Pipeline transportation has become one of the main methods of contemporary material transportation. The use of long-distance pipelines to transport oil and gas resources has become the most important mean of energy transportation in the world today.
The major oil and gas producing and consuming countries in the world all use long-distance pipelines to solve the transportation problem of oil and gas resources. Among them, more than 95% of natural gas transmission is by pipeline.
According to statistics, the total length of existing long-distance oil and gas pipelines in the world exceeds 2.6 million kilometres, of which the total length of natural gas pipelines is about 1.4 million kilometers and more than half of the total pipeline length.
With the same conveying throughput, it is more economical to build a large diameter pipeline than several small-diameter pipelines; Increasing the pressure of the medium in a certain range can also increase the efficiency.
Long distance transportation pipelines have long distances. The pipelines pass through deserts, rain forests, swamps, mountains, rivers, and plains. The weather in the areas it passes is bad and the environmental conditions are poor.
Therefore, the requirements of long-distance pipeline valves are much higher than those of general-purpose valves. Long distance pipeline valves are required to have higher reliability, tightness and strength to ensure the safe and reliable operation of long distance pipelines.
Related standards for pipeline ball valves
- API 6D Pipeline valve
- API 6D Fire resistance test of valve
- API 607Fire resistance test of soft seal and 90 ° steering valve
- API598 Inspection and testing of valve
- ANSI B 16.34 Flanged, threaded and end welded valves
- J B/T 7745 Pipeline ball valve
Features and requirements of pipeline ball valves
In long-distance pipelines, it requires line cut-off valves–pipeline ball valves have the functions which can control the medium in the pipeline, switch on and off, change the flow direction of the medium and prevent backflow, prevent accidents, automatically and emergency shut off, close or open the pipeline, etc.
#1 Reliable sealing performance
Long distance pipelines can only be inspected on a regular basis, and sometimes need to pass through inaccessible mountains, deserts, grasslands and earthquake areas. A small leakage will cause a large amount of media leakage, and the waste of energy.
Especially in the long-distance natural gas pipeline project, the sealing of the pipeline is more important. In addition, the sealing performance of emergency grease injection is also required.
#2 Long service life is required
Once the pipeline is put into operation, it is not allowed to stop operation for a few years or even decades. The longer the operation time, the better.
Natural gas is for large users, it’s raw materials or energy sources of large factories and enterprises, and the momentary interruption is not allowed.
Therefore, the key components such as valve seats are required to have a long life.
#3 High strength and safety against the external force of pipeline valves
During the process of application, affected by complex external forces such as thermal expansion, contraction of temperature, equipment vibration, earthquake disasters, and foundation changes, the valves in the pipeline are often subjected to tensile, bending and compression etc.
Sufficient strength must be required to ensure the normal use
#4 Pipeline ball valves should be corrosion resistant
Natural gas contains hydrogen sulfide, it can also react with iron to form iron sulfide, which can corrode the valve, so pipeline ball valves materials should be corrosion-resistant.
#5 High automation
The pipeline ball valve is controlled in the central control room, which is far away. It should be capable of implementing remote control or remote control, and it can be turned off in an emergency.
The shutdown time is required to reach about 15 seconds. When the pipeline is operating normally, it may not move for several years. Once it is operated, it must be accurate and reliable.
#6 Pipeline valves require lightweight, compact structure, full bore
In order to ensure the valve is easy to install, bury and repair in complex sites, the valve is required to be light in weight, compact in structure, and full in diameter so that it can be cleaned when the pipeline runs normally.
Design and Research
Main technical parameters of pipeline ball valve：
- Normal pressure PN=10.0MPa
- Normal diameter DN=1000mm
- The Actual diameter D=1016mm
- Environmental extreme temperature：-36℃ – 80℃
- Medium: Natural Gas(Contains hydrogen sulfide and carbon dioxide)
- on-off time: turning off time ＜15s turning on time=600s
According to the requirements of applications and standards, as well as the requirements of long-distance pipeline ball valves, combined with the technical parameters of pipeline ball valves, we made the following design research :
In order to prevent leakage of the valve, improve the anti-deformation ability of the valve, and reduce weight, a full forged welding structure is required.
Full forged welded structure, which uses a forged valve body and is welded after assembly, which has changed the previous casting and bolt connection structure, and there will be no leakage of the valve body part.
Compared with the casting, the wall thickness of the forging can be thinner and high strength, this eliminating the connection between the middle flange and dozens of pairs of bolts, so the weight is greatly reduced.
#2 Leak-proof structure
The sealing structure is the key design of the sealing performance of the ball valve. Providing a good sealing structure directly affects the service life of the ball valve. According to research, we introduce the following structures that meet the actual requirements:
Double-piston effect valve seat structure
The basic principle of the double piston effect valve seat is that the valve has two seal valve seats. If the upstream valve seat is damaged, the medium enters the middle cavity, and the pressure in the middle cavity can still be enable to seal the downstream valve seat.
Therefore, when there is pressure in the middle cavity, the medium strength can press the valve seat against the ball to achieve the purpose of sealing.
Double seal structure
For more effective valve sealing, the structure adopts a double seal structure, that is, the soft seal of PTFE. Coupling with metal hard seals, if soft seals have problems, metal seals can also play a role.
At the same time, the metal hard seal is also a fire-resistant design, that is, when the soft seal is burned by fire, the metal hard seal can still keep sealing.
Emergency grease injection seal structure
If foreign matter or other reasons damage the sealing surface, the sealing grease filling system in the valve seat provides a quick and easy way to recover tight shutoff. Fill with sealing grease to achieve a seal.
In addition, the filling system can also be used in the sealed area of the valve seat in cyclical situations. At the same time, an emergency grease injection seal supplement is added to the valve stem seal.
Anti-static and fire-resistant structure
The standard requires that the ball valve must have an anti-static and fireproof structure. The valve is provided with an electrostatic structure between the ball , the valve stem and the valve body. A fireproof structure is provided in the sealing ring, when a fire occurs, the metal sealing ring can still be sealed.
The emergency shut-off device structure
When a pipeline accident occurs, the ball valves at both ends of the pipeline are required to be cut off urgently. Generally, the valves at both ends need to be closed within 15 seconds, or in a shorter time.
Now, most valve manufacturers use gas-liquid linkage emergency Shut-off device. The device directly uses the medium conveyed by the pipeline and uses the pressure of the medium to sense the accident signal by the induction device or the instruction of the main control room to directly control the valve to achieve the purpose of emergency shut-off of the valve.
Fixed ball structure
In order to reduce the bending stress on the sphere and the valve stem caused by the pressure of the medium , the connection between the valve stem and the sphere is designed into a segment structure to prevent the medium pressure from directly acting on the valve stem, which makes it difficult to open and close the valve. In addition, the sphere’s supporting cross-sectional area is increased to improve its rigidity.
In summary, the characteristics of the above mentioned several schemes can meet the requirements of the standards for valves, and also meet the needs of engineering.
The development trend of pipeline ball valves
In recent years, with the rapid development of long-distance pipelines, pipeline ball valves, as one of the emergency shut-off valves, have developed very quickly, the trend mainly presents in the following aspects:
- Large scale and high parameters
- High-strength corrosion-resistant materials
- Multiple sealed structures
- High reliability and fast shutdown
- Higher automation