Complete knowledge points of pipeline piping

What are the requirements for pipeline layout design?

(1) The pipeline layout design should comply with the requirements of the process pipeline and instrument flow chart;

(2) The pipeline layout should be planned in a comprehensive manner to ensure safety, reliability, economic rationality, and meet the requirements of construction, operation, maintenance, etc., and strive to be neat and beautiful;

(3) When determining the orientation and laying method of pipelines entering and exiting the device (unit), internal and external coordination should be achieved;

(4) The laying of the whole plant pipeline within the factory area should be coordinated with the devices (units), roads, buildings, etc. within the factory area to avoid the pipeline surrounding the device (unit) and reduce the intersection of the pipeline with the railway and road;

(5) The pipeline 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, and above-ground pipelines should be laid on pipe racks or piers;

(7) When arranging pipelines on pipe racks or piers, the vertical and horizontal loads on the pipe racks or piers should be balanced;

(8) A 10%-30% margin should be left on the pipe racks or piers throughout the plant (including those crossing culverts), and their loads should be taken into account. A 10%-20% margin should be left on the pipe racks of the main pipe gallery of the device, and their loads should be taken into account;

(9) The layout of pipelines with special requirements for distance, angle, height difference, etc. for the conveying medium and large-diameter pipelines should comply with the requirements of equipment layout design;

(10) The pipeline layout should not hinder the installation, maintenance and passage of equipment, pumps and their internal components;

(11) The pipeline layout should give the pipeline system the necessary flexibility. While ensuring the flexibility of the pipeline and the force and torque of the pipeline on the equipment and pump nozzles do not exceed the allowable value, the pipeline should be as short as possible and have the least components;

(12) The support point setting should be considered while planning the pipeline. The natural shape of the pipeline should be used to achieve self-compensation;

(13) The pipeline layout should be "step by step" or "step by step" to reduce air pockets or liquid pockets. When it is unavoidable, venting and cleaning should be set according to operation and maintenance requirements, and the pipeline layout should reduce "blind intestines";

(14) When the pipeline of gas-liquid two-phase flow is divided from one channel to two or more channels, the pipeline layout should consider symmetry or meet the requirements of the pipeline and instrument flow chart.

(15) Except for those that need to be connected with valves, instruments, equipment, etc. by flanges or threads, pipelines should be connected by welding.

The following conditions should consider flanges, threads or other detachable connections: occasions where disassembly is required for maintenance, cleaning, or purging; lined pipes or jacketed pipes; pipes composed of two sections of dissimilar materials and not suitable for welding; pipe connection points where on-site heat treatment of welds is difficult; galvanized pipes with a nominal diameter less than or equal to 100 mm; locations where blind plates or "8" blind plates are installed.

(16) Gas branches should be connected from the top of the main pipe.

(17) Toxic medium pipes should be connected by welding, and flanges or threads should not be used unless there is a special need. Toxic medium pipes should be clearly marked to distinguish them from other pipes, and toxic medium pipes should not be buried.

(18) When arranging pipes for solid materials or pipes containing solid materials, the pipes should be as short as possible. Fewer bends and no dead corners: The connection between the branch pipe of solid materials and the main pipe should be beveled along the flow direction of the medium, and the angle should not be greater than 45°; the bending radius of the elbow on the solid material pipeline should not be less than 6 times the nominal diameter of the pipeline; slurry pipelines containing a large amount of solid materials and high-viscosity liquid pipelines should have a slope.

(19) For pipelines that require thermal compensation, the entire pipeline system should be analyzed from the starting point to the end point to determine a reasonable thermal compensation solution.

(20) For pipelines that require a slope when laid on the pipe gallery, the height of the pipe support can be adjusted. This can be achieved by adding steel or steel plate cushions to the pipe support. The venting gas main (or flare main) should be arranged at the top of the pipe gallery column to facilitate adjustment of the elevation.

(21) When arranging pipelines connected to rotating mechanical equipment, the pipeline system should have sufficient flexibility to meet the allowable force requirements of the equipment pipe opening. If necessary, the following measures can be adopted: change the direction of the pipeline to enhance the natural compensation capacity; use spring supports and hangers; use metal bellows compensators; set limit brackets at appropriate locations.

