A compilation of common issues in pipeline design – keep this handy!

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01 What are the requirements for pipeline layout design? (1) The pipeline layout design shall meet the requirements of the process piping and instrumentation diagram ； (2) The piping layout should be planned comprehensively to ensure safety, reliability, and economic efficiency; it must meet the requirements for construction, operation, maintenance, etc., while striving to achieve neatness and aesthetic appeal ； (3) When determining the orientation and laying method of the pipes for the inlet and outlet devices (units), coordination between the interior and exterior aspects should be ensured ； (4) The installation of plant-wide pipelines within the factory area should be coordinated with the installations (units), roads, buildings, etc. in that area, to avoid pipelines surrounding the installations (units) and to reduce intersections between pipelines and railways or roads ； (5) Pipelines should be installed overhead or on the ground. If necessary, it can be buried or laid in a trench ； (6) Pipelines should be arranged in rows; pipelines above the ground should be laid on pipe racks or pipe supports ； (7) When laying pipes on pipe supports or pipe piers, the vertical and horizontal loads acting on the pipe supports or piers should be balanced ； (8) A 10%–30% margin should be reserved on plant-wide pipe racks or pipe supports (including those passing through culverts), taking their loads into account. A 10%–20% margin should be reserved for the main corridor pipe supports of the installation, taking their loads into consideration ； (9) The layout of pipelines with special requirements regarding distance, angle, elevation differences, etc., as well as large-diameter pipelines, shall comply with the requirements of the equipment layout design ； (10) The piping layout shall not hinder the installation, maintenance of equipment, pumps and their internal components, nor the passage of fire trucks ； (11) The piping layout should provide the piping system with the necessary flexibility. While ensuring the flexibility of the pipeline and that the forces and torques exerted by the pipeline on the equipment and pump nozzles do not exceed allowable values, the pipeline should be as short as possible with as few components as possible ； (12) The placement of support points should be considered concurrently with pipeline planning. It is advisable to utilize the natural shape of the pipeline to achieve self-compensation ； (13) The pipeline layout should be arranged in a manner that gradually increases or decreases in level, in order to reduce the formation of air pockets or liquid pockets. When it is inevitable, vents and drains should be provided in accordance with operational and maintenance requirements; the piping layout should minimize the formation of \"dead ends\"” ； (14) When a pipeline for gas-liquid two-phase flow splits from one branch into two or more branches, the piping layout should consider symmetry or meet the requirements of the piping and instrumentation diagram. (15) Except for pipes that need to be connected to valves, instruments, equipment, etc. using flanges or threads, welding shall be used for connections. Flanges, threads, or other detachable connections should be considered in the following situations: instances where disassembly is required for maintenance, cleaning, or purging ； Lined pipe or jacketed pipe ； Pipelines composed of two sections of different materials that are not suitable for welding connection ； Pipe joints where on-site heat treatment of welds is difficult ； Galvanized pipes with a nominal diameter of 100 mm or less ； Set the position of the blind flange or “figure-8” blind flange. (16) Gas branch pipes should be connected from the top of the main pipe. (17) Pipelines for toxic media shall be connected by welding; flange or threaded connections shall not be used unless there are special requirements. Pipes carrying toxic media should be clearly marked to distinguish them from other pipes, and such pipes must not be laid underground. (18) When installing pipes for solid materials or pipes containing solid materials, the pipes should be made as short as possible. Fewer bends and no dead corners: The connection between the branch pipes carrying solid materials and the main pipe should be made at an angle along the flow direction of the medium, with the angle not exceeding 45° ； The bending radius of elbows on pipelines for solid materials should not be less than 6 times the nominal diameter of the pipeline ； Pipes for slurries containing large amounts of solid material and pipes for high-viscosity liquids should have a slope. (19) For pipelines requiring thermal compensation, the entire piping system must be analyzed from its starting point to its end point in order to determine a reasonable thermal compensation scheme. (20) For pipes laid in a pipe rack that require a certain slope, the height of the pipe supports can be adjusted. This is achieved by adding section steel or steel plate pads on top of the pipe supports. The vent gas main (or flare discharge main) should be located at the top of the pipe rack columns to facilitate elevation adjustment. (21) When installing pipes connected to rotating mechanical equipment, the piping system should have sufficient flexibility to meet the allowable stress requirements at the equipment’s pipe connections. If necessary, the following measures can be taken: change the pipeline route to enhance natural compensation capacity ； Use spring hangers ； Select metal bellows compensators ； Install limit brackets in the appropriate positions. (22) When laying out piping connected to reciprocating compressors, the natural frequency of mechanical vibrations of the piping system and the natural frequency of the air column within the pipes should be kept away from the excitation frequency of the machine. If necessary, the following measures can be taken: adding anti-vibration supports ； Appropriately increase the pipe diameter ； Add a pulsation dampener or orifice plate ； Set the buffer appropriately, avoid resonant tube lengths, and minimize elbows as much as possible. (23) Branch pipes should not be installed at locations where the bending moment is high on vibrating pipes. (24) At the bends of pipelines prone to vibration (such as the outlet pipes of reciprocating compressors and reciprocating pumps), elbows with a bending radius of not less than 1.5 times the nominal diameter should be used. The branch pipe ensures a straight flow of the medium to the external connection. (25) When a branch pipe with a nominal diameter of 40 mm or less is branched off from a pipe where vibrations may occur, reinforcing measures shall be taken at the joint, regardless of whether there are valves on the branch pipe or not. (26) Horizontal pipes carrying fluid by gravity should have a slope of not less than 3‰ in the direction of flow. (27) When pipes pass through the floor, roof, or walls of a building, sleeves should be used, and any gaps between the sleeves and the pipe ends must be sealed. The diameter of the sleeve should be larger than the outer diameter of the pipe’s insulation layer, and it must not affect the thermal displacement of the pipe. Welds on the pipe shall not be inside the sleeve, and shall be at least 150 mm away from the end of the sleeve. The sleeve should protrude 50 mm above the floor or roof surface. When pipes pass through the roof, a rain cover should be installed; pipes must not pass through firewalls or explosion-proof walls. (28) When installing pipelines for corrosive media, toxic media, and high-pressure fluids, precautions must be taken to prevent hazards to personnel and equipment caused by leaks from flanges, threads, packing seals, etc. Leak-prone areas should be avoided above walkways or pumps; otherwise, safety protections should be installed. (29) For pipes with insulation, pipe supports should be provided at pipe piers and pipe racks. For uninsulated pipes, pipe supports may be omitted if not required. When the thickness of the insulation layer is 80 mm or less, a pipe support with a height of 100 mm should be used ； When the thickness of the insulation layer is greater than 80 mm, use pipe supports that are 150 mm in height ； When the thickness of the insulation layer is greater than 130 mm, use pipe supports that are 200 mm high ； Insulated pipe supports should be used for insulated pipes. (30) When there is a large elevation difference in the plant area, the layout of pipelines throughout the plant should be adjusted to match this elevation difference. Adjust the elevation of the pipe gallery at the appropriate location. The minimum slope of the pipeline should be 2‰. The pipe slope change point should be located at a turn or near a fixed point. (31) For pipelines that cross over or run beneath railways and roads within a plant area, no valves, metal bellows compensators, flanges, threaded joints, or other pipeline components shall be installed on the crossing or underpass sections. (32) For buried pipes subject to thermal displacement, retaining piles can be installed provided the pipe’s curvature permits it; otherwise, thermal compensation measures should be adopted. (33) When laying pipes, the placement of pipe welds shall meet the following requirements: The distance between the center of the butt weld and the starting point of any bend shall be no less than the outer diameter of the pipe; this distance must also be at least 100 mm ； Center distance between two adjacent butt welds on the pipe: a. For pipes with a nominal diameter of less than 150 mm, it shall not be less than the outer diameter, nor less than 50 mm ； b. For pipes with a nominal diameter of 150 mm or greater, it shall not be less than 150 mm ； The clear distance between the circumferential weld and the edge of the support or hanger should not be less than 50 mm ； The minimum clear distance between a weld that requires heat treatment and the edge of a support or hanger should be greater than 5 times the width of the weld, and must not be less than 100 mm. 02 What factors should be considered in determining the width, span, and height of the main corridor in the facility? Width of the pipe rack: l) The width of the pipe rack is primarily determined by the number of pipes and their diameter. Taking into account a certain reserved width, generally a 10%–20% margin should be left for the main corridor pipe rack, while also considering its load. At the same time, the effects of structures such as equipment and passages beneath the pipe gallery, as well as air-cooling equipment above it, must be taken into account. If it is required to install instrument cable trays and power cable trays, their required width should also be taken into consideration. Pipes on the pipe rack can be arranged in a single layer or a double layer; in case of necessity, a triple layer can also be used. The width of the pipe gallery should generally not exceed 10m ； 2) When air coolers are installed on the pipe gallery, the span between the supports should be the same as the spacing between the air coolers, so that the centerlines of the pipe gallery columns and the air cooler supports are aligned ； 3) When installing pumps under the pipe gallery, consideration should be given to the layout of the pumps as well as the width of the passages required for operation and maintenance. If the cable used to power the pump is laid underground, the required width of the cable trench must also be taken into consideration. In addition, the required width of the main pipes for the cooling water and drainage pipes of the pump must also be considered ； 4) Since the pipeline layout density varies throughout the entire pipe gallery, there are usually fewer pipelines in the sections at the beginning and end of the gallery. Therefore, if necessary, the width of the pipe galleries at the beginning and end can be reduced, or a double-layer pipe gallery can be converted into a single-layer one. Span of the pipe gallery: The column spacing and the span of the pipe gallery are determined by the allowable bending deflection resulting from the vertical loads exerted by the pipes laid within it, and are typically 6–9 meters. In small and medium-sized installations, where there are many pipes of small diameter, a secondary beam can be installed between the two supports to reduce the span of the pipes. Furthermore, the spacing between the pipe rack columns should be consistent with that of the equipment frame pillars to allow pipes to pass through. In the case of concrete pipe racks, a φ20 round steel bar or steel plate should be embedded at the top of the crossbeam to reduce friction between the pipes and the crossbeam. The height of the pipe gallery can be determined based on the following conditions: 1) The space available across the road. When the duct tunnel crosses above a road, its clear height should be as follows: the maintenance access within the tunnel must be at least 4.5 m; factory roads must have a clear height of at least 5.0 m ； The railway should be no less than 5.5m ； The maintenance passage under the pipe gallery should be no less than 3m. When the pipe rack has trusses, it shall be calculated based on the height at the bottom of the trusses. 2) Minimum height of pipes under the pipe tray. To make effective use of the duct space, pumps are usually installed under the pipes. Considering the operation and maintenance of the pump, at least 3.5m is required ； When pipes on the pipe rack are connected to sectional equipment, they should generally be 600–1000 mm lower or higher in elevation than the pipes on the lowest level of the pipe rack. Therefore, the minimum elevation of the pipe bottom at the bottom layer of the conduit tunnel is 3.5 m. When shell-and-tube heat exchange equipment is installed under the pipe gallery, the increased height of the equipment requires an increase in the clear height available there. 3) Height difference between vertically intersecting pipe corridors. If the ducts change direction or intersect at right angles, the height difference depends on the minimum size required for connecting the pipes, with 500–750 mm being a suitable range. A height difference of 1000 mm can also be used for large installations. Structural dimensions of the pipe gallery. When determining the height of the utility tunnel, the structural cross-sections and types of the transverse and longitudinal beams must be taken into account; it is essential that the heights of the beam bottoms and the framework bottoms meet the requirements specified for determining the tunnel height. For double-deck utility tunnels, the distance between the upper and lower decks is generally 1.2–2.0 m, which is mainly determined by the diameter of the largest pipe in the tunnel. As for the height of the pipe gallery between the units, it depends on the specific conditions of the area through which the pipe supports pass. If the tank area is located along the edge of the factory, in areas that do not affect traffic within the factory or future expansion, pipe supports can be used for installation, considering both economic factors and ease of maintenance; a height of 300–500 mm above the ground level is sufficient to meet the requirements. 03 What are the principles for pipeline design of flammable liquids, flammable gases, and liquefied hydrocarbons? The design principles for pipelines carrying flammable liquids, flammable gases, and liquefied hydrocarbons are: (l) Pipelines shall not pass through buildings that are not related to them ； (2) Piping should be installed overhead or along the ground ； (3) When conduit burial is necessary, measures must be taken to prevent the accumulation of gases or liquids within the conduit, and sealing barriers should be installed at the inlet and outlet devices as well as at the plant building ； (4) The wastewater in the trench should be sealed with a water seal and discharged into the production wastewater pipeline ； (5) Sampling pipes should not lead into the laboratory ； (6) For metal pipes, welding shall be used for connections, except in cases where flanged connections are specifically required. 04 Which medium pipelines must be electrically grounded? What are the requirements for the grounding connection points and grounding resistance values of pipeline networks? Pipelines for combustible gases, liquefied hydrocarbons, combustible liquids, and combustible solids shall be equipped with static grounding facilities at the following locations: (1) For pipelines within each relatively independent building or structure in the plant area, static grounding can be achieved by connecting them to the metal casing of the process equipment (via flange connections) ； (2) Grounding connection points shall be provided at pumps, filters, buffers, etc., within the pipeline network ； (3) The pipelines in the pipe network at the entrances and exits to the plant area, at the boundaries between different explosion-hazardous areas, and at pipeline junctions shall be grounded; for long-distance pipelines without branches, they shall be reliably connected to grounding electrodes every 80–100 meters ； (4) For the non-conductive sections in the middle of metal pipes (such as PVC pipes), in addition to shielding protection, the metal pipes at both ends should be connected to the grounding main line respectively, or connected together using 6mm² multi-core insulated copper wires and then grounded ； (5) Metal components on non-conductive pipe sections shall be grounded. The grounding resistance value of the dedicated static grounding electrode in each group should be less than 100&#8486 ； In areas with high soil resistivity in mountainous regions, the ground resistance value should be less than 1000&#8486. 