Weld testing is a critical and important step in ensuring the quality of welds. There are many different types of weld tests, each with its own objective & testing requirements. Some common weld tests include Visual Inspection, Bend Testing, tension test, visual inspection, and radiography testing.
Welders must be able to produce high-quality welds that meet the requirements specified by the customer or code (E.g., AWS D1.1/ ASME Section IX).
To ensure that welds meet these requirements, they must be tested. Weld testing is a way to evaluate the quality of a weld and identify any defects that may exist.
There are many different types of weld tests (destructive Tests & Non-Destructive Tests) as explained in this post, each with its own objectives.
Some common weld tests include Bend tests, tensile tests, visual inspection, penetrant testing, and radiography testing. Each of these tests has its own advantages and disadvantages.
WHY DO WE NEED A WELDING TEST?
Welding is an important process in manufacturing and construction. It is used to join two or more metal parts together. Welding is a special process (as per ISO 9001) that makes it necessary to make sure that the welder is capable of doing the job correctly.
That is why we need a welding test. The welding test will evaluate the welder’s skills and abilities.
It will also help to ensure the safety of the welder and the people around him. A welding test is essential for ensuring the quality of welds and preventing accidents.
Another purpose of Weld Testing is to ensure that the welds meet the requirements for mechanical and technological properties for their intended use.
For this, samples cut from the welding joint are subjected to various tests (e.g. bend test, corrosion test, hardness test, or RT) to verify and ensure the weld integrity.
WELD TESTING METHODS
Weld testing methods are necessary to ensure the quality of a weld. There are a variety of weld testing methods, each with its own advantages and disadvantages.
Weld Testing methods can be classified into two main types:
- Destructive Testing- Fracture test, Bend Test, Macro test, Tensile Test, etc.
- Non-Destructive Testing- Visual Testing, Penetrant Testing, Radiography Testing, etc.
The most common weld testing methods are manual visual inspection, radiography, ultrasonic testing, magnetic particle inspection, and liquid penetrant inspection.
WHAT IS A DESTRUCTIVE TEST?
Destructive Testing is a type of testing which involves the deliberate destruction of a weld for weld testing.
Destructive testing is used to evaluate the strength, soundness and reliability of a welding joint. There are several types of destructive tests, including:
- Tensile testing,
- Fracture toughness testing,
- Impact Test
- Bend Test
- Macro Test
- Hardness testing
- Nick Break Test
- Fracture Test, etc. to name a few types.
All these destructive tests are used to evaluate the strength and reliability of welds by subjecting them to weld testing. Welds are usually subjected to mechanical loading to see how they respond.
NDT is another type of welding test method that is used to evaluate the soundness, integrity, and reliability of components. NDT stands for Non-Destructive Testing. NDT involves inspecting components without damaging them.
As the world strives to become more environmentally friendly, Non-Destructive Testing (NDT) has become an increasingly important part of many industries.
NDT allows products and components to be inspected without causing damage, which means they can be reused or recycled.
There are a variety of NDT techniques, each with its own strengths and weaknesses. Some of the most common techniques include:
- Visual Inspection,
- Penetrant Testing
- Ultrasound Testing,
- Radiography Testing,
- Magnetic Particle Inspection.
- Eddy Current Testing
- Magnetic Flux leakage Testing
- Leak Test
Welding is a process that can create some of the strongest bonds in metalworking. However, welding can also cause defects in the weld joint that may weaken the structure.
Non Destructive Testing (NDT) allows welders to detect these defects and fix them before they cause any problems. NDT can also be used to inspect welds for quality control purposes.
TYPES OF DESTRUCTIVE TESTING FOR WELD TESTING
Destructive testing is a type of testing that is used to determine the quality of a weld. There are many different types of destructive testing, but some of the most common are fracture mechanics testing, impact testing, and hardness testing.
Fracture mechanics testing is used to determine the strength and toughness of a weld. Impact testing is used to see how well a weld withstands impact loading. And hardness testing is used to measure the hardness of a weld.
1. BEND TEST FOR WELD TESTING
Bend testing is a common welding inspection method that is used to verify weld quality. The bend test is performed by bending the welded part around a specified notch or radius.
The weld should not fail and the metal should not crack under the stress during bending for an acceptable bend test result.
The bend test is specified in ASME section 9 and AWS D1.1 for welder testing & weld testing for performance & procedure qualification.
2. TENSILE TEST FOR WELD TESTING
Welding is the process of joining two or more pieces of metal by heating the pieces to their welding temperature and then bringing them into contact with each other.
The welded joint must have the same strength as the base metal. In order to ensure that the welded joint has the same strength as the base metal, a tensile test must be performed on the welded joint.
The tensile test is performed by pulling on the welded joint until it fails under tension. The amount of force required to pull the welded joint apart is called the breaking strength or ultimate strength. The breaking strength is measured in pounds per square inch (psi) or megapascals (MPa) or N/mm2.