(22) When arranging pipelines connected to reciprocating compressors, The mechanical vibration natural frequency of the pipe system and the natural frequency of the air column of the pipeline should avoid the excitation frequency of the machine. If necessary, the following measures can be adopted: add anti-vibration brackets; appropriately expand the pipe diameter; add pulsation attenuators or orifice plates; reasonably set buffers to avoid the resonance pipe length and reduce elbows as much as possible.

(23) Branch pipes should not be installed at locations with large bending moments on vibrating pipes.

(24) At the bends of pipes that are 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. Branch pipes are connected directly to the outside in the direction of medium flow.

(25) When connecting a branch pipe with a nominal diameter less than or equal to 40 mm from a pipe that may vibrate, whether there is a valve on the branch pipe or not, strengthening measures should be taken at the connection.

(26) Self-flowing horizontal pipes should be There should be a slope of not less than 3‰ in the direction of medium flow.

(27) When the pipeline passes through the floor, roof or wall of a building, a sleeve should be added, and the gap between the sleeve and the pipe door should be sealed. The diameter of the sleeve should be larger than the outer diameter of the pipe insulation layer and should not affect the thermal displacement of the pipe.

The weld on the pipe should not be inside the sleeve and should not be less than 150mm away from the end of the sleeve. The sleeve should be 50mm higher than the floor and roof surface. When the pipeline passes through the roof, a rain cover should be installed, and the pipeline should not pass through a firewall or explosion-proof wall.

(28) When arranging corrosive media, toxic media and high-pressure pipelines, hazards to personnel and equipment caused by leakage of flanges, threads and packing seals should be avoided. Leakage-prone parts should not be located above pedestrian walkways or pumps, otherwise safety protection should be provided.

(29) For pipelines with insulation layers, the pipe piers should be installed with a rain cover. , pipe supports should be installed at the pipe rack. For pipes without insulation layer, pipe supports are not required if there is no requirement. When the thickness of the insulation layer is less than or equal to 80mm, use a pipe support with a height of 100mm; when the thickness of the insulation layer is greater than 80mm, use a pipe support with a height of 150mm; when the thickness of the insulation layer is greater than 130mm, use a pipe support with a height of 200mm; cold insulation pipe supports should be used for cold insulation pipes.

(30) When the elevation difference of the plant area is large, the pipeline laying of the whole plant should be consistent with the terrain elevation difference. Adjust the elevation of the pipe gallery at appropriate locations. The minimum slope of the pipeline should be 2‰. The slope change point of the pipeline should be set at the turning point or near the fixed point.

(31) For pipelines crossing or passing through railways and roads within the plant area, valves, metal bellows compensators, flanges, threaded joints and other pipeline components shall not be installed on the crossing section or crossing section.

(32) For buried pipelines with thermal displacement, retaining piers may be installed under the condition that the curvature of the pipeline allows, otherwise thermal compensation measures should be taken.

(33) The setting of pipeline welds during pipeline layout shall meet the following requirements: The distance between the center of the pipeline butt weld and the bending point of the elbow shall not be less than the outer diameter of the pipe: and shall not be less than 100mm; The center spacing between two adjacent butt welds on the pipeline: a. For pipelines with a nominal diameter less than 150mm, it shall not be less than the outer diameter, and shall not be less than 50mm; b. For pipelines with a nominal diameter equal to or greater than 150mm, it shall not be less than 150mm; The net distance between the girth weld and the edge of the support or hanger shall not be less than 50mm; The minimum net distance between the weld that requires heat treatment and the edge of the support or hanger shall be greater than 5 times the weld width, and shall not be less than 100mm.

What factors should be considered in determining the width, span and height of the main corridor in the device?

Width of the corridor: 1) The width of the corridor is mainly determined by the number of pipes and the size of the pipe diameter. And consider a certain reserved width. Generally, the main corridor pipe rack should have a margin of 10%-20%, and consider its load. At the same time, the influence of the equipment and passages under the corridor and the air-cooling equipment on the corridor should be considered. If it is required to lay instrument cable troughs and power cable troughs, the required width should also be considered. The pipes on the corridor can be arranged in a single layer or double layer, and three layers can also be arranged if necessary. The width of the corridor should generally not be greater than 10m;

2) When arranging air coolers on the corridor, the span of the pillars should be the same as the spacing size of the air coolers, so that the corridor columns are aligned with the center line of the air cooler pillars;

3) When arranging pumps under the corridor, the layout of the pumps and the width of the required operation and maintenance channels should be considered. If the cable for the pump drive is laid underground, the required width of the cable trench should also be considered. In addition, the required width of the main pipes of the cooling water pipes and drainage pipes for pumps should also be considered;

4) Since the pipe layout density of the entire pipe gallery is not the same, the number of pipes in the first and last sections of the pipe gallery is usually less. Therefore, when necessary, the width of the first and last sections of the pipe gallery can be reduced or the double-layer pipe gallery can be changed to a single-layer pipe gallery.

