Roughly categorizing municipal pipeline engineering, it belongs to a branch of municipal engineering. According to its different functions, it can be divided into categories such as water supply pipeline engineering, drainage pipeline engineering, gas pipeline engineering, power pipeline engineering, communication pipeline engineering, and thermal pipeline engineering. Below are brief introductions of each category.
1、 Water supply pipeline engineering
The water supply pipeline project aims to provide safe and clean tap water supply for urban residents. Water supply pipeline engineering generally consists of water transmission pipelines and distribution pipelines. Water transmission pipelines usually use two parallel lines, which are used between the water source and the water plant, or directly connected to the distribution pipeline. They have long distances, large diameters, and high flow rates; The water distribution pipe branches off the water pipeline and then branches to each household, with a short distance and small flow rate and diameter.
The general process of water supply pipeline engineering:
Water source collection: The first step in water supply pipeline engineering is to determine a reliable water source, which can be groundwater, rivers, lakes, or reservoirs. The selection of water sources should consider the feasibility of water quality, quantity, and continuous supply.
Water treatment: The collected water source needs to be treated to ensure compliance with safe drinking water standards, usually including purification, disinfection, removal of suspended solids and impurities, and other steps to ensure clean water quality.
Design of water supply pipeline system: Based on the scale and demand of the city, design the layout of the water supply pipeline system, determine the location of main pipelines, branch pipelines, distribution networks, as well as facilities such as water tanks and wells.
Pipeline laying: According to the design plan, carry out the laying work of water supply pipelines, including digging trenches, installing pipelines, connecting fittings, and conducting pressure testing and disinfection of pipelines.
Equipment installation: Install necessary equipment in the pipeline system, such as pump stations, water pumps, water meters, etc., to regulate water pressure, measure water volume, and monitor the operation of the water supply system.
Operation and maintenance: Once the construction of the water supply pipeline system is completed, it needs to be operated and maintained, including regular inspections, pipeline cleaning, repairing damaged parts, updating equipment, etc., to ensure the normal operation of the pipeline system and water quality safety.
2、 Drainage pipeline engineering
The main purpose of drainage pipeline engineering is to effectively discharge sewage, rainwater, and wastewater generated within the city, in order to maintain the city's sanitary environment and prevent floods. Drainage pipeline engineering includes aspects such as sewage treatment, rainwater discharge, and wastewater treatment.
The general process of drainage pipeline engineering:
● Sewage system design: Based on the size and demand of the city, design the layout and capacity of the sewage pipeline network, including the location and planning of facilities such as sewage collection pipelines, sewage treatment plants, pump stations, and sewage interceptors.
Rainwater system design: Design a rainwater discharge system to prevent rainwater accumulation and flooding in the city, including the planning and design of rainwater collection facilities, rainwater pipelines, rainwater gardens, rainwater ponds, etc.
Pipeline laying: According to the design plan, carry out the laying work of drainage pipelines, including excavating trenches, installing pipelines, connecting pipe fittings, and conducting pressure testing and inspection of pipelines.
Wastewater treatment: The collected wastewater is transported through a pipeline system to a wastewater treatment plant for treatment, which typically includes physical treatment, chemical treatment, and biological treatment to remove suspended solids, organic matter, and pollutants, and to meet discharge standards.
Wastewater treatment: Some specific industries and facilities generate wastewater that requires specialized treatment. The wastewater treatment process includes physical, chemical, and biological treatments to remove harmful substances and pollutants, ensuring the safe discharge or recycling of wastewater.
● Operation and maintenance: Once the drainage pipeline project is completed, regular operation and maintenance work is required, including pipeline inspection, cleaning, dredging, equipment maintenance and updates, to ensure the normal operation and treatment effect of the drainage system.
3、 Gas pipeline engineering
Gas pipeline engineering aims to transport and distribute gas supply to cities and buildings. Gas pipeline engineering involves the design, construction, and maintenance of transportation, storage, and supply systems for gases such as natural gas or liquefied petroleum gas (LPG).
