Various Weld Quality Testing Techniques – DT & NDT Methods

Various Weld Quality Testing Techniques - DT & NDT Methods

Welding Quality tests ensure the satisfactory performance of a welded project. They help us evaluate the welds and provide numeric values of strength and other factors associated with a welded joint. Weak welds may not withstand the stresses applied during service.

They can create difficulty and, in some cases, may hurt the user, so a proper evaluation method is required to check whether the given weld is according to user needs.

A specific weld acceptance criterion has been used that checks whether the designed structures meet the needs of the job requirement. In many cases, different welding codes and standards are used to test the quality of the joint.

These codes and standards have been developed for various fabrication processes and services to help particular industries. The following Guide from My Welding Yard will help you to develop an understanding of weld quality assurance.

Types of Weld Inspection Process 

There are generally two types of welding quality tests used commonly. We will deal with both of these methods separately.

Non-Destructive Welding test

These are the most commonly used type of inspection processes. In these types of examinations, a welding joint is tested without destroying the integrity of the weld. Most of the productions are examined with these methods. Non-destructive welding tests can help you to comply with legal requirements.

You can confirm standard specifications. These tests are common because they can be performed on-field or anywhere required. After completing these examinations, measurements are documents for further liability of the company and future usage.

With the latest American welding society standards or European Norms, a fabrication process must be dealt with care, and all levels of standards must be assured. A wide range of non-destructive tests is available as per need. In this article, we will discuss some of them.

Visual Inspection

Cracks and surface discontinuities can be inspected with the help of a visual inspection test. In this method, a skillful worker watches the welded joint closely. The examiner overlooks the weld pool and cooling metal closely.

A particular type of microscope or several measuring instruments is used to look at the weld accurately. Whenever an investigator looks closely upon the weld and finds any faults, he marks the respective area.

Liquid or Dye penetration Inspection

A dye is used in this technique to cover the welded part. As the paint is only applied to the surface, this method only inspection for surface cracks and discontinuities. Initially, the weld surface is cleaned of any impurities and splatter. A detergent wash is used to remove dirt, paint, or grease on the body is also removed by using a pickler. When the surface is crystal clear, the dye penetration process begins.

There are two types of sprays that are needed to be used for a thorough inspection. Firstly, the penetrant is sprayed all over the welded part. This spray has penetrating abilities and penetrates the joint within minutes. Then the surface is wiped off to clear any penetrant remaining on the surface.

Penetrants on the cracks stay wet, and they can be easily seen with the naked eye. The other spray known as the developer is sprayed to draw out the penetrant from the cracks. The developer draw-out the penetrant and behaves like blotting paper and changes color to magnify the presence of gap.

The advantage of a dye penetration test over visual inspection is that it doesn’t require any costly instruments to aid the viewing procedure. The color is clear enough to be seen with a naked eye.

Magnetic Particle Inspection

As the name suggests, this method deals with magnetic field changes to detect the surface and under surface defects. An instrument is used to generate and record the behavior of a magnetic field.

The magnetic field around a crack produces distortion. Powdered magnetic filings around a lot can show distortion. This method is only useful on ferromagnetic (substances having no net magnetic effect).

Metal probs are placed on each side of the weld, bypassing the current or putting the metal parts in a magnetic field; a magnetic effect is induced. Once the magnetic field is established, a few powdered colored metal particles are placed on the region.

The pattern created by these metal filings is examined for field distortions. Particles can be used wet or dry, depending on the type of job you are dealing with. This test is useful over others because it enables the investigator to look into the surface defects.

Eddy’s Current Inspection

In this method, the current flow through a part is used to test for cracks or faults. AC is flowed through a coil to create a magnetic field around it. Suppose this magnetic field is brought near a conducting metal, eddy’s current starts flowing through that conductor. This eddy current creates an opposing magnetic field in response to the coil’s magnetic field.

Due to discontinuity, if the second magnetic field changes, then the first magnetic field also changes. Which, in turn, changes the current through the primary coil. This change in current flow is detected, giving an inspection of the weld’s cracks or impurities.

This method is used to detect the defects deep into the surface of the welded part. Depth up to 2.5cm is seen with the help of this testing method. Frequency and the amperage rating of the current can be used to measure the discontinuities.

This approach is used to test steel floors and walls. A crawling scanner is used to test the changes in eddy’s current on the monitoring screen. When a fault is detected, the surface is marked for further preceding.

Ultrasonic Inspection

Sound waves with very high frequencies are called ultrasounds. They are used for a wide range of applications, including this one. In this technique, Ultrasonic waves are sent into metal using an emitter.

These waves can pass through metals but are bounced off by cracks or any discontinuity. A monitoring screen displays the response of these waves. The impurities’ size and location are displayed on the monitor, which can be used for further examination purposes.

