The Selection Logic of the Valve Stