Page 104 - SSAB Welding Handbook Edition 2

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18.0 Non destructive evaluations Welding handbook

18.1 Visual testing 18.2 Penetrant testing
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Visual testing of the joint is a vital method that can The fundamental principle of penetrant testing is to
detect many types of discontinuities and its simplicity use a special type of liquid and/or powder to detect
makes it the most commonly used NDE method. This potential surface breaking discontinuities in and
procedure may, in certain situations, be viewed as an around the joint.
obvious method and paid limited attention. However,
when properly addressed and planned for, it facilitates Before testing, the inspection area should be cleaned
fast and cost efficient examination of the joint. to remove contaminants such as dirt, rust and grease
that can cover discontinuities in the joint. The area
Inspections of the joint can take place prior to, should be cleaned by applying suitable measures
during and after the completion of welding to for the particular contaminant such as solvents or
monitor that the desired welding conditions apply. a brush. Any paint and primer that is present in
the parent metal adjacent to the weld metal should
Furthermore, when the NDE examination also also be removed by either brushing or grinding. A
includes penetrant testing or magnetic particle liquid, called penetrant, is then applied to the joint. Its
testing, the visual inspection can reveal surface purpose is to penetrate possible discontinuities. The
breaking discontinuities that are more difficult to liquid needs to soak for a specified period, often in the
detect with the two former methods. range of 5-60 min. The excess liquid is then removed
from the inspected area according to the instructions
An inspection of the joint, in this case, can be for the penetrant while the liquid in the discontinuity,
performed with or without a supporting instrument. if present, remains.
The aid of an instrument is illustrated in fig. 18.1.
Next, a liquid or a powder developer is applied. If
a discontinuity is detected, the penetrant is drawn
into the developer by a reversed capillary action
and a distinct marking occurs at the location of the
discontinuity. The developer usually takes between
10-30 minutes, according to the specific product, to
10
15
1/2
reveal discontinuities.
The character of the discontinuity can be identified
to some extent even if the exact shape and depth
are hard to determine. Larger discontinuities appear
0 1/4 1/2 3/4 1
0 more quickly and have a more pronounced marking
IN 5 10 15 20 1/2 15
than smaller variants. The indications from linear
10
MM
discontinuities, cracks for example, are straighter
than the more rounded types. The indication from a
discontinuity is larger than its actual size.

Fig. 18.1: Visual assessment of the joint performed with a weld gauge.
The picture above illustrates measurement of the throat thickness
and the lower picture shows measurement of the height of the excess
weld metal.

104 This handbook contains general suggestions and information without any expressed or implied warranty of any kind. SSAB hereby expressly disclaims
all liability of any kind, including any damages, in connection with the use of the information and for their suitability for individual applications.
It is the responsibility of the user of this brochure to adapt the recommendations contained therein to the requirements of individual applications.