Main causes of damage to the static sealing surface of valves

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In valve operation, the sealing surfaces that do not experience relative motion and remain in a state of relative stillness are known as static seals; the surfaces that perform the sealing function are called static sealing surfaces. On valves, there are many structural types for the static sealing surfaces: they can be flat or conical, and they may use gaskets or not; in addition, there are forced sealing and self-sealing types. The static seal surface is an important part of the valve, and it is also one of the main areas where leaks can occur. The main reasons for the damage to the static seal surface are listed in the table below. Causes of damage to static sealing surfaces, forms of damage, reasons for damage, and examples:
Severe rusting of the static sealing surface – mainly due to corrosion by the medium and improper selection of the valve.
Severe scratches and dents on the static sealing surface – primarily resulting from violations of operating procedures during disassembly, cleaning, and assembly, as well as from impacts, scratches, and excessive force.
For globe valves and gate valves with rigid planar sealing connections, obvious indentations on the static sealing surface – usually caused by the use of gaskets with too high hardness or low surface finish, or by the presence of contaminants such as sand particles or weld residues during assembly.
For globe valves and gate valves connected using mirror-flat gaskets or conical gaskets, an uneven surface on the static sealing surface – mainly due to prolonged use, erosion by the medium, and lack of regular inspection and maintenance.
In cases of planar threaded connections without gaskets or with rigid sealing surfaces, obvious grooves appear on the static sealing surface. After leaks occur due to scratches on the static sealing surface, if they are not repaired in time, the severe erosion by the medium causes the scratches to become larger and form grooves.
In flange connections with smooth surfaces or inclined self-sealing connections, deformation of the static sealing surface occurs – either because the stiffness of the static sealing surface is insufficient and excessive force is applied during assembly, or due to thermal creep at high temperatures.
In flange connections with keyed surfaces, cracks appear on the static sealing surface – often caused by poor material selection and manufacturing quality, improper installation or operation, or fatigue cracks resulting from long-term exposure to alternating loads.
In flange connections with keyed surfaces or trapezoidal surfaces, as well as in planar rigid sealing connections, leakage holes may appear on the static sealing surface – usually due to defects such as wrinkles, pores, and inclusions resulting from poor manufacturing quality.
These issues can occur on most static sealing surfaces.
Repair of static sealing surfaces: 1. Trimming of the convex outer surface – In cases where there are uneven surfaces or keyed surfaces, poor manufacturing quality can cause damage or deformation to these surfaces, preventing the convex surface from fitting properly into the concave surface. In addition to turning, it can be shaped with a file. The method of trimming it is as follows: clamp the workpiece in a vise, place a flat file on the outer surface of the convex part, with the smooth side of the file against the back edge of the workpiece. While filing, move the file back and forth while also making circular motions up and down; after filing for a while, change the direction and continue filing around the entire circle. File the arc connections smoothly until the desired dimensions are achieved; the fit clearance between the convex and concave surfaces should be H11/d11. 2. Repair of trapezoidal grooves: Trapezoidal grooves are damaged due to corrosion and impact. During repair, clamp the workpiece on the lathe and use a dial indicator for alignment; then mill off about 1 mm of material from the surface of the trapezoidal groove. After that, create a new trapezoidal groove according to its dimensions, ensuring that the roughness on both the inner and outer sides of the groove is ≤3.2. 3. Repair of threaded plugs: Threaded plugs are common static sealing points on valve bodies and valve covers, used for water filling during pressure testing or for discharging fluids. Depending on the operating conditions and degree of damage, the following methods are used for repair. Minor damage is addressed by grinding, replacing the gasket, or wrapping polytetrafluoroethylene tape, sealant, etc., around the plug’s threads ； If the plug is damaged, it should be replaced ； For stripped screw holes, reaming and tapping can be used; alternatively, a new plug can be fabricated or the screw hole can be filled by welding before drilling and tapping it again. 4. Surfacing repair of the static seal surface: Remove the defects on the static seal surface, select welding rods appropriate to the material of the main body. To prevent the loss of weld metal, it is necessary to pre-construct a structure that fixes the surfacing area on the inner side; this structure should be made of the same material as the main body. Then welding is carried out in accordance with the surfacing procedures, and a new static seal surface is turned. The surfacing layer shall be free from defects such as cracks and pores, and pass the strength test. 5. Replacement of the static seal surface: When the static seal surface cannot be repaired due to severe corrosion, cracks, or chipping, it can be replaced. The newly machined static seal surface should meet the dimensions and technical requirements of the original static seal surface; if the dimensions of the static seal surface are not available, it can be machined based on the actual measured dimensions of the static seal surface. (1) Welding replacement. For welding replacement, a pre-made static seal ring (with appropriate machining allowance) is inserted into the already machined body, and then welding is performed to integrate the static seal ring with the body; subsequent machining and grinding are carried out. (2) Adhesive replacement. When welding is not a feasible option for replacing cast iron or non-metallic valves, an appropriate adhesive can be used to firmly attach a pre-made static seal ring to the valve body, followed by grinding to make adjustments.