How to calculate the pressure drop in medium-pressure steam pipelines

Do you need to provide the pipe specifications? The pressure drop for the long-distance transmission of superheated steam can be calculated manually using formulas, or it can be determined by referring to process diagrams; it shouldn’t be difficult, but the basic parameters used in the calculations must be accurate. Let me do a rough calculation for you: (1) The specific volume of superheated steam at 4.0 MPa and 420°C is 7.0 Kg/m3. (2) The steam flow velocity is taken as u = 40 m/s, and the pipe diameter is denoted as D m. (3) Using the formula 0.785D2X40X3600X7.0 = 270X1000, the calculated value for D is 0.584 m; therefore, a pipe with a nominal diameter of 0.6 m is used in practice. The actual flow velocity is calculated to be u=38 m/s. ⑷ Resistance is calculated based on the above conditions: (the details of this calculation are omitted; I determined it by referring to process diagrams, considering only the straight pipe section). The pressure drop ΔP is 0.26 MPa, with a pressure drop of 6.5 KPa per 100 meters (this value is too low, so the pipe diameter needs to be changed). ⑸ The steam flow velocity is set at u=50 m/s, and the pipe diameter is denoted as D m. ⑹ Using similar calculations, it is determined that D=0.522 m; therefore, a pipe with a nominal diameter of D=0.5 m is used. The actual flow velocity is u=55 m/s. ⑺ The resistance is calculated based on the adjustment criteria: the pressure drop △P is 0.50 MPa, with a pressure drop of 12.5 KPa every 100 meters (which is a reasonable value). Regarding your questions: ⑴ When considering the overall pressure drop, the pressure drop caused by frictional resistance in the straight pipe sections alone is around 0.50 MPa (if a DN500 pipe diameter is used). ⑵ You are using a relatively high superheat level for the steam, which is necessary as it involves long-distance transportation; the temperature drop depends on the insulation of the pipes as well as the resistance losses throughout the piping system, and this also needs to be determined through calculations. I hope the above explanation can be helpful to you! This post was last edited by Li Yiheng on 2008-2-24 at 16:34.]

You are using superheated steam; the pressure drop is related to the diameter of the pipes, the number of bends, and the length of the pipeline. The temperature drop is related to the insulation properties of the pipes as well as the materials used. Since your gas consumption is quite high, it is recommended to use pipes with a larger inner diameter!

It is recommended to use 18-inch pipes; the pressure drop should be calculated using the principles of fluid dynamics from chemical engineering. I had a software for this before but can’t find it now. You can turn to a design firm, as what you calculate is only an approximate value – a professional design firm is needed to carry out the actual calculations. Also, first prepare the pipeline layout diagram and count the elbows, valves, and other pipe fittings

Original poster, the pressure drop in steam pipes is related to the pipe diameter. The total pressure drop in the system must not exceed 20% of the boiler’s maximum pressure; this refers to the overall pressure drop, including that caused by the pipes, valves, and so on. The temperature drop should be related to the steam mass, the type and thickness of the insulation material, the length of the pipes, and the ambient temperature. Our company produces medium-pressure steam at 3.5 MPa; the temperature at the boiler outlet is around 450 degrees. The steam travels about 600 meters to the turbine, where the pressure drops to 3.28 MPa and the temperature falls to around 430 degrees. Your pipelines will be very long, and I think the pressure and temperature losses might be greater. It is recommended to hire a design institute to handle the design, as this will make it more reliable.

(1) Whether the pipe diameter is suitable for the steam consumption should be determined based on the intended use. Regarding heat loss, generally, smaller diameters of steam pipes result in less heat loss, making them more economical. However, if small pipes are used for the main pipeline, the high steam flow velocity inside the pipes can cause resonance, so the steam flow velocity is generally kept at around 50 meters per second. Depending on the type of steam used, whether superheated steam or saturated steam, the flow rate of the steam inside the pipe also varies. The flow rate range for saturated steam is narrow, with 20–30 meters per second being appropriate. Therefore, the pipe diameter is determined by the flow velocity range of the steam inside the pipe. (2) For the route of the pipeline to the steam usage location, the shortest distance should be chosen if possible. When the distance is large, pressure drop must be taken into account; at the same time, considerations such as the thermal expansion of pipes caused by steam and the use of expansion joints, as well as the proper selection of elbow expansion joints and methods for draining condensate from the pipes, are necessary. (3) To maintain stable steam pressure inside the pipe, it is necessary to carry out regular maintenance to ensure that the pressure relief valve is functioning properly and that the safety valve can activate accurately. Furthermore, with long-term use, steam leakage can occur at pipe joints and valves, so it is necessary to consider timely and regular maintenance in order to improve the leakage situation. To automatically remove air or condensate that enters the steam pipes, traps must be installed in appropriate locations and their operation checked in order to improve the efficiency of steam usage. In particular, air mixed in with the steam reduces its partial pressure and lowers its temperature; therefore, traps must be used to remove the air and recover the condensed water. The pipe material can be 20G carbon steel. The \"Technical Specifications for the Design of Steam and Water Pipes in Thermal Power Plants\" specify that the recommended operating temperature for 20G steel is between -20 and 430°C. This temperature limit can be increased to 450°C if the service life is 20 years, but metal monitoring should be intensified during use. In the design, the steam temperature is close to 450°C, and the use of 20G piping already reaches the upper limit for such temperatures. If alloy steel pipes are used, the cost will **increase**. Considering the technical and economic analysis, it can be determined that 20G carbon steel should be selected for the pipe material. However, to ensure the safe operation of the pipeline, measures should be taken to strengthen metal monitoring, namely by implementing creep monitoring. Technical Specifications for the Design of Steam and Water Pipelines in Thermal Power Plants – Power Pipeline Design Manual http://bbs.hcbbs.com/viewthread.php?tid=8912 Typical Design Manual for Steam and Water Pipelines in Thermal Power Plants http://bbs.hcbbs.com/thread-55638-1-1.html Illustrated Guides for the Typical Design, Calculation, and Installation of Steam and Water Pipelines, Supports, Brackets, and Components in Thermal Power Plants, along with Guidelines for Applying for Construction Qualifications http://bbs.hcbbs.com/thread-130385-1-1.html Last edited by ssmith2007 on 2008-2-25 10:42]

