Steel 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
Furthermore, EN 1090 does not require that the test personnel be qualified for visual inspections (VT). It seems as if the welder is allowed to carry out the test after the welding process without additional training. However, ISO 17636 is referred to here as the execution standard. This standard requires only qualified personnel trained according to ISO 9712 to carry out the test.
If you want to be on the safe side: training courses are held by the welding training and testing institutes, the DGZfP and other organizations. The cost of the training course is about 3000€ and takes about one week.
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
The DIN EN ISO 5817 offers a catalog of dissimilarities. By preparing a qualified VT report, about 60% of the expected irregularities will be found. An irregularity does not necessarily mean a defect. The ISO 5817 shows a tolerance range for many phenomena. However, cracks are not to be tolerated in any case.
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In the following I provide a free VT report.