What Does Maximum Allowable Operating Pressure (MAOP) Mean?
The maximum allowable operating pressure (MAOP) is the pressure limit within which gas pipelines must operate. Exceeding this limit means the pipeline is operating with levels of pressure that are unsafe and beyond the equipment's capacity.
MAOP is used interchangeably with maximum operating pressure (MOP), maximum permissible pressure, and design pressure.
Safeopedia Explains Maximum Allowable Operating Pressure (MAOP)
The maximum allowable operating pressure is usually set by a government body and applies to compressed gas pipelines, pressure vessels, and storage tanks.
Calculating the MAOP of a Pipeline
The calculation that determines a pipeline's MAOP takes into account its wall thickness, outer diameter, and specified minimum yield stress (SMYS). The formula used to calculate MAOP is:
MAOP = Factors of safety x SMYS x pipe wall thickness / pipe outer diameter
Pressure levels that exceed the MAOP can result in loss of life and significant damage to infrastructure. As such, a margin of safety is employed when calculating a pipeline's MAOP.
The Yield Stress and Grade of Pipe Material
The specified minimum yield stress (SMYS) is an integral factor for calculating the MAOP of a pipeline. The SMYS is the yield strength that is stated for the pipe material and must be documented in the grade certification.
The yield strength of the pipe refers to the point where plastic deformation of the steel starts to take place. The ultimate tensile strength is the maximum stress that the steel can resist before necking. The grade of the pipe material is determined by its chemical composition and mechanical properties. The chemical composition of the steel used for pipe production must adhere to standards specified in Specification 5L of the American Petroleum Institute (API).
MAOP for Steel or Plastic Pipelines
§192.619 Maximum allowable operating pressure: Steel or plastic pipelines states, in part:
(a) No person may exceed the MAOP while operating a segment of steel or plastic pipelines as determined under paragraphs (c), (d), or (e) of this section, or the lowest of the following:
1. The design pressure of the weakest element in the segment…
2. The pressure obtained by dividing the pressure to which the pipeline segment was tested after construction…
3. The highest actual operating pressure to which the segment was subjected during the 5 years preceding the applicable date…
4. The pressure determined by the operator to be the maximum safe pressure after considering and accounting for records of material properties…
(c) The pressure restriction requirements do not apply if:
(1) The operator finds the pipeline segment to be in satisfactory condition with regard to its operating and maintenance history…
(2) For any Type C gathering pipeline under §192.9 existing on or before May 16, 2022, previously not subject to this part and for which the operator is unable to determine actual operating pressure…
(d) The steel pipeline segment operator meeting conditions in §192.620(b) may choose to operate the segment at MAOP determined under §192.620(a)
(e) Onshore steel transmission pipeline operators who meet the criteria in §192.624(a) must establish and document the MAOP in accordance with §192.624