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Cause and Parameter Discussion of Internal Pressure Leakage Valve Leakage
1, Overview Internal pressure self-sealing structure is a high temperature and pressure valve flange seal often used in the structure of the structure, a test bench installed two identical flange seal pair of internal pressure self-sealing structure of the swing-type Check valve. In the test bench alternating working pressure and temperature after the completion of the test, the pressure was raised again before the normal temperature during the pressure test, one of the swing check valve in the flange of the secondary leak, take maintenance measures None of the valves solved the problem of leakage. And another swing check valve in the test bench after a few years, the flange seal also leaks. Therefore, through the analysis of the leakage problem of this valve, it is necessary to elaborate on the selection of design and design parameters for some special test benches and special valve products for engineering application. 2, Technical parameters Two Swing Check Valves have been carried out before the factory P = 42.0MPa machine valve strength and flange seal sealing test, no leakage. (1) The maximum working pressure of the test bench 14.0MPa The maximum working temperature of 260 ℃ Design pressure 17.2MPa Design temperature 350 ℃ Working medium water Test circuit Pipe diameter 65mm Test bench test pressure 21.5MPa After each drop to normal pressure again Test pressure before pressurization 15MPa (2) Swing check valve Nominal pressure 28.0MPa (non-standard nominal pressure grade) Nominal diameter 65mm Valve body and bonnet material 1Cr18Ni10Ti Seal ring material N6 and test bench loop Connection method Welding 3, the fault 3.1, the first leak and repair test bench in the number of atmospheric pressure rose to the maximum working pressure and alternating pressure, alternating temperature (according to the provisions of the lifting temperature and pressure rate changes) to the maximum working pressure, temperature After running and testing, down to normal temperature and pressure maintenance. When the pressure test at normal temperature (P = 9.8MPa) is carried out again before the pressurization and temperature increase, a swing check valve on the test bench has a slight external leakage (hereinafter referred to as the first leak) at the middle flange seal. Disassemble the bonnet, seal ring Check the leak site, seal ring outer surface and the valve body flange sealing surface left a slight trace of leakage. Sealing ring outer surface sealing surface of the media leak marks the outer surface of the acute angle at the axial length × width of about 3 × 115mm caterpillar-like traces of its traces through the sealing surface, with a magnifying glass to observe the internal defects of suspected material. In the valve body flange sealing surface there is a slight trace of media leakage watermark, sealing ring sealing surface and the caterpillar-like traces corresponding. Specific parts of the vertical valve body in the direction of the axis of the channel (hereinafter referred to as the horizontal axis) of the end of the flange sealing surface, the valve body flange sealing surface of the other parts of the sealing ring outside the sealing surface of the other parts of the sealing ring sealing surface and head Seal surface no signs of leakage, sealing surface seal indentation uniform. When disassembling and overhauling the flange seal pair in the swing check valve, the diameter dimension of the flange sealing surface and the seal ring outer seal surface in the valve was measured. The flange faces and the outer sealing face of the seal ring appear inconsistent in diameter in both vertical and horizontal directions. The major axis is in the transverse axis of the valve body and the minor axis is in the axial direction of the valve body passage (hereinafter referred to as the axial direction). Valve body flange sealing surface length difference D2-D1 = 0.10mm, sealing ring outside the sealing surface length difference d2-d1 = 0.04mm. Valve body flange sealing surface short axis and vertical seal ring Leakage traces corresponding to the size difference D1-d1 = 0.02mm, the valve body flange sealing surface and sealing ring leakage traces corresponding size difference D2-d2 = 0.08mm. The first leak to take the repair measures for the replacement of a new seal ring. Flange sealing surface of the valve body in the test bench is not reliable tooling and technology to ensure the roundness of grinding sealing surface, so the sealing surface is not grinding, only the surface finish. The diameter of the outer seal surface of the new seal ring d = 120.16mm, which is 0.196mm larger than the upper limit value required by the drawing, and the diameter clearance in the axial direction of the flange sealing surface in the valve body is D1-d = 0.02mm, and the horizontal axis direction diameter clearance D2 -d = 0.08mm, with the gap in line with the drawings given allowable maximum clearance (0.291mm). At the same time, it is assumed that the new seal ring is excessively plastically deformed in the axial direction (the minor axis direction of the flange seal face in the valve body) by the sealing force provided by the test pressure to increase the transverse axis direction (the major axis of the flange seal face in the valve body Direction) than the pressure seal to avoid the possibility of longitudinal axis of the leak. The new seal ring in the pressure test (room temperature test pressure of 15.2MPa) in the process of sealing the valve body flange seal, and under the conditions of the test pressure at room temperature pre-tightening bolts preload, increase the seal ring Of the deformation, so that the direction of the horizontal axis of the gap to make up to make up to ensure that the sealing seal sealing pressure required. 3.2,2 leaks and demolition seized test bench again hot working conditions test, the high temperature and pressure (pressure 14.0MPa, temperature 240 ℃) run more than 4h, when the pressure dropped to 8.9MPa, the temperature of 212 ℃ or so, The valve leaks again at the center flange seal (hereinafter referred to as the second leak). After disassembling the bonnet and the seal ring again, the specific parts of the leak are symmetrical with the axis at both ends of the sealing surface in the direction of the transverse axis of the sealing surface of the flange, and the leakage traces can remove the iron red (different from other parts). The corresponding sealing ring outer sealing surface acute angle at a width of about 20mm, axial length 6mm, left and right symmetrical 2 leakage scour marks, traces of intensive linear groove marks, valve body flange sealing surface other parts of the seal ring Other parts of the sealing surface, the sealing ring sealing surface and the head sealing surface, etc. No signs of leakage. Flange sealing surface of the valve body is consistent with the first leak inspection, the sealing ring has deformation during dismantling, and the outer sealing surface of the sealing ring has no measurement. 