Pipeline Valve Layout

What are the main functions of valves? What are the principles for their selection?

Valves are important components of industrial pipeline systems and play an important role in the production process.

The main functions of valves are:

1) Connect and cut off the medium - gate valves, butterfly valves, and ball valves can be selected;

2) Prevent the medium from flowing back - check valves can be selected;

3) Regulate the medium pressure and flow - stop valves and regulating valves can be selected;

4) Separate, mix or distribute the medium - plug valves, gate valves, and regulating valves can be selected;

5) Prevent the medium pressure from exceeding the specified value to ensure the safe operation of the pipeline or equipment - safety valves can be selected. The selection of valves is mainly based on the two aspects of trouble-free operation of the device and economy. .

The principles for selecting valves are as follows: the nature of the conveying fluid; the function of the valve; the size of the valve; the resistance loss of the valve; the working temperature and working pressure of the valve; (two for both) the material of the valve.

What are the general requirements for valve installation?

The general requirements for valve installation, the most suitable installation height, the valve on the horizontal pipeline, and the direction of the valve stem are as follows:

(1) The valve should be located in a place that is easy to access, operate, and maintain. Valves on rows of pipes (such as pipes entering and exiting devices) should be arranged in a centralized manner, and operating platforms and ladders should be considered. For valves on parallel pipes, their center lines should be aligned as much as possible. The net distance between handwheels should not be less than 10Qmm. In order to reduce the distance between pipes, valves can be staggered;

(2) The installation position of frequently operated valves should be convenient for operation, and the most suitable installation height is about 1.2m from the operating surface. When the height of the valve handwheel center exceeds 2m from the operating surface, a platform should be set for centralized valve groups or frequently operated individual valves and safety valves. Appropriate measures should also be taken for infrequently operated individual valves (such as sprockets, extension rods, movable platforms and movable ladders, etc.). The chain of the sprocket should not hinder passage. Valves on pipes and equipment for hazardous media shall not be installed within the height range of a person's head to avoid hitting the head or directly injuring the face of a person due to valve leakage;

(3) Valves used for partition equipment should be directly connected to the equipment pipe or close to the equipment. The valves on the pipelines connected to the equipment with extremely hazardous or highly hazardous toxic media should be directly connected to the equipment valley, and the valves shall not be operated by sprockets;

(4) Accident handling valves such as fire water valves and fire steam valves should be arranged in a dispersed manner, and safe operation in the event of an accident should be considered. Such valves should be arranged behind the control room, behind the safety wall, outside the factory door, or in an area with a certain safe distance from the accident site; so that operators can operate safely in the event of a fire accident;

(5) Unless there are special requirements for the process, valves on the bottom pipelines of equipment such as towers, reactors, and vertical containers shall not be arranged in the skirt seat;

(6) The shut-off valve of the horizontal branch pipe drawn from the main pipe should be installed on the horizontal pipe section close to the root;

(7) Lift check valves should be installed on horizontal pipes, and vertical lift check valves should be installed on vertical pipes where the medium in the pipe flows from bottom to top. Swing check valves should be installed on horizontal pipes first, and can also be installed on vertical pipes where the medium in the pipe flows from bottom to top; foot valves should be installed at the vertical pipe end of the centrifugal pump suction pipe; butterfly check valves can be used to reduce the installation height of the pump outlet cut-off width; when the pump outlet is inconsistent with the connected pipe diameter, a different diameter check valve can be used;

(8) The center distance of the handwheel of the valve arranged around the operating platform should not be greater than 450mm from the edge of the operating platform. When the valve stem and handwheel extend above the platform and the height is less than 2m, it should not affect the operation and passage of the operator;

(9) Valves of underground pipelines should be installed in the trench or valve well. If necessary, valve extension rods should be installed. Fire water valve wells should be clearly marked;

(10) For valves on horizontal pipelines, the direction of the valve stem can be determined in the following order: vertically upward; horizontally; tilted upward 45°; tilted downward 45°; not vertically downward;

(11) For open-stem valves with horizontally installed valve stems, the valve stem shall not affect passage when the valve is open.

What are the requirements for the installation of breathing valves?