This method is useful for deep cracks and cannot serve for the detection of near-surface faults. The surface should be smooth enough to be used by prob. Sometimes grease is used for proper acoustic connection between the proband a metal surface. If the weld is peaked too high, an advanced method is known as the “reflected sound method” is used.

The ultrasonic Inspection method has the benefit of detecting the faults deep into the surface. The size of the crack detected depends on the wavelength of the soundwave used. The defects of about half the wavelength of the soundwave used can be detected using this method. By using an ultrasonic wave of 2MHz, a catch of 1.5mm can be seen.

Acoustic Emission Monitoring

Acoustic emissions are a particular type of stressed wave produced due to the vibrational motion of stressed metals. These waves travel through the structure and work in the same way as ultrasonic inspection works. This method is usually used to monitor the response of the whole system.

Sensors are plotted all over the structure about 5 to 7 meters apart.  This method is of narrowing down the area of defect. If any default is detected in a region, then one of the other techniques as narrated above is used to thoroughly understand the type and location of the crack.

This method has a defect of contamination by background noises. This contamination can be avoided by filtering the signals in any electronic way. Acoustic Emission monitoring is one of the most abandoned used techniques because of comprehensive area coverage and deep detection of cracks.

Industrial Radiography

This is an expensive method but used in several industries for high-end projects. Mostly X-rays or gamma rays are used to penetrate through metals of different densities and detect cracks. This method is used for almost all materials with great depths than any other form.

This technique is similar to a standard X-ray of any human bone. A photographic film is placed on another side of the metal, and rays are emitted from one side. Discontinues make x-rays to bounce off or deviate from original paths. This response helps in the detection of cracks or incomplete welds. Check Also: Best Welding Helmet

Destructive Testing of Welds

These methods involve the physical destruction of welds to characterize their response. These methods are also used in many applications for qualifying different welded jobs. Some of the procedures involve complete breakage of the welded part. Some of the destructive tests that are common are as follow:

Macro Etching Test

This method involves removing a sample from the welded part and using these samples for further examinations. These samples are polished and then etched using some mild acid. These etched parts provide a clear view of the inside section of the welded joint.

The fusion line (the line separating the weld and base material) is given particular importance in this regard. Such items as the depth of penetration, lack of fusion, inadequate root penetration, internal porosity, cracking, and inclusions can be detected during an inspection of the etched sample. This type of test is used in projects where failure analysis is to be done to complete the behavior of the material.

Fillet Weld Break test

This test involves breaking a sample fillet that is welded on one side only. A pressing load is applied to the surface transverse to the welded part, typically in the direction of the unwelded side. The load is continuously increased until the weld suffers from failure.

In just a small amount, this test provides a great understanding of the behavior of the complete length of the weld. This type of weld inspection can detect such items as lack of fusion, internal porosity, and slag inclusions. This test is often used with a macro etching test for the complete understanding of any weld. Best Spot Welder

Guided Bent Test

This test is used to initiate bending in a specimen up to a specified radius of bents. This helps in evaluating the ductility and soundness of the welded joint. Like the Fillet weld break test, this test is also used transverse to the welded part.

Face bend tests are made with the weld face in tension, and root bend tests are made with the weld root in stress. This type of testing is particularly good at finding liner fusion defects, often opening up in the plate surface during the testing procedure. It is one of the frequently used tests in industries for the evaluation of welded parts.

Some Common Welding Defects

There are also some welding defects which are common like porosity, undercutting & lack of fusion they significantly affect the weld quality. for a quick understanding, you can watch the video.

Frequently Asked Questions FAQs

How many types of welding tests are there?

Two main types of welding tests are available, Destructive, and Non-Destructive welding test. Non-destructive test deals with the evaluation of the welding joint without destroying or making any changes to the physical structure. On the other destructive welding, tests involve the destruction of the welded part by applying stress or bending force to know about stress ratings and other characteristics.

What is the most commonly used method of weld inspection?

Radiography and ultrasonic weld inspection are the two most commonly used welding test. They have the benefits of wide-area coverage and in-depth diagnose. They can be used to know about the cracks or impurities within welded surfaces.

What is the hardest welding test?

6G pipe weld is most difficult to achieve because of tricky conditions. In order to pass this test, the welder has to weld a pipe at 45 degrees angle and restrict the movement. To do so, you need to weld on all sides and in all directions. This creates difficulty for the worker to pass out this test without hard work and a skilled job.

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Hello Everyone, I am James from Kentucky and been into this welding fiasco for 13 years in that time I have worked as a private welder and did most of the auto restoration work. In this recent, COVID-19 outbreak I decided to start a welding blog and share welding tips along with product reviews.

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