Leaks often occur at the flanges of fire protection pipes
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Hello everyone, the fire protection pipes used at our dock consist of DN350*8mm pipes totaling over 900 meters, as well as DN300*8mm and DN150*4.5 pipes totaling over 500 meters； The pipes are connected using flanges (the elbows also have flanges), and the pipes and fittings are made of red-coated epoxy seamless steel pipes (standard GB/T5135.20-2010) ； GB/T28897-2012), elbows (standard CJ/T120-2008). The fire-fighting water supply is provided by a constant-pressure pump system at the rear; the outlet pressure of the electric pumps and diesel pumps is around 1.1–1.4 MPa. Under normal conditions, constant-pressure pumps are used for supplying water, but when the water pressure drops too low, the electric or diesel pumps are switched on automatically. Often, after the pressure rises momentarily in such situations, there are leaks in the pipes along the dock area, either at one of the flanges or at other flanges as well. Method used: A pressure relief valve was added ； Some flange gaskets have been replaced (they were rubber-based before, but are now metal-graphite wound gaskets), as well as the high-strength bolts ； All painted surfaces of the flanges have been cleaned. I don’t know what to do; there are too many flange connections, around 100 of them. If that doesn’t work, I’ll cut off the flanges and weld the pipes directly together. But it’s not known where the source of the leak is.
Possible reasons include: poor flange sealing, incorrect installation, uneven bolt tightening, inappropriate material selection, and sudden changes in water pressure. The following aspects can be checked: 1. Whether the sealing surface of the flange is damaged or contains foreign objects. 2. Is the preload of the bolts even and appropriate? 3. Is the connection between the flange and the pipe correct? 4. Is the material of the flange gasket suitable and resistant to high pressure? 5. Does the piping system have buffering measures to reduce pressure surges? If these measures still do not solve the problem, considering changing the type of seal – such as using a mechanical seal or a welded connection – or consulting a professional pipeline engineer for a detailed analysis and solution may be necessary. .
It’s best to send a video of the site; usually, such piping components are designed for use in fire protection systems, or they require professional installation by fire service teams. Flanges are static sealing points, and there are also differences among various grades. For example, choices such as pressure rating, operating temperature, and material. Your situation is most likely caused by the use of non-standard flanges; it would be best to send some images for further discussion. If the impact pressure is too high, it is advisable to choose a flange with a pressure rating of 2.5 MPa. For reference.
Leaks at the flange connections in fire protection water supply systems are a common but tricky problem. You have already taken some measures, such as installing pressure relief valves, replacing flange gaskets and bolts, and cleaning the coated surface of the flange, but the problem still persists. Here are some suggestions that should help you identify the source of the leak and resolve the issue: 1. Inspect the quality of the flange connections: Although you have replaced some of the flange gaskets and bolts, it is recommended to conduct a thorough inspection of all flange connections. Ensure that the flange surface is flat and free of damage, that the parallelism of the flanges at both ends meets the requirements, that the gaskets are installed correctly, and that the bolts are tightened evenly. A torque wrench can be used to ensure that the bolts achieve the appropriate tightening torque. 2. Pipe support and vibration analysis: Check whether the pipe supports are appropriate and whether there is excessive vibration. Inappropriate support or vibration can cause the flange connection to loosen or become damaged. 3. Consider alternative solutions: If the above measures still cannot resolve the issue, you can consider replacing the flange connection with another type of connection, such as welding. But before making this decision, please ensure to evaluate the feasibility, cost, and safety of alternative options.
This was during the installation phase; later, the coating on the flange surface was removed
3. Fire cooling water system: This project is equipped with a fixed fire cooling water system. This system uses 1 DN350 plastic-coated seamless steel pipe for the high-pressure fire water supply pipeline, which is connected at the design boundary. The main pipes located on the pipe rack are connected using flanges, and they are insulated with 30mm aluminum silicate fiber insulation. Based on the verified calculation value of 50 L/s for the flow rate of the selected fire monitor, with a operation duration of 6 hours, the water volume required for firefighting in such an incident is 1080 m³. 4. Water consumption for the water curtain at the dock front: 60 L/s, for a duration of 1 hour; total water consumption for fire fighting in case of a fire: 216 m³ ； The water consumption for the water curtain in the firefighting turret is 20 L/s, with a duration of 6 hours; the total water amount required to extinguish a fire is 432 m³. 5. Water consumption for outdoor fire hydrants: The water consumption for the outdoor fire hydrants at the dock is determined in accordance with Article 3.4.9, Clause 5 of the \"Technical Code for Fire Fighting Water Supply and Fire Hydrant Systems\" GB50974-2014. This project is located in the Wu-Yu section of the Yangtze River, and according to industry classifications, it belongs to the category of river port docks. Therefore, the water flow rate for the outdoor fire hydrants is 30 L/s, with a duration of 6 hours. The water consumption for outdoor fire hydrants in a fire was 648 m³. 6. The fire-fighting water demand for this project is calculated based on a 5,000-ton class chemical tanker as per the design. The fire-fighting water demand for the dock design includes the water required for 1 fire cannon, 1 foam cannon, a water curtain at the front of the dock, a water curtain on the turret, and the water needed when all the fire hydrants are in use. Thus, the total fire-fighting water demand is 208 L/s, while the total water demand for extinguishing a fire and producing