05 What are the various methods of pipe laying? What are its advantages and disadvantages? There are two main categories of pipeline installation methods: above the ground and below the ground. (1) Overhead installation, which takes place above the ground, is the primary method for installing pipelines in industrial production facilities. It has advantages such as ease of construction, operation, inspection, maintenance, and cost-effectiveness ； (2) Underground installation 1) Buried installation: Advantages: It makes use of the space underground, keeping the space above the ground tidy, and no support measures are required ； Disadvantages: The pipes are highly corrosive, making inspection and maintenance difficult; special treatment is sometimes required at road surfaces to withstand heavy loads. Drainage from lower points is inconvenient, and it is hard to deal with situations where viscous oils solidify inside the pipes. Pipes with insulation layers also find it difficult to maintain their effective insulating properties. Therefore, they are only used when it is not possible to install them above the ground ； 2) Trench laying: Advantages: It allows for full utilization of underground space and provides convenient conditions for inspection and maintenance ； Pipelines carrying high-temperature, easily solidifying, or corrosive media with insulation layers can also be used ； Disadvantages: high cost, large space requirement, need for drainage points, tendency to accumulate oil and gas which increases safety risks, and difficulty in cleaning accumulated dirt. Therefore, trench laying is used within the device only when necessary. 06 Under what conditions are pipes allowed to be laid directly underground? (1) Pipelines for transporting non-corrosive, non-toxic, and non-explosive liquids or gases that, for some reason, cannot be laid on the surface ； (2) Process medium pipelines related to underground storage tanks or underground pump rooms ； (3) Cooling water and fire-fighting water or foam fire-fighting pipelines ； (4) Thermal pipelines with an operating temperature of less than 150°C. 07 What are the requirements regarding the burial depth of pipes laid underground? The burial depth of pipes laid underground should be determined on the principle that the pipes remain undamaged, taking into account factors such as the maximum depth of frozen soil and the groundwater level. The distance from the top of the pipe to the ground should not be less than 0.5 m ； In areas with concrete floors, whether indoors or outdoors, the distance between pipes and the floor should not be less than 0.3 m. The clearance under the passage for mechanical vehicles should not be less than 0.7 m, or protective sleeves should be used. 08 What are the principles for arranging pipes on a utility tunnel? (1) Large-diameter pipes should be arranged near the pipe rack columns ； (2) Small-diameter gas pipes and utility pipes are laid directly in the middle of the corridor ； (3) Process pipelines should be arranged on the side of the equipment connected to the utility corridor ； Process pipelines can be arranged on the upper or lower layer depending on the elevation of the equipment connections at their ends ； (4) High-temperature pipelines that require a type “Ⅱ” compensator should be located near columns, and type “Ⅱ” compensators ought to be installed in groups ； (5) Low-temperature medium pipelines and liquefied hydrocarbon pipelines should not be arranged near hot pipelines ； It should also not be placed directly above the hot pipe ； (6) For double-layer pipe galleries, gas pipes, hot pipes, utility pipes, pressure relief main pipes, flare main pipes, as well as tray systems for instrumentation and electrical cables, etc., should be arranged on the upper layer ； General process pipelines, pipelines for corrosive media, low-temperature pipelines, etc. are arranged directly in the lower layer ； (7) When designing the pipes in the pipe rack, a margin of 10%–20% should be reserved. 09 What aspects are included in the design of low-temperature pipelines? (1) Low-temperature pipelines are used in various industries, especially widely in petrochemical enterprises. Carbon steel pipes remain in a ductile state within the range of +5°C to –19°C, allowing for normal use. If the operating temperature is below or equal to –20°C, the carbon steel pipes gradually become more brittle, which limits their usability under such conditions. Therefore, pipes with temperatures below or equal to –20°C are considered low-temperature pipes. (2) The layout of low-temperature pipelines mainly takes two issues into consideration. The first is \"low-temperature brittleness,\" which requires designers to select steel plates with high \"impact toughness,\" and at the same time to prevent brittle fracture in pipe design and piping fabrication. The second aspect is the design of the pipeline’s insulation structure and its compliance with the relevant insulation requirements; this directly affects energy consumption as well as the operation, construction, and maintenance of the equipment pipelines. 10. What are the requirements for the layout of low-temperature pipelines? (l) The layout of low-temperature pipelines should ensure that the entire pipeline has sufficient flexibility, making full use of the natural compensation of the pipes. When the design temperature is very low and natural compensation is not possible, a compensator should be installed. (2) When installing low-temperature pipelines, pipeline vibration should be avoided; in particular, for pumps, compressors, and exhaust pipes, it is necessary to prevent vibration throughout the entire pipeline. If there are mechanical sources of vibration, vibration-damping measures should be employed. Elastic elements such as bellows compensators should be installed on the pipelines near these vibration sources in order to isolate them. (3) On low-temperature pipelines made of carbon steel or low-alloy steel, for branch pipes equipped with safety valves, exhaust pipes, or drain valves, it is necessary to consider whether the low-temperature liquid medium will vaporize immediately after being discharged. If vaporization occurs, a large amount of heat will be absorbed, leading to condensation and eventually freezing, which reduces the temperature of the pipeline significantly. Therefore, in areas prone to freezing, such branch pipes should be made of austenitic stainless steel; flanges can then be used to connect branch pipes made of different materials. (4) The stress is greatest at the bends of low-temperature pipelines; therefore, the bends are most prone to brittle fracture. Welding of supports and hangers should be avoided at these locations. (5) On low-temperature pipelines, near elbows or tees, it is generally not permitted to weld flanges directly. To remove the bolts without damaging the insulation layer on the main pipeline, it is necessary to extend a certain length (by attaching a short pipe) before welding the flange. In the mating flange, it is only necessary to ensure that there is enough space at one end of the flange for installing and removing bolts. For the piping of the valve bank, it should be designed so that any individual valve can be removed easily without affecting the pipe’s insulation structure. (6) Support structures for low-temperature insulation pipelines must include measures to prevent the formation of \"cold bridges\" ； When low-temperature pipes are laid horizontally, wooden blocks or rigid insulating material blocks are generally placed at the bottom of the pipes to prevent heat loss from within the pipes. When low-temperature pipes are installed vertically and the supports are fixed to the low-temperature equipment, wooden blocks or rigid insulating material blocks should be placed on both the equipment and the pipes. 11 What are the principles for arranging pipeline sampling tubes? (1) Sampling nozzles should not be installed on equipment and pipes that are subject to vibration, such as pumps and compressors; they should also be avoided on pipes that are directly connected to vibrating equipment. If it is difficult to avoid, vibration reduction measures should be taken ； (2) The arrangement of the sampling tubes shall meet the process requirements, and dead corners or ‘pouch shapes’ shall be avoided. The sampling valve should be located in a location that is easy to access; otherwise, a platform should be provided, and the length of the pipe section between the equipment or pipeline and the sampling valve should be kept as short as possible. (3) Location of the gas sampling tube outlet: When sampling from a horizontal pipe, the sampling tube should be installed at the top of the pipe ； When taking samples from a riser, when gas flows from bottom to top, the sampling port should be led out at a 45° angle upward from the riser ； When the gas contains solid particles, the sampling tube should extend to the center of the tube ； The sampling tube should be positioned horizontally when the gas flows from top to bottom. (4) Location of the liquid sampling tube: When the liquid flows from bottom to top in a vertical pipe, the sampling tube can be installed on either side of the vertical pipe ； When liquid flows from top to bottom in a vertical pipe, it is not advisable to locate a sampling point in such a situation unless it can be ensured that the liquid fills the sampling tube; in that case, the sampling tube can be placed on either side of the vertical pipe ； Horizontal pipelines: Under pressure transfer conditions, the sampling tube can be installed at any position along the pipeline ； When the liquid contains solid particles, the sampling tube should be placed on both sides of the horizontal pipeline ； When sampling in a horizontally flowing pipe, the sampling