Choose liquid before gas as the test medium if possible because liquid is much safer.
+ Do not use water colder than 4 DEG C because it can cause brittleness especially for equipment with thick walls.
+ For stainless steels (e.g. Type 304, 316), use demineralized water or boiler feed water with chloride content < 50 wppm due to “Stress Corrosion Cracking (SCC)” concern.