This Picture shows a eletric troughhull conection plate just weld to an
submarine endcap. The weld was tested by a chemical test device : 
cleaner - red coulor - cleaner - white developer. 
After a couple of minutes every crack normaly invisible in the weld with
goes up to the surface will be visible as red line or spot as shown
here. This cracks has to be grinded out, preheated and welded again. 
Picture taken on 16 Jan. 2005 on Euronauts troughhull Number 14.