Nine tests cover almost every weld inspection you will meet. Six are non-destructive, three are not.
| Test | Destructive? | What it detects | Typical use |
|---|---|---|---|
| Visual (VT) | No | Cracks, porosity, undercut, incomplete penetration on the surface | Every weld, first pass; AWS or ASNT certified inspector |
| Radiographic (RT) | No | Internal porosity, slag, lack of fusion | Pressure pipe and vessels |
| Ultrasonic (UT) | No | Internal flaws, and wall thickness | Thick sections, and materials RT handles poorly |
| Magnetic particle (MT) | No | Surface and near-surface cracks | Ferromagnetic materials only: carbon steel |
| Liquid penetrant (PT) | No | Surface-breaking defects | Non-magnetic materials: stainless, aluminium |
| Eddy current (ET) | No | Cracks, corrosion, wear, lack of fusion; also thickness | Non-ferrous materials, tubing |
| Bend | Yes | Ductility and soundness of the weld | Welder and procedure qualification |
| Tensile | Yes | Strength and elongation | Procedure qualification, material acceptance |
| Charpy impact | Yes | Toughness under sudden load, at temperature | Low-temperature and offshore service |
In this article we will learn more about welding tests and what they are performed on our products and systems. Welding is an important process in various industries. Weld quality affects the structural integrity of systems. Therefore, various test methods are used to inspect welds.
The Importance of Welding Tests
As mentioned earlier, welding affects the safety of the system. Quality welding is the backbone of reliable structural integrity. Even one weak weld can yield catastrophic consequences. That is why engineers use various testing methods. Welding tests serve several crucial purposes, including: Many of the defects these tests look for start before the arc does, in the preparation of the joint: contamination, a rough bevel or the wrong surface profile. Preparing the seam with milling discs for weld preparation cuts a clean bevel without the heat and smearing an abrasive leaves behind.
- Quality Assurance
- Welder Certification
- Material Compatibility
- Welding Procedure Qualification
- Defect Detection
Types of Welding Tests
There are various testing methods for welding. Each method assesses a different aspect of the weld. The most common methods of testing are below.
Visual Inspection (VT):
Visual inspection is the most basic testing. A certified inspector checks for cracks, porosity, or incomplete penetration. Some of the most sought-after certifications are from AWS (American Welding Society) or ASNT (American Society for Nondestructive Testing).
Radiographic Testing (RT):
RT uses X-rays or gamma rays to create an image of the internal structure of a weld. This method is very important for detecting internal defects. While it allows for a comprehensive inspection, it requires special equipment.
Ultrasonic Testing (UT):
UT uses high-frequency sounds to inspect the weld. It can also measure the thickness. It is very useful to inspect materials that are not suitable for RT, such as composites.
Magnetic Particle Testing (MT):
MT applies magnetic particles on the welding surface. Any defects will disrupt the welding surface, indicating faulty areas. MT is the primary testing method for ferromagnetic material.
Liquid Penetrant Testing (PT):
The inspector applies a colored penetrant on the weld surface. After a while, excess paint is removed and the weld is inspected under UV light. Penetrant trapped in defects highlights them.
Eddy Current Testing (ET):
ET testing uses electromagnetic induction to detect flaws in welds. ET can detect cracks, corrosion, wear, and lack of fusion. It is very useful to detect defects in non-ferrous materials and it can also measure thickness.
The testing methods mentioned so far are non-destructive. Meaning, the base material is not damaged during the test. Sometimes a more thorough inspection is required. The following testing methods are called destructive testing methods. In certain areas, they provide more detailed information about the welding at the cost of damaging the material.
Bend Testing
Bend testing assesses a weld’s ductility. In this test, the weld is subjected to bending tension. This evaluates the weld’s strength against this specific load type.
Tensile Testing
Tensile strength is an important parameter for various structures. Tensile testing applies pulling force from opposite ends of the material to measure the weld’s strength. The amount of elongation before failure is also measured to detect elasticity.
Charpy Impact Testing
Charpy impact testing measures a weld’s resistance to sudden, high-impact loads. A notched sample is subjected to impact forces, and the energy absorbed during fracture is recorded.
Weld test for a job application (3G/4G)
If you’re taking a weld test for a job, you are almost certainly doing a bend test on a 3G (vertical) or 4G (overhead) plate coupon. The inspector checks the coupon visually, then bends it: any crack over 3 mm on the face or root fails.
Conclusion
Welding is a fundamental process in various industries. Safe and reliable welds are well sought after. That is why a variety of testing methods for welds have been developed over the years. In this article, we’ve curated the most commonly used testing methods out there.