tube should be placed at the bottom of the pipe. (5) For the sampling of highly hazardous and extremely hazardous toxic substances, on-site venting for sampling is not permitted; closed-loop sampling must be used. 12. What are the special requirements for the layout of the torch main pipe within the unit? (1) The flare main pipe within the unit is generally arranged at the edge of the upper level of the main pipeline corridor, or supported by a T-shaped pipe rack along the corridor columns ； (2) The main flare pipe should slope toward the liquid separation tank at the plant boundary line or the plant’s main flare pipe; it should not form a \"pouch\" shape, and if this does occur, measures should be taken to drain the liquid ； (3) When determining the position of the flare main pipe, it should be ensured that the safety valve and its discharge pipe are located above the flare main pipe. There should be no “pocket-like” areas. The discharge pipe should be connected at a 45° angle to the top of the flare main pipe, following the direction of the medium flow, so as to minimize local resistance as much as possible ； (4) When an “8”-shaped blind flange and a shut-off valve are installed on the torch main pipe at the plant boundary, a drain pipe with a diameter of DN 20–40 should be installed before the shut-off valve (on the inner side of the plant), and double shut-off valves should be fitted at its root. Condensate should be recovered and must not be discharged indiscriminately ； (5) At the ends of the torch main pipe where it is possible to purge all pipes, steam or nitrogen purging pipes shall be provided. When the purging medium is steam, the flare main pipe shall be equipped with horizontally installed “П”-shaped compensators or bellows compensators. (6) The main torch assembly should have pipe clamps or stoppers to prevent slipping ； (7) There shall be no dead corners on the main flare pipe; when changing the direction of the pipe, elbows with R≥1.5DN should be used. 13 What requirements must be met for the installation of torches within the unit? (1) It is strictly prohibited to discharge flammable gases into the flare along with flammable liquids ； (2) The height of the torch should be such that the radiant heat from the flame does not pose a risk to personnel or equipment safety ； (3) A lighting lamp or other reliable ignition device should be installed at the top of the torch; (4) The release of combustible gases is strictly prohibited within 30 meters of the torch barrel. 14 What is the purpose of piping for exhaust and drainage? Where in the pipeline should venting or drainage be installed? Purpose of venting: 1) When an \"air pocket\" forms in the inlet pipe of the pump, it should be vented before starting the pump ； 2) When the unit is started up, to prevent air lock in the piping system, it is necessary to vent at its highest point ； 3) When conducting hydrostatic testing and purging of the piping system, temporary venting must be provided at the highest points of the pipes ； 4) To remove the fluid from the pipeline as quickly as possible, a vent is installed at a high point to allow drainage using atmospheric pressure. Purpose of draining: 1) To remove liquid from the pipes: after the hydrostatic test, drain the liquid ； Drainage before shutdown for maintenance ； Drainage for pipe anti-freezing. 2) Injection pipe used as a fluid during hydrotesting ； 3) Used as the air and steam purge outlet for the piping system. Gas should be provided in the following locations: 1) Areas where the liquid pipeline forms a \"gas pocket\", such as the inlet pipeline of a pump, at the upper part where such a \"gas pocket\" is inevitably formed ； 2) Places marked on the P&ID ； 3) Exhaust pipes should be installed at a high position on the equipment or answering system. Drainage is provided in the following areas: 1) the areas that form a “liquid bag” ； 2) Places marked on the P&ID ； 3) The ends of the utility pipes on the pipe tray; 4) Other cases: for example, when the average temperature in the coldest month is 0°C or below the freezing point of the medium, a drain pipe should be installed behind the valve. This drain pipe should be located near the isolation valve, while the drain valve itself should be placed near the main pipe ； 5) A drain pipe should be installed between the control valve and the shut-off valve ； 6) Large-diameter pipelines (such as crude oil pipelines) are difficult to purge completely, and a low-point drain pipe should be installed. What are the specific requirements for installing the exhaust and drain pipes on 15 pairs of pipelines? (1) The location of the high-point vent on the pipeline should be near platforms, supports, structures, and areas where it is easy to access ； (2) Near the location where the low-point drain on the pipeline is installed, a floor drain or gutter should be provided, or a hose should be used to connect it to such a drain or gutter ； (3) To ensure the maintenance of valves, as well as the removal of plugs, pipe caps, and flanges and the connection of hoses, the clear distance between the end of the pipe at its lowest point and the ground or floor surface must not be less than 100 mm ； (4) The installation locations of the vent and drain ports on the pipeline should be placed as far downstream as possible along the flow direction, near the elbow, but not on the elbow itself ； The valves installed for venting and draining on the pipeline should be located near the main pipe ； (5) The drain pipe on pipes that are prone to self-agglomeration, freezing, solidification, or contain solid media should not have any bends ； For slurry pipes, it is not advisable to install exhaust and drainage pipes; if a drainage pipe must be installed, it should be positioned at a tangent to the bottom of the horizontal slurry pipe ； (6) Pipes with a diameter smaller than DN40 do not require a high-point vent ； For plant-wide processes, condensate water, and water pipelines (non-buried), in areas where the average temperature in January over the years is above 0°C ； Fewer low-point drains should be installed ； (7) Sealed venting with a diameter less than DN40 on vibrating pipes. Reinforcement measures should be taken at the interface at the back of the drain pipe ； (8) The outlet of the drainage pipe for grounded drains or open tanks should be at a height of 50 mm or more above the drain opening or tank mouth ； (9) For the isolation valves on the vent or drain pipes, gate valves are recommended; a short pipe with a pipe cap can be connected after the valve ； For pipelines carrying high-pressure, extremely hazardous, and highly hazardous media, double valves shall be installed. When a single network is set up, a blind flange or flange cover should be used ； (10) The drain valve at the lowest point of the combustible gas pipeline, which is operated continuously, should be a dual-valve system, and the liquid discharged should be sent to a closed system ； For drain valves used only during startup and shutdown, a single valve can be installed along with a threaded plug, pipe cap, blind flange, or flange cover. When a shut-off valve is installed on the drain pipe of flammable liquid pipelines and steam pipelines with a pressure greater than 2.5 MPa, a pipe cap (plug), blind flange, or flange cover should be fitted at the end. What requirements must be met regarding the height of vent pipes for non-flammable gases discharged into the atmosphere? (1) The vent openings on equipment or pipelines shall be at least 2 meters above the surface of the adjacent operating platform ； (2) The vent openings located adjacent to buildings, structures, or the equipment or pipes installed inside them shall be at a height of more than 2 meters above such buildings and structures. 17 What are the requirements regarding the height of flammable gas exhaust stacks and vent pipes? The height of flammable gas exhaust stacks and vent pipes shall comply with the following requirements: (1) The top of a continuously emitting flammable gas exhaust stack or the outlet of a vent pipe shall be at least 3.5 m above the roof of a platform or building within a radius of 20 m ； (2) The exhaust stack or vent for intermittently emitted combustible gases shall be at least 3.5 m above the roof of a platform or building within a 10-m radius. Platforms or buildings located more than 10 m away shall meet the requirements of Figure 5.2.73 ； (3) The vent pipes for starting up, stopping, and operation of Class A, B, and C equipment may discharge into the atmosphere locally; the height of the vent pipe openings should be at least 2.2 m above the platform. These vent pipe openings are generally oriented vertically upward and equipped with rain guards ； (4) The combustible gas discharge pipes and flare main pipes shall be equipped with anti-static grounding facilities. 