Crack monitoring uses a brittle conductive lacquer painted over an insulating surface to detect and monitor cracks in machine components. The lacquer cracks along with the material and its cracks can be detected through a monitoring network connected to the lacquer tracks. Laboratory tests showed the system can accurately detect the start of cracks. It has advantages of a thin brittle layer, sensitivity, flexibility in track shapes, and simplicity of application to complex surfaces. Proper cleaning and experience applying the lacquer system are important for effective crack monitoring.

1. CRACK MONITORING
General:
This test technique is applied in order to observe machine components with cracks suspected and/or
in order to monitor incipient cracks or cracks already existing.
Introduction
Enhanced diagnosis activities with crack testing during the overhaul of old generators resp. motors
sometimes reveal cracks that are possibly rather old and have not yet resulted in a failure of the
machine. Some diagnostic test also may show incipient cracks or – stated from design calculations
or experiences obtained by the inspection of similar machines – cracks must be suspected to occur
in highly stressed components later on.
If it is not possible to repair the cracks and/or to eliminate the origin of these cracks, a large repair of
replacement of the component is necessary which normally is only possible after a longer time for
design, provision of material and manufacturing.
During this time (or for continuation of operation) the generator/motor in many cases may stay in
services, but often operation has
To be reduced and additionally assurance companies probably will raise their rates or make the
assurance dependent on a monitoring of the cracks (s).
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2. Cracks Monitoring
A system for crack monitoring was developed (and patented) by ELIN, based on a brittle conductive
lacquer painted over an insulating varnish and protected by an insulating coat (schematic sketch see
(figure 1).
A lot of such conductive tracks may be connected by normal wiring to a monitoring network. The
lacquer system was chosen to be brittle enough to crack together with the material. But should not
crack due to ageing.
The sensitivity of this monitoring in laboratory-tests proved to be very high: starting of cracks in
alternating bended test samples could be accurately detected.
The advantages of this system are the thin brittle layer and its good sensitivity, the freedom in
choosing the shape of the conductive tracks and the simplicity of good application to all surface
shapes especially to welded joints.
General requirements
In most cases the application of the conductive lacquer is done during major overhauls; the
applicability during short machine-stops depends on the actual spot of the expected/existing crack.
The extent of disassembly work depends on this actual spot, too.
In any case a visual inspection of the component under test is indispensable. Other crack detection
techniques such as PT, RT, UT, MT may be necessary prior to the application of the lacquer in order
to find the most effective track.
Cleaning of the actual component is strongly recommended, cleaning is indispensable in cases
where a track has to be painted.
Experience in choosing the track and in the application of the lacquer system is indispensable.
© This QM-Instruction is properly of PNG Power and must neither be copied nor used in any other
way without the written consent of PNG Power. Neither is it to be handed over nor in other way
communicated to a third party. Infringement will lead to prosecution.
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