Tim Blok

Tim Blok

Tim Blok was trained as a metallurgist specializing in welding technology and has spent his entire working life in metal and welding technology. For many in the field, he is also known as a lecturer at the IWE and IWT courses.

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Welding imperfections

Cavities in welded joints

Cavities in welded joints have a detrimental effect on the integrity of a welded joint. The presence of large cavities may even cause the joint

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Welding imperfections

An imperfection is not a defect yet

When a weld is made there will always be welding imperfections present. The question is whether these are acceptable. In many cases they are. We only speak of weld defects when they affect the integrity and therefore the reliability of the weld.

When is it a welding defect? That is when the weld does not meet the acceptance criteria. These criteria are laid down in various standards. A widely applied standard in the visual examination of a welded joint is the NEN-EN-ISO 5817:2014.

Types of welding imperfections

Different types of welding imperfections can occur. Think for example of cracks, porosity, a convex or hollow weld. These are also recorded and described in a standard. The NEN-EN-ISO 6520-1:2007. In this standard, welding imperfections are subdivided into the following groups:

  1. Cracks
  2. Cavities
  3. Solid inclusions
  4. Bonding errors and inadequate weld penetration
  5. Geometric deviations
  6. Other imperfections

According to this standard, each welding imperfection is indicated by a three- or four-digit code, with the first digit indicating the group. Some examples are:

  • 1011 – Longitudinal crack
  • 2013 – Porosity
  • 3011 – Slag inclusion
  • 4021 – Inadequate penetration
  • 5011 – Indentation
  • 602 – Welding spatter

Many of these imperfections can be seen with the naked eye and will therefore be noticed during the visual examination of the welded joint.

Non-destructive testing

Some imperfections are too small to be seen during a visual inspection. Or they are present inside the weld and therefore not visible. These imperfections can be found with non-destructive testing (NDT). This is an examination in which the weld is not damaged or lost. Visual examination is therefore also a non-destructive type of testing. Other important NDT methods are:


The investigation and assessment of welding imperfections requires a certain expertise. The examination of a welded joint and the passing of a final judgement (acceptable or unacceptable) is therefore done by qualified personnel. 

On the report of the examination, only the imperfections are mentioned that are not acceptable and are therefore qualified as welding defects. 

The welder has a major influence on whether or not welding imperfections occur. But there are more influences. The material to be welded, the weld seam shape, weld tension and the welding procedure can also have an influence. 

How the welder can prevent or limit the various types of imperfections will be discussed in the following articles.

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