(1) The breathing valve should be installed at the highest point of the gas phase space of the storage tank to reduce the evaporation loss of the material and to provide the most direct and largest channel to the breathing valve. Usually for vertical tanks, the breathing valve should be installed within the central roof of the tank as much as possible. For tanks that require an insulation layer on the tank top, it can be installed near the ladder platform;

(2) When two breathing valves need to be installed, they should be arranged symmetrically with the center of the tank top;

(3) If the breathing valve is used on a nitrogen-sealed tank, the position of the nitrogen supply pipe should be away from the breathing valve interface and inserted into the tank from the top of the tank about 200mm, so that the nitrogen will not be discharged directly after entering the tank, achieving the purpose of nitrogen sealing.

What are the general requirements for the installation of the regulating valve group?

(1) The installation position of the regulating valve should meet the requirements of the process design and should be close to the primary indicating instrument related to it, so that the primary instrument can be observed when the bypass valve is manually operated;

(2) The regulating valve should be arranged on the ground or platform and convenient for operation and maintenance;

(3) The regulating valve should be installed upright and vertically on the horizontal pipeline. It can be installed horizontally or tilted in special circumstances, but it must be supported;

(4) When the regulating valve group (including regulating valve, bypass valve, cut-off valve and drain valve) is installed vertically, the regulating valve should be installed below the bypass. Regulating valves with a nominal diameter of less than 25mm can also be installed above the bypass;

(5) The clearance between the bottom of the regulating valve and the ground or platform surface should not be less than 4oomm. For single-seat and double-seat regulating valves with reverse-mounted valve cores, it is advisable to leave space for extracting the valve core under the valve body;

(6) There should be a clearance of not less than 2mm above the top of the regulating valve diaphragm head. The regulating valve and bypass valve should be arranged in different positions when arranged up and down;

(7) The cut-off valve should be a gate valve, and the bypass valve should be a stop valve. However, when the nominal diameter of the bypass valve is greater than 150 mm, a gate valve can be used. The two cut-off valves and the regulating valve should not be arranged in a straight line;

(8) A drain valve should be installed at the low point of the pipeline between the inlet side of the regulating valve and the cut-off valve upstream of the regulating valve. The drain valve can be a gate valve;

(9) The regulating valve on the pipeline containing solid particles in the medium should be arranged on the same plane as the bypass valve or the bypass valve should be arranged below the regulating valve;

(10) One of the two brackets of the regulating valve group on the low-temperature and high-temperature pipelines should be a fixed bracket and the other a sliding bracket;

(11) The regulating valve should be installed in an environment with an ambient temperature not higher than 60 ℃, not less than -40℃, and away from vibration sources;

(12) When there are many regulating valve groups in one area, they should be consistent in form, neat, beautiful and easy to operate;

(13) When the diameters of the regulating valve and the isolation valve are different, the reducer should be installed close to the regulating room;

(14) Pay attention to whether the process has special requirements for the position of the regulating valve.

To ensure the safety of pressure pipelines, which pressure pipelines should be equipped with safety valves?

To ensure the safety of pressure pipelines, the following pressure pipelines should be equipped with safety valves:

(1) Safety valves should be installed on the outlet pipelines of positive displacement pumps such as electric reciprocating pumps, gear pumps or screw pumps. The vent pipe of the safety valve should be connected to the pump inlet pipe, and an emergency stop interlock device should be installed (except when the equipment itself has a safety valve);

(2) Safety valves should be installed at the outlet of each section of the flammable gas reciprocating compressor, and the vent pipe of the safety valve should be connected to the inlet pipe of each section of the compressor or the inlet pipe of one section of the compressor;

(3) Safety valves should be installed in pipelines where flammable gases and flammable liquids may expand due to heat and exceed the design pressure;

(4) Safety valves or other safety measures should be installed on liquefied hydrocarbon pipelines that may be closed at both ends and cause pressure increase;

(5) When the equipment connected to the outlet of the blower, centrifugal compressor, centrifugal pump or steam reciprocating pump cannot withstand its maximum pressure, the outlet pipe of the above pumps must be equipped with a safety valve. The above pipelines may cause the pressure in the pipeline to exceed the design pressure due to fire, operating failure or water or power outage, so safety valves or other safety measures should be installed.

