Valve Seat Failure Causes and Structural Improvement Suggestions

After doing valve projects for these years, to be honest, I have seen too many cases of valve seat problems. Most of the time, the user complains about valve leakage, in fact, not a spool problem, but the valve seat has long been worn out. Sometimes it is the material is not good, sometimes it is the structure of the design simply did not take into account the working conditions.

We previously installed in a coking plant ball valves, media with dust, high temperature, the design drawings written on the stainless steel soft seat, the results of less than half a year of operation, the return visit found that several units of serious internal leakage. Disassembled and found that the sealing ring scraped, the edge of the valve seat is also a little collapsed. Later replaced with hard-surfaced welded metal valve seat, life increased by more than two years.

There are several common failure modes: one is the sealing surface wear, especially with solid particles of media, high frequency opening and closing under the scraping very quickly; the second is the weld layer peeling, which is mostly the surfacing process is not in place or heat treatment stress is not released; there is also a hidden problem is the spool and seat assembly is not concentric, the result is that one side of the old strain, one side of the leakage.

If the design stage does not take the valve seat seriously, problems are almost inevitable. We have a customer in the alumina production line with dozens of V-ball valves, valve seat is all ordinary stainless steel, running less than a year on the jamming, cleaning can not be cleaned out. Later, we gave them a version of the taper to strengthen the structure, added limit bevelled and internal support groove, running for two years without significant wear and tear.

Structurally, it is recommended that the design consider three points: First, the sealing surface as much as possible to do replaceable, out of the problem can be repaired on-site; Second, the material can be stacked welding on the do not want to save trouble with a single stainless steel; Third, the assembly plus centring limit, do not rely on manual alignment to get together. Otherwise, a slight installation deviation, switch a few hundred times after the start of the ‘gnawing spool’.

In the valve seat structure that we have done, like the combination of metal bevelled limit + composite sealing insert, the performance is very stable in the working conditions of coal oil, ammonium phosphate, high salt waste liquid. Now many customers have directly incorporated our customised structure into their technical packages, which shows that this kind of solution can really solve the problems in the field.

Valve seat is something that no one pays attention to when designing, and if something goes wrong, it's a big deal. Suggest that all design, do procurement counterparts, do not just look at the data sheet, to listen to the field operation and maintenance of people how to say. Because the working conditions never wait for people, the structure is good, installed three months to know.