The span of the pipe gallery: The column spacing of the pipe gallery and the span of the corridor are determined by the allowable bending deflection caused by the vertical load of the pipes laid on it, which is usually 6-9m. For example, in small and medium-sized devices, when there are many small-diameter pipes, a secondary beam can be set between the two pillars to reduce the span of the pipe. In addition, the spacing of the pipe gallery columns should be consistent with the spacing of the equipment frame pillars to facilitate the passage of the pipes. If it is a concrete pipe rack, a φ20 round steel or steel plate should be buried on the top of the beam to reduce the friction between the pipe and the beam.

The height of the pipe gallery can be determined according to the following conditions:

1) Space across the road. When the pipe gallery crosses over the road, its clearance height is: the maintenance road in the device should not be less than 4.5m; the factory road should not be less than 5.0m; the railway should not be less than 5.5m; the maintenance passage under the pipe gallery should not be less than 3m. When the pipe gallery has a truss, it should be calculated according to the bottom height of the truss.

2) The minimum height of the pipeline under the pipe gallery. In order to effectively utilize the space of the pipe gallery, pumps are often arranged under the pipe. Considering the operation and maintenance of the pump, at least 3.5m is required; when the pipeline on the pipe gallery is connected to the partition equipment, it should generally be 600~1000mm lower or higher than the bottom pipe elevation of the pipe gallery. Therefore, the minimum bottom elevation of the bottom pipe of the pipe gallery is 3.5m. When shell and tube cold exchange equipment is arranged under the pipe gallery, the clearance under the pipe gallery needs to be increased due to the increase in equipment height.

3) The height difference of vertically intersecting pipe galleries. If the corridor changes direction or the two corridors intersect at right angles, the height difference depends on the minimum size of the interconnected pipes, which is generally 500~750mm. For large-scale equipment, a height difference of 1000mm can also be used.

Structural dimensions of the pipe gallery. When determining the height of the corridor, the structural section and type of the crossbeam and longitudinal beam of the corridor must be taken into account, and the height of the bottom of the beam and the bottom of the rack must meet the above requirements for determining the height of the corridor. For double-layer corridors, the distance between the upper and lower layers is generally 1.2 to 2.0m, which is mainly determined by the diameter of the largest pipe on the corridor.

As for the height of the corridor between the devices, it depends on the specific conditions of the area where the pipe rack passes. For example, if the tank area is formed along the edge of the factory, it will not affect the traffic and expansion of the factory area. Considering the economy and convenience of maintenance, it can be laid with pipe piers, and the height of 300 to 500mm above the ground can meet the requirements.

What are the principles for the design of pipelines for flammable liquids, flammable gases, and liquefied hydrocarbons?

The principles for the design of pipelines for flammable liquids, flammable gases, and liquefied hydrocarbons are:

(1) Pipelines must not pass through buildings that are not related to them;

(2) Pipelines should be laid overhead or along the ground;

(3) When trench laying is necessary, measures should be taken to prevent gas or liquid accumulation in the trench, and seal partitions should be established at the inlet and outlet devices and factory buildings;

(4) Sewage in the trench should be sealed and discharged into the production sewage pipeline;

(5) Sampling pipelines should not be introduced into the laboratory;

(6) Metal pipelines should be connected by welding except for special flange connections.

Which media pipelines need to be electrostatically grounded?

What are the requirements for the grounding connection points and grounding resistance values of the pipeline network?