What are the key points of safety valve installation and pipeline layout design?

(1) Safety valves should be installed upright and close to the equipment or pipeline to be protected. If it is not possible to arrange them close together, the total pressure drop from the protected equipment or pipeline to the safety valve inlet should not exceed 3% of the safety valve set pressure value.

(2) A maintenance platform should be set up for the safety valve. When arranging a heavy safety valve, the possibility of lifting the safety valve after disassembly should be considered, and a lifting rod should be installed if necessary.

(3) Long radius elbows should be used for the safety valve inlet pipeline.

(4) The design of the safety valve outlet pipeline should consider that the back pressure does not exceed a certain value of the safety valve set pressure. For ordinary spring-loaded safety valves, the back pressure does not exceed 10% of the safety valve set pressure value.

(5) When the medium discharged into the vent main pipe or the flare main pipe contains condensate or condensable gas, the outlet of the safety valve should be higher than the main pipe; otherwise, drainage measures should be taken.

(6) The outlet pipe of the safety valve discharged into the closed system should be connected to the top of the discharge main pipe at a 45° angle along the flow direction of the medium to prevent the condensate in the main pipe from flowing back into the branch pipe and reduce the back pressure of the safety valve.

(7) When a cut-off valve is installed on the inlet and outlet pipes of the safety valve, a single-disc gate valve should be selected and sealed with lead. The valve stem should be installed horizontally to prevent the valve plate from sliding down when the pin connecting the valve stem and the valve plate corrodes or loosens. When the safety valve is equipped with a bypass valve, the valve should be sealed with lead.

What are the general requirements for the arrangement of pipe fittings?

(1) Elbows should be long-radius elbows with a radius of curvature equal to 1.5 times the nominal diameter; pipes conveying gas-solid and liquid-solid two-phase flow materials should use elbows with large curvature radius;

(2) For horizontal pipe reducer connections on corridors, if there are no special requirements, bottom-flat eccentric reducers should be used; concentric reducers should be used for vertical pipes;

(3) For horizontal suction centrifugal pumps, when the inlet pipe changes diameter, an eccentric reducer should be installed near the pump inlet. When the pipeline enters the pump from bottom to top, it should be installed flat on the top; when the pipeline enters the pump from top to bottom, it should be installed flat on the bottom;

(4) Flat welding flanges should not be directly connected to elbows without straight pipe sections;

(5) Valves and other static sealing joints should be installed near the pipe support points;

(6) Unless there are special requirements for the process, flanges and threaded joints shall not be arranged on the pipes in the skirts of equipment such as towers, reactors, and vertical containers;

(7) Carbon steel pipes in the lubricating oil system of pumps and pipes conveying solid deposits and coking media should be flanged in sections. The number of elbows on each section of the carbon steel pipeline of the pump lubricating oil system should not exceed 2;

(8) The end of the lubricating oil main pipe of the pump lubricating oil system should be closed with a flange cover;

(9) The reducers on the pipelines on both sides of the regulating valve should be close to the regulating valve;

(10) When using a reducing flange connection, the flow direction of the conveying medium should be from the small diameter to the large diameter.

What are the requirements for the layout of the flame arrester?

(1) The pipeline flame arrester on the heating furnace fuel gas main pipe should be close to the heating furnace and easy to repair. The distance between the pipeline flame arrester and the burner should not be more than 12m;

(2) The tank flame arrester should be directly installed on the pipe mouth on the top of the storage tank. It is usually used in conjunction with the breathing valve, but can also be used alone.

What are the requirements for the layout of the filter?

(1) Filters should be installed at the inlet of the pump. The installation position of the filter should be close to the protected equipment;

(2) The arrangement of the filter should meet the following requirements: Angle T-type filters must be installed in the occasion of 90° bend in the pipeline; Straight-through T-type filters must be installed on the straight pipe of the pipeline. When installed on the riser, the filter should be conveniently pulled out; When installed on the horizontal pipe, the filter should be pulled out in the downward direction; When the Y-type filter is installed on the horizontal pipe, the filter should be pulled out in the downward direction.