18. When the outlet medium of a safety relief device is permitted to be discharged into the atmosphere, what requirements must be met? (1) The vent opening must not face adjacent equipment or areas where people walk ； (2) The height of the vent opening shall be 3 m above the highest operating platform within a radius of 8 m centered on the safety pressure relief device. What is the main function of valve 19? What are the selection principles? Valves are important components of industrial piping systems and play a crucial role in the production process. The main functions of valves are: 1) To connect and disconnect the medium — gate valves, butterfly valves, and ball valves can be used for this purpose ； 2) Prevent backflow of the medium – a check valve can be used ； 3) Adjusting medium pressure and flow rate — globe valves or control valves can be used ； 4) Medium separation, mixing, or distribution – ball valves, gate valves, control valves can be used ； 5) Prevent the medium pressure from exceeding the specified value to ensure the safe operation of pipelines or equipment – safety valves can be used for this purpose. The selection of valves is primarily based on two considerations: fault-free operation of the installation and cost efficiency. . The principles for selecting valves are as follows: the properties of the fluid being transported ； Functions of valves ； Size of the valve ； Resistance loss of the valve ； Operating temperature and operating pressure of the valve ； (Material of the valve; can be two.) What are the general requirements for installing valves 20? General requirements for valve installation, the most suitable installation height, valves on horizontal pipes, and the direction of the valve stem are as follows: (1) Valves should be installed in locations that are easily accessible and convenient for operation and maintenance. Valves on rows of pipes (such as those of inlet and outlet devices) should be arranged collectively, and consideration should be given to providing operating platforms and ladders. For valves on pipes arranged in parallel, their centerlines should be aligned as much as possible. The clear distance between handwheels should not be less than 10Q mm; to reduce the spacing between pipes, the valves can be arranged offset from each other ； (2) The installation position of valves that are operated frequently should be convenient for operation; the most suitable installation height is around 1.2 meters above or below the operating surface. When the height of the center of the valve handwheel exceeds 2 m above the operating surface, platforms should be provided for valve banks arranged together, for individual valves that are operated frequently, and for safety valves. Appropriate measures should also be taken for individual valves that are not operated often (such as sprockets, extension rods, movable platforms, and movable ladders). The chain of the sprocket should not obstruct passage. Valves on pipelines and equipment handling hazardous materials must not be installed at a height corresponding to human head level, to prevent injury to the head or direct damage to the face in the event of a valve leak ； (3) Valves used to isolate equipment should be connected directly to the equipment nozzles or located close to the equipment. Valves on pipes connected to equipment that handles extremely hazardous or highly hazardous toxic substances should be connected directly to the equipment’s inlet; such valves must not be operated using sprockets ； (4) Accident handling valves, such as those for fire water and fire steam, should be arranged separately, with consideration given to safe operation in the event of an accident. Such valves should be installed behind the control room. Behind safety walls, outside factory buildings, or in areas at a certain safe distance from the site of the incident ； So that in the event of a fire, operators can carry out their tasks safely ； (5) Unless the process has special requirements, valves on the pipelines at the bottom of equipment such as towers, reactors, and vertical vessels shall not be installed within the skirt ； (6) The isolation valve for the horizontal branch pipe leading off from the main pipe should be located on the horizontal section near its root ； (7) Lift-type check valves should be installed in horizontal pipes, while vertical lift-type check valves should be installed in vertical pipes where the medium flows from bottom to top. Swing check valves should be installed in horizontal pipes preferentially, but can also be installed in vertical pipes where the medium flows from bottom to top ； The foot valve should be installed at the vertical pipe end of the suction pipe of the centrifugal pump ； To reduce the installation height of the pump outlet shut-off valve, a butterfly check valve can be used ； When the diameter of the pump outlet does not match that of the connected pipeline, a reduced-diameter check valve can be used ； (8) The center distance between the handwheels of the valves located around the operating platform and the edge of the platform should not exceed 450 mm. When the valve stems and handwheels extend above the platform and their height is less than 2 m, they should not interfere with the operator’s ability to operate or move around ； (9) Valves for underground pipelines should be installed in pipe trenches or valve chambers; when necessary, valve extension rods should be provided. The fire water valve well should have clear markings ； (10) For valves on horizontal pipes, the direction of the valve stem can be determined in the following order: vertically upward ； Horizontal ； Tilt upward at 45° ； Tilt downward at 45° ； It must not be directed vertically downward ； (11) In straight-through valves with the valve stem installed horizontally, the valve stem must not obstruct passage when the valve is open. 21 What are the requirements for installing a breathing valve? (1) The breather should be installed at the highest point of the gas space in the storage tank, in order to reduce material evaporation losses and to provide the most direct and largest path leading to the breather valve. For vertical tanks, the breather valve should generally be installed as close as possible to the central roof area of the tank. For tanks whose roofs require insulation, it can be installed near the ladder platform ； (2) When two breather valves need to be installed, they should be arranged symmetrically with respect to the center of the tank roof ； (3) If a breather valve is used on a nitrogen-sealed tank, the connection point of the nitrogen supply pipe should be placed far away from the breather valve interface, and it should be inserted into the tank from the top by about 200 mm, so that the nitrogen entering the tank is not discharged directly, thereby achieving the purpose of nitrogen sealing. 22 What are the general requirements for the installation of control valve assemblies? (1) The installation location of the control valve shall meet the requirements of the process flow design, and it shall be located near the primary indicating instruments related to it, so that these instruments can be observed easily when manually operating the bypass valve ； (2) The control valve should be installed on the ground or a platform in a location that facilitates operation and maintenance ； (3) The control valve should be installed vertically and upright in a horizontal pipeline; in special cases, it may be installed horizontally or at an angle, but support must be provided ； (4) When installing the control valve assembly (including control valves, bypass valves, shut-off valves, and drain valves) in elevation, the control valve should be installed below the bypass. Control valves with a nominal diameter of less than 25 mm can also be installed above the bypass ； (5) The clear height from the bottom of the control valve to the ground or platform surface should not be less than 400 mm. For single- and double-seat control valves with reverse-mounted spools, it is advisable to leave space below the valve body for removing the spool ； (6) There should be a clearance of not less than 2 mm above the top of the control valve diaphragm head. When the control valve and the bypass valve are arranged one above the other, their positions should be spaced apart ； (7) Gate valves should be used for isolation valves, while globe valves should be used for bypass valves; however, when the nominal diameter of the bypass valve is greater than 150 mm, a gate valve can also be used. The two isolation valves and the control valve should not be arranged in a straight line ； (8) A drain valve should be installed at the lowest point in the pipeline between the inlet side of the control valve and the shut-off valve upstream of it; a gate valve can be used as this drain valve ； (9) On pipelines containing solid particles in the medium, the control valve and the bypass valve should be arranged on the same plane, or the bypass valve should be placed below the control valve ； (10) Among the two supports of the control valve assembly on low-temperature and high-temperature pipelines, one should be a fixed support and the other a sliding support ； (11) The control valve should be installed in an environment where the temperature is not higher than 60 °C and not lower than -40 °C, and away from sources of vibration ； (12) When there are multiple control valve assemblies in one area, it is necessary to consider consistency in design, as well as neatness, aesthetics, and ease of operation ； (13) When the diameters of the control valve and the isolation valve differ, the reducer should be installed near the control chamber ； (14) Pay attention to whether there are any special requirements from the process for the position of the control valve. 