Stress-relieving treatment is one of the most
effective measures in preventing DHC, a time-
dependent process. It takes considerable time
for hydrogen to reach the highly stressed area
and to precipitate out as hydride platelets. The
platelets must grow large enough for cracking to
occur Depending on many factors, it sometimes
takes two years for DHC to happen, but five
week after welding is the shortest known period
for Zr705 to suffer DHC at room temperature.
This provides a base for the Boiler and Pressure
Vessel Code of the ASME (Ref 26):