Welding is a skillful art that requires precision and carefulness. Nevertheless, even the most experienced welders can face defects in welding that affect their work’s quality and strength. Welding defects are deviations or irregularities on the surface that affect its appearance, behaviour, or durability. Such issues can result in costly reworks and delays, posing safety and reliability risks.
Fortunately, there are steps to prevent defects in welding through knowledge, techniques, and inspections. This blog will discuss the anatomy of weld defects, how S.T. & W Inspections prevent them, common causes, cures, failure of welds, and the best practices for proactive welding.
The anatomy of weld defects
Weld defects can be classified into two main categories: weld cracks and welding imperfections. Weld cracks are fissures or splits in weld metal or in the base metal that may originate during or subsequent to welding. Welding imperfections are departures from the desired shape, dimension, or outline of the weld that may influence its appearance or performance.
Understanding weld cracks
The most severe type of weld defect is crack weld as it can develop and lead to complete failure of the weld itself. Cracks in welds can be attributed to thermal stress, hydrogen embrittlement, incomplete fusion, inappropriate filler and poor design. Some common types of weld cracks are:
- Longitudinal cracks: Longitudinal or base metal cracking down the line.
- Transverse cracks: Longitudinal cracks parallel to the weld direction or base metal.
- Crater cracks: Forms of cracks that occur at the end of a weld bead, during the rapid solidification of the weld pool.
- Toe cracks: Cracks develop along the perimeter of the weld, which is between the weld metal and the base.
- Root cracks: The bottom of the weld is penetrated by cracks which lead to cracks that form at the bottom of the weld.
- Undercut cracks: Cracks that develop in the edge of the weld, where the base metal is dissolved by the arc.
Weld cracks may lessen the strength and ductility of the weld, creating stress concentrations which may further lead to additional cracking or failure. This implies that one should always check the weld cracks to prevent and detect them immediately upon occurrence.
Identifying welding imperfections
While not as serious as weld cracks, welding imperfections may affect the quality or performance capabilities of a weld. Welding imperfections can arise due to factors like unsuitable welding techniques, wrong welding parameters, poor preparation, and unfavourable conditions in the surroundings. Some common types of welding imperfections are:
- Porosity: Trapped gas or other contaminants causing small holes or cavities in the weld metal.
- Inclusions: Incomplete cleaning or inadequate shielding causing foreign materials or slag trapped in the weld metal.
- Lack of fusion: Inadequate heat or penetration resulting in a gap or discontinuity between the weld metal and the base metal.
- Lack of penetration: This is a lack or interruption in heat or filler material at the weld’s root.
- Underfill: Insufficient filler material or excessive travel speeds cause depression or concavity on the weld face.
- Overfill: Excessive fill metal or low travel speed, resulting in a bump or bulge on the weld face.
- Distortion: Uneven heating and cooling that brings change of shape or dimensions of the weld or the base metal.
They can be cosmetic, dimensional or they may affect the usability of the weld, they can be weak points and even stress raisers that could lead to cracking or even failure. Hence, the welding imperfections, which are to be identified, evaluated, and corrected according to the relevant codes and specifications, need to be established.
Common causes and solutions
Understanding the common causes and solutions for defects in welding will help prevent them. Here, some of the most common causes of weld defects, and how to avoid them will be discussed.
Reasons for weld defects
Some of the common causes of weld defects are:
- Improper welding technique: Weld defects may result from poor or incorrect welding and can include such as lack of fusion, lack of penetration, porosity, and distortion. For instance, the weld quality can be influenced by wrong angle, direction, speed of welding torch, too little or excessive pressure.
- Incorrect welding parameters: A crack, porosity, underfill or overfill is the most common weld defect. For instance, selecting the wrong current, voltage, polarity, or gas flow, or choosing the wrong electrode, filler material or shielding gas influences the quality of the weld.
- Inadequate preparation: Weld defects such as cracks, porosity and inclusions could occur as a result of inadequate preparation. For example, failure to clean or degrease the weld area, to remove scale, rust, and paint, or to preheat or post-heat the weld, may all affect the quality of the weld.
- Environmental conditions: Weld defects may comprise cracks, porosity, or distortion in a bad or unfavourable environmental condition. For instance, welding in a windy, humid or dusty environment or exposing the weld to rapid cooling or heating can affect the quality of the weld.
The Role of S.T & W Inspections Ltd.
S.T & W Inspections Ltd. is one of the most competent providers of welding inspection and testing in the United Kingdom. S.T & W Inspections Ltd. has over two decades of experience and expertise in preventing defects in welding and ensuring good welds in projects you are undertaking. S.T & W Inspections Ltd. offers a range of services and methodologies for preventing welding defects, such as:
- Welding procedure qualification: The process involves proving that a particular welding procedure can be used in the production of the weld that conforms to specified specifications.
- Welder qualification: It is an important step in checking whether a welder is skilful enough and competent to do a particular welding operation.
- Non-destructive testing (NDT): Non-destructive examination conducted by one or more means of checking (such as visual inspection, magnetic particle test, liquid-penetrant test, ultrasonic testing, radiography) that allow the inspector to see internal irregularities in the weldment without destroying it.
- Destructive testing (DT): Destructive testing whereby a specimen weld is inspected and tested by destroying it in the process through methods like tensile testing, bend testing, impact testing or hardness testing.
How to prevent cracks in welding?
Weld cracks are the most serious and dangerous type of weld defect, but they can be prevented by ensuring you:
- Choose the right welding procedure
- Choose the right filler material
- Choose the right shielding gas
- Control the heat input
- Control the cooling rate
- Perform regular inspections and tests
Implementing these procedures will help you avoid cracks in welding and ensure good weld quality. Nevertheless, for such advice and help contact S.T & W Inspections. We will provide you with competent and trustworthy welding inspection and testing. S.T. & W Inspections Ltd. brings experienced people with knowledge to help you avert failure of welds in your projects and attain high-quality weld deposits. Reach us at S.T & W Inspections Ltd. today for free quotes on welding inspections and tests.