23. To ensure the safety of pressure pipelines, on which pressure pipelines should safety valves be installed? To ensure the safety of pressure pipelines, safety valves should be installed on the following types of pressure pipelines: (1) Safety valves should be installed on the outlet pipes 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 pipeline, and an emergency shutdown interlock device is recommended (except when the equipment itself is already equipped with a safety valve) ； (2) Safety valves shall be installed at the outlets of each stage of the reciprocating compressor for combustible gases, and the vent pipes of these safety valves shall be connected to the inlet pipes of each stage of the compressor or to the inlet pipe of the first stage of the compressor ； (3) Pipes in which combustible gases and liquids may expand due to heat and thus exceed the design pressure should be equipped with safety valves ； (4) On liquefied hydrocarbon pipelines that may be closed at both ends, thereby causing pressure buildup, safety valves should be installed or other safety measures taken ； (5) Where the equipment connected to the outlet of blowers, centrifugal compressors, centrifugal pumps, or steam reciprocating pumps cannot withstand their maximum pressure, safety valves must be installed on the outlet pipes of such pumps and compressors. The above pipelines may experience explosion accidents due to pressure inside them exceeding the design pressure as a result of fires, operational failures, or disruptions in water or power supply; therefore, safety valves or other safety measures should be installed. What are the key points for the installation of safety valves and the design of their piping layout? (1) The safety valve shall be installed vertically and close to the equipment or pipeline to be protected. If proximity is not possible, the total pressure drop in the piping from the equipment or pipeline to be protected to the inlet of the safety valve shall not exceed 3% of the set pressure of the safety valve. (2) A maintenance platform should be provided for the safety valve. When installing heavy safety valves, consideration must be given to the possibility of lifting them after removal; if necessary, lifting rods should be provided. (3) Long-radius elbows should be used for the inlet pipeline of the safety valve. (4) The design of the safety valve outlet pipeline should take into account that the back pressure shall not exceed a certain value of the safety valve’s set pressure. For standard spring-loaded safety valves, the back pressure shall not exceed 10% of the valve’s set pressure value. (5) When the medium discharged into the vent main or the flare main contains condensate or condensable gases, the outlet of the safety valve should be located above the main ； Otherwise, drainage measures should be taken. (6) The outlet pipe of the safety valve leading into a closed system should be connected at a 45° angle to the top of the discharge main, in line with the flow direction of the medium, in order to prevent condensate in the main from flowing back into the branch pipes and to reduce the back pressure on the safety valve. (7) When cut-off valves are installed on the inlet and outlet pipes of the safety valve, single-plate gate valves should be used, and these valves should be sealed with lead. The valve stem should be installed horizontally, so that if the pins connecting the valve stem to the valve plate become corroded or loosen, the valve plate will not slide down. When a safety valve is equipped with a bypass valve, this valve shall be sealed with lead. What are the general requirements for the layout of 25 pipes and fittings? (1) Elbows should preferably be long-radius elbows with a radius of curvature equal to 1.5 times the nominal diameter ； Pipes for transporting gas-solid and liquid-solid two-phase flow materials should use elbows with a large radius of curvature ； (2) For the diameter-changing connections of horizontal pipes on provincial corridors, unless there are special requirements, eccentric reducers with a flat bottom should be used ； Concentric reducer pipes are advisable for use on vertical pipes ； (3) For horizontally suctioned centrifugal pumps, when the diameter of the inlet pipe changes, an eccentric reducer should be installed near the pump’s inlet. When the pipeline enters the pump from below, horizontal installation at the top should be used; when it enters the pump from above, horizontal installation at the bottom is advisable ； (4) Butt-weld 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 the process has special requirements, flanges and threaded connections shall not be installed on the pipes within the pedestals of equipment such as towers, reactors, and vertical vessels ； (7) Flanges shall be installed at intervals on carbon steel pipes in the lubricating oil systems of machinery and pumps, as well as on pipes conveying media with solid deposits and coking tendencies. In the carbon steel piping of the pump lubrication system, there should be no more than 2 elbows per section of piping ； (8) The end of the main lubricating oil pipeline in the machine pump lubrication system should be sealed with a flange cover ； (9) The reducers on the pipes on both sides of the control valve should be positioned close to the control valve ； (10) When using reducer flanges for connection, the flow direction of the medium should be from the smaller diameter to the larger diameter. 26. What are the requirements for the placement of flame arresters? (1) The pipeline flame arrester on the main fuel gas line of the heating furnace should be located close to the furnace to facilitate maintenance; the distance between the pipeline flame arrester and the burner should not exceed 12 meters ； (2) The flame arrester for tanks should be installed directly on the pipe outlet at the top of the storage tank; it is usually used in conjunction with a vent valve, but can also be used alone. 27 What are the requirements for the layout of filters? (1) Filters should be installed at the inlet of all pumps. The filter should be installed near the equipment to be protected ； (2) The installation of filters shall meet the following requirements: Angular T-type filters must be installed at points where the pipeline makes a 90° turn ； Straight-through T-type filters must be installed on straight sections of the pipeline; when installed on vertical pipes, consideration should be given to facilitating the removal of the filter screen ； When installed in a horizontal pipe, the filter screen should be pulled out downward ； When a Y-type filter is installed on a horizontal pipeline, the direction in which the filter screen is pulled out should be downward. (3) The pump inlet filter installed on the standpipe; to reduce the height of the pump inlet valve, a reducer filter can be used ； (4) When a Y-type filter is installed on a vertical pipe with the medium flowing from bottom to top, a backflow type should be selected ； (5) A filter or a removable spool piece shall be installed on the compressor inlet pipe to facilitate the installation of a temporary filter and the cleaning of the pipe prior to startup. 28 What are the general requirements for the piping layout design of filtration equipment? (1) When performing hydraulic calculations for pipelines transporting filter slurry and calculating the NPSH of pumps, it is necessary to conduct calculations regarding the physical properties of the slurry and resistance based on a liquid-solid two-phase flow model. The flow velocity inside the slurry pipelines can be set at 1.5 to 2 times the settling velocity of solid particles in the slurry. If no measured value for the settling velocity is available, the flow velocity within the pipeline is generally set at 2.5–3 m/s ； (2) The pipes should run in a straight line as much as possible; the installation slope should be steep (minimum slope of I≥10%). Use bends as little as possible, and the radius of curvature of the bends should be large enough (R≥4DN). Sudden increases in pipe diameter should be avoided ； (3) Welding should be used sparingly for pipe connections; flanges or threaded connections are preferred to facilitate disassembly and cleaning. Eccentric reducers are directly connected using flanges, while vacuum pipes are welded; flange connections are used less frequently ； (4) On each liquid-solid two-phase flow pipeline, flushing (or purging) nozzles and drain pipes for emptying the contents are installed at appropriate positions. The connection point for the flushing water pipe is located above or to the side of the material pipeline, and the valves on the flushing pipe should be installed as vertically as possible ； (5) For the pulp flow pipes, valves with straight fluid passages within the valve body and no dead corners should be selected; diaphragm valves and clamp valves are recommended. Soft-sealed butterfly valves, ball valves, or plug valves. When the valve is installed horizontally, drain pipes equipped with valves as well as flushing connections are installed on the material pipes before and after the valve; when it is installed vertically, drainage and flushing fittings are installed on the material pipe above the valve ； (6) To prevent clogging in the slurry pipeline, no bypass is provided; a control system with idlers is used instead ； (7) When the filter cake is a crystalline slurry containing crystals, the piping system must be equipped with jackets or trace heating for thermal insulation. For valves, ball valves with thermal insulation and heating structures or soft-sealed butterfly valves should be selected ； (8) The pipeline design requirements for the filtrate pump and wash liquid pump of the filtration system shall comply with HG/T 20549.2 ； (9) No valves are installed for the exhaust from the slurry filtration tank and the filtrate tank; when the material is flammable, volatile, or toxic, a vent valve and a flame arrester must be installed on the exhaust pipes. 