and more accurately than human inspections. In addition, it is possible to inspect during welding and inside the weld, which stabilizes and improves quality.
In this article, we will explain the types of weld inspections and the advantages of their introduction. Please use it to understand weld inspection and use it as a reference for which inspection equipment to install.
- If you receive welding inspection consulting,
- I want to reduce costs by saving labor and labor.
- I want to increase productivity and sales
- We want to reduce human error and increase quality value.
- I don’t know which manufacturer’s automation equipment will be efficient
1. What is Weld Inspection
Welding inspection is to inspect whether the quality of the welded part is maintained.
Welding inspections are performed in the following four situations.
(1) Before welding
Weld inspection inspects the base metal before welding. The contents of the inspection include the shape and dimensions of the bevel, the condition of the bevel, and the presence of rust, discoloration, and dirt.
(2) During welding
During welding work, it is inspected twice: “first layer” and “after slag removal”. The shape and penetration state of the first layer are inspected for defects in the weld such as shape, cracks, poor fusion, poor penetration, and slag entrapment after slag removal.
(3) After completion of welding
After welding is completed, we inspect the appearance, shape of excess metal, undercuts, pits, blowholes, etc.
(4) After operation of welded structure
This inspection is performed after the welded structure is in operation. The main purpose is to detect weld fatigue and stress corrosion cracking.
2. Types and Mechanisms of Welding Inspection
There are five types of tests and inspections for welds:
(1) Visual inspection
It is a method of inspecting the surface of products and parts. We mainly check for scratches, dirt, foreign matter, deformation, damage, etc. and judge whether it is pass/fail.
The most popular visual inspection is a visual inspection performed by a person. Passing or failing is determined by checking scratches and deformations with human eyes and comparing them with limit samples. Also, when inspecting dimensions, scales, calipers, etc. are used.
In recent years, some devices have been inspected using cameras and image processing technology.
In the case of weld inspection, visual inspection is performed at all inspection timings. It is important to note that the appearance inspection only inspects the appearance, so the inside of the weld cannot be inspected.
(2) Magnetic particle testing (MT)
This test method can detect scratches on the surface of ferromagnetic materials (steel, etc.).
When the test object is magnetized, a “magnetic flux leakage” is generated only in the area where there is a scratch. When magnetic powder mixed with pigments and phosphors is sprayed there, the magnetic powder adheres to the leaking magnetic flux and can visually detect scratches.
It is mainly performed during welding work after slag removal, after welding is completed, and after the welded structure is put into operation.
It should be noted that the magnetic powder deep flaw test is a test method that can only be applied to ferromagnetic materials, and the test material is limited to some extent. In addition, since magnetic powder adheres to the wound area, it is not possible to know how deep the wound is.
(3) Penetrant testing (PT)
This test method can inspect almost any material.
A highly permeable liquid with a color that is easy to see is applied to the test object and allowed to penetrate into scratches on the surface. Wipe off excess liquid and use a developer to suck out the penetrant. This test method can be visually detected by sucking out the penetrating liquid in the scratched area.
It is mainly performed during welding work after slag removal, after welding is completed, and after the welded structure is put into operation.
It should be noted that the penetration deep flaw test sucks out the penetration liquid into the developer, so the exact size and depth of the wound cannot be determined.
(4) Radiographic test (RT)
This is a test method that emits radiation and imulates images on photographic film.
Radiation has the property of penetrating materials, and this property can be used to inspect the inside of welds.
If there is an internal defect such as a blowhole, the amount of radiation transmitted will be higher than that of the healthy part. The higher the amount of radiation transmitted, the blacker it appears on the film, and the internal condition can be confirmed from the photograph of the difference in shade.
It is mainly performed during welding work after slag removal and after welding is completed.
It should be noted that radiographic testing uses radiation that is harmful to the human body, so safety measures and control are required.
(5) Ultrasonic flaw detection test (UT)
This is a test method that measures the magnitude and strength of ultrasonic waves that emit ultrasonic waves and are reflected from scratches inside the weld.
The reflected ultrasonic waves are projected on the display unit as undulations of a wavy line graph. The graph gradually descends from the transmit pulse and undulates again at the bottom. If there are undulations in the middle, there is an internal defect. This is a test method that can grasp the position and size of internal defects by the position and size of the undulations.
It is mainly performed during welding work after slag removal and after welding is completed.
Ultrasonic deep flaw testing is good at detecting flat scratches perpendicular to the direction of travel of ultrasonic waves, but it is important to note that spherical scratches cannot be detected correctly due to diffuse reflection of reflected ultrasonic waves.
3. The Introduction Of Welding Inspection Equipment Offers 3 Advantages
(1) Stability and improvement of quality
The first benefit is that quality can be stabilised and improved.
When people inspect using their five senses, inspection results are influenced by personal judgement and physical condition. In addition, it is difficult for a person to inspect the inside of a weld, so quality is not stable. When inspections are automated, the equipment makes pass/fail decisions based on certain criteria, so inspection results are stable.
(2) Improved inspection accuracy
The second advantage is that inspections can be performed with greater accuracy than by skilled personnel.
By using cameras, ultrasonic waves, etc., it is possible to detect defects that cannot be seen by humans.
(3) Reduced inspection costs
The third advantage is reduced inspection costs. In welding inspections, there are many inspection items such as scratches and contamination. If these items are inspected one by one by a person, a lot of time is required and inspection costs become high.
Automated inspection makes it possible to perform multiple inspections at the same time, thus reducing inspection time.
4. Examples of Welding Inspection Equipment
Here are some examples of weld inspection equipment. Please refer to them as reference for inspection equipment.
(1) Spot weld inspection
This is an example of using a robot to inspect spot welds using ultrasonic depth flaw testing. By using an articulated robot, even spot welds at an angle can be inspected accurately.
(2) Fully automated visual flaw inspection
This is an example of a device that automatically inspects exterior flaws. By automating all magnetic powder depth scratch testing, there is no need for human intervention in the inspection process. A combination of a black light and a camera is used to take pictures, and the inspection results are determined from the images taken. Using a robot to transport the test piece can also make it unmanned.
(3) Visual inspection of welded parts
This is an example of equipment that uses a robot and camera to inspect the presence or absence of welded parts. A single robot can perform conveyance, inspection, and sorting into good or bad. By using an articulated robot, it is possible to inspect complex shapes.