Core requirements of API standards for union joint hoses
In the field of oil drilling and high-pressure fluid transportation, quick connecting hoses need to balance sealing reliability, ease of operation, and pressure safety. Taking the example of a union joint hose with a diameter of 65mm and a rated working pressure of 25MPa, its design must strictly follow the relevant standards of API (American Petroleum Institute), and meet the requirements of complex working conditions through material optimization and structural innovation.
1、 Core requirements of API standards for union joint hoses
The API standard system provides clear specifications for the key performance of high-pressure hoses:
Pressure rating and sealing: According to API 6A standard, the union joint must pass a hydrostatic pressure test at 1.5 times the working pressure (such as a 25MPa hose that needs to withstand a pressure of 37.5MPa for 30 minutes), and the roughness of the sealing surface must be ≤ Ra3.2 μ m to ensure no leakage.
Corrosion resistance: For acidic environments containing hydrogen sulfide (H ₂ S), the API RP 14E standard requires that sealing materials (such as nitrile rubber NBR) must pass MR-01-75 certification, with a H ₂ S permeability of ≤ 0.05g/m ² · 24h.
Full bore design: The inner diameter of the hose should be consistent with the inner diameter of the connecting pipeline (the Φ 65mm hose should be matched with Sch.40 to XXS grade pipe wall pipelines), to avoid eddy currents and resistance during fluid transportation and reduce pressure drop.
2、 Technical Implementation Path of Φ 65mm 25MPa Hose
1. Union joint design: modularity and angle compensation
The union joint adopts a locking structure of male head (spherical joint) and female head (horn mouth joint), and achieves quick connection by fastening the wing nut. Its core design features include:
Pressure classification: According to API standards, 25MPa hoses are usually selected with FIG602 or FIG1002 type unions. The former has a rated pressure of 6000psi (41.4MPa), while the latter has a rated pressure of 10000psi (69MPa), both of which meet the requirements of 25MPa working conditions.
Angle compensation: The swivel ball seat can provide ± 7.5 ° deflection adjustment, with a total deflection capacity of 15 °, suitable for equipment vibration or pipeline deformation scenarios.
Sealing structure: Adopting a dual sealing system, the inner PTFE gasket resists high pressure, and the outer rubber ring compensates for small deformations, ensuring reliable sealing within the temperature range of -20 ℃ to 120 ℃.
2. Hose body structure: multi-layer reinforcement and fire-resistant protection
The hose body needs to achieve a pressure capacity of 25MPa through the following design:
Enhancement layer: Adopting a 4-storey high-strength steel wire spiral winding process, with a steel wire diameter of 2.0mm and a winding pitch of 10mm, forming a three-dimensional mesh support structure. Through finite element analysis verification, this structure can achieve a minimum burst pressure of 75MPa (three times the rated pressure) for the hose.
Lining material: NBR (nitrile rubber) lining is selected, and the acrylonitrile content is optimized to 42% -45% to enhance the anti swelling ability of aromatic hydrocarbons, esters and other media in drilling fluid. Meanwhile, by filling and modifying with nano silica, the hardness of the material is increased to 70 ± 5 Shore A, enhancing its resistance to internal pressure deformation.
Outer layer protection: The outer layer is composed of chlorosulfonated polyethylene (CSM) refractory rubber and 304 stainless steel armor composite. The former can withstand open flame combustion at 705 ℃ for 30 minutes, while the latter provides mechanical scratch resistance and UV aging protection.
3、 Key control points in engineering applications
1. Installation specifications
Bending radius: The minimum bending radius of the hose shall not be less than 8 times the diameter of the pipe (i.e. 520mm) to avoid internal pressure failure caused by wire layer fracture.
Support spacing: When installed horizontally, the spacing between support points should be ≤ 1.2m to prevent stress concentration caused by the sagging of the hose due to its own weight.
Connection method: It is recommended to use threaded connection or butt welding connection, combined with a 24 ° conical sealing design, to ensure a leakage rate of ≤ 1 × 10 ⁻⁹ Pa · m ³/s under a pressure of 25MPa.
2. Maintenance strategy
Regular inspection: preventive replacement should be carried out every 2000 working hours, with a focus on inspecting inner bulges, exposed steel wires, and outer cracks.
Pressure monitoring: Install pressure sensors to monitor the pressure inside the hose in real time. When the pressure fluctuation exceeds ± 5%, an alarm will be triggered to avoid overpressure operation.
Environmental adaptation: In sulfur-containing environments, it is necessary to regularly check the hardness changes of the NBR inner layer. If the hardness decreases by more than 10%, the hose should be replaced immediately.