API-RP-576

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Valve Reclosing. In most applications a properly sized safety valve will decrease the pressure in the vessel when discharging. The pressure in the vessel will decrease at any subsequent point, but not later than the end of the upset situation. A decreasing pressure in the vessel will lower the force Fp. At set pressure however the flow is still acting on the enlarged disc area, which will keep the valve open. A further reduction in pressure is required until the spring force Fs is again greater than F p and the safety valve begins to reclose. At the so called reseating pressure the disc will touch the nozzle again and the safety valve recloses. Blowdown is the difference between set pressure and reseating pressure of a safety valve expressed as a percentage of set pressure. Typical blowdown values as defined in codes and standards are -7% and -10%, ranging from -4% to -20% depending on the code and service (steam, gas or liquid). Blowdown is the difference between set pressure and reseating pressure of a safety valve expressed as a percentage of set pressure. Fion Zhang/ Charlie Chong
Functional Diagram. The following diagram shows a typical functional curve of a spring loaded safety valve. Operation of a Series 526 <strong>API</strong> safety valve with adjusting ring and initial audible discharge set pressure definition Fion Zhang/ Charlie Chong
Page 1 and 2: API-RP-576 Inspection of Pressure-r
Page 3 and 4: Fion Zhang/ Charlie Chong Speaker:
Page 5 and 6: 5 Causes of Improper Performance 5.
Page 7 and 8: 1 Scope Fion Zhang/ Charlie Chong
Page 9 and 10: The recommendations in this publica
Page 11 and 12: This publication does not cover tra
Page 13 and 14: pressure-relief valves Fion Zhang/
Page 15 and 16: pilot-operated pressure-relief valv
Page 17 and 18: upture disks Fion Zhang/ Charlie Ch
Page 19 and 20: 2 Normative References Fion Zhang/
Page 21 and 22: • ASME PTC 25, Pressure Relief De
Page 23 and 24: 3.1 General For the purposes of thi
Page 25 and 26: galling Fion Zhang/ Charlie Chong
Page 27 and 28: 3.2 Dimensional Characteristics of
Page 29 and 30: inlet size outlet size Fion Zhang/
Page 31 and 32: Fion Zhang/ Charlie Chong huddling
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Page 35 and 36: Basic Function of a Spring Loaded S
Page 37 and 38: Valve Closed. In a direct spring lo
Page 39 and 40: The pressure below the valve must i
Page 41: Fion Zhang/ Charlie Chong F p = p*A
Page 45 and 46: 3.3 Operational Characteristics—S
Page 47 and 48: 3.3.3 maximum allowable working pre
Page 49 and 50: 3.3.4 maximum operating pressure Th
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Page 53 and 54: 3.4.5 burst-pressure tolerance The
Page 55 and 56: 3.4.10 marked burst pressure or rat
Page 57 and 58: 4 Pressure-relieving Devices Fion Z
Page 59 and 60: 4.2 Pressure-relief Valve Fion Zhna
Page 61 and 62: 4.3 Safety Valve. Fion Zhnag/ Charl
Page 63 and 64: 4.3.1 General. A safety valve is a
Page 65 and 66: 4.3.2 Applications A safety valve i
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Page 69 and 70: 4.4.1 General. A relief valve is a
Page 71 and 72: 4.5 Safety-relief Valve. Fion Zhnag
Page 73 and 74: 4.6 Conventional Safety-relief Valv
Page 75 and 76: 4.6 Conventional Safety-relief Valv
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Page 81 and 82: Conventional safety valves Fig. 9.2
Page 83 and 84: Types Mediums Limitations Safety-re
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4.8 Pilot-operated Pressure-relief
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What is a Pilot operated safety val
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4.8 Pilot-operated Pressure-relief
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Figure 9—High-pressure Pilot-oper
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Fion Zhnag/ Charlie Chong
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4.8.2 Applications Pilot-operated s
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4.9 Pressure- and/or Vacuum-vent Va
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4.9.1 General. • A pressure- and/
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Figure 7—Low-pressure Diaphragm-t
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Figure 10—Weight-loaded Pallet Ve
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Figure 11—Spring and Weight-loade
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Fion Zhnag/ Charlie Chong
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5 Causes of Improper Performance Fi
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Fion Zhang/ Charlie Chong Figure 22
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Figure 25—Monel Rupture Disks Cor
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Fion Zhang/ Charlie Chong
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Fion Zhang/ Charlie Chong Figure 35
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5.1 Corrosion Fion Zhang/ Charlie C
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Corrosion is a basic cause of many
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http://www.valveworld.net/safetyequ
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Because there is metal-to-metal con
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Basic interferometry The interferen
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As light travels through the Optica
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Example: 1 a series of fringes indi
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Causes of damaged valve seats; 1. C
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Spring failures. 2 modes of failure
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Fion Zhang/ Charlie Chong The size
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Incorrect calibration of pressure g
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How to adjust a PSV The spring dete
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http://www.cicpro.com/products/safe
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The design of the shroud must be su
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Adjustment pin affect the character
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5.5 Plugging and Sticking Fion Zhan
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5.6 Misapplication of Materials Fio
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Typical ball valve material selecti
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5.7 Improper Location, History, or
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Fion Zhang/ Charlie Chong V-203
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Rough handling can occur during;
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The following table summarises the
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Greater differentials between opera
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5.10 Improper Discharge Piping Test
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Fion Zhang/ Charlie Chong When hydr
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Fion Zhang/ Charlie Chong the bello
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5.11 Improper Handling, Installatio
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Rupture disk problems are often ass
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6.1 Reasons for Inspection and Test
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6.2.2 Safety 1. proper authority an
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National Board approved ASME stamps
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The Kdr or aW value can vary accord
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6.2.5 Removal of Device from System
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Exercise; Dismantling of PSV Fion Z
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Highly Reactive Materials Water-Rea
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6.2.7 Inspection of Adjacent Inlet
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Fion Zhang/ Charlie Chong Rupture d
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6.2.10 Visual Inspection This inspe
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6.2.11 Dismantling of Valve. Disman
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Portable Test Separator Internal &
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The pilot assembly and dome area co
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6.2.13 Reconditioning and Replaceme
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Fion Zhang/ Charlie Chong Most test
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After the valve has been adjusted,
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Check for leakage during pressuriza
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6.2.17 Completion of Necessary Reco
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when a valve operates in nonfouling
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ASME BPVC Section I requires; • B
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6.2.20 Inspection, Testing, Mainten
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6.2.21 Inspection, Testing, Mainten
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6.3 Visual On-stream Inspection Vis
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6.4.2 Frequency of Shop Inspection/
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Manufacturer’s Basis • Manufact
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API572, 6.4.3 Frequency of Visual O
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Routine • inspection least interf
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7.1 Objective The primary objective
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7.3 Responsibilities Some companies
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Annex A (informative) Pressure-reli
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API576 Charlie Chong/ Fion Zhang/ H
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A.1 Need and Function of Test Block
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A.2 Testing with Air • Air is com
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A.4 Description of Test Block The s
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Key 1. test station 2. adaptor for
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