Accumulation is pressure above the maximum allowable working pressure that vessel experience during high pressure event. Hence, when we say ‘accumulation’, its mean we are talking about the vessel or equipment. On the other hand, Overpressure is pressure above the set pressure of the pressure safety valve that PSV experience during high pressure event. Hence, when we say ‘accumulation’, its mean we are talking about the pressure relief valve.

1. Accumulation and
Overpressure
Varun Patel, B.E- Mechanical, PMP®
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2. Accumulation and Overpressure
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Chart Source :http://process-eng.blogspot.com/

3. Accumulation
• Accumulation is pressure above the maximum
allowable working pressure of the vessel that
vessel will experience during the high operating
pressure event
• Accumulation is related to vessel
• Refer chart
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4. Overpressure
• Overpressure is pressure above the setting pressure
of the relief valve that relief valve experience
before pressure start reducing
• Overpressure is related to the pressure relief valve
• Refer chart
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5. Different Types of Pressure for Equipment
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Hydro test Pressure 130% of Design Pressure
Max. Allowable accumulation (fire) 121% of Design Pressure
Max. Allowable accumulation
Multiple valve – Non fire
116% of Design Pressure
Max. Allowable accumulation
Single valve – Non fire
110% of Design Pressure
MAWP (Maximum Allowable Working Pressure) 100% of Design Pressure
(Minimum or more)
Design Pressure
Operating Pressure 90% of Design Pressure
Set Pressure of PSV

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