Analysis of Causes for Blind Plate Valve Seal Failures

In pipeline systems of industries such as petroleum, chemical, and power, blind plate valves are critical safety isolation devices. By switching between the through-hole plate (open position) and the solid plate (blind position), they achieve unobstructed flow and complete isolation of pipeline media, serving as a vital guarantee for equipment maintenance, process switching, and safe production. In actual operation, poor sealing is the most common and serious fault of this type of valve. Leakage not only causes media loss and environmental pollution but may also lead to safety accidents such as fires and explosions. Therefore, quickly and accurately diagnosing and handling poor sealing problems is one of the core skills of equipment maintenance personnel.

I. Fault Phenomena and Preliminary Diagnosis
Poor sealing mainly manifests as: after the valve is switched to the blind position (solid plate isolation), media seepage or dripping occurs at the flange connection; under maintenance isolation conditions, if the pressure in the isolated pipe section drops abnormally, or if the presence of media is detected downstream, it can be determined that the blind plate seal has failed.

Preliminary diagnosis must strictly follow safe operating procedures and be carried out under the premise of safe system depressurization and effective isolation. Leaks can be precisely located by listening (to hear hissing sounds), visually inspecting (leaking traces), and testing (using explosion-proof tools/specialized instruments), along with soapy water or specialized leak detectors. Leaks are often concentrated in the flange sealing area.

II. Common Causes and Analysis of Inadequate Sealing The causes of inadequate sealing in spectacle blind valves are varied, but can be broadly categorized into two main types:

(I) Sealing Element Failure The sealing gasket is the primary factor leading to sealing failure:

1. Inappropriate gasket selection: The material was not selected in conjunction with the corrosiveness of the medium, temperature, pressure, and other operating parameters. For example, using ordinary rubber gaskets in high-temperature oil pipelines can lead to rapid aging and hardening, resulting in loss of sealing elasticity.
2. Aging or physical damage to the gasket: Gaskets that have been in operation for a long time are prone to stress relaxation, medium corrosion, and high-temperature creep. Gaskets with defects such as creases, scratches, and blistering before installation can directly create potential leakage hazards.
3. Gasket Size Mismatch: If the inner diameter of the gasket is too large, it will extend into the flow channel, obstructing or eroding the medium flow; if the outer diameter is too small, it will not be able to completely cover the sealing surface, forming a direct leakage channel.

(II) Flange Sealing Surface Damage: The flange sealing surface is the foundation of the sealing structure, and its integrity directly determines the sealing effect:

1. Mechanical Damage: During blind flange switching, valve transportation, and storage, the sealing surface is prone to damage such as impacts, dents, and tool scratches, disrupting the continuity of the sealing line and leading to seal failure.
2. Corrosion and Erosion: Corrosive components and high-speed flowing solid particles in the medium will continuously erode the sealing surface, forming defects such as pitting, dents, and grooves, causing the surface roughness to exceed the standard and preventing effective sealing.
3. Sealing Surface Deformation: Factors such as additional stress in the pipeline, uneven bolt tightening force, and localized high temperatures can cause the flange sealing surface to warp and deform, resulting in uneven contact between the sealing surface and the gasket, leading to gap leakage.

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