Reinforcement of openings in Pressure vessels

[arksurat]

As per ASME SEC VIII, Div I , certain sizes of openings in Pressure
vessels not subjected to rapid fluctuations in pressure are exempted from reinforcements. What exactly does it mean by 'rapid fluctuations'?
Can it be quantified?

 

[prex]

I suggest using the criteria of Div.2 AD-160, excluding thermal cycles: in other words, for integrally reinforced nozzles (full penetration welded: this is normally the case for small nozzles) no more than 1000 cycles with pressure variations exceeding 20% of the design pressure. prex
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