The general process of gas pipeline engineering:
Gas supply station design: The gas supply station is the starting point of the gas pipeline system, responsible for introducing gas into the supply system from the gas source (such as natural gas fields or storage tanks). Design includes selecting suitable gas supply stations, setting up safety facilities, and planning the capacity of gas supply stations.
● Gas pipeline design: Based on the demand for gas transmission and the scale of the city, design the layout and capacity of gas pipelines, including the location and planning of main pipelines, branch pipelines, valves, pressure regulating stations, and other facilities.
Pipeline laying: According to the design plan, carry out the laying work of gas pipelines, including excavating trenches, installing pipelines, connecting pipe fittings, and conducting pressure testing and inspection of pipelines.
Gas pressure regulation and metering: In order to ensure the stability and safety of gas supply, it is necessary to set up pressure regulation stations in the pipeline system to adjust the pressure of gas to meet user needs. At the same time, install measuring equipment to measure the consumption of gas.
Installation of gas supply facilities: Install gas meters, valves, and other supporting equipment in buildings and user terminals to ensure controllable and safe gas supply.
● Operation and maintenance: Once the gas pipeline project is completed, regular operation and maintenance work is required, including pipeline inspection, cleaning, overhaul, equipment maintenance and updates, etc., to ensure the normal operation and safety of gas supply.
4、 Power pipeline engineering
Power pipeline engineering is a municipal pipeline project specifically designed for transmitting electricity, aimed at constructing and maintaining urban power supply systems. Power pipeline engineering includes aspects such as transmission lines, substations, cable channels, and distribution networks.
The general process of power pipeline engineering:
Transmission line design: Based on power supply demand and urban scale, design the layout and capacity of transmission lines, including determining the direction of main transmission lines, the location and spacing of power towers, and considering the safety and reliability of transmission lines.
Substation design: A substation is a facility that converts high-voltage transmission lines into low-voltage electricity suitable for urban distribution. Design includes selecting suitable sites, configuring and capacity planning of substation equipment, as well as connecting and regulating with transmission lines.
Cable channel design: Cable channels are used to protect and isolate cables used in power transmission, including determining the layout, material selection, and installation methods of cable channels to ensure safe operation and easy maintenance of cables.
● Distribution network design: Design the distribution network within the city to transmit electricity from substations to end users. This includes selecting appropriate distribution equipment, determining the layout and capacity of distribution lines to meet user needs and ensure the stability of power supply.
Pipeline laying and installation: According to the design plan, carry out the laying and installation of transmission lines, cable channels, and distribution equipment, involving steps such as civil engineering, cable laying, equipment installation, and power access.
● Operation and maintenance: Once the construction of the power pipeline project is completed, regular operation and maintenance work is required, including inspection, repair, and maintenance of transmission lines and equipment, to ensure the reliability and safety of power supply.
5、 Communication pipeline engineering
The communication pipeline project aims to build and maintain the communication network infrastructure in the city, including the transmission lines and facilities of telephone, Internet, television and other communication services.
The general process of communication pipeline engineering:
Network planning and design: Based on the size of the city and communication needs, develop a communication network planning and design plan, including determining the network topology, selecting signal transmission technologies and equipment, and designing the layout of backbone and branch lines.
Pipeline laying: According to the design plan, carry out the laying work of communication pipelines, including digging trenches, laying optical fibers, installing pipelines and joints, as well as testing and debugging the lines.
Fiber optic cabling: Fiber optic is a key component of modern communication networks. In communication pipeline engineering, fiber optic cabling is required to install fiber optic cables in the pipeline to achieve high-speed and stable signal transmission.
Equipment installation: Install necessary equipment in the communication pipeline system, such as fiber optic switches, transmission equipment, signal amplifiers, etc., to control and manage the transmission and distribution of communication signals.