(3) For the pump inlet filter installed on the riser, a different diameter filter can be used to reduce the height of the pump inlet valve;

(4) When the Y-type filter is installed on a vertical pipe where the medium flows from bottom to top, a counter-flow type should be selected;

(5) A filter or a detachable short section should be installed on the compressor inlet pipe to facilitate the installation of a temporary filter and cleaning of the pipe before starting.

What are the general requirements for the layout design of the filtration equipment pipeline?

(1) When calculating the hydraulics of the pipeline conveying the filter slurry and the NPSN of the pump, the filter slurry physical property data and resistance calculation must be carried out according to the liquid-solid two-phase flow. The pipeline flow rate in the slurry pipe can be calculated according to the settling velocity of the solid particles in the filter slurry l. 5 to 2 times the value. If there is no sedimentation velocity measurement, the flow velocity in the pipe is generally 2.5 to 3 m/s;

(2) The pipeline should be as straight as possible, the installation slope should be large (minimum slope I ≥ 10%), elbows should be used less, the curvature radius of the elbow should be appropriately large (R ≥ 4DN), and sudden enlargement of the pipe diameter should be avoided;

(3) Pipe connections should be less welded and more flanges or threaded connections should be used for easy disassembly and cleaning. The eccentric reducer with flange connection is used for the reducer, and the vacuum pipeline is welded and flange connection is used less;

(4) On each liquid-solid two-phase flow pipeline, a flushing (or purge) connection and a discharge and drainage pipe are installed at appropriate positions. The connection point of the flushing water pipe is set above or on the side of the material pipeline, and the valve on the flushing pipe is installed as vertically as possible;

(5) The valve on the slurry pipeline should be a straight-through valve with no tortuous fluid passage in the valve body and no dead angle. Diaphragm valves and pipe clamp valves are recommended. Soft-sealed butterfly valves, ball valves or plugs. When the valve is installed horizontally, a drain pipe with a valve and a flushing connection pipe are installed on the material pipelines before and after the valve. When it is installed vertically, a discharge and flushing joint is installed on the material pipe on the upper side of the valve;

(6) In order to prevent blockage, the filter slurry pipeline does not have a bypass, and a control with a guide wheel is selected;

(7) When the filter slurry is a crystal slurry containing crystals, the pipeline system needs to be equipped with a jacket or heat insulation, and the valve should be a ball valve with a heat insulation heating structure or a soft-sealed butterfly valve;

(8) The pipeline design requirements for the filtrate pump and the washing liquid pump of the filtration system shall comply with HG/T 20549.2;

(9) There is no valve for the exhaust of the filter slurry tank and the filtrate tank. When the material is flammable, volatile, or toxic, a breathing valve and a flame arrester are required for the exhaust pipe.

What are the requirements for the layout of the compensator on the pipeline?

(1) When the geometric shape of the pipeline system is limited due to equipment layout or other factors and the compensation capacity cannot meet the requirements, the compensator should be installed at an appropriate position in the pipeline system.

(2) The distance between the "Π"-shaped compensator and the fixed point should not be less than one-third of the distance between the two fixed points.

(3) The arrangement of unconstrained metal bellows compensators should meet the following requirements: Only one compensator can be arranged between two fixed supports;

The pipeline must be strictly protected, especially the part close to the compensator should be equipped with a guide frame. The distance between the first guide frame and the compensator should be less than or equal to 4 times the nominal diameter, and the distance between the second guide frame and the first guide frame should be less than or equal to 14 times the nominal diameter to prevent the compensator from being damaged by bending and radial displacement of the pipeline.

(4) When the seismic intensity is equal to or greater than 7 degrees, there is uneven settlement, and the nominal diameter is equal to or greater than 150mm, a metal hose for tank earthquake resistance should be installed on the pipeline in front of the tank. The diameter of the metal hose should not be less than the diameter of the inlet and outlet of the tank. The metal hose should be arranged between the first valve and the second valve close to the tank wall.

What are the general requirements for the arrangement of instruments or measuring elements on the pipeline?