The pipelines of flammable gas, liquefied hydrocarbon, flammable liquid and flammable solid shall be provided with electrostatic grounding facilities at the following locations:

(1) The pipelines in the relatively independent buildings (structures) in the device area can be electrostatically grounded by connecting to the metal shell of the process equipment (flange connection);

(2) Grounding connection points shall be set at pumps, filters, buffers, etc. in the pipeline network;

(3) The pipelines in and out of the device area, at the boundaries of different explosion hazardous environments, and at the pipeline bifurcations shall be grounded. For long-distance non-branched pipelines, they shall be reliably connected to the grounding body every 80-100m;

(4) For the non-conductive pipe sections in the middle of the metal pipeline (such as polyvinyl chloride pipes), in addition to shielding protection, the metal pipes at both ends shall be connected to the grounding trunk line respectively, or connected to the grounding line with 6mmrn multi-strand copper core insulated wires;

(5) Metal parts on the non-conductive pipe sections shall be grounded. The grounding resistance value of each set of specially designed electrostatic grounding bodies should be less than 100Ω in places with high soil resistivity in mountainous areas, the grounding resistance value should be less than 1000&#8486.

What are the types of pipeline laying methods? What are their advantages and disadvantages?

There are two major types of pipeline laying methods: above ground and below ground:

(1) Overhead laying Above ground is generally called overhead laying and is the main method of pipeline laying in industrial production equipment. It has the advantages of being easy to construct, operate, inspect, maintain and economical.

(2) Underground laying

1) Buried laying: Advantages: It makes use of underground space, making the space above the ground simpler and not requiring support measures.

Disadvantages: The pipeline is highly corrosive, difficult to inspect and maintain, and sometimes requires special treatment at the roadway to withstand large loads. It is inconvenient to drain liquid at low points and difficult to handle when easily condensable oil solidifies in the pipe. It is difficult for pipes with insulation layers to maintain their good insulation function. Therefore, it is only used when it is impossible to lay overhead.

2) Trench laying: Advantages: It can make full use of underground space and provide more convenient inspection and maintenance conditions. It can also lay pipelines with high temperature, easily condensable media or corrosive media with insulation layers.

Disadvantages: High cost, large footprint, need to set up drainage points, easy accumulation or single entry of oil and gas increases unsafe factors, easy accumulation of dirt is difficult to clean, etc. Therefore, trench laying is only used when necessary in the device.

What conditions allow pipelines to be directly buried underground?

(1) Liquid and gas pipelines that are non-corrosive, non-toxic and non-explosive and cannot be laid on the ground for some reason;

(2) Process medium pipelines related to underground storage tanks or underground pump rooms;

(3) Cooling water and fire water or foam fire fighting pipelines;

(4) Thermal pipelines with an operating temperature of less than 150°C.

What are the requirements for the buried depth of underground pipelines?

The buried depth of underground pipelines should be based on the principle that the pipeline will not be damaged, and the maximum frozen soil depth and groundwater level should be considered.

The top of the pipe should not be less than 0.5m from the ground; in areas with concrete floors indoors or outdoors, the top of the pipe should not be less than 0.3m from the ground. The passage for mechanical vehicles should not be less than 0.7m or casing protection should be used.

What are the principles for arranging pipelines on pipe corridors?

(1) Large diameter pipelines should be arranged close to the pillars of the pipe corridor;

(2) Small diameter, gas pipelines, and utility pipelines should be arranged directly in the middle of the corridor;

(3) Process pipelines should be arranged on the side of the equipment connected to the corridor; process pipelines can be arranged on the upper or lower layer depending on the elevation of the equipment pipes connected to both ends;

(4) High temperature pipelines that require "Ⅱ" type compensators should be arranged close to the pillars, and "Ⅱ" type compensators should be arranged in a centralized manner;

(5) Low temperature medium pipelines and liquefied hydrocarbon pipelines should not be arranged close to hot pipelines; nor should they be arranged directly above hot pipelines;

(6) For double-layer pipe corridors, gas pipelines, hot pipelines, utility pipelines, pressure relief mains, flare mains, instrument and electrical cable racks, etc. should be arranged on the upper layer; general process pipelines, corrosive medium pipelines, low Low-temperature pipelines are directly arranged in the lower layer;

(7) When designing pipelines on the pipe gallery, a 10%-20% margin should be reserved.

What scope does the design of low-temperature pipelines include?

(1) Low-temperature pipelines are used in all walks of life, especially in petrochemical enterprises. Carbon steel pipes are in a ductile state in the range of +5℃ to -19℃ and can be used normally. If the operating temperature is lower than or equal to -20℃, carbon steel pipes gradually become brittle and their use is subject to certain conditions. Therefore, pipelines below or equal to -20℃ are low-temperature pipelines.

