【Haichuan Chemical Valve Knowledge】Leaking again? Unveiling the six main reasons for damaged valve sealing surfaces!

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1. Erosive damage: When the medium contains solid particles (such as catalyst powder, rust, sand grains) or when a high-speed gas-liquid two-phase flow passes through the valve, the sealing surface may develop grooves or pitting due to frequent impacts. Especially under throttling conditions, the flow velocity increases dramatically, and the sealing surface is very prone to developing radial flow marks as a result of being \"blown\". The typical manifestation is linear wear along the flow direction of the medium. 2. Plastic deformation and indentation caused by contact stress: At the moment the valve is closed, the sealing surface is subjected to extremely high contact compressive stress. If the material hardness is insufficient or the closing force is too high, plastic deformation may occur – dents may appear on the surface of soft materials, while hard materials may experience localized flaking. Repeated shutdowns over a long period can also cause the surface layer of the sealing surface to gradually undergo cold working hardening, resulting in microcracks that expand and lead to delamination failure. 3. Creep and softening at high temperatures: Under high-temperature conditions (such as in steam or hot oil pipelines), the material of the sealing surface may undergo two opposite but both harmful changes: one is softening of the material, with a decrease in hardness and a loss of resistance to scratching ； Second, creep occurs under continuous pressure, causing the seal surface contour to deform and preventing proper fitting. Furthermore, high temperatures accelerate the formation of scale, and the flaking oxide increases friction and wear. 4. Electrochemical corrosion and crevice corrosion: When different metal pairs are used (such as a stainless steel valve seat with a Stellite alloy welded on the sealing surface), a galvanic cell is formed in an electrolytic medium. What’s worse are the tiny gaps that remain after the sealing surfaces are closed; the accumulation of fluid in these gaps along with differences in oxygen concentration lead to localized corrosion in those areas, resulting in deep pits or corrosion holes. Stress corrosion cracking can also occur on stainless steel sealing surfaces in the presence of chloride ions. 5. Cracks and spalling caused by thermal shock: Frequent and rapid opening and closing (such as in programmable valves and safety valves) causes the sealing surfaces to experience sudden heating and cooling repeatedly. Cyclic thermal stresses are generated because the surface temperature changes faster than that of the matrix. When the stress exceeds the material’s fatigue limit, network-like thermal fatigue cracks appear on the surface. The cracks extend vertically and connect with each other, ultimately leading to the peeling away of small sections of the sealing surface, resulting in a \"cracked\" failure pattern. 6. Accelerated corrosion caused by medium retention between the sealing surfaces: When a valve remains in a partially open or slightly leaking state for an extended period, the medium on the high-pressure side continuously washes against the sealing surfaces, while corrosive media accumulate on the low-pressure side. In the stagnant zone, due to changes in pH value, ion concentration, and product accumulation, the corrosion rate can be several times higher than under normal flow conditions; this leads to the formation of local pits that quickly penetrate the sealing surface.