High Requirements of Pipe Transmission on Ball Valves
Long distance pipeline is a global energy supply line, from Arctic Circle to Equator, high mountains to seabed, high lands to deserts, crossing through earthquake zone, marshland, rivers, lakes and mountain slopes. Some of pipelines are erect. Some are buried under the ground and some are operated in the field. Difficult maintenance requires service of pipeline as long as 30 years. Generally, transmitted oil and gas still contain sulfur, rust and metal particles although through processing. And they also demand zero level sealing. Practical wicked operating environment and importance of energy supply line have higher requirements for ball valves.
1. Strength and toughness
Besides pressure of media, valves also should endure bearing of foundation. Axial tension and pressure caused by environmental temperature changing, external load caused by landslide, land subsidence and floods must be taken into consideration. If the valves are used in frigid zone or frost region, impact toughness of materials under low temperature needed to be consider to prevent low temperature brittle rupture. For welded joints and heat affected zone in full welded valves, CTOD should be concerned according to fracture mechanics theory.
2. Zero level sealing
Valves need zero level sealing to ensure effective cutting off on downstream pipelines. For impact of metal particles in media on zero level sealing, metal to metal sealing is used the primary sealing. PTFE/rubber to metal sealing is used as secondary sealing. Once sealing loses efficacy, emergency sealing measures should be taken.
3. Fire safe and anti-static
Fir safe should also be considered, when design ball valves. Once fire occurs, outer leakage and inner leakage of valves cannot exceed leakage standard stipulated by API 607. Static may be caused for ball being clamped by non-metal materials. So ball must connect with body. Resistance value is lower than 10 ohm under 24VDC.
4. Double brock & bleed
When valve core is excreting, upstream seat and downstream seat should cut off automatically at the same time, to ensure security during excretion.
Medium inside valve core can be excreted. Sealing on valve can be detected online through drain hole.
6. Transmission chain
Torque of transmission chain should be at least 2 times of maximum torque of ball valves.
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