Seel construction products that receive a declaration of conformity in the sense of EN 1090 (independent of the EXC) must, among other things, be subjected to a visual inspection; the result of the inspection is a VT report. A visual inspection (also known as VT or visual testing) evaluates superficial quality features such as imperfections, shape deviations or other surface conditions. The test is carried out with the naked eye, a magnifying glass or other optical aids. General principles are described in EN EN 13018.
In general, test and inspection plans must be available for welding processes in many regulated areas. Requirements for test plans for welding work in the construction industry are set out in EN ISO 3834 in its respective level.
Non-destructive testing procedures must be in accordance with EN ISO 17635
The scope of the supplementary NDT must be defined individually for each weld in EXC1 to EXC3
Direct and indirect visual test
As mentioned above, there is the possibility of using aids in the case of NDT. Aids for the visual inspection can be:
- magnifying glass
- Video systems
As soon as the light steel emanating from the weld seam no longer hits the eye directly, this is referred to as indirect visual inspection. This can be the case if a video endoscope is used, for example.
In direct visual inspection, observation is made with the “naked eye”. There are optical endoscopes and other devices that direct the light beam directly onto the eye. This is also called direct inspection.
Waiting time for visual inspection
The visual inspection may only be carried out after the required waiting time has elapsed. These are up to 24 hours for procedure A according to EN 1011-2 for thicknesses of more than 12mm. For thicknesses below 12mm, 16 should be waited, or for thicknesses below 6mm, material can be obtained after the cooling phase with the examination. Procedure B distinguishes between material thicknesses greater and less than 20mm. If the cross-section is larger than 20mm, wait 24 hours. For small dimensions, the examination can be started directly after the cooling phase.
Attention: The time between welding and testing must be recorded in the test report. The component temperature should also be documented.
Qualification visual inspector
DIN EN 1090 does not explicitly require that the inspection personnel be qualified for the visual inspection (VT). This suggests that the welder can carry out the inspection after the welding process without special additional training. However, this standard refers to ISO 17636, which requires qualified personnel trained to ISO 9712 to perform the visual inspection. This means that additional training of the inspection personnel is required to ensure that the inspection is carried out according to internationally recognised standards.
To ensure that the inspection is carried out by qualified personnel, welding training and testing institutes, the German Society for Non-Destructive Testing (DGZfP) and other organisations offer training courses. These courses cost about 3000 € and last about one week. It is therefore important to invest in the training of the inspection personnel to ensure that the visual inspection is carried out correctly and possible welding defects are detected.
Visual inspections for new welding instructions
After new procedure qualification tests, visual inspections as well as supplementary NDT must be carried out on the first five welds. Minimum length 900mm. And this under manufacturing conditions and evaluation group B of EN ISO 5817. If the welding was not successful, an investigation must be undertaken. In short: a fault must be found.
Routine inspection of the welds
All welding seams that are put into circulation in connection with the Construction Products Ordinance must be tested. The extent of the test is defined by table 24 of the standard EN 1090. For EXC4, the manufacturer must determine the scope of testing individually.
It may be advisable to train welding personnel in small companies for the performance of a visual inspection and possibly supplementary NDT. This way, an inspection of the welds can be performed immediately after waiting for the waiting time.
For larger companies with their own QA department, it is almost obligatory to have seconded personnel for inspections.
Minimum requirements visual inspection (VT)
A visual inspection is usually carried out after the waiting period has been observed. In addition, the VT inspection is carried out first; only after all apparent irregularities have been documented may the additional NDT take place. At least the VT-test must be included:
- Testing for the presence of all required welds.
- Inspection according to EN ISO 17637.
- Ignition points and areas with weld spatter.
Irregularities to be expected
DIN EN ISO 5817 is an international standard that specifies requirements for the visual assessment of welded joints. The standard defines different levels of visual assessment and specifies tolerance limits for each level. The tolerance limits describe which irregularities in the welded joint are still acceptable and which are to be regarded as defects.
However, the standard itself also contains inaccuracies, so that errors can occur during the visual assessment of welded joints. To minimise these errors, a qualified VT report can be prepared. VT stands for “visual inspection”. With a qualified visual inspection, approx. 60 % of the expected irregularities can be detected. However, it should be noted that the presence of an irregularity is not synonymous with a defect.
As already mentioned, DIN EN ISO 5817 specifies a tolerance range for many phenomena. This means that certain irregularities in the welded joint may be present but must be within a certain tolerance range to be considered acceptable. However, there are also irregularities that must not be tolerated under any circumstances. These include, for example, cracks in the weld seam.
It is therefore important that the visual assessment of welded joints takes into account both the standard and possible inaccuracies and tolerance ranges. A qualified visual inspection can already detect many irregularities that can help to ensure that the welded joint meets the requirements.
Quality levels for imperfections
There are four evaluation groups in ISO 5817, from the highest to the lowest class: B, C and D. Each rating group has different requirements for weld quality and has different requirements for the size, shape and distribution of irregularities. The evaluation groups are also referred to as quality grades.
Evaluation group B has the highest demands on weld quality and requires welds that are almost free of defects. Quality levels C and D have increasingly larger tolerances for irregularities and defects. Group E allows the largest irregularities and defects, but these may still be acceptable for a particular application.
The rating groups are determined by visual inspection criteria such as the size, number, distribution and shape of the irregularities. The rating groups may vary depending on the application and manufacturing context. It is therefore important that welders and inspectors are familiar with the assessment groups and understand the requirements for each application.
Overall, ISO 5817 is an important standard for assessing weld quality. By using evaluation groups, the quality of welded joints can be assessed objectively, resulting in safer and more reliable welded joints.
In the following I provide a free VT report.