● Operation and maintenance: Once the construction of the communication pipeline project is completed, regular operation and maintenance work is required, including inspection, cleaning, repair, and upgrading of the lines, to ensure the normal operation and signal quality of the communication network.
6、 Thermal pipeline engineering
Thermal pipeline engineering is mainly used for urban centralized heating, providing heating or industrial heat services to residents, enterprises and institutions by transporting hot water or steam. Thermal pipelines need to ensure efficient heat transfer, reduce heat loss, and meet the safety and stability requirements of the pipeline system.
The general process of thermal pipeline engineering:
Determine the heat source based on the heating demand, select the type of heat source (such as cogeneration, gas boilers), evaluate the efficiency and economy of the heat source, and ensure stable heating.
Design and plan the pipeline path of the heat transfer pipeline system, reasonably partition the heating pressure, calculate the flow rate, pipe diameter, and insulation parameters, and optimize the system operation efficiency.
Efficient insulation materials are selected for insulation and anti-corrosion design to reduce heat loss, and external anti-corrosion coatings or cathodic protection are used in combination with the laying environment to extend the service life of pipelines.
Pipeline laying and construction shall be carried out by selecting buried or overhead laying methods according to the terrain, completing pipeline welding, assembly, insulation and anti-corrosion treatment, and conducting pressure testing and acceptance.
Thermal power station and equipment installation: Construct a thermal power station to regulate the temperature and pressure of supply and return water, install circulating pumps, heat exchangers, and other equipment to ensure efficient operation of the heating system.
● System trial operation and debugging gradually increase the temperature and pressure of the system, detect the operating status, and optimize the parameters of each area to meet the design requirements.
Operation and maintenance monitoring of heating system operation data, regular inspection of pipelines and equipment, timely cleaning or replacement of aging parts, to ensure long-term stable operation.

 

In daily work, PN and MPa are often used to represent pressure, but do you understand the difference and relationship between the two? Before writing this article, I was very confused. Now, let me share with you what I have sorted out.
1、 The difference between PN and MPa
● Different definitions:
——PN: PN stands for"nominal pressure", which is a standardized nominal value that is not the actual measured pressure, but a reference value for easy classification and identification. Note: PN is defined based on the standard temperature (usually 20 ° C) and the pressure resistance of standard materials (such as steel). In design and use, PN not only reflects pressure resistance, but also comprehensively considers material strength and temperature effects.
——MPa: MPa is an abbreviation for"Megapascal", representing the unit of pressure"megapascal"(1 MPa=10 ⁶ Pa), which is an actual pressure value that describes the true force applied per unit area.
● Different uses:
——PN: Mainly used for pressure grading and matching of pipelines and fittings (such as flanges and valves), mostly used in Europe and Asia (represented by Class in American standards). The unit of PN is bar, 1 bar=0.1 MPa. For example, PN10 represents a nominal pressure of 10 bar, which is 1.0 MPa.
——MPa: commonly used to measure actual working pressure, such as fluid pressure inside pipelines, pressure output from pumps or pressure equipment. MPa is an internationally recognized engineering unit that directly represents physical quantities and is related to the actual operating status of equipment.
2、 The relationship between PN and MPa
In practical applications, PN and MPa are interrelated:
When the actual pressure of the fluid (MPa) is known, select the appropriate PN level to ensure safety in the selection of pipelines and fittings. For example, if the working pressure of a pipeline is 0.8 MPa, choose PN10 (1 MPa) pipeline fittings.
The effect of temperature on PN is usually the nominal value at 20 ° C. As the temperature increases, the strength of the material decreases, and the corresponding actual withstand voltage value may be lower than the PN value. For example, the actual pressure resistance value of PN40 flange at 200 ° C may only be around 2.5 MPa (refer to the standard table).
