Cold shut is where an oxide layer has formed in an area of the casting preventing the metal on each side of the oxide from fusing together. It is a lot like incomplete fusion while welding.
I think your technician needs to go back to his/her training manuals and learn what a cold shut is. As GRoberts already mentioned this discontinuity is specific to castings. My guess is there is some overlap/incomplete fusion.
From www.bibliomania.com which has the 1913 websters dictionary (when welding was still commonly done by forging).
Cold-shut
(Cold"-shut`) a. (Metal.) Closed while too cold to become thoroughly welded; — said of a forging or casting. — n. An imperfection caused by such insufficient welding.
From gdict (the gnu dictionary)
Cold shut, the imperfection in a casting caused by the
flowing of liquid metal upon partially chilled metal;
also, the imperfect weld in a forging caused by the
inadequate heat of one surface under working.
You could extend this to include poor fusion in a weld although it might not be common usage. Fusion welding being in a way a sort of casting. Distortion from welding could also cause a preexisting cold shut to leak.
Bill
My 2 cents.
I've been taught that the proper term is "cold lap". This pertains to the casting defect which bill best describes "Cold shut, the imperfection in a casting caused by the flowing of liquid metal upon partially chilled metal. In laymens terms it is when liquid metal flows into a casting and cools then more liquid metal flows in on top of the adready solidified metal and cools itself. No fusion has occured between the 2 flows of metal.
A cold lap is almost the same thing as an overlap (welding defect).
kam
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