The detailed calculation of the pressure drop caused by the flow of the medium inside the pipe is quite complex; first, it is necessary to determine the flow regime of the medium within the pipe (i.e., laminar or turbulent flow, with different regions often exhibiting different flow regimes). We usually determine the Reynolds number based on theoretical charts derived from experiments. Secondly, it is then possible to calculate the friction coefficient based on the flow condition and the relative roughness of the pipe wall ； In addition, it is also necessary to determine the local resistance coefficients of pipe fittings such as elbows, valves, compensators, tees, and reducers (the number of elbows has a significant impact on the pressure drop in the pipeline; therefore, the use of such pipe fittings should be minimized) ； With the above data, the pressure drop of the medium in the pipeline can be calculated in detail. The flow in the steam and water pipes within the steam plant is mostly in the turbulent regime inside rough pipes; although a small portion is not in this regime, the difference in friction coefficients is minimal! However, the 4 km transmission distance for medium-pressure steam mentioned by the poster is quite long; if construction is to take place, a detailed pressure drop analysis should be conducted after performing stress calculations. The investment required for this approach is likely to be high. When using DN450 20G seamless steel pipes, the pressure drop is approximately 2–3 Mpa. This post was last edited by ssbayf on 2008-3-10 at 15:41

The design of thermal pipelines, especially those with large diameters, should be carried out by qualified design institutes; otherwise, it will be difficult to obtain approval for the installation. For self-estimation, you can refer to the \"Handbook of Chemical Process Diagrams\".

Thank you. I visited two design firms today, and their opinions differed greatly: one said the pressure drop per kilometer should be 1–1.5 kilograms, while the other said it should be around 4 kilograms

The pipe pressure drop is also related to the steam volume, pipe diameter, and flow velocity – are you providing them with the same data? If they are not the same, there will definitely be differences.

I remember there seem to be books on these topics in the forum; you can give them a search

Both pressure drop and temperature drop are related to those factors: 1. The insulation of the pipes is the most significant factor. If FBT insulation is used, it tends to crack easily; our factory uses ceramic fiber insulation, which requires a greater thickness – at least 4 layers of 50 thickness each. 2. The quality of insulation work carried out by the construction contractor. Details determine success or failure! This is an issue that must be taken into account. Our factory uses steam from a power plant; the temperature is 450 degrees, with a pressure of 4.32 MPA. After 400 meters, the temperature rises to 420 degrees while the pressure remains at 4.17 MPA. After 2.5 kilometers, the temperature is only 325 degrees and the pressure is 3.8 MPA.

The detailed calculation of the pressure drop caused by the flow of the medium inside the pipe is quite complex; first, it is necessary to determine the flow regime of the medium within the pipe (i.e., laminar or turbulent flow, with different regions often exhibiting different flow regimes). We usually determine the Reynolds number based on theoretical charts derived from experiments. Secondly, it is then possible to calculate the friction coefficient based on the flow condition and the relative roughness of the pipe wall ； In addition, it is also necessary to determine the local resistance coefficients of pipe fittings such as elbows, valves, compensators, tees, and reducers (the number of elbows has a significant impact on the pressure drop in the pipeline; therefore, the use of such pipe fittings should be minimized) ； With the above data, the pressure drop of the medium in the pipeline can be calculated in detail. This post was last edited by *anpangpang on 2008-11-17 09:27]

Hello, I found your explanation of the calculation for steam pipeline pressure drop to be very insightful. However, there are two points I’m not clear about: 1) how to view the process diagrams related to steam, and 2) why a pressure drop of 6.5 KPa is considered too low, while 12.5 KPa seems more appropriate

I am currently working on a project in which I need to transport medium-pressure steam with parameters of 3.8 MPa and 380°C from a boiler to another equipment area located 1000 meters away. The flow rate required is 40 tons per hour; it is necessary to determine the pressure, temperature, and pipe diameter at the location of that equipment area. I would like to seek advice from everyone on this matter. Thank you!

If you don’t commission a design, they will only be able to give you estimates; conducting a detailed calculation is quite complicated. You can entrust a company that has handled similar projects with the design work, and at the same time you can examine the performance of the projects they have completed.