Maximum allowable working pressure pipes

Maximum Allowable Working Pressure -As defined in the construction codes for pressure vessels, the maximum allowable working pressure depends on the type of material, its thickness, and the service conditions set as the basis for design. The vessel or equipment may not be operated above this pressure, or its equivalent stress at any other metal, temperature. However, ANSI B31.3, Petroleum Refinery Piping Code, permits variations above the maximum allowable working pressure, as follows ... 

Maximum allowable working pressure MAWP) Highest pressure to which the system can be subjected during operation. Thus, pressure is established by a relief device set pressure and must be less than or equal to the material strength limitations of equipment. This pressure e.stabli.sh-es piping class for fittings and pipe wall thickness requirements, both of which are discussed in Volume 1. 

If more than one standard pipe size is indicated, calculate the wall thickness for each standard pipe size based on required maximum allowable working pressure and select a standard wall thickness for each -Size. 

A Pressure Relief Device (not shown) is required by NFPA 86 (sect. 4-4.3.12) whenever it is possible to have an event leading to an oxygen supply pressure that is greater than the MAWP (maximum allowable working pressure) of any of the components or piping within the oxygen pipeline. The pressure relief device must be sized properly per manufacturer and industry standards. The outlet of the pressure relief device must be piped to a safe location per NFPA 86 (sect. 4-4.3.7). 

Williams Natural Gas Company, Engineering Group. 1996. Pipe Characteristics Handbook. Tulsa, OK Pennwell Books. Although billed as a handbook, virtually the entire work is two sets of data tables 200 pages on maximum allowable working pressure as a percent of specified minimum yield, and less than 20 pages on properties of pipe. 

The function of a relief valve is to protect a vessel, piping system, or heat exchanger from exceeding its maximum allowable working pressure (MAWP). The MAWP is shown on the code stamp (a metal plate) attached to each process vessel, and by design is determined by the size of the impeller on the pump upstream of the vessel (see Sec. 34.4.1 in Chap. 34). Normally, the relief valve is set to open at this MAWP pressure. The relief valve setting is adjustable and is done by a machinist at a shop pressure-testing facility. 

Are safety valves installed with full-sized discharge piping properly supported and directed to a point of safe discharge and is safety valve set pressure equal to or less than boiler maximum allowable working pressure, because safety valve relieving capacity must be equal to or greater than boiler output ... 

As process temperatures increase the metal walls of pressure vessels will weaken thus reducing the maximum allowable working pressure (MAWP). (If the equipment of piping is made of synthetic materials, high temperature may lead to a sudden failiue.) Hence a very high temperature, such as would occur in a runaway reaction, could lead to vessel failure at quite low pressures. Therefore, MAWP values should always be quoted with a corresponding temperature value. 

Set pressure The PRV is set at this pressure to open and relieve. It is usually the design pressure of the equipment or piping, but less than or equal to the maximum allowable working pressure (MAW ) of the equipment or piping. 

In addition to these equations, there is a pressure called hve pressure (denoted by Pjjve) that is used in both codes for the design of overwrap repair. Live pressure is basically the operating pressure at the time of application of repair which is namrally lower than or equal to the maximum allowable working pressure of the defected pipe. 

For a clamp designed to a maximum allowable working pressure (MAWP) of 7 MPa, and for a repair of an 8 in nominal diameter pipeline, it has a 35-mm shell thickness (S), 56-mm flange thickness (F) and an inner mould line of diameter (Dj) of 223 mm, leaving a clearance gap between the clamp inner mould line and pipe (i.e. an annulus) of... 

Estimate the safe working pressure for a 4 in. (100 mm) dia., schedule 40 pipe, SA53 carbon steel, butt-welded, working temperature 100°C. The maximum allowable stress for butt-welded steel pipe up to 120 °C is 11,700lb/in (79.6N/mm ). 

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