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Tuesday, 21 May 2019
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Raw materials & technologies, Production and testing

Corrosion testing - the correct introduction of scribe marks

Tuesday, 23 July 2013

Corrosion testing is a frequently used important method to test the durability and resistance to weathering of coatings. To mark the right scribe is more than important to get reliable results. Get insights here.

Th right scribe is necessary for reliable test results

Source: Philipsteinphotographer

Th right scribe is necessary for reliable test results

Source: Philipsteinphotographer

Ingrid Bloss, Zehntner GmbH Testing Instruments, Switzerland presents at the European Coatings Conference "Protective coatings" on 12./13. September in Dusseldorf, Germany which instrument and scribe achieves best usability and reliable test results.

Modern coatings are very hardwearing; making testing of an unblemished surface is mostly useless. In most cases, the test surface is therefore furnished with artificially created damages like for example scribe marks. Introducing defined scribe marks is an important factor to achieve reproducible results.

Salt spray test done with artificial damages of the surface

The test panels are then subjected to artificial corrosion procedures, mostly in the form of salt spray of different composition like, for example, neutral salt spray (fog) according to ISO 9221-NSS or acetic salt spray according to ISO 9227-ASSS. The exposure time is dependent on the material under inspection; it can vary between 2 and 1000 hours.
The scratching tools, however, are not described in the corresponding salt spray standards, therefore standard ISO 17872 gives guidelines for the correct introduction of scribe marks on metallic panels for corrosion testing. Different scratching tools can be used and the scribe marks should penetrate the coating completely down to the metallic substrate and should be aligned according to defined patterns.

Instruments and tools for the right scratches

Since there are a large variety of tip shapes which are used to introduce scribe marks, the ideal solution is an instrument with interchangeable cutters.
Which scratching tool is most suitable depends on the coating. Different tip shapes can produce considerably different results.
Therefore the manner of execution of scribe marks plays an important role in corrosion testing. Since the existing standards leave much room for variation the execution of the test should be agreed upon previously by all parties involved.

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