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 application. 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 accordance to established rules (e.g. DIN EN 23277, allowable limit 1or 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 efficient 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 afterwards. 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.