Pressure Measurement · Glossary

What is Maximum Allowable Working Pressure?

Symbol: MAWPvessel rating at temperaturePressure Measurement

Maximum allowable working pressure is the highest gauge pressure permitted at the top of a vessel at its design temperature.

Maximum Allowable Working Pressure Explained

MAWP is calculated from the actual vessel thickness and material under the pressure vessel code, such as ASME Section VIII. It is at least equal to the design pressure.

The relief valve protecting the vessel is normally set at or below MAWP, and the code limits how far pressure may rise above MAWP while it relieves.

Maximum Allowable Working Pressure: Typical Values

Allowable accumulation, single relief valve	10 % of MAWP (ASME VIII, API 520)
Multiple relief valves	16 %
Fire case	21 %

Calculators for Maximum Allowable Working Pressure

CalculatorRelief Valve Sizing Calculator for GasFree online calculator with formula and worked example.CalculatorHydrostatic Test Pressure CalculatorFree online calculator with formula and worked example.CalculatorPipe Wall Thickness CalculatorFree online calculator with formula and worked example.

Frequently Asked Questions

What is Maximum Allowable Working Pressure?

Maximum allowable working pressure is the highest gauge pressure permitted at the top of a vessel at its design temperature.

Is MAWP the same as design pressure?

Not always. Design pressure is chosen by the process engineer; MAWP comes from the vessel as built and is equal or higher.

Why is MAWP at the top of the vessel?

Liquid head adds pressure lower down, so the code defines MAWP at the top and adds static head for lower parts.

Learn more on the blog

Instrumentation and control standards

A practical guide on instrumentationblog.in with more detail on maximum allowable working pressure and how it is applied on real plants.

Read Full Article

More Pressure Measurement Terms

Pressure termBlowdownBlowdown is the difference between the set pressure of a relief valve and the pressure at which it closes…Pressure termBack PressureBack pressure is the pressure at the outlet of a relief valve, from the discharge system or from flow…Pressure termHydrostatic Test PressureHydrostatic test pressure is the pressure at which piping or vessels are tested with liquid to prove…Pressure termBourdon TubeA Bourdon tube is a curved tube of oval cross section that straightens as pressure rises, moving the…Pressure termDiaphragm SealA diaphragm seal isolates a pressure instrument from the process with a flexible diaphragm and a sealed…Pressure termFill FluidFill fluid is the incompressible liquid inside a pressure sensor or diaphragm seal that transmits…

All pressure measurement terms · Full glossary A to Z