Final answer:
Socket welds larger than NPS 2 should not be used under severe cyclic conditions, according to ASME codes, due to increased susceptibility to fatigue cracking.
Step-by-step explanation:
The subject of this question pertains to engineering, specifically to the guidelines involved in welding practices for piping systems under certain conditions.
When dealing with socket welds, which are a common type of welding joint used to connect pipes to fittings, there is a restriction on their use under severe cyclic conditions (such as vibration or thermal cycling) that can lead to fatigue failure.
According to the ASME B31.1 Power Piping Code and B31.3 Process Piping Code, socket welds larger than NPS 2 (Nominal Pipe Size 2 inches) should not be used under such conditions as they are more susceptible to fatigue cracking due to the larger weld size and subsequent stresses applied during cyclic loading.