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I The first method: Installation of flow-limiting orifice plates in pipelines 1. General provisions 1.1 Purpose Flow-limiting orifice plates are installed on the pipelines of chemical plants and petrochemical plant facilities in order to limit the flow rate of fluids or reduce their pressure. 1.2 Scope The flow-limiting orifice plates for pipelines are applied in the following areas: The flow-limiting orifice plate is a concentric sharp-orifice plate used to limit the flow rate of a fluid or reduce its pressure. A pressure drop occurs as fluid passes through the orifice plate, and the flow rate through the orifice plate increases as this pressure drop increases. However, when the pressure drop exceeds a certain value, that is, beyond the critical pressure drop, regardless of how much the outlet pressure decreases, the flow rate will remain at a constant level and will not increase any further. A flow control orifice plate is used based on this principle to limit the flow rate of a fluid or reduce its pressure. 1.2.1 The process materials require pressure reduction and have low precision requirements. 1.2.2 When a large pressure drop is required upstream and downstream of a valve in a pipeline, in order to reduce fluid erosion on the valve, an orifice plate can be connected in series upstream of the valve, provided that throttling through the orifice plate does not result in the formation of a gas phase. 1.2.3 Places where the fluid requires a low flow rate and continuous circulation, such as pump flushing pipes, bypass pipes for hot standby pumps (low-flow protection pipes), analysis sampling pipes, etc. 1.2.4 Areas where pressure reduction is needed to reduce noise or wear, such as vent systems. 1.3 Basis for preparation: Article 15 on the installation of flow-limiting orifice plates in piping systems, as specified in the \"Technical Regulations for the Design of Process System Engineering\" HG/T20570.15-1995 issued by the Society of Chemical Engineers. *Unless otherwise specified in these regulations, all pressures are absolute pressures. 2 Classification and Selection Criteria 2.1 Classification Throttling orifice plates are classified into single-orifice plates and multi-orifice plates based on the number of openings on the plate ； Based on the number of boards, they can be divided into single-board and multi-board types. 2.2 Key Points for Selection 2.2.1 Gases, Steam To avoid choked flow in pipelines using flow control orifice plates, the pressure behind the orifice plate (P2) must not be less than 55% of the pressure before the plate (P1), that is, P2≥0.55P1; therefore, when P2