(2) There are two main issues to consider when arranging low-temperature pipelines. The first is "low-temperature brittleness", which requires designers to reasonably select steel plates with high "impact toughness" and prevent brittle fracture and cracking from the piping design and pipe system manufacturing. .

The second is the cold insulation structure design of the pipeline and meeting the cold insulation design requirements, which is directly related to energy consumption and the operation, construction, and maintenance of equipment pipelines.

What are the requirements for low-temperature pipeline layout?

(l) The layout of low-temperature pipelines should consider that the entire pipeline has sufficient flexibility and make full use of the natural compensation of the pipeline. When the design temperature is very low and natural compensation is not possible, a compensator should be installed.

(2) When arranging low-temperature pipelines, pipeline vibration should be avoided, especially pumps, compressors and exhaust pipes. The vibration of the entire pipeline must be prevented. If there is a mechanical vibration source, vibration-absorbing facilities should be adopted. Elastic elements such as corrugated compensators should be installed on the pipelines close to the vibration source to isolate the vibration source.

(3) On carbon steel and low-alloy steel low-temperature pipelines, branches equipped with safety valves, exhaust pipes or drain valves need to be noted Pay attention to whether the low-temperature liquid medium will vaporize immediately after being discharged. If it vaporizes, it will need to absorb a lot of heat, and it will condense until it freezes, which will reduce the temperature of the pipeline to a very low level. Therefore, such branch pipes should be made of austenitic stainless steel in the easy-to-freeze range, and then flanges should be used to connect branch pipes of different materials.

(4) The stress at the elbow of the low-temperature pipeline is the greatest, so the elbow is most prone to brittle cracks, and the support bracket should not be welded.

(5) Direct welding of flanges is generally not allowed near elbows or tees on low-temperature pipelines. In order to avoid damaging the insulation layer on the main pipeline when removing the bolts, it is necessary to extend a certain length (connect a short pipe) before welding the flange. In the butt flange, only one end of the flange needs to have a spacing for loading and unloading bolts. For the piping of the valve group, it should be considered that any valve can be removed smoothly without affecting the pipeline insulation structure.

(6) For the low-temperature insulation pipeline support, measures must be taken to prevent the formation of "cold bridges"; when the low-temperature pipeline is laid horizontally, wooden blocks or hard insulation material blocks are generally placed at the bottom of the pipeline to avoid loss of cold in the pipeline.

When low-temperature pipelines are laid vertically, if the bracket is rooted on low-temperature equipment, wooden blocks or hard insulation material blocks should be placed on the equipment and pipelines.

What are the layout principles for pipeline sampling tubes?

(1) Sampling tubes should not be installed on vibrating equipment and pipelines, such as pumps, compressors, etc., and should also be avoided on pipelines directly connected to vibrating equipment. If it is difficult to avoid, vibration reduction measures should be taken;

(2) The setting of sampling tubes should meet the requirements of the process and avoid dead corners or "bags". The sampling valve should be arranged in a place that is easy to operate, otherwise a platform should be set up, and the pipe section between the equipment or pipeline and the sampling valve should be as short as possible.

(3) Gas sampling tube lead-out position: When sampling from a horizontal pipe, the sampling tube should be set at the top of the pipeline; when sampling from a vertical pipe, when the gas flows from bottom to top, the sampling port should be led out from the vertical pipe at a 45° angle; when the gas contains solid particles, the sampling tube should extend to the center of the tube; when the gas flows from top to bottom, the sampling tube should be opened horizontally.

(4) When the liquid flows from bottom to top in a vertical pipe, the sampling tube can be set on any side of the vertical pipe; when the liquid flows from top to bottom in a vertical pipe, unless it can be guaranteed that the liquid fills the sampling tube, the sampling tube can be set on any side of the vertical pipe, otherwise it is not appropriate to set a sampling point in this case; horizontal pipe: under pressure transmission conditions, the sampling tube can be set at any part of the pipe; when the liquid contains solid particles, the sampling tube should be set on both sides of the horizontal pipe; when sampling on a self-flowing horizontal pipe, the sampling tube should be set at the bottom of the pipe.

(5) For sampling of extremely hazardous and highly hazardous toxic media, on-site emptying sampling is not allowed, and closed-loop sampling should be adopted.