API St 520-2 pdf free download

API St 520-2 pdf free download.Sizing, Selection, and Installation of Pressure-relieving Devices Part II—Installation.
5.7 Inlet Stresses that Originate from Static Loads in the Discharge Piping 5.7.1 General Improper design or construction of the discharge piping from a PRD can set up stresses that will be transferred to the PRD and its inlet piping. Static loads are stresses that occur during normal operation while the relief device remains closed. These stresses may cause a PRV to leak or malfunction, may change the burst pressure of a rupture disk, or may cause connected equipment flanges to leak. The PRD manufacturer should be consulted about permissible loads. 5.7.2 Thermal Stresses Fluid flowing from the discharge of a PRD may cause a change in the temperature of the discharge piping. A change in temperature may also be caused by prolonged 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 PRD and its inlet piping. The PRD should be isolated from piping stresses through proper support, anchoring, or flexibility of the discharge piping. 5.7.3 Mechanical Stresses Discharge piping should be independently supported and aligned. Discharge piping that is supported by only the PRD will induce stresses in the PRD and the inlet piping. Forced alignment of the discharge piping will also induce such stresses.5.8 Inlet Stresses that Originate from Discharge Reaction Forces 5.8.1 General The discharge of a PRD will impose a reaction force (F) as a result of the flowing fluid (see Figure 6). This force will be transmitted into the PRD and into the mounting nozzle and adjacent supporting vessel shell unless designed otherwise. The precise magnitude of the loading and resulting stresses will depend on the reaction force and the configuration of the piping system. The user is cautioned that terminating the PRV discharge piping to any angle other than vertical with a perpendicular cut may increase the system stresses. The designer is responsible for analyzing the discharge system in compliance with the code of construction (e.g. ASME B31.3 [6] ) to determine if the reaction forces and the associated bending moments will cause excessive stresses on any of the components in the system. A method for the design of piping systems to withstand reaction forces from PRDs is given in Appendix II of ASME B31.1 [5] . The magnitude of the reaction force will differ substantially depending on whether the installation is open or closed discharge. When an elbow is installed in the discharge system to direct the fluid up into a vent pipe, the location of the elbow and any supports is an important consideration in the analysis of the bending moments.5.8.2.2 Two-Phase Discharge Although this paragraph provides a formula for the calculation of reaction forces for a two-phase release to atmosphere, the reader is cautioned to carefully consider the decision for atmospheric discharge. Due consideration should be given to the potential for liquid portions of the release to cause a hazardous condition. Consult API 521 [3] for additional guidance on atmospheric discharge. The following formula can be used to determine the reaction force on inlet piping from an open discharge of a two-phase fluid. The formula assumes that the two-phase mixture is in homogeneous flow condition (no- slip).API St 520-2 pdf download.