29 What are the requirements for pipeline layout regarding compensators? (1) When the geometric shape of the piping system is restricted due to equipment layout or other factors, and the compensation capacity is insufficient, compensators should be installed at appropriate locations within the piping system. (2) The distance between the “Π”-shaped compensator and the fixed points should not be less than one-third of the distance between the two fixed points. (3) The installation of unrestrained metal bellows compensators shall meet the following requirements: only one compensator may be installed between two fixed supports ； The pipeline must be strictly protected; in particular, guide frames should be installed near the compensator. The distance between the first guide frame and the compensator should be less than or equal to 4 times the nominal diameter, while the distance between the second guide frame and the first one should be less than or equal to 14 times the nominal diameter. This is to prevent bending or radial displacement of the pipeline from causing damage to the compensator. (4) Metal flexible hoses for seismic protection of storage tanks should be installed in the pipelines in front of the tanks when the seismic intensity is 7 degrees or higher, uneven settlement occurs, and the nominal diameter is 150 mm or greater. The diameter of the metal flexible hose should not be smaller than the diameter of the inlet and outlet pipes of the storage tank. The flexible metal hose should be installed between the first valve and the second valve, near the tank wall. What are the general requirements for the layout of instruments or measuring elements on a 30-inch pipeline? (1) The layout of instruments or measuring elements on the pipelines shall comply with the provisions of the current relevant design codes for instrument piping and wiring in industrial enterprises ； (2) The arrangement of instruments or measuring elements on the pipeline should facilitate installation, observation, and maintenance. A dedicated operating platform or ladder should be provided if necessary ； (3) The length of the instrument nozzle should be determined based on the thickness of the pipeline’s insulation layer. 31 What are the requirements for the layout of flow measurement instruments? (1) To ensure accurate measurement by the orifice flow meter, there should be a straight pipe section of 15–20 times the inner diameter of the pipe in front of the orifice, and a straight pipe section of at least 5 times the inner diameter of the pipe behind it ； (2) The installation of flow meters shall comply with the following requirements: 1) Rotameters must be installed in vertical pipes without vibration, with the medium flowing from bottom to top. During installation, it is necessary to ensure that there is a straight pipe section in front of the flow meter with a length of at least 5 times the inner diameter of the pipe, and this length should be no less than 300 mm ； 2) When the medium being measured contains solid suspensions, the target flowmeter needs to be installed horizontally. When a target flowmeter is installed in a vertical pipe, the liquid flow should be from bottom to top. The length of the straight pipe section ahead of the inlet of the target flow meter should not be less than 5 times the inner diameter of the tube, while the length of the straight pipe section behind the outlet should not be less than 3 times the inner diameter of the tube ； 3) The gear flow meter should be installed in front of the control valve. When on-site calibration of the flow meter is required, two calibration gate valves with quick connectors should be installed before and after the cut-off valve upstream of the gear flow meter. 32 What are the requirements for the layout of pressure measuring instruments? (1) To accurately measure the static pressure, the pressure gauge sampling point should be located on a straight pipe section, away from the shut-off valve. (2) The pressure gauge at the pump outlet should be installed in front of the outlet valve and facing the operation side. (3) The installation height of the pressure gauge at the site should be between 1.2 and 1.8 m; when it exceeds 2.0 m, a platform or straight ladder should be provided. 33 What are the requirements for the layout of temperature measuring instruments? (1) Thermometers and thermocouples should be installed in straight pipe sections, and the minimum pipe diameter requirements for their installation are as follows: for industrial mercury thermometers, DN50; for thermocouples, thermal resistors, and bimetallic thermometers, DN80 ； Pressure thermometer, DN150 ； The length of the expansion tube should not be less than 250 mm. (2) When thermometers and thermocouples are installed at pipe bends, the pipe diameter shall not be less than DN40, and they must be in countercurrent contact with the flow direction of the fluid inside the pipe. (3) The thermometer can be installed vertically or at a 45° angle; when installed at a 45° angle, it should make contact with the fluid flow in the pipe in a counterflow direction. (4) The installation height of the on-site indicating thermometer should be 1.2~1.5 m. When the height exceeds 2.0 m, a straight ladder or movable platform should be provided. For ease of maintenance, the distance from the platform should not be less than 300 mm. (5) For process pipelines with branches, when installing thermometers or thermocouples, special attention must be paid to ensuring that the installation location is in line with the process flow; they must not be installed in dead corners or blind areas of the process pipeline. 34 What are the requirements for the layout of level measurement instruments? (1) Glass tube level gauges and glass plate level gauges should be installed directly on the equipment, and their location should not obstruct personnel passage. (2) The installation location of the external floating ball level gauge should not obstruct pedestrian traffic. The upper end of the gauge’s display panel should not be higher than 1.8 m above the ground or platform; if it is higher than 2.0 m, an additional platform should be provided. (3) The height of the internal floating ball level gauge above the platform or ground should be 1.0 to 1.5 meters. It should be installed in a location that does not obstruct passage, with sufficient space available for maintenance and adjustment. 35 What are the general requirements for safety protection settings? The design should evaluate the various factors from (1) to (4) below, and in line with the safety protection objectives and requirements specified in various sections of the standards, appropriate safety protection measures should be taken: (1) The hazard level of the fluid, determined by its properties as well as the operating pressure and temperature ； (2) Pipeline safety determined by the pipeline material, structure, connection method, and its experience in safe operation ； (3) Once the pipeline is damaged or leaks, the amount of fluid that leaks out and the degree of damage it causes to the surrounding environment and equipment ； (4) The degree of hazard posed by pipeline accidents to operators, maintenance personnel, and all potentially exposed individuals. 