Overpressurization of low-heat-flux systems e. Factors affecting the calculation include:. Seat leakage. Shading effects.
API 521: Pressure Relieving and De-Pressuring Systems
Piping can be exposed to any combination of light, which makes it difficult to determine actual heat flux. Nonisothermal fluids. Viscous fluids 1, centipoise such as polymers generally do not conduct heat very well, so heating and expansion of the fluid are dampened. Also, polymers have a complex molecular geometry; therefore, they might compress better than a simple molecule.
Piping layout. A piping system usually has high points that will prevent the system from filling completely with liquid or long instrument sensing lines that entrap gases such as air or nitrogen. This small vapor space will act as a pressure absorber, reducing ultimate pressure. Administrative procedures. Based on the sequence in which block valves are closed, fluids can drain partially from the system, creating a small vapor space.
Protection by design. Piping systems designed with heavy-rated components withstand higher pressures. For water, the value determined through the following equation would be used to determine pressure rise:. However, this equation can lead to erroneous results because it does not account for the elasticity of the pipe. A more rigorous formula recently has been suggested.
Equation 8 considers the elasticity of the pipe, but assumes isothermal fluid temperature. Other methods for protecting low-heat-flux systems from thermal expansion involve the use of hydropads or compensators.
They offer an advantage primarily in situations in which a discharge collection system such as a scrubber or a flare is not available. Analyses show that for 2-in. Typical compressibility values are given in Table 2.
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It stands to reason that the lowest compressibility values in Table 2 are for elemental mercury and water. Straight-chain molecules appear to be much more compressible than aromatic compounds of similar molecular weight and composition. Therefore, one could draw the conclusion that long-chain polymers compress very well under pressure, although no data were collected to support this theory. A word of caution: Liquid compressibility varies over a wide range, and no substitute can replace experimental data.
The engineer should be overly cautious when making PRV determinations in situations in which the handled fluid potentially could impact human health, cause severe environmental consequences or bring about a large economic impact. Furthermore, caution should be used with systems having a design that cannot be compared to similar piping systems. We use the information you provided at registration to determine if specific white papers might be of interest to you.
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API (Historical Edition) Guide for Pressure-Relieving and Depressuring Systems
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We satisfy the listed regulatory requirements; while leaving a system, which can be maintained by a knowledgeable process engineer. SlideShare Explore Search You. Submit Search. Successfully reported this slideshow.
Pressure-relieving and Depressuring Systems, Sixth Edition
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Published in: Engineering. Full Name Comment goes here. Are you sure you want to Yes No. No Downloads. Views Total views. Actions Shares. Embeds 0 No embeds. No notes for slide. Minimal Requirements for Relief Systems Documentation 1. Tidwell Rd. All of the referenced documentation is currently stored on the OSHA web site www. Compliance guidelines and enforcement procedures CPL Summary and Explanation of the Final Rule Documentation requirements To support safe design and operation OSHA requires relief systems documentation to contain at least the following information.
The items below are requirements and assumed to be developed based on applicable industry and company standards. The following is a summary list of what documentation is required to satisfy the PSM requirements Identification and description of the relief device including set pressure and valve type 2. Listing of all equipment and design pressures that the relief device protects 3.
Listing of all the overpressure sources considered. Identification of the design case 5.