Maximum allowable working pressure limit

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. 

When a pressure vessel is exposed to external heat or fire, supplemental pressure relieving devices are required for this excessive pressure. These devices must have capacity to limit the overpressure to not more than 21% above the maximum allowable working pressure of the vessel. (See Figures 7-7A and 7-7B.) A single relieving device may be used to handle the capacities of paragraph UG-125 of the code, provided it meets the requirements of both conditions described. 

A more conventional approach is to provide a safety relief valve or rupture disc to protect the vessel by venting material when pressure approaches certain limits, such as the maximum allowable working pressure. 

Maximum allowable working pressure (MAWP) The maximum permissible gauge pressure of a vessel in its operating position at a designated temperature. The pressure is based on calculations for each element in a vessel, using nominal thickness exclusive of additional metal thickness allowed for corrosion. The MAWP is the basis for the upper limit of pressure setting of the safety relief devices that protect the vessel (see Section 3.6). 

In general, when you work with a pressurized hydrogen system, limit the maximum allowable working pressure (MAWP) to the parameters of the component with the lowest pressure rating in the system. MAWP is the maximum allowable working pressure at which a system is designed to operate safely. So, it makes sense to consider the MAWP to be the pressure limit on the lowest rated component in the system. If a system consists of two components, one rated at 150 psi and the other rated at 1500 psi, the MAWP for the system should be 150 psi. 

The hydrostatic test pressure is 1.25 times the design pressure corrected for temperature, rather than the usual 1.5. Division 2 establishes upper limits for the test pressure relative to the yield strength at test temperature. The pneumatic test pressure is 1.15 times the design pressure corrected for temperature rather than 1.25 required by Division 1. Division 2 has no provision for proof tests to establish the maximum allowable working pressure. But Appendix 6, Experimental Stress Analysis, provides for the determination of the critical or governing stresses for unusual geometries for which theoretical stress analysis is inadequate. 

An engine operates on an actual reheat open Brayton cycle (Fig. 4.15a)). The air enters the compressor at 60°F and 14.7 psia, and exits at 120psia. The maximum cycle temperature (at the exit of the combustion chamber) allowed due to material limitation is 2000°F. The exit pressure of the high-pressure turbine is 50 psia. The air is reheated to 2000° F, and the mass flow rate of air is 1 Ibm/sec. The exit pressure of the low-pressure turbine is 14.7 psia. The compressor efficiency is 86% and the turbine efficiency is 89%. Determine the power required for the compressor, the power produced by the first turbine, the rate of heat added in the reheater, the power produced by the second turbine, the net power produced, back-work ratio, and the... 

We have demonstrated in this paper that two and four samples can be extracted in parallel with supercritical carbon dioxide without significant impact on data quality. Modifications made to an off-line extractor involved addition of a multiport manifold for the distribution of supercritical fluid to four extraction vessels and of a 12-port, two-way switching valve that allowed collection of two fractions per sample in unattended operation. The only limitation that we have experienced with the four-vessel extraction system was in the duration of the extraction. When working with 2-mL extraction vessels and 50-/zm restrictors, and using the pressure/temperature conditions mentioned above, the 250-mL syringe pump allows us a maximum extraction time of 60 min. During this time, two 30-min fractions can be collected with the present arrangement. 

---