The sealing surface of a valve is the core component that prevents medium leakage, and its performance directly determines the sealing reliability and service life of the valve.
Sedelon Valve elaborated on it from two aspects: materials and the causes of damage.
I. Materials of Sealing Surfaces
The selection of sealing surface materials shall be based on the characteristics of the medium (temperature, pressure, corrosivity, particle content, etc.), which are mainly divided into three categories: metal, non-metal and composite materials.
1. Metal Materials (Suitable for medium and high pressure, high temperature, wear-resistant scenarios)
| Metal Material | Characteristics | Applicable Scope | Common Application Scenarios | Remarks |
| Cast Iron | Low cost, poor strength and corrosion resistance | Low pressure (≤1.6MPa), normal temperature (≤200℃), non-corrosive media (e.g. water, air) | Low-pressure gate valves, butterfly valves | Only applicable to low-pressure, normal-temperature and non-corrosive medium scenarios |
| Carbon Steel | Higher strength than cast iron, temperature resistance up to 425℃ | Medium pressure (1.6-6.4MPa), non-corrosive media (e.g. oil products, steam) | Sealing surface substrate of globe valves and gate valves | Performance can be improved by surfacing welding |
| Stainless Steel | Excellent corrosion resistance (316 has stronger chloride ion corrosion resistance), temperature resistance of 304 up to 600℃ and 316 up to 800℃ | Medium and high pressure, corrosive media (e.g. chemical industry, food, medicine) | Sealing surfaces of ball valves and globe valves | A commonly used material in chemical, food, pharmaceutical and other industries |
| Cemented Carbide | Strong wear resistance and high temperature resistance, applied on the surface of metal substrate by surfacing welding or spraying | High pressure (≥10MPa), high temperature (≥500℃), media with particles (e.g. steam, coal powder, ore pulp) | High-pressure valves | Common types include cobalt-based, nickel-based and iron-based alloys |
| Ceramic | High hardness (HRC≥85), extremely strong corrosion resistance (except for a few media such as hydrofluoric acid), but high brittleness | Media with hard particles (e.g. mud, dust) | Ceramic ball valves, gate valves | Mainly composed of alumina (Al₂O₃) and zirconia (ZrO₂), suitable for wear-resistant and corrosion-resistant scenarios |
Common types of cemented carbide:
2. Non-metal Materials (Suitable for low pressure, corrosive or elastic sealing required scenarios)
Rubber: Excellent elasticity, can fill the tiny gaps of the sealing surface through deformation, with good sealing performance, but limited temperature resistance (-50~120℃) and pressure resistance (≤1.6MPa), and not resistant to oil and organic solvents.
| Material Name | Characteristics | Application Scenarios |
| Nitrile Butadiene Rubber (NBR) | Oil-resistant | Hydraulic systems |
| Ethylene Propylene Diene Monomer (EPDM) | Acid and alkali resistant, aging resistant | Water, steam |
| Fluoro Rubber (FKM) | Temperature resistance up to 200℃, oil and chemical corrosion resistant | Severe working conditions |
| Polytetrafluoroethylene (PTFE) | Extremely strong corrosion resistance (except molten alkali metals, etc.), temperature resistance from -200 to 260℃, but high rigidity and prone to cold flow (deformation under long-term pressure) | Low pressure (≤6.4MPa), strong corrosive media (e.g. acid, alkali), commonly used for fluorine-lined valves (e.g. fluorine-lined ball valves, globe valves) |
Flexible graphite: Made of graphite through expansion treatment, with high temperature resistance (-200~650℃), good corrosion resistance, both elasticity and thermal conductivity. It is suitable for medium and high pressure sealing (e.g. valve stuffing box, flange sealing), and often used in combination with metal (e.g. metal-clad graphite gasket).
3. Composite Materials (Balancing multiple properties)
II.Analysis of Causes for Damage to Valve Sealing Surfaces
The damage of valve sealing surfaces is usually caused by various factors, including material selection, working conditions, operation methods and maintenance. The following is a classified summary of common causes:
| Category | Cause | Specific Performance |
| Mechanical Damage | Wear | Solid particles in the medium (e.g. sediment, welding slag) erode the sealing surface, resulting in scratches or grooves. |
| Scuffing | Friction and wear caused by the relative movement of the sealing surface during the opening and closing of the valve (especially for metal sealing pairs). | |
| Impact Damage | Collision and deformation of the sealing surface caused by high-speed medium impact or rapid opening and closing of the valve. | |
| Chemical Corrosion | Medium Corrosion | Acidic, alkaline or oxidizing media directly corrode the sealing surface material (e.g. corrosion of metals by H₂S and chloride ions). |
| Electrochemical Corrosion | A galvanic cell reaction is formed by the sealing pairs of different metal materials in the electrolyte solution. | |
| Erosion Corrosion | The combined action of corrosive medium and high-speed flow accelerates material loss. | |
| Thermal Damage | Thermal Fatigue | Frequent temperature fluctuations cause thermal expansion and contraction of the sealing surface, resulting in cracks or deformation. |
| High-temperature Oxidation | Oxidation, hardening or burning of the sealing surface at high temperatures (e.g. steam valves). | |
| Thermal Shock | Cracking of the sealing surface caused by contact with instantaneous high or low temperature medium (e.g. condensation and dewing). | |
| Improper Installation and Operation | Installation Deviation | Incorrect valve installation and excessive pipeline stress lead to uneven stress on the sealing surface. |
| Over-tightening | Excessive pre-tightening force of the valve stem or bolts crushes the sealing surface (e.g. soft sealing gaskets). | |
| Rough Operation | Rapid opening and closing or excessive force cause impact damage to the sealing surface. | |
| Material Defects | Improper Material Selection | The sealing surface material is not resistant to medium corrosion, high temperature or wear (e.g. ordinary carbon steel used in acid working conditions). |
| Manufacturing Defects | Blowholes, inclusions in the surfacing layer of the sealing surface or poor heat treatment reduce wear resistance. | |
| Abnormal Working Conditions | Cavitation/Erosion | Bubble rupture caused by medium pressure change impacts the sealing surface (common in pump outlet valves). |
| Scaling/Deposition | Impurities in the medium accumulate on the sealing surface, affecting the tightness of closure (e.g. calcium compounds, polymers). | |
| Inadequate Maintenance | Lack of Lubrication | Seizure of the valve stem or transmission parts leads to failure of the sealing surface to fit normally. |
| Infrequent Inspection | Minor damages are not handled in time and expand into large-area damages. | |
| Improper Cleaning | Foreign bodies remain during maintenance (e.g. scratches by tools, unremoved welding slag). |
Preventive Measures
By comprehensively analyzing the specific working conditions and damage characteristics, the valve design, operation and maintenance strategies can be optimized in a targeted manner to extend the service life of the sealing surface.
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