4. Conclusions for the PT application
The results of the investigations show that the PT application
on components for use under vacuum conditions can in general be
allowed. The following details should be adhered to:
The test surface should have a simple geometry. In no case they
should have gaps or holes, in which the penetrant can get.
Vacuum boundary welds have to be leak tested before PT appli-
cation. So there is no risk of subsequent leaks which are blocked by
the PT medium before.
With PT detached small indications,that are acceptable in accor-
dance to established rules (e.g. DIN EN 23277, allowable limit 1
or AD2000 HP 5/3) could be left. Larger indications, which could
include a sizeable portion of penetrant, should be grinded and
repaired.
An efficient cleaning after PT is necessary. But obviously an effi-
cient cleaning with ethanol and cloth until no contaminations are
visible is sufficient.
In comparison to MAG weld seams, TIG weld seams are basically
more convenient to PT application and the cleaning is easier after-
wards. If PT is foreseen TIG should used as the welding procedure.
PT tested components should be baked out after the cleaning
in a vacuum chamber at min. 150 ◦C, especially if the components
should be used at high temperatures later. For simple components
few hours are sufficient.
This investigation was performed with one special PT medium.
Other test media may show a different behavior and therefore,they
should be investigated in a similar way before they are used for
vacuum- or UHV-components.