The tensile test can be performed in two ways for testing welds:
- Transverse Tensile Test and
- Longitudinal Tensile Test (all weld tensile tests).
3. WELD MACRO TEST FOR WELD TESTING
The welding macro test is a test to measure the quality of weldment by observing its weld penetration, welding zone, HAZ & microstructure against the presence of welding discontinuities. The test is performed by etching and polishing the weldment to reveal its microstructure.
The quality of weldment can be determined from the microstructure, such as the size and shape of the grains, the presence of defects, and the degree of separation between grains is checked & reported.
4. CHARPY IMPACT TEST FOR WELD TESTING
A Charpy impact test is a welding test used to determine the toughness of a welded joint. The test is performed by striking the weld with a falling pendulum and measuring the amount of energy required to break the weld.
The energy required to make the fracture is called the “Charpy V-notch” toughness or energy.
The Charpy impact test is used to determine the toughness of a welded joint and to compare the toughness of different welding processes.
5. NICK-BREAK TEST FOR WELD TESTING
This test is applied to a welded butt joint in a plate or pipe to check weld soundness. The typical specimen dimensions for plate and pipe.
Read more: Nick Break Test in depth.
It is not necessary to remove the weld reinforcement. The sample is braced as shown in the Below figure and ruptured by giving one or more sudden heavy blows with a hammer at the point of the nick or the notch as indicated.
The rate of applying the force is not critical, because it has no effect on the appearance of the fractured surface.
The surface of the fracture is examined for the presence of internal defects, such as lack of fusion, slag inclusions, and porosity.
This test can be conveniently carried out in shops and at Sites for quick assessment of weld quality, since no elaborate equipment is necessary, and the interpretation is relatively simple.
6. FREE-BEND TEST FOR WELD TESTING
Free Bend Test measures the ductility of the weld metal in a butt joint in a plate or pipe in terms of elongation percentage.
The thickness of the specimen is the same as that of the plate or the pipe, the width is 1.5times the thickness and the length is anywhere between 150 mm for 6 mm t and 450 mm for 50 mm t. The length is not mandatory.
The weld is dressed to the plate level by filing, grinding, or machining, bearing in mind that the tool marks should be lengthwise to the specimen.
It is important that the line between the weld metal and the base metal is distinctly visible, and if necessary the surface of the specimen should be etched with a suitable reagent.
Two gauge lines are lightly marked on the specimen. The distance between the gauge lines should be 3 mm less than the width of the weld.
7. FILLET-WELD-BREAK TEST FOR WELD TESTING
This test is similar to the nick-break test and is meant to test the weld soundness. The test specimen, as shown in below figure consists of two plates making a tee joint and a fillet weld laid on the outer side of the joint.
The base metal, weld metal, and welding parameters must be strict as prescribed in the welding procedure being qualified.
Tack welds at the ends of the joints should be avoided as they make it difficult to rupture the specimen. The manner of positioning the specimen and the direction of force is also shown in the above figure.
The forces may be applied by means of a testing machine, a press or hammer blows. The fractured surfaces are examined for internal defects such as porosity, incomplete root penetration, and slag inclusions.
8. HARDNESS TEST FOR WELD TESTING
The term, hardness of a metal, cannot be precisely defined and has many meanings. In general, hardness usually implies resistance to deformation, and in the case of metals, it is a measure of their resistance to plastic or permanent deformation.
The harder a metal is, the more it resists scratching, wear, penetration, machining, and mechanical cutting.
Tensile strength also increases with hardness. The hardness of the base metal and weld-metal of a welded joint is affected by chemical composition, the metallurgical effects of welding, cold working of the metal, heat treatment, and several other factors.
Limitations have to be placed on the hardness of the heat-affected zone and weld-metal, because if they are too hard, they will not have sufficient ductility for the service conditions and their corrosion resistance may also be impaired.
- Brinell hardness
- Vickers hardness
- Rockwell hardness.
9. DROP-WEIGHT TEST FOR WELD TESTING
This test is designed to measure fracture initiation characteristics of structural materials heavier than 18 mm.
The specimen dimensions vary according to plate thickness. For 25.4 mm t, length and width are 355 and 90 mm; for 19 mm t, the corresponding dimensions are 127 and 51 mm. A weld bead, 63.5 mm long and 12.5 mm wide, is deposited on the tension surface of the specimen using a special hard-facing electrode.
It is fixed by punch marks at A, B and C. Actually two beads are laid, one from A to C and the other from B to C as indicated in the figure, so that the end craters meet at point C.
The weld bead which is a brittle material is called the crack-starter weld. A notch is made at the center of the bead length and is placed at right angles to the weld bead and parallel to the specimen.
