Maximum Allowable Pressure defined

The maximum allowable pressure below the lowest service temperature is defined by paragraph NB-2332, Section III of the ASME Code, to be 20% of the preoperational hydrostatic test pressure. This test pressure is 125% of the design pressure (2500 psia), or 3125 psia, and 20% of this value is 625 psia. Therefore, the maximum pressure below the lowest service temperature is 625 psia (actual fluid pressure at the inside surface of the beltline). 

The first, 1914 edition of the ASME Code did basic things like defining the term maximum allowable working pressure, and defining the minimum allowable distance between rows of rivets. The 1914 Code stipulated that the maximum allowable pressure on cast iron boiler headers should not exceed 160 psig (about 10 atmospheres or 10 bar). Minimum capacities for boiler pressure relief valves were defined. 

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. 

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 ... 

When the maximum vapor-relieving requirement of the flare system has been established and the maximum allowable back pressure (as just described) has been defined, line sizing reduces to standard flow calculations. 

All pressure easing eomponents (ineluding seal glands and seal chambers) as defined in 1.4.40 shall be hydrostatically tested with liquid at a minimum of 1.5 times the maximum allowable working pressure, with the special provisions specified below ... 

Here Tmax represents a maximum allowed temperature. This can be defined to avoid triggering secondary reactions or to avoid high pressures. In fact, it corresponds to the worst case approach presented in Section 3.4. 

Most localities mandate compliance with national engineering codes such as the ASME (American Society of Mechanical Engineers) Boiler Pressure Vessel Code [1]. These codes govern mechanical design and provide the maximum allowable stresses and required low-temperature toughness, as a function of temperature, for approved materials. The codes also define requirements for fabrication procedures such as PWHT. All codes contain rules that ensure the selected material of construction will not be susceptible to brittle fracture at the minimum design temperature. Users of the codes must develop a familiarity with these rules. Eor example, code rules help avoid specifying materials at temperatures for which they are not permitted. 

In most engineering calculations, especially when designing structures and pressure vessels, the engineer must determine the maximum stress that a structure can withstand safely without any risk of rupture. As a rule of thumb, it is useful to introduce the maximum allowable stress denoted and defined by... 

The final step in the ECDA process is postassessment, which provides an opportunity to assess the overall effectiveness of direct assessment and define reassessment intervals based on remaining-life calculations. Various methods can be used to calculate the remaining life from the corrosion-growth rate, wall thickness, calculated failure pressure, 5deld pressure, maximum allowable operating pressure, and appropriate safety margin. 

It is seen that there will be a unique value for (dp), the optimum particle diameter, (dp(opt)), that will meet the equality defined in equation (14) and allow the minimum HETP to be realized when operating at a maximum column inlet pressure... 

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