Maximum Allowable Operating Pressure (MAOP)
Maximum Allowable Operating Pressure (MAOP)
Maximum Allowable Operating Pressure (MAOP) is the maximum pressure that can be safely operated by a pipeline.The thickness of the wall, pipe outer diameter, and Specified Minimum Yield Stress are used to calculate the MAOP of a pipe. A more detailed coverage of this calculation and the entire process associated with this calculation are illustrated below.
What is Maximum Allowable Operating Pressure?
MAOP is calculated through the formula below:
Factors of safety x specified minimum yield stress x pipe wall thickness / pipe outer diameter
Pipeline operators need to be aware of the MAOP of their lines and understand that when this maximum pressure is exceeded, it could result in a catastrophe that may involve infrastructure damage and even fatalities. Hence, a margin of safety needs to be employedwhen calculating MAOP. Accurate determination of MAOP is a critical issue for undocumented pipelines.
Specified Minimum Yield Stress
The specified minimum yield strength is the yield strength that is stated for the steel when bought and it must be documented in the grade certification. When a pipeline is built, the specified minimum yield stress is specified by the operator according to the requirements of the construction project. The actual pipe on hand often exceeds the minimum. This is because pipes are manufactured with multi-grade joints in a single certificate stating multiple grades. However, the operator is not allowed to run their pipeline at a higher pressure than the pressure that the pipeline was designed for. This makes the specified minimum yield stress an integral factor when calculating the maximum operating pressure allowed for a pipeline.
Grade
Grade is determined by the mechanical properties and chemical composition of a specific pipe steel. The steel chemical composition that is used in the production of pipe must adhere to the standards specified in the Specification 5L of the American Petroleum Institute. The chemical analysis of pipe steel must be comprised of the specifications of the following elements: carbon, phosphorus, manganese, chromium, sulfur, copper, columbium, nickel, molybdenum, silicon, vanadium, and titanium. The yield strength and ultimate tensile strength also needs to be measured. Yield strength refers to the point whereby the steel starts to deform plastically, and ultimate tensile strength refers to the maximum stress the steel can resist before necking in a tensile test specimen.To ensure adequate steel ductility to endure service-induced cracks, the ratio between the ultimate tensile strength and yield strength cannot go over 0.93. Steels that go beyond this ratio are considered to be brittle or low-toughness and are at more risk of a failure.
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