When selecting pipelines and equipment, the safety factor usually leaves a certain safety margin for the PN value. For example, if the actual working pressure is 1.2 MPa, PN16 accessories can be selected.
I should be able to understand it now. Simply put, PN is a concept defined by humans to facilitate the classification and grading of pipeline fittings. The unit is bar and it is commonly used in the standard systems of Asia and Europe; And MPa is a unit that describes the actual pressure magnitude.

 

Regarding the issue of pressure testing for ground source heat pump pipelines
The following is a description of specific operating conditions:
The depth of the pipeline burial well is 150 meters. According to calculations, the working water pressure of the pipeline should be 1.5 MPa, and the pipeline specification selected for the project is 1.6 MPa. (Note: The pipeline here refers to HDPE water supply pipe, which complies with the standard GB/T 13663.2)
Then we need to conduct a pressure test on the project now, because according to the relevant regulations of the national standard for this water pressure test, if it is less than 1.0MPa, the pressure test should be conducted at 1.5 times the working pressure, and if it is greater than 1.0MPa, 0.5MPa should be added. (The relevant regulations for hydrostatic testing come from GB50366-2005"Technical Specification for Ground Source Heat Pump System Engineering")
4.5.2 The hydrostatic test shall comply with the following regulations:
1. Test pressure: When the working pressure is less than or equal to 1.0MPa, it should be 1.5 times the working pressure and should not be less than 0.6MPa; When the working pressure is greater than 1.0MPa, it should be the working pressure plus 0.5MPa.
Water pressure test steps:
1) Before inserting the vertical buried heat exchanger into the borehole, the first water pressure test should be conducted
Test. Under the test pressure, stabilize the pressure for at least 15 minutes, and the pressure drop after stabilization should not exceed 3%, and there should be no leakage phenomenon; After sealing it, insert it into the borehole under pressure and maintain the pressure for 1 hour after grouting is completed. Before placing the horizontal buried heat exchanger into the trench, the first water pressure test should be conducted. Under the test pressure, stabilize the pressure for at least 15 minutes, and the pressure drop after stabilization should not exceed 3%, with no leakage phenomenon.
2) After the vertical or horizontal buried heat exchanger is assembled with the loop header,
A second hydrostatic test should be conducted before backfilling. Under the test pressure, stabilize the pressure for at least 30 minutes, and the pressure drop after stabilization should not exceed 3%, with no leakage phenomenon.
3) After the connection between the loop manifold and the machine room water collector is completed, it should be filled before backfilling
Conduct the third hydrostatic test. Under the test pressure, stabilize the pressure for at least 2 hours without any leakage.
4) The geographic tube heat exchange system has been fully installed, and flushing, exhaust, and return processes have been carried out
After completion, the fourth hydrostatic test should be conducted. Under the test pressure, stabilize the pressure for at least 12 hours, and the pressure drop after stabilization should not exceed 3%.
So according to regulations, based on the current working pressure of 1.5MPa, the water pressure test should be 1.5MPa+0.5MPa, which is 2.0MPa. However, the pipe only has 1.6MPa, and the pressure cannot be maintained during the test. Moreover, this pressure is a bit high and may also have an impact on the pipeline. However, based on feedback from previous projects, the pressure test for ground source heat pumps is generally not so high, and a 1.6MPa pipeline can also meet the usage requirements.

 

From a standard perspective, the design does require the use of a 2.0MPa pipeline, but in terms of cost, the cost of a 2.0MPa pipeline is too high. Therefore, we have encountered some projects that used a 1.6MPa pipeline before, but we have not tested it at such a high pressure before
This pressure test requirement is about the safety factor of pipeline design. If a 1.6MPa pipe is used to withstand a working pressure of 1.5MPa, it is not suitable to operate. In principle, a 1.6MPa pipe can operate at a pressure of 1.6MPa, but it also involves issues such as temperature, pipeline pressure fluctuations, etc. In the design process, the service life and so on must also be considered.