1. Sealing performance characteristics of cast iron ball valves
Limitations of sealing structure
Cast iron ball valves mostly use copper seals or rubber seals (such as EPDM/NBR), which can meet basic sealing requirements in medium and low pressure scenarios (such as urban water supply and drainage systems), but long-term use is prone to leakage due to material aging or wear;
The hardness of the cast iron valve body is relatively low. In media containing solid particles (such as mud and sand), the sealing surface is easily eroded and damaged, and frequent maintenance is required.
Corrosion resistance effect
Cast iron has good corrosion resistance in ordinary water media, but in strong acid, alkaline or high chloride ion environments, the valve body and sealing surface are easily corroded, accelerating the failure of the seal;
Surface painting or galvanizing can extend the life of the seal, but the maintenance cycle is usually 6-12 months, and the overall cost is relatively high.
2. Sealing performance characteristics of carbon steel ball valves
Sealing material and process advantages
The sealing surface of carbon steel ball valves is often made of stainless steel or hard alloy (such as tungsten carbide). The hard sealing structure can withstand higher pressure (≥PN40) and temperature (≤425℃), and the sealing life is 2-3 times that of cast iron valves;
The valve body and valve seat are tightly matched through precision machining, and the leakage rate is lower than that of cast iron valves, which is especially suitable for high-pressure and harsh working conditions such as petroleum and chemical industries.
Ability to resist medium impact
The carbon steel material has high hardness and can effectively resist the erosion and wear of particle-containing media, reducing the risk of sealing surface damage;
In high-temperature steam or corrosive chemical media, it can still maintain long-term sealing stability with flexible graphite or metal hard seals.
3. Comparison of typical scenarios
Low pressure/non-corrosive environment (such as building water supply and drainage):
Cast iron ball valves can still meet the sealing requirements due to their low cost and simple maintenance, but the status of the seals needs to be checked regularly;
High pressure/high temperature/corrosive media (such as refineries, chemical pipelines):
Carbon steel ball valves achieve excellent sealing performance through a combination of high-strength valve body + hard seal, and the leakage rate can be controlled below 0.01%;
Solid medium scenario (such as mud transportation):
The wear-resistant hard seal of carbon steel ball valves (such as tungsten carbide) is significantly better than the soft seal of cast iron, which can reduce the failure of seals caused by particle erosion.
4. Maintenance and cost impact
Cast iron valves: The frequency of seal maintenance is high, and the corrosion problem of the valve body needs to be dealt with simultaneously when replacing the seals. The comprehensive maintenance cost may exceed that of carbon steel valves;
Carbon steel valves: The hard seal structure is durable, and only the status of the valve stem and the sealing surface needs to be checked regularly, and the long-term operation and maintenance cost is lower