(1) The layout of instruments or measuring elements on the pipeline should comply with the current provisions of the relevant industrial enterprise instrument piping and wiring design specifications;

(2) The layout of instruments or measuring elements on the pipeline should be convenient for installation, observation and maintenance. If necessary, a dedicated operating platform or ladder should be set up;

(3) The length of the instrument nozzle should be determined according to the thickness of the pipeline insulation layer.

What are the requirements for the layout of flow measurement instruments?

(1) In order to ensure the accuracy of the orifice flowmeter, there should be a straight pipe section of 15 to 20 times the inner diameter of the pipe in front of the orifice plate, and a straight pipe section of not less than 5 times the inner diameter of the pipe behind the orifice plate.

(2) The installation of the flowmeter shall comply with the following provisions:

1) The rotor flowmeter must be installed on a vibration-free vertical pipeline where the medium flows from bottom to top. During installation, it is necessary to ensure that there is a straight pipe section in front of the flowmeter that is not less than 5 times the inner diameter of the pipe and not less than 300mm;

2) When the measured medium contains suspended solids, the target flowmeter needs to be installed horizontally. When the target flowmeter is installed on a vertical pipeline, the liquid flow direction should be from bottom to top. The length of the straight pipe section before the inlet end of the target flowmeter should not be less than 5 times the inner diameter of the pipe, and the length of the straight pipe section after the outlet end should not be less than 3 times the inner diameter of the pipe;

3) The rotary flowmeter should be installed in front of the regulating valve. When the flowmeter needs to be calibrated on site, two calibration gate valves with quick connectors should be installed before and after the cut-off valve in front of the rotary flowmeter.

What are the requirements for the layout of pressure measuring instruments?

(1) In order to accurately measure the static pressure, the pressure gauge pressure point should be on the straight pipe section without a cut-off valve.

(2) The pressure gauge at the pump outlet should be installed in front of the outlet valve and facing the operating side.

(3) The installation height of the field indicating pressure gauge should be 1.2~1.8m. When it exceeds 2.0m, there should be a platform or a vertical ladder.

What are the requirements for the layout of temperature measuring instruments?

(1) Thermometers and thermocouples should be installed on straight pipe sections. The minimum pipe diameter for installation is as follows:

Industrial mercury thermometer, DN50;

Thermocouple, thermal resistor, bimetallic thermometer, DN80; Pressure thermometer, DN150; The expansion pipe length should not be less than 250mm.

(2) When the thermometer and thermocouple are installed at the bend of the pipeline, the pipe diameter should not be less than DN40 and should be in countercurrent contact with the flow direction of the fluid in the pipe.

(3) The thermometer can be installed vertically or tilted at 45°. When installed at 45°, it should be in countercurrent contact with the flow direction of the fluid in the pipe.

(4) The installation height of the field indicating thermometer should be 1.2~1.5m. When the height is higher than 2.0m, a vertical ladder should be installed to form a movable platform. For the convenience of maintenance, the minimum distance from the platform should not be less than 300mm.

(5) For process pipelines with branches, when installing thermometers or thermocouples, special attention should be paid to the installation position being consistent with the process flow, and they should not be installed in the dead corners or blind positions of the process pipelines.

What are the requirements for the layout of liquid level measuring instruments?

(1) Glass tube liquid level gauges and glass plate liquid level gauges should be installed directly on the equipment, and the location of the liquid level gauge should not hinder the passage of personnel.

(2) The installation location of the external float liquid level gauge should not hinder the passage of personnel, and the upper end of the liquid level gauge head should not be higher than 1.8m from the ground or platform. If it exceeds 2.0m, a platform should be added.

(3) The height of the internal float liquid level gauge from the platform or the ground is 1.0 to 1.5m. The installation location should not hinder the passage of personnel, and sufficient space should be left for maintenance and adjustment.

What are the general requirements for safety protection settings?

The design should evaluate the following factors (1) to (4), and take corresponding safety protection measures in combination with the safety protection objectives and requirements specified in various parts of the specification:

(1) Fluid hazard determined by fluid properties and operating pressure-temperature;

(2) Pipeline safety determined by pipeline materials, structures, connection forms and safe operation experience;

(3) The amount of fluid leakage and the degree of harm to the surrounding environment and equipment caused by pipeline damage or leakage;

(4) The degree of harm caused by pipeline accidents to operators, maintenance personnel and all possible contact personnel.

