Welds can be tested by destructive and non-destructive techniques. Most production is tested by use of non-destructive methods. The most common non-destructive tests to check welds are Visual Inspection, Liquid Penetrant, Magnetic Particle, Eddy Current, Ultrasonic, Acoustic Emission and Radiography.
5 Types of Tests for Welder Performance Qualification
- Visual Inspection (VT)
- Bend Test (face, root, side)
- Macroetch Test.
- Fillet Weld Break Test.
- Radiographic Test (RT) – can be done in lieu of bend tests.
Weld Testing can broadly be broken down into two different types; non-destructive testing (NDT) and destructive testing.
To get the results in KJ/in or KJ/mm, divide the result by 1000.
- Example 1: If a welder takes 2 minutes to complete an 18 inches long weld.
- Answer:
- Travel Speed = Length of Weld/Time to weld = 18 inches/2 minutes = 9 in/min.
- Voltage = 24 volts.
- Current = 120 amps.
- Heat Input = (24 X 120 X 60)/ 9 = 19200 J/in.
- Table – 1.
The quality of a weld can mean different things depending on the requirements of clients. The most important factors include the size and type of weld, edge preparation, metal thickness, reinforcement members and distortion. Each of the above factors can affect and change the process of welding.
Porosity in welding happens when a contaminant or gas is absorbed into the weld puddle. These impure welds are commonly referred to as cavities.
As the welding processes require high current (50-300A) at relatively low voltage (10-50V),the high voltage mains supply (230 or 400V) must be reduced by a transformer.
Self-directed and independent, they are good at moving quickly, adapting to changing situations, responding to emergencies, and taking action. They are more interested in putting tools to practical use than in the mere theory behind their use. These are all very valuable traits in a welder.
What is polarity in welding? The electrical circuit that is created when you turn on the welder has a negative and a positive pole – this property is called polarity. Polarity matters greatly in welding because choosing the right polarity affects the strength and quality of the weld.
Welding has limitless possibilities depending on the kind of welding you are looking to learn. There are four main types of welding. MIG – Gas Metal Arc Welding (GMAW), TIG – Gas Tungsten Arc Welding (GTAW), Stick – Shielded Metal Arc Welding (SMAW) and Flux-cored – Flux-cored Arc Welding (FCAW).
Electrodes can be effectively examined by rolling them on a table top, as excessive wobbling indicates a lack of straightness. The eccentricity which results from bent electrodes may negatively affect the welding performance.
If the imperfections are surface breaking, they can be detected using a penetrant or magnetic particle inspection technique. For sub surface imperfections, detection is by radiography or ultrasonic inspection. Radiography is normally more effective in detecting and characterising porosity imperfections.
Radiographic and ultrasonic weld inspection are the two most common methods of NDT used to detect discontinuities within the internal structure of welds.
The main reason that weld quality assurance is so important is because a poor-quality weld is more likely to break or leak. The consequences of weld failure can range from a small inconvenience, such as a kitchen pipe bursting, to something that's far more dangerous like the structural failure of a bridge or gas pipe.
Two methods are widely used to evaluate the fixed strength of spot-welded joints: the tensile shear test and the peel test [1,2]. Owing to their destructive nature, these tests are expensive and time-consuming.
