Maximum Allowable Operating Pressure or MAOP is a pressure limit set, usually by a government body, which applies to compressed gas

pressure vessels A pressure vessel is a container designed to hold gases or liquids at a pressure substantially different from the ambient pressure. Construction methods and materials may be chosen to suit the pressure application, and will depend on the size ...

, pipelines, and

storage tank Storage tanks are containers that hold liquids, compressed gases (gas tank; or in U.S.A "pressure vessel", which is not typically labeled or regulated as a storage tank) or mediums used for the short- or long-term storage of heat or cold. The t ...

s. For pipelines, this value is derived from Barlow's Formula, which takes into account wall thickness, diameter, allowable stress (which is a function of the material used), and a

safety factor In engineering, a factor of safety (FoS), also known as (and used interchangeably with) safety factor (SF), expresses how much stronger a system is than it needs to be for an intended load. Safety factors are often calculated using detailed analy ...

. The MAOP is less than the MAWP (maximum allowable working pressure). MAWP is defined as the maximum pressure based on the design codes that the weakest component of a

pressure vessel A pressure vessel is a container designed to hold gases or liquids at a pressure substantially different from the ambient pressure. Construction methods and materials may be chosen to suit the pressure application, and will depend on the size o ...

can handle. Commonly standard wall thickness components are used in fabricating pressurized equipment, and hence are able to withstand pressures above their design pressure. The MAWP is the pressure stamped on the pressure equipment, and the pressure that must not be exceeded in operation. Design pressure is the pressure a pressurized item is designed to, and is higher than any expected operating pressures. Due to the availability of standard wall thickness materials, many components will have a MAWP higher than the required design pressure. For pressure vessels, all pressures are defined as being at highest point of the unit in the operating position, and do not include static head pressure. The equipment designer needs to account for the higher pressures occurring at some components due to static head pressure.

Relief valve A relief valve or pressure relief valve (PRV) is a type of safety valve used to control or limit the pressure in a system; pressure might otherwise build up and create a process upset, instrument or equipment failure, or fire. The pressure is r ...

s are set at the design pressure of the pressurized item and sized to prevent the item under pressure from being over-pressurized. Depending on the design code that the pressurized item is designed, an over-pressure allowance can be used when sizing the relief valve. This is +10% for PD 5500, and

ASME The American Society of Mechanical Engineers (ASME) is an American professional association that, in its own words, "promotes the art, science, and practice of multidisciplinary engineering and allied sciences around the globe" via " continuing ...

Section VIII div 1 & 2 (with an additional +10% allowance in ASME Section VIII for a fire relief case). ASME has different criteria for steam boilers. Maximum expected operating pressure (MEOP) is the highest expected operating pressure.

References

Fluid dynamics Pressure vessels {{engineering-stub

See also

References