How to set up safety protection and measures in pipeline design?

(1) Set up necessary safety protection and measures according to the characteristics of production operations: fire extinguishing systems and sprinkler facilities;

Fireproof structures of buildings (fire walls, explosion-proof walls, etc.);

Ventilation to remove toxic, corrosive or flammable vapors;

Telemetry and remote control devices;

Emergency facilities for handling hazardous substances (storage or recovery devices, torches or incinerators, etc.).

(2) In brittle material pipeline systems or flanges. Protective covers should be installed at joints, valve covers, instruments or sight glasses to limit and reduce the degree of harm caused by leakage.

(3) Automatic or remote emergency shut-off, over-flow valve, additional shut-off valve, flow-limiting orifice plate or automatic shut-off of pressure source should be used to limit the amount and speed of fluid leakage.

(4) Valves used to handle accidents (such as emergency venting, accident isolation, fire steam, fire hydrants, etc.) should be arranged in safe, obvious and convenient places.

(5) Combustible and toxic materials entering and leaving the device should be equipped with shut-off valves at the boundary of the boundary area, and "8"-shaped blind plates should be installed on the side of the device to prevent mutual influence in the event of a fire.

(6) Necessary protective masks, gas masks, emergency breathing systems, and special agents should be installed. Portable flammable and toxic gas detection and alarm systems and other hygienic and safety equipment. Emergency showers and eyewash stations should be installed near discharge points or leakage points that may cause accidental harm to the human body.

(7) For radioactive fluids, shielding protection and automatic alarm systems should be installed, and special masks, gloves and protective clothing should be equipped.

(8) Static grounding measures should be taken for pipeline systems that may generate static electricity hazards in explosion and fire hazardous places. Grounding can be achieved through the grounding grid of equipment, pipelines and civil structures. Other anti-static requirements should comply with the provisions of the General Guidelines for Preventing Static Electricity Accidents GB12158.

(9) The setting of blind plates should meet the following requirements: When the device is shut down for maintenance, for pipelines outside the device that may or are required to continue to operate, in addition to the shut-off valve at the boundary of the device, a blind plate should be installed at the flange of the valve on the device side; during operation, when some equipment needs to be shut down for maintenance, a blind plate should be installed at the flange joint between the valve and the equipment. For pipelines with toxic or flammable fluids, when a vent valve is installed between the valve and the blind plate, the pipeline after the vent valve should be led to a safe place.

(10) When connecting utility pipelines (steam, air, nitrogen, etc.) to GC1 and GC2 pipelines, the following requirements shall be met: A check valve shall be installed on the utility pipeline in continuous use, and a shut-off valve shall be installed at its root; Two shut-off valves shall be installed on the utility pipeline in intermittent use, and a check valve shall be installed between the two valves.

What measures should be taken when the pipeline passes through the floor, roof or wall of a building?

When the pipeline passes through the floor, roof or wall of a building, a sleeve shall be added to the perforation, and the gap between the sleeve and the pipeline shall be sealed with soft materials.

The diameter of the sleeve shall be larger than the outer diameter of the insulation layer of the pipeline or heat-limiting pipeline, and shall not affect the thermal displacement of the pipeline. The sleeve shall be 50mm higher than the floor or roof. If necessary, a rain cover shall be installed on the top floor.

The weld of the pipeline shall not be located inside the sleeve, and the sleeve end shall be not less than 150mm. The pipeline shall not pass through fire walls and explosion-proof walls.

What are the commonly used heating media for process pipelines in the device? What is its scope of application?

There are four common heating media for process pipelines:

(1) Hot water: suitable as a heat source for heating when the operating temperature is not high or high-temperature heating media cannot be used;

(2) Steam: generally used for heating when the operating temperature of the medium in the pipe is less than 150°C;

(3) Heat carrier: generally used for jacket heating systems where the operating temperature of the medium in the pipe is greater than 150°C. Commonly used heat carriers include heavy diesel or distillate oil with a distillation range greater than 300°C, biphenyl-biphenyl ether or hydrogenated terphenyl, etc.;

(4) Electric heating: Electric heating is not only suitable for various situations of steam heating but also for heat-sensitive medium pipelines. It can effectively control temperature and prevent pipeline temperature from overheating; it is suitable for heating pipelines or equipment that are dispersed or far away from the steam supply point and equipment with irregular shapes (such as pumps).

