Views: 0 Author: J-VALVES Publish Time: 2024-10-31 Origin: Site
In industrial fields such as petroleum, natural gas, and chemical engineering, BALL VALVES are the core components of fluid control systems. As two mainstream designs, the performance differences between FLOATING BALL VALVES and TRUNNION BALL VALVES are particularly significant under high-pressure fluctuating working conditions. Taking the DN300 PN40 (nominal diameter of 300mm and nominal pressure of 40Bar) model as an example, this paper discusses the stability performance of the two through structural analysis, comparison of measured data, and industry application cases.
1.COMPARISON OF STRUCTURE AND SEALING MECHANISM
Indicator | Floating Ball Valve | Trunnion Ball Valve |
Sphere Fixing Method | Only supported by the top valve stem, allowing the sphere to move slightly (float). | Fixed by the top valve stem and the bottom trunnion, ensuring the sphere has no displacement. |
Sealing Principle | The medium pressure pushes the sphere to press against the downstream seat, achieving one-way sealing. | The spring-loaded seat presses the sphere in both directions, enabling two-way sealing. |
Seat Material | High-elasticity materials like PTFE are needed to withstand dynamic pressure. | Wear-resistant alloys with elastic compensation structures are adopted to adapt to high-pressure wear. |
2.APPLICABLE RANGE AND PRESSURE BEARING CAPACITY
· Floating Ball Valve: It is suitable for medium and low pressure (≤PN25) and small diameter (≤DN200) scenarios. It relies on the medium pressure to achieve sealing and is prone to leakage due to seat wear under long-term high pressure.
· Trunnion Ball Valve: It is specially designed for high pressure (up to PN100) and large diameter (up to DN600). With mechanical fixation and spring compensation, it has higher stability.
1.REQUIREMENTS FOR KEY PARAMETERS
Parameter | Standard Value | Testing Basis |
Nominal Diameter (DN) | 300mm | ISO 6708 and GB/T 1047 |
Nominal Pressure (PN) | 40Bar | EN 1092 - 1 and ASME B16.5 |
Material Strength | Valve Body: WCB/CF8M | API 6D and ISO 15848 - 1 |
Leakage Class | ≤ISO 5208 Class IV | API 598 |
2.SIMULATION OF HIGH-PRESSURE FLUCTUATING WORKING CONDITIONS
1.Testing Standard: Referring to API 6FA and ISO 15848 - 1, simulate the pressure fluctuation range from 0.45P_t (18MPa) to 1.0P_t (40MPa), with the number of cycles ≥ 10,000 times.
2.Testing Stages:
Stage A: 0 - 18MPa, 4,500 cycles (simulating daily fluctuations).
Stage D: 0 - 40MPa, single peak pressure (simulating extreme working conditions).
1.SEALING PERFORMANCE AND LEAKAGE RATE
Testing Item | Floating Ball Valve | Trunnion Ball Valve |
Initial Leakage Rate | ≤0.01% | ≤0.005% |
Leakage Rate after 10,000 Cycles | 0.15% (Sealing failure due to seat wear) | 0.03% (Sealing maintained by spring compensation) |
Leakage at Peak Pressure (40MPa) | Instantaneous leakage reaching 0.5% | No visible leakage |
2.OPENING AND CLOSING RESPONSE AND TORQUE CHANGE
· Floating Ball Valve:The initial torque is low (≤200N·m). However, after cycles, due to the increased friction of the seat, the torque rises to 350N·m, and the opening and closing time is extended by 30%.
· Trunnion Ball Valve:The bearing support reduces friction, and the torque is stable at 150 - 180N·m, with the error of the opening and closing time being ≤5%.
3.MECHANICAL FATIGUE AND LIFE PREDICTION
Aspect | Floating Ball Valve | Trunnion Ball Valve |
Seat Wear Rate | 0.12 mm per 10,000 cycles | 0.03 mm per 10,000 cycles |
Predicted Life (at PN40) | 5 - 7 years | 10 - 15 years |
Failure Mode | Plastic deformation of the seat and sphere displacement | Bearing wear and attenuation of spring elasticity |
1.COMPARISON OF APPLICABLE SCENARIOS
Application Scenario | Recommended Valve Type | Reason |
Long-distance Petroleum Pipelines | Trunnion Ball Valve | There are frequent high-pressure fluctuations, so two-way sealing and long service life are required. |
Medium-Pressure Reaction Systems in Chemical Plants | Floating Ball Valve | It is cost-sensitive and the medium has low corrosiveness. |
Emergency Shut-off of LNG Storage Tanks | Trunnion Ball Valve | A quick response and zero leakage are needed. |
2.CERTIFICATION AND COMPLIANCE
· API 6D: Mandatory certification for TRUNNION BALL VALVES, covering design, materials, and testing processes.
· ISO 15848: Floating ball valves need to pass Class C leakage certification (low fugitive emissions).
Under the high-pressure fluctuating working conditions of DN300 PN40, the TRUNNION BALL VALVE shows significant advantages by virtue of its mechanical fixed structure, two-way sealing, and spring compensation mechanism. The leakage rate is as low as 0.03%, and the service life can be more than twice that of the floating valve. Although the floating BALL VALVE has a lower initial cost, its long-term maintenance cost and shutdown risk are higher.
