In industrial pipeline systems, the connection method between valves and pipelines or equipment is of vital importance, as it directly affects the system's sealing performance, stability, and service life. This article will provide a detailed introduction to several common valve connection methods, including flange connection, wafer connection, welded connection, threaded connection, clamp connection, and ferrule connection, to help you better choose a suitable pipeline connection solution.
Flange connection is the most widely used connection form between valves and pipelines or equipment. It consists of flanges, gaskets, and bolts connected together, forming a combined sealing structure with a detachable feature. Pipeline flanges are mainly used for piping in installations, while equipment flanges are used for the inlet and outlet connections of equipment.
The advantages of flange connections lie in their ease of use and ability to withstand greater pressure, making them suitable for valves of various nominal sizes and nominal pressures. However, they have certain limitations regarding usage temperature. Under high-temperature conditions, flange bolts are prone to creep, leading to leakage. Therefore, flange connections are generally recommended for environments with temperatures not exceeding 350℃.
According to the shape of the mating surface, flange connections can be divided into the following types:
Smooth flanges are suitable for valves with low pressure, with a relatively simple machining process. The sealing of such flanges mainly relies on the tight contact of flange surfaces and the elastic deformation of gaskets, suitable for medium and low-pressure conditions.
Raised-face flanges work under higher pressure and can use medium-hard gaskets. Their design allows for better sealing effect, suitable for medium and high-pressure conditions. The sealing surfaces consist of a raised face and a recessed face, tightly fitting together to achieve good sealing performance.
Tongue-and-groove flanges are applicable to gaskets with larger plastic deformation, especially suitable for corrosive media environments. They offer good sealing and are widely used in pipelines in the chemical, pharmaceutical, and other industries. Their sealing surface resembles a mortise-tenon structure, with the gasket embedded in the groove and sealed by bolt tightening.
Trapezoidal-groove flanges use elliptical metal rings as gaskets, suitable for valves with working pressure ≥ 60 kg/cm² or high-temperature valves. Their sealing performance is highly reliable, maintaining good sealing under high-pressure and high-temperature environments.
Lens flanges use lens-shaped gaskets made of metal. They are suitable for high-pressure valves or high-temperature valves with working pressure ≥ 100 kg/cm². Their design distributes pressure evenly under force, achieving better sealing.
O-ring flanges are a relatively new form of flange connection, with sealing performance more reliable than flat gaskets. When pressurized, the O-ring elastically deforms to fill micro-gaps between flange faces, achieving good sealing.
Wafer connection is a form where bolts directly clamp the valve and two pipeline ends together. Its advantage is very convenient installation and disassembly, especially suitable for occasions requiring frequent removal and maintenance. Wafer connections are usually used in medium and low-pressure conditions, with good sealing performance to meet general industrial pipeline requirements.
Welded connection refers to a connection form in which the valve body has a welding groove and is joined to the pipeline system by welding. Welded connections are divided into butt-weld connection (BW) and socket-weld connection (SW).
Butt-weld connections are suitable for various sizes, pressures, and high-temperature conditions. By machining a groove at the connection between the valve and pipeline, then welding, a strong connection is formed. The advantages include high connection strength, ability to withstand great pressure and temperature variation, and suitability for harsh working conditions. However, installation is relatively complex, requiring professional welding skills and equipment, with strict post-weld inspections such as radiographic nondestructive testing to ensure weld quality.
Socket-weld connections are generally applicable to valves with nominal diameter ≤ DN50. This method inserts the valve socket into the pipe socket and then welds. Advantages include convenient installation, suitable for small-caliber valves. However, gaps between socket and pipe may be corroded by some media, and vibration may cause fatigue at the joint, so usage is limited.
Valves with welded connections perform excellently in long-term operation, especially in power plants, nuclear projects, ethylene projects, and other cases with extremely high reliability requirements. However, they are difficult to disassemble and reinstall, thus generally limited to occasions requiring long-term reliable operation.
Threaded connection is a simple connection method, often used for small valves. It can be external thread or internal thread. External threads seal directly; to ensure no leakage, lead oil, hemp, or PTFE tape is usually used. Among them, PTFE tape is widely applied, with excellent corrosion resistance, sealing performance, easy use and storage, and removable intact when disassembling, far superior to lead oil and hemp.