What are the requirements for the layout of reducers?

(1) When installing a reducer near a tee, for a converging tee, the reducer should be arranged on the pipe before the converging; for a diverting tee, the reducer should be arranged on the pipe after the diversion;

(2) The eccentric reducer on the horizontal pipe of the pump inlet should be arranged eccentrically downward.

What are the requirements for valve layout?

(1) Valves should be arranged in places that are convenient for operation, maintenance and repair;

(2) Heavy valves and larger welded valves should be arranged on horizontal pipes with the valve stem facing vertically upward; heavy valves should also consider necessary lifting measures;

(3) For flange-connected valves or cast iron valves, they should be arranged in places with smaller bending moments;

(4) For horizontally arranged valves, the valve stem should not face downward unless there are special requirements;

(5) For valves in trenches, the valve stem can be exposed to the ground when it does not hinder ground passage, and the operating handwheel is generally more than 150mm above the ground; otherwise, simple operating measures should be considered.

What issues should be paid attention to when arranging pipelines with gas-liquid two-phase flow?

(1) The pipeline should be vertically oriented first and then horizontally oriented according to the flow direction of the medium, and the pipeline should be short and straight;

(2) The regulating valve on the pipeline should be arranged as close as possible to the container receiving the medium. If conditions permit, the regulating valve should be directly connected to the container receiving the medium;

(3) The first turning elbow after the regulating valve should be replaced with a tee connection, and a plug should be added to the end of the tee straight connection;

(4) Limits or fixed supports should be set at appropriate positions of the pipeline system.

What are the principles for selecting pipeline categories?

(1) The pipeline category should be selected based on the properties and parameters of the medium in the pipe and the safety and economy of operation under various working conditions;

(2) Seamless steel pipes are suitable for pipelines of various parameters;

(3) High-quality welded steel pipes can be used for low-temperature reheat steam pipelines;

(4) Welded steel pipes can be used for pipelines with PN2.5MPa and below;

(5) Welded steel pipes for low-pressure fluid transportation are only suitable for media with PN1.6MPa and below and a design temperature not exceeding 200℃.

What are the main principles for selecting flanges?

For pipelines with a design temperature of 300℃ or less and a nominal pressure of less than or equal to 2.5 MPa, flat welding flanges should be used; for pipelines with a design temperature greater than 300℃ or a nominal pressure greater than or equal to 4.0MPa, butt welding flanges should be used.

Which pipelines should be considered for heat preservation or cold preservation?

(1) Equipment and pipelines with one of the following conditions should be insulated:

1) Equipment and pipelines with an outer surface temperature greater than 50℃ and an outer surface temperature less than or equal to 50℃ but the process requires insulation. For example, the liquefied hydrocarbon pipeline at the pump inlet that may often be exposed to sunlight: the distillation tower top distillation line (tower to condenser pipeline), the tower top reflux pipeline, and the fuel gas pipeline after liquid separation should be insulated;

2) Equipment and pipelines whose medium freezing point or freezing point is higher than the ambient temperature (referring to the annual average temperature). For example, crude oil with a freezing point of about 30°C, equipment and pipelines in areas with an annual average temperature below 30°C; equipment and pipelines in cold or extremely cold areas, where the freezing point of the medium is not high but the medium contains water, water pipelines in cold areas that may not flow frequently, etc.

(2) Equipment and pipelines that have any of the following conditions must be kept cold:

1) It is necessary to reduce the temperature rise or vaporization of the cold medium during production or transportation (including sudden decompression and vaporization to produce ice);

2) It is necessary to reduce the cold loss of the cold medium during production or transportation, or to stipulate the allowable cold loss;

3) It is necessary to prevent condensation on the outer surface of the equipment or pipeline at ambient temperature.