Maximum allowable working pressure equipment

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 ... 

Manual Valve - Inadvertent operation of a block valve while the plant is onstream may expose equipment to a pressure that exceeds the maximum allowable working pressure. For the purpose of design, it is considered that only one manual valve is opened or closed and control devices are in their normal design position. A PR valve is required if the block valve is not locked or car sealed in the open position and if closure of such valve can result in overpressure. 

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. 

The pressure increase depends on the nature of the pressure source, that is, gas or vapor pressure. Further, the characteristics of the system, that is, if the reactor is closed or open to the atmosphere will determine the consequences. In an open system, the gas or vapor will be released from the reactor, whereas in a closed system, the result of a runaway will be a pressure increase. The resulting pressure can be compared to the set pressure of the pressure relief system (Pset) or to the maximum allowed working pressure (PJ, or also to the test pressure (PM) of the equipment... 

To identify blocked oudet scenarios, all maximum pressures of all inlet sources were compared to maximum allowable working pressure (MAWP) of the equipment under consideration. In addition, the potential for heat input from the process to result in vaporization at MAWP was considered. 

This type of installation has been shown to create a hazardous condition in the event that the rupture disk develops a pinhole leak that allows the pressure between the rupture disk and the relief valve to equilibrate with the process pressure. In order for the rupture disk to burst at its specified set pressure, the backpressure on the device needs to be low (typically atmospheric pressure). In the event of a pinhole leak, the rupture disk backpressure can rise until it reaches the equipment operating pressure, which effectively raises the burst pressure by a like amount. Depending on the set pressure of the rupture disk relative to the maximum allowable working pressure (MAWP) of the equipment, the equipment can be subjected to an overpressure that is unsafe. The typical layer of protection is to install a tell tale pressure gage between the rupture disk and the relief valve that is frequently monitored by operations. When pressure is noted, the rupture disk is replaced with a new one. 

In the revamp project, the maximum allowable working pressure (MAWP) of existing equipment may have to be either increased or decreased. Similarly, some new pressure... 

High-pressure operations should be carried out only with equipment specifically built for this use and only by those trained especially to use this equipment. Reactions should neva- be carried out in, nor heat applied to, an apparatus that is a closed system unless it has been designed and tested to withstand pressure. To ensure that the equipment has been properly designed, each pressure vessel should have stamped on it, or on an attached plate, its maximum allowable working pressure, the allowable temperature at this pressure, and the material of construction. Similarly, the relief pressure and setting data should be stamped on a metal tag attached to installed pressure-relief devices, and the setting mechanisms should be sealed. Relief devices used on pressure regulators do not require these seals or numbers. 

The ASME Code requires all equipment to be protected by pressure-relieving devices to prevent the pressure from rising above the maximum allowable working pressure. In some cases, the pressure can be permitted to rise to a value of ten percent higher than the maximum allowable working pressure. 

In field applications, it is assumed that the equipment has already been fabricated and been shop-tested for the maximum allowable pressure (MAP). The MAP is defined as the maximum allowable pressure of the vessel in the new and cold condition. It is more often determined in the shop before delivery. After the vessel is delivered, any test performed after operation begins is the maximum allowable working pressure (MAWP). The MAWP can also be used for new construction. The maximum allowable working pressure is defined as the maximum gauge pressure permissible at the top of the completed vessel in its operating condition for a designated temperature. Thus, in the field, you are likely to hear the term MAWP much more than MAP. 

Specify the maximum pressure that will be applied to the equipment. Normally, the pressure should be kept below the system s design pressure. If a higher pressure is required, determine the maximum allowable working pressure (MA WP) for each piece of equipment being pressurized. 

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. 

MAWP (maximum allowable working pressure) of a protected system EquipmeiU manufacturer makes an equipment per specified design pressure at design temperature, llie maximum pressure at the design temperature, which the final product can stand, is the MAWP. 

Sample preparation, including carbon or gold sputtering, used to be rather time consuming and examination had to take place in vacuum. However, modem environmental SEM (E-SEM) equipment employs a pressure chamber and short working distance and allows immediate observation without sputtering and vacuum. The maximum sample size that will fit in the measurement chamber is typically about 15 X 15 cm. ... 

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