Technical Articles
The Design of Trunnion Mounted Titanium Ball Valve
Posted: 03/11/2016 16:30:00  Hits: 132
Titanium has already applied in chemical engineering, health care, salt manufacturing, chlor-alkali, aviation and other industries, for its good mechanical property and excellent corrosion resistance. In chemical engineering, titanium is mainly used for pressure vessel, pipelines and pump valve. Among that, trunnion mounted titanium ball valve is widely used for petroleum and chemical engineering due to its good sealing, excellent corrosion resistance and adaptation to high working pressure. At present, there is no trunnion mounted titanium ball valve in China, only floating titanium ball valve. The U.S., Germany, Japan and only a few developed countries can manufacture trunnion mounted titanium ball valve around the world. To meet the requirements of high working pressure, good sealing and good corrosion resistance in petrochemical industry and expand application range of titanium material, the design of trunnion mounted titanium ball valve is carried out. Nowadays, trunnion mounted titanium ball valve whose dimensions were DN80, DN50, DN40, DN25 and working pressure reach as high as 9.8MPa has been produced, filling up the blank and laying the foundation of mass production. It also provides technology and material guarantee to localization of corrosion resistance equipment in large petrochemical enterprises.  
 
Design of trunnion mounted titanium ball valve:
 
Technical parameter:
Working medium: acetic acid;
Working temperature: 225℃;
Working pressure: 9.8MPa;
Nominal diameter: 80mm.
 
Materials
According working temperature and density of acetic acid, corrosion rate of titanium is below 0.127mm/a. Compared with corrosion resistant stainless steel and other nonferrous metals, TA2 is more suitable; based on working pressure, to ensure the strength of structure, TA2 is used as forging; based on working temperature and working pressure, flexible graphite and antimony filler carbon are chosen for sealing materials.
 
Calculation
1. Design of thickness of body
Formula: SB=DN(K0-1)/s+C; result: 16mm.
2. Attachment bolts between bonnet and body
According to working pressure, 8 1Cr18Ni9Ti bolts with 30mm×55mm are chosen which can meet the requirements of strength.
 
Key technology
Due to working pressure as high as 9.8MPa, sealing bearing are the key technologies. During development, the following 3 measures can be used for the solution
1. Maintain concentricity between body and up and down stem;
2. Maintain perpendicularity between up and down stem and through hole with Φ80mm;
3. Maintain surface roughness.
 
Designing special tools, processing and sealing technologies can meet the requirements of sealing and bearing. 
 
Structural features
Compared with floating ball valve, trunnion mounted ball valve has the following 3 features:
1. Rear sealing is adopted in terms of sealing principles. 
2. Suitable for high pressure and viscous liquids.
Common floating titanium ball valve is unreliable under high pressure. When the media are viscous liquids, tiny floating gap between ball and sealing ring can be blocked easily so that the valve is opened difficultly or loses sealing. Trunnnion mounted ball valve uses spring, so the sealing ring are always tightly contacting with ball, using high pressure media to realize good sealing performance. 
3. Using line sealing
Common floating ball valve is spherical sealing between ball and sealing ring, having low sealing pressure ratio on unit area. What’s more, convex-concave point on microscopic surface can easily cause leakage under high pressure, failing to meet the requirements of sealing. However, trunnion mounted ball valve uses line sealing between body and sealing ring, increasing sealing pressure ratio on unit area. What’s more, the higher pressure is, the better sealing is, ensuring the reliability under high pressure.
 
The Design of Trunnion Mounted Titanium Ball Valve