Characteristics and Types of Valve Sealing Surface Materials

The sealing surface is a part of the valve that is easily damaged due to the fact that it is often eroded and worn by media. Its quality is a direct factor of service life of valves. The basic requirement of the sealing surface is that safe and reliable sealing should be ensured under specified operating conditions.

Characteristics of sealing surface materials:

• Excellent sealing performance. In other words, the sealing surface should be able to prevent media leakage effectively.
• Certain intensity. The sealing surface should be able to withstand the sealing pressure ratio under the effect of medium pressure difference.
• Corrosion resistance. The sealing surface should have relatively high corrosion resistance consistent with design standards under long-term impact of corrosive media and stress.
• Abrasion resistance. All valve sealing pair is dynamic seal, so friction exists between sealing pair when opening and closing.
• Erosion resistance. The sealing surface should resist the scouring of media at a high speed and the impact of solid particles.
• Excellent thermal stability. The sealing surface should have certain intensity and oxidation resistance at high temperature conditions, and it should have cold brittleness resistance under low temperature conditions.

Following are the common sealing materials and their applicable working conditions.  

• Rubber (NBR, EPDM, etc.). Widely used in low pressure pipelines with oil and water media; generally applicable to sealing surface of low pressure soft seal gate valves, check valves, butterfly valves, diaphragm valves, etc.
• Plastic (PTFE, NYLON, etc.). Mainly applied to pipelines with corrosive media; high corrosion resistance and low friction coefficient; frequently used in soft seal ball valves.
• Copper alloy. High abrasion resistance and corrosion resistance in water and steam; applicable to water and steam with PN≤1.6Mpa and temperature≤200℃; applied to globe valves, cast iron gate valves, check valves, plug valves, etc.
• Chromium stainless steel. Excellent corrosion resistance; used in valves of water, oil, steam, and other media with PN≤32Mpa and temperature≤450℃.
• Stellite. Applicable to various type of valves and diverse media with temperature between -268 and 650℃, especially highly corrosive media; superb corrosion, erosion, and abrasion resistance; ideal sealing material; often overlay welded.
• Cr-ni stainless steel. High erosion, corrosion, and heat resistance; suitable for steam, nitric acid, and other media.
• Inconel. Suitable for corrosive media; Monel, Hastelloy B, and Hastelloy C are frequently used sealing materials.
• Babbitt metal. High corrosion resistance and grinding-in performance; applied to the sealing surface of ammonia globe valves with PN≤2.5Mpa and temperature between -70 and 150℃.
• Nitriding steel. High corrosion resistance and abrasion resistance; usually used in gate valves of thermal power station and the ball of hard seal ball valves.