4, analysis 4.1, the reasons for the first leak (1) sealing ring caterpillar-like traces of leakage of suspected material internal defects may be material forging internal defects. In the alternating pressure, alternating high temperature and pressure and the maximum working pressure and temperature, resulting in sealing ring leakage material forging internal defects continue to expand, resulting in forging internal defects at the media leakage. (2) The diameter of the flange sealing surface in the valve body is not the same. The size of the sealing ring in the axial direction limits the floating of the sealing ring, resulting in a smaller specific pressure in the horizontal direction. By its alternating pressure, alternating high temperature and high pressure and the maximum working pressure and temperature, the axial direction of the size of the ring more restrictive floating, and may make the horizontal axis of the pressure drop than the pressure, can not guarantee the sealing requirements, the occurrence of media Leakage, scouring expands the seal ring forging internal defects, with the development of leakage will continue to expand. 4.2, the second leakage causes (1) the valve body flange sealing surface in the horizontal axis and axial direction of the existence of dimensional error has not been repaired. Sealing ring outside the sealing surface in the valve body flange sealing surface in the gap between the two directions are inconsistent, the valve body flange sealing surface in the direction along the channel axis and sealing ring outer sealing surface clearance is small, the valve body flange Sealing surface in the direction of the horizontal axis and sealing ring outer sealing surface of the gap. The medium pressure (maximum test pressure 15.0MPa after valve inspection) provides the sealing force to the center flange. The pressure difference in the flange seal pair along the valve body passage axis and the transverse axis is inconsistent. The flange seal in the valve body is smaller than the pressure in the transverse axis direction and can not provide enough sealing force to increase the sealing pressure in the transverse axis of the valve body as the factory test pressure (42.0MPa) To meet the high temperature and pressure and alternating pressure and temperature conditions of the media seal. (2) sealing ring outer sealing surface Flange sealing surface in the valve body seal in the two directions of the gap is inconsistent. Under the action of alternating pressure and temperature, the clearance in the direction of the axis of the valve body passage and the gap in the direction of the transverse axis of the valve body passage can be changed by the alternating pressure and the temperature. Ensure seal, resulting in media leakage. 4.3, Flange seal error causes from the part of the processing size detection, the valve body flange sealing surface along the axis of the valve body channel and the direction of the horizontal axis the same size. Sealing ring outside the sealing surface measuring the size of the vertical direction is basically the same, a difference of 0.002mm (thin-walled parts are normal), the sealing ring outer sealing surface roundness does not affect the seal (seal ring sealing surface contact with the bonnet will seal Ring outside the sealing surface round). The analysis and verification, the valve body flange sealing surface along the axial direction and transverse axis direction inconsistent size is due to the valve 42MPa strength and flange seal sealing test. 5, the choice of parameters Self-styled swing check valve is based on the actual use of special test bench design. The technical parameters of the test bench to introduce non-standard pressure level of the valve pressure level and the prescribed test pressure, the nominal pressure of 28.0MPa, the test pressure of 42.0MPa. Valve body flange sealing surface in the axial direction and the direction of transverse axis deformation inconsistent and exceed the allowable deformation, from the calculation point of view is due to the valve body flange sealing surface strength is not enough, under the influence of the test pressure exceeds Allowable amount of deformation. The same swing check valve by a dedicated valve design. Design parameters for the design pressure 17.16MPa, design temperature ≤ 350 ℃, working pressure 13.73MPa, hydrostatic test pressure 21.45MPa. The product is applied to the other test bench in the same working condition, and it has been proved that it has not leaked for several decades. Practical application note, the valve design should carefully analyze its working conditions parameters, can not blindly introduce the standard requirements of the parameters. This valve is due to the introduction of the standard non-pressure rating, and according to the standard test pressure of hydraulic test (42.0MPa), and did not press this design flange strength, the valve body flange sealing surface in 2 Inconsistent and excessive deformation of the direction. In particular, this phenomenon does not meet the repeated high-temperature and high pressure operating conditions. 6 Conclusion analysis and the use of results show that if the test bench under the pressure of the design and testing, the valve will not have problems that save material and meet the needs of the working conditions. Therefore, for some special projects designed valve products, you can not blindly use the standard or reference to the high parameters of the standard. If the valve product is designed specifically for a project and the bench (not the project and bench selection of standard valve products), we must consider to meet the operating conditions and special conditions, the blind reference standard in the bench and engineering On the technical parameters is not desirable. If you must choose the standard high parameters (these parameters in the special bench and engineering conditions and tests never used), you must carefully check the strength of each part, doing so will result in the valve structure increases, Resulting in waste, not suitable for special test bench and engineering special needs, once the application may also give the test bench and engineering leakage of the product risks. More Keywords Search: Valve