36 How to establish safety protections and measures in pipeline design? (1) Install necessary safety protections and measures based on the characteristics of the production process: fire suppression systems and sprinkler facilities ； Fire protection structures for buildings and structures (firewalls, blast walls, etc.) ； Ventilation to remove toxic, corrosive, or flammable vapors ； Telemetry and remote control devices ； Facilities for the emergency handling of hazardous substances (storage or recovery units). Torches or incinerators, etc.). (2) In brittle material piping systems or flanges. Protective covers are provided at joints, valve caps, instruments, or sight glasses to limit and reduce the risk of leakage. (3) Use automatic or remotely controlled emergency shut-offs, flow-over valves, additional shut-off valves, flow-limiting orifice plates, or automatically shutting off the pressure source to limit the amount and rate of fluid leakage. (4) Valves used for accident handling (such as emergency venting, accident isolation, fire steam, fire hydrants, etc.) should be installed in a safe, visible, and easily accessible location. (5) For flammable and toxic materials entering and leaving the unit, isolation valves should be installed at the boundary of the boundary zone, and \"8\"-shaped blind plates should be placed on the unit side to prevent mutual interference in the event of a fire within the unit. (6) Provide necessary protective masks, gas masks, emergency breathing systems, and specialized chemicals. Health and safety equipment such as portable combustible and toxic gas detection and alarm systems. Emergency showers and eye wash stations should be installed near any emission or leakage points that could cause accidental harm to people. (7) For radioactive fluids, shielding protection and automatic alarm systems must be installed, along with specialized masks, gloves, and protective clothing. (8) Static grounding measures shall be taken for all pipeline systems in areas where there is a risk of explosion or fire, as these may pose a static electricity hazard. It can be grounded through the grounding network of equipment, pipelines, and civil structures. Other anti-static requirements shall comply with the provisions of the General Guidelines for Preventing Static Electricity Accidents, GB12158. (9) The installation of blind plates shall meet the following requirements: When the unit is shut down for maintenance, for pipelines outside the unit that may need to continue operating, in addition to installing isolation valves at the unit’s boundary, blind plates shall also be installed on the flange side of the valve that is adjacent to the unit ； During operation, when some equipment needs to be shut down for maintenance, a blind flange should be installed at the flange connection between the valve and the equipment. For pipelines carrying toxic or flammable fluids, if there is a vent valve between the valve and the blind flange, the pipeline downstream of that vent valve should be led to a safe location. (10) When utility pipes (steam, air, nitrogen, etc.) are connected to GC1-class and GC2-class pipes, the following requirements shall be met: Check valves shall be installed on the continuously used utility pipes, with isolation valves placed at their bases ； Two isolation valves should be installed on utility pipelines that are used intermittently, with a check valve placed between the two valves. 37 What measures should be taken when pipes pass through a building’s floor, roof, or walls? When a pipe passes through a building’s floor, roof, or wall, a sleeve should be installed at the point of penetration, and the gap between the sleeve and the pipe should be sealed with a soft material. The diameter of the sleeve should be larger than the outer diameter of the insulation layer of the pipe or heat-restricted pipe, without affecting the thermal displacement of the pipe. The sleeve should be 50 mm above the floor or roof. Those at the top level should be equipped with a rain cover if necessary. The weld of the pipe shall not be located inside the sleeve, and it shall be at least 150 mm away from the end of the sleeve. Pipes should not pass through firewalls and explosion-proof walls. What are the common heat tracing media used for process pipelines in Unit 38? What is its scope of application? There are four common types of heat tracing media used in process pipelines: (1) Hot water: It is suitable as a heat source for heat tracing in situations where the operating temperature is not high, or when high-temperature heat tracing media cannot be used ； (2) Steam: Generally used for heating in pipelines where the operating temperature of the medium is below 150°C ； (3) Heat carrier: Generally used in jacketed heating systems where the operating temperature of the medium inside the pipe is greater than 150 °C. Common heat carriers include heavy diesel or distillates with a boiling point above 300°C, biphenyl-biphenyl ether, or hydrogenated triphenyls, etc ； (4) Electric heating: Electric tracing is suitable not only for various situations involving steam tracing but also for pipelines carrying thermosensitive media; it enables effective temperature control and prevents the pipeline temperature from becoming too high ； Suitable for trace heating of pipes or equipment that are dispersed or located far from steam supply points, as well as equipment with irregular shapes (such as pumps). 39. What are the requirements for the layout of reducers? (1) When installing an elbow near a tee, for a converging tee, the elbow should be placed on the pipe before the convergence point ； For branch tees, reducers should be installed on the branched pipelines ； (2) For the eccentric reducers on the horizontal pipe at the pump inlet, they shall be arranged eccentrically downward. What are the requirements for the layout of 40 valves? (1) Valves should be installed in locations that are convenient for operation, maintenance, and repair ； (2) Heavy-duty valves and larger welded valves should be installed on horizontal pipelines, with the valve stem pointing vertically upward ； For heavy-duty valves, necessary lifting measures should also be considered ； (3) For valves with flange connections or cast-iron valves, they should be installed in areas where the bending moment is low ； (4) For valves arranged horizontally, unless otherwise specified, the valve stem shall not point downward ； (5) For the valves in the gutter, provided it does not hinder passage on the ground surface, the valve stem may extend above the ground level, with the operating handle generally being at least 150 mm above the ground ； Otherwise, simple operational measures should be considered. 41 What issues should be considered when designing piping systems with gas-liquid two-phase flow? (1) Pipelines should preferably run vertically first in the direction of the medium flow, and then horizontally, with the pipelines being short and straight ； (2) The control valve on the pipeline should be placed as close as possible to the container that holds the medium; if conditions permit, the control valve should be connected directly to that container ； (3) The first turning elbow after the control valve should be replaced with a tee connection, and a plug should be installed at the straight-through end of the tee ； (4) Limit stops or fixed support brackets should be installed at appropriate positions in the piping system. 42 What are the principles for selecting pipeline categories? (1) The pipeline category should be selected based on the properties and parameters of the medium inside the pipe, as well as its safety and economic viability under various operating conditions ； (2) Seamless steel pipes are suitable for pipelines with various parameters ； (3) High-quality welded steel pipes can be used for low-temperature reheat steam pipelines ； (4) For pipes with parameters of PN2.5MPa and below, welded steel pipes can be used ； (5) Welded steel pipes for low-pressure fluid transport are suitable only for media with a pressure of PN1.6MPa or less and a design temperature of not more than 200°C. 43 What are the main principles for selecting flanges? For pipes with a design temperature of 300°C or lower and a nominal pressure of 2.5 MPa or less, flat welding flanges should be used ； For pipes with a design temperature greater than 300°C or a nominal pressure of 4.0 MPa or higher, butt-weld flanges should be used. 44 Which pipes should be considered for insulation or cooling? (1) Equipment and pipelines with one of the following conditions shall be insulated: 1) Equipment and pipelines whose outer surface temperature is greater than 50°C, and those whose outer surface temperature is less than or equal to 50°C but for which insulation is required due to process needs. For example, liquefied hydrocarbon pipelines at the pump inlet that are often exposed to sunlight: the distillation column top outlet lines (pipelines from the column to the condenser), the column top reflux lines, and the fuel gas pipelines after liquid separation should all be insulated ； 2) Equipment and pipelines whose medium freezing point or ice point is higher than the ambient temperature (referring to the annual average temperature). For example, crude oil with a freezing point of around 30°C, in equipment and pipelines located in areas where the average annual temperature is below 30°C ； In cold or extremely cold regions, although the freezing point of the medium is not high, equipment and pipes containing water within that medium – such as water pipes that do not flow frequently in cold areas – may be affected. (2) Equipment and pipelines with any of the following conditions must be insulated: l) It is necessary to reduce the temperature rise or vaporization of the cooling medium during production or transportation (including freezing due to sudden pressure reduction resulting in vaporization) ； 2) It is necessary to reduce the heat loss of the cooling medium during production or transportation, or to specify an allowable level of heat loss ； 3) It is necessary to prevent dew formation on the outer surfaces of equipment or pipelines at ambient temperature.