foam amounts to 2576 m3. Calculations show that to meet the fire protection design requirements of this project, the technical specifications for the fire protection cooling water pipes at the design boundary line are as follows: D377×8 (DN350) pipes, with a flow rate of 208 L/s and a pressure of 1.20 MPa; the amount of water required for firefighting in the event of a fire is 2576 m³. 7. Fire protection support: Behind the dock of this project is the factory complex of Anhui Hua Yi Chemical Co., Ltd. The dock is connected to the land area via a newly built approach bridge and a jetty over the dike, adjacent to the factory complex behind it. The fire water supply for the dock is provided by the existing fire pump room and fire water tanks in the factory area at the back. The rear fire water tank is replenished by the plant’s own water supply system, with a refilling time of less than 48 hours. For the high-pressure fire water supply pipes at the dock of this project, the fire water supply pipes from the existing pipeline gallery in the plant area are connected at the design boundary of the newly constructed pipeline gallery on land. According to the fire protection facility information provided by the owner, there is a fire pump room within the premises of Anhui Huayi Chemical Co., Ltd.’s own water treatment plant (approximately 400 meters away from this project). The pump room is equipped with 2 electric fire pumps with a water supply capacity of 250 L/s, 2 diesel fire pumps with the same capacity, as well as one set of pressure stabilization pumps with a capacity of 10 L/s. The supply pressure of the fire pump set is 1.4 MPa. The clear water tank of the on-site water treatment plant holds 5,000 m³ of fire-fighting water. The entire system is a constant-high-pressure fire water supply system, with the main fire water supply pipe having a diameter of DN500. The fire water source in the rear factory area can meet the fire protection requirements of the dock for this project. 8. Drainage: The comprehensive facilities at the dock are equipped with environmentally friendly toilets, and there is no discharge of domestic wastewater. Collection ditches are installed around the loading/unloading platform area at the dock and the approach bridge’s emergency shut-off valves to collect any leaked fluids in case of accidents. The locally washed wastewater and initial rainwater are collected in wastewater tanks and then pumped to the facilities at the back site for treatment. For details, see the Environmental Protection specialty. 9. Two eye wash stations are installed on the dock platform to enable employees to wash their eyes in case of accidental exposure to chemicals. IV. Installation Instructions for Water Supply, Drainage, and Fire Protection Pipes 1. All dimensions in the drawings are given in mm, while elevations are expressed in m; the elevation system used is the 1985** elevation system. 2. Fire cooling water pipes and foam mixture pipes are made of plastic-coated seamless steel pipes designed for fire protection purposes (with an anti-corrosion epoxy resin coating thickness of >0.4 mm). Elbows with a radius of R=1.5D are generally used (unless otherwise specified); flange connections are employed for the main pipes in pipe racks, while clamping connections or threaded connections are used for pipes with diameters ranging from DN15 to DN50. The water curtain pipes are made of plastic-coated seamless steel pipes designed for fire protection purposes (with an anti-corrosion epoxy resin coating thickness of >0.4 mm), and are connected using clamps or threads. The water supply pipes for domestic use are made of plastic-coated composite steel pipes (in accordance with standard GB/T28891-2012); the main pipes are connected using flanges, while the branch pipes are connected using clamps or threads. 3. In accordance with Article 8.2.9 of the \"Technical Code for Fire Water Supply and Fire Hydrant Systems\" (GB50974-2014), overhead fire protection pipes should be connected using clamps, threads, flanges, etc.; welding connections should not be used. 4. The pipe flanges shall be selected in accordance with the specifications of HG/T20615-2009, and equal-length double-headed bolts (GB901-88) shall be used for fastening. Hex nuts (GB6170-86) are used for the nuts. Gaskets are made of nitrile rubber or polytetrafluoroethylene gaskets.
It is suspected that this is caused by a combination of factors such as insufficient flange sealing surfaces, inadequate bolt tightening torque, and pipeline vibration.
This post was last edited by CHANGBAISHI on 2024-1-5 at 07:46. Given your operating pressure of 1.4 MPa, PN16 valves can be used for the on-site valves; this is acceptable as long as there is a stable operating condition. If it’s the shock caused by the pump starting, the sensation is less intense. In particular, this valve doesn’t appear to meet the standard specifications; its flange and valve body are too slender in shape. There is paint in the groove of the flange sealing surface that has almost filled the sealing groove. This is the main cause of the leakage. It is recommended to thoroughly clean the grooves on the flange sealing surface. It is also advised to visit a hardware store to check whether there are standard valves that meet national specifications, as there may be differences between the valves currently in use and those standard ones; the valves currently in use seem to be non-standard, while standard valves have flange thicknesses identical to those of your current flanges. ). If possible, it is advisable to choose valves with a PN25 pressure rating, for reference.
For emergency shut-off valves that require quick opening and closing, feel free to contact me
You’re right; at first glance, this valve isn’t a standard PN16 three-eccentric butterfly valve – the flange is thin and the outer diameter is small, as well as the valve stem. Large companies use better-quality valves, which can help save money for the owners in other areas; fire safety must be given proper attention. Leakage occurs immediately due to overpressure; surely the flange sealing groove is not deep enough, or the two mating flange surfaces are not flat enough. Remove all the paint from the sealing surface, then try using some high-pressure asbestos gasket.
The paint on the flange sealing surface must be removed completely, as well as any recessed lines; it is advisable to replace the valve as well. For reference.