The notch dimensions are shown in Fig. 13.35. It is important that the notch is present only in the weld deposit and that the cutting tool (abrasive disc, hacksaw, etc.) does not touch the plate surface.
The specimen is mounted on an anvil provided with a stop block. The impact load is applied by dropping weight. A machine design suggested by ASTM permits the use of various weights and various drop heights according to the strength level of the metal.
NON DESTRUCTIVE TESTING (NDT) FOR WELD TESTING
Non-Destructive Testing, or NDT, is a process of inspecting and evaluating a weld without causing damage. There are many different types of NDT, but the most common are visual inspection, radiography, ultrasonic, and magnetic particle testing.
Visual inspection is simply looking at the weld to see if it meets the requirements. Radiography uses X-rays to image the weld and check for any defects.
Ultrasonic uses sound waves to detect discontinuities in the weld. Magnetic particle testing uses a magnetic field and ferrous particles to identify cracks and other defects.
All of these methods have their own advantages and disadvantages. For example, radiography can detect very small defects, but it can be expensive and time-consuming. Ultrasonic is relatively cheap and fast, but it can only detect discontinuities that are a certain size or larger.
1. PENETRANT TESTING (PT)
Liquid Penetrant Testing (DP Test) is a nondestructive testing (NDT) method that uses a penetrant liquid to detect discontinuities in a weldment.
The penetrant is forced into the weldment by capillary action and drawn out by the action of a developer.
Any discontinuities in the weldment will allow the penetrant to seep through and be drawn out by the developer, causing a visible indication on the surface of the weldment.
There are two types of penetrants: water-soluble and solvent-based.
Water-soluble penetrants are less aggressive than solvent-based penetrants and are less likely to cause damage to the weldment. Solvent-based penetrants, however, are more aggressive and can cause damage to the weldment if not properly removed.
2. MAGNETIC PARTICLE TESTING (MT or MPI)
Magnetic particle testing (MPT), or magnetic particle inspection (MPI), is a type of non-destructive testing (NDT) that is used to inspect & locate surface & subsurface imperfections in ferromagnetic materials.
The principle behind the technique is that a magnetic field will cause magnetic particles to cluster around discontinuities in the material.
MPT can be used to detect cracks, seams, laps, voids, and other defects in ferromagnetic materials.
The most common application of MPT is in the welding industry. Welders use MPT to inspect welds for defects before releasing them for use. MPT is also used to inspect welds that have been repaired.
3. ULTRASONIC TESTING (UT)
Ultrasonic testing (UT) is a nondestructive testing (NDT) method that uses sound waves to examine the internal structure of a material. UT can be used to detect discontinuities, such as cracks or porosity, in both welds and base materials.
There are two main types of ultrasonic testing:
- pulse-echo and
In pulse-echo testing, a burst of sound waves is sent into the material, and the reflected waves are detected by a receiver.
The time between the sending of the burst and the reception of the reflected waves can be used to calculate the distance to the discontinuity.
In through-transmission testing, a probe is inserted into the material and ultrasound is transmitted through it. The reflected ultrasound is then detected by another probe on the other side of the material.
4. RADIOGRAPHIC TESTING (RT)
Radiographic testing, also known as RT or X-ray, is a common method of inspecting welds for defects.
A radiograph is a picture of the weld that is created by radiation passing through the weld and striking a film on the other side. By looking at the characteristics of the image on the film, inspectors can identify any defects in the weld.
One advantage of radiographic testing is that it can be used to inspect both surface and subsurface defects.
Additionally, it can be used to inspect both joints and welds themselves. However, radiographic testing is expensive and time-consuming, so it is not always practical for use in every situation.
5. VISUAL TESTING (VT)
Visual Testing is a method of inspecting welds and weldments for defects. The technique uses the human eye to examine welds for discontinuities, Lack of Fusion, porosity, slag inclusions, and other Welding defects.
Visual inspection is often used as the primary method of inspection for welds that are not readily accessible or that are too large to be tested by other methods.
Visual testing is typically performed by a welder who is qualified to inspect welds. The inspector examines the weld visually and looks for any signs of defects.
Defects that are found can be repaired before the welding process is finished or the part is put into service.
6. ELECTROMAGNETIC EDDY CURRENT TESTING
An eddy current test is a non-destructive test (NDT) that uses the principle of electromagnetism to detect flaws in metal objects.
A coil of wire is placed around the object to be tested and an electric current is passed through the coil.
This creates a magnetic field which causes currents to flow through the metal object in a circular pattern (eddy currents).
If there are any flaws in the metal, they will disrupt the flow of these eddy currents and this will be detectable by changes in the magnetic field.
Eddy current testing is often used to inspect welds for defects. The weld itself can be tested or the surrounding area may be tested if there is any doubt about the quality of the weld. The test can be used to detect cracks, porosity, lack of fusion, and other flaws.