Jul,01

API 520-2-2003 pdf download

API 520-2-2003 pdf download

API 520-2-2003 pdf download.Sizing, Selection, and Installation of Pressure-Relieving Devices in Refineries Part II—Installation.
4.1.1 Flow and Stress Considerations Inlet piping to the pressure-relief devices should provide for proper system performance. This requires design consid- eration of the ßow-induced pressure drop in the inlet piping. Excessive pressure losses in the piping system between the protected vessel and a pressure-relief device will adversely affect the system-relieving capacity and can cause valve instability. In addition, the effect of stresses derived from both pressure-relief device operation and externally applied loads must be considered. For more complete piping design guide- lines, see ASME B31.3. 4.1.2 Vibration Considerations Most vibrations that occur in inlet piping systems are ran- dom and complex. These vibrations may cause leakage at the seat of a pressure-relief valve, premature opening, or prema- ture fatigue failure of certain valve parts, inlet and outlet pip- ing, or both. Vibration in inlet piping to a rupture disk may adversely affect the burst pressure and life of the rupture disk. Detrimental effects of vibrations on the pressure-relief device can be reduced by minimizing the cause of vibrations, by additional piping support, by use of either pilot-operated relief valves or soft-seated pressure-relief valves, or by pro- viding greater pressure differentials between the operating pressure and the set pressure. 4.2 PRESSURE-DROP LIMITATIONS AND PIPING CONFIGURATIONS For pressure-drop limitations and piping conÞgurations, see Figures 1, 2, 4, and 5. 4.2.1 Pressure Loss at the Pressure-Relief Valve Inlet Excessive pressure loss at the inlet of a pressure-relief valve can cause rapid opening and closing of the valve, or chattering. Chattering will result in lowered capacity and damage to the seating surfaces. The pressure loss that affects valve performance is caused by non-recoverable entrance losses (turbulent dissipation) and by friction within the inlet piping to the pressure-relief valve.
4.2.3.2 Installation Guidelines Remote sensing lines should measure static pressure where the velocity is low. Otherwise, the pilot will sense an artiÞ- cially low pressure due to the effect of velocity. Ensure that the pilot sensing point is within the system pro- tected by the main valve. For ßowing pilots, remote sensing lines shall be sized to limit the pressure loss to 3 percent of the set pressure based on the maximum ßow rate of the pilot at 110 percent of set pressure. Consult the manufacturer for size recommendations for the remote sensing line. For non-ßowing pilots, remote sensing lines with a ßow area of 0.070 in. 2 (45 mm 2 ) should be sufÞcient since no sys- tem medium ßows through this type of pilot when the main valve is open and relieving. Consult the manufacturer for remote sensing line size recommendations. Consider using pipe for remote sensing lines to ensure mechanical integrity. If a block valve is installed in the remote sensing line, the guidelines in Section 6 should be followed. A closed block valve in a remote sensing line renders the pressure-relief valve inoperative and may allow the valve to open.
4.3 INLET STRESSES THAT ORIGINATE FROM STATIC LOADS IN THE DISCHARGE PIPING Improper design or construction of the discharge piping from a pressure-relief device can set up stresses that will be transferred to the pressure-relief device and its inlet piping. These stresses may cause a pressure-relief valve to leak or malfunction or may change the burst pressure of a rupture disk. The pressure-relief device manufacturer should be con- sulted about permissible loads. 4.3.1 Thermal Stresses Fluid ßowing from the discharge of a pressure-relief device may cause a change in the temperature of the discharge pip- ing. A change in temperature may also be caused by pro- longed exposure to the sun or to heat radiated from nearby equipment. Any change in the temperature of the discharge piping will cause a change in the length of the piping and may cause stresses that will be transmitted to the pressure-relief device and its inlet piping.

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