Español
Stainless Steel Union Compression Tube Fittings, with its excellent leak-free sealing performance, has shown significant advantages in high-pressure, high-vibration and corrosive media transmission systems. The realization of its core sealing mechanism relies on the synergy of precise mechanical structure design, in-depth exploration of material properties and advanced manufacturing processes.
Synergy of the double ferrule sealing system
The core of the joint's sealing lies in its unique double ferrule structure. When the nut is tightened, the two conical ferrules produce complex mechanical behavior under axial pressure. The front ferrule (close to the pipe end) first contacts the outer wall of the pipe, and the serrated design of its inner wall is embedded in the microscopic unevenness of the pipe wall to form an initial sealing line. As the nut continues to tighten, the rear ferrule (close to the joint body) pushes the front ferrule to move toward the joint conical surface. This process causes the front ferrule to expand radially and form a high-pressure sealing interface with the joint conical surface. The double ferrule design not only provides redundant sealing protection, but also improves sealing reliability through the pressure self-enhancement effect (the internal pressure of the system pushes the ferrule to expand further). Even under long-term pulsating pressure, the residual stress between the ferrule and the pipe wall and the joint conical surface can still maintain an effective seal.
Elastic memory and corrosion resistance of stainless steel materials
Ferrules made of high-grade austenitic stainless steel (such as 316L) have excellent mechanical properties and chemical stability. The high elastic modulus of stainless steel (about 195 GPa) enables it to undergo significant elastic deformation to fill the surface defects of the pipe when subjected to axial compression, and to partially restore its original shape after the pressure is released, avoiding permanent plastic deformation and sealing failure. This "elastic memory" effect ensures the reusability of the joint. At the same time, the natural corrosion-resistant barrier of stainless steel (such as chromium oxide film) can effectively resist the erosion of corrosive media such as chloride ions and sulfides, and prevent the ferrule from losing its sealing ability due to pitting or stress corrosion cracking. Experimental data show that in a salt spray test containing 3.5% NaCl, the 316L stainless steel ferrule can still maintain more than 90% of its original sealing performance after 2000 hours of exposure.
Improvement of material density and dimensional accuracy by forging process
Unlike traditional casting or machining methods, the forging process uses high-temperature forging to dynamically recrystallize the stainless steel billet to form a uniform and dense grain structure. This process eliminates defects such as pores and inclusions inside the material, increases the yield strength of the material by about 20%, and ensures that the tolerance of key parameters such as the ferrule taper and wall thickness is controlled within ±0.02mm. Precise dimensional control ensures that the matching angle of each ferrule and the taper surface of the joint is exactly the same, avoiding seal failure caused by local stress concentration. Comparative tests show that the fatigue life of forged ferrules in cyclic pressure tests is more than 3 times longer than that of castings.
Three-stage compression mechanism during installation
The installation process of the joint involves precise torque control and is divided into three stages: initial contact, main seal formation and locking. In the initial stage (torque reaches 30% of the rated value), the front ferrule begins to contact the pipe and deforms slightly; in the main sealing stage (torque reaches 60-80%), the rear ferrule pushes the front ferrule deep into the taper surface of the joint to form a high-pressure sealing line; in the final locking stage (torque reaches 100%), residual compressive stress is generated between the ferrule and the pipe and the main body of the joint, and the sealing interface remains in close contact even if the system pressure fluctuates or vibrates. It is worth noting that the contact pressure between the ferrule and the taper surface of the joint can reach 1500 MPa during installation, which is far higher than the sealing pressure of conventional pipe joints (usually <800 MPa).
Performance verification under extreme working conditions
In the hydraulic control system of the oil production platform, the joint compression joint needs to operate under 15000 psi pressure, ±10℃ temperature fluctuation and high-frequency vibration (50 Hz) environment. Long-term monitoring data shows that the leakage rate of the joint with double ferrule design is 97% lower than that of the traditional ferrule joint, and the sealing performance has not declined after 5000 pressure cycles. In the strong acid transmission application in the chemical industry, after immersion in 98% sulfuric acid medium for one year, the sealing interface of the 316L stainless steel ferrule still maintains metal-level contact, and no obvious corrosion signs are detected.
Comparative advantages with traditional joints
Compared with the permanence of welded joints and the single-use limitation of ferrule joints, joint compression joints support quick disassembly and assembly (average installation time <3 minutes) and multiple reuse (typical life >100 cycles). For thin-walled pipes with a wall thickness of ≥0.5mm, the double-ferrule structure can provide higher tensile strength than the single-ferrule joint (increased by about 40%). In maintenance scenarios, technicians can replace damaged parts without cutting the pipe, significantly reducing system downtime and maintenance costs.