Threaded valves are mainly those with nominal diameter below 50 mm. The valve inlet and outlet ends are machined into tapered or straight pipe threads to connect with threaded joints or pipelines. Because threaded connections may form large leakage channels, sealants, sealing tape, or fillers can be used to block them and enhance sealing. If the valve body material is weldable, sealing welds can be applied after threading to further improve sealing.
Advantages include simple structure, light weight, and convenient installation, removal, inspection, and replacement. However, because valves expand with environmental and medium temperatures, design must consider expansion coefficients of materials at connection ends to ensure good sealing.
Clamp connection is structurally similar to flange but lighter and lower in cost, commonly used in sanitary pipelines and equipment. Sanitary pipelines require frequent cleaning, with no residues allowed to prevent bacterial growth; thus, flange and threaded connections are unsuitable, and welded connections are difficult to install and remove. Clamp connections are known for their simple structure and quick assembly/disassembly, especially suited to food, pharmaceutical, and biotech sanitary fields requiring frequent cleaning and sterilization.
The main parts include a pair of clamps (usually stainless steel), silicone or fluororubber gaskets, and grooved pipe ends. Installation is done by placing the gasket in the groove and tightening with the clamp to seal. Its key advantage is no need for special tools, with disassembly and cleaning in just minutes. Smooth pipe walls and gasket design effectively prevent residue, meeting strict hygiene standards. Overall cost is low, structure simple, easy to maintain.
However, limitations exist: mainly for medium and low-pressure conditions (≤16 bar), gasket aging at high temperatures, and high machining precision requirements for pipe end grooves. Thus, clamp connection selection must consider working conditions and medium properties.
Ferrule connection is a hard-seal method with strong pressure resistance and reliable sealing. It consists of a ferrule (metal ring with sharp edge), nut, and valve body or joint with tapered sealing face. When the nut is tightened, the ferrule deforms radially under pressure: its front edge bites into the pipe wall forming the first seal, while the rear end tightly fits the tapered face forming the second seal.
Advantages include high pressure resistance (dozens to hundreds of bar), making it common in instrumentation, hydraulic transmission, petrochemical, and gas transportation in high-pressure, high-purity, or hazardous media environments. The metal-to-metal hard seal is resistant to vibration loosening, adaptable to wider temperature ranges and harsh conditions. Precision requirements are not high, allowing easy installation in elevated positions.
However, installation requirements are stricter, needing special tools to control preload precisely. Over-tightening may damage pipes or ferrules, and high requirements exist for pipe diameter and roundness. Disassembly is also relatively cumbersome. Therefore, installation must strictly follow operating procedures to ensure reliability and safety.
When choosing a valve connection method, the following factors must be comprehensively considered.
Different methods suit different ranges. Flanges fit medium to high pressure but ≤350℃; welded fits high pressure/high temperature but difficult to disassemble; threaded fits low pressure with DN ≤ 50 mm; clamps fit medium/low pressure sanitary use; ferrules fit high pressure but require strict installation.
Corrosiveness, toxicity, and purity influence choice. For example, tongue-and-groove flanges and ferrules resist corrosion well; ferrules also prevent leakage effectively in high-purity media.
For frequent removal and maintenance, wafer and clamp connections are better. Flanges and welded joints are more complex, requiring more effort for reinstallation.
Costs vary: flanges are higher cost but reliable; threaded and clamp are lower cost but narrower in application; ferrules have higher material cost but lower maintenance cost.
Selection of valve connection methods requires comprehensive consideration of working conditions, medium properties, installation and maintenance needs, and costs. Flanges are suited for medium/high pressure, welded for high pressure/high temperature, threaded for low pressure, clamps for sanitary applications, and ferrules for high pressure. Each has its advantages and disadvantages. Choosing the right connection method ensures sealing, stability, and service life of pipeline systems, while also meeting economic and maintenance requirements.
In practice, it is recommended to fully evaluate all factors during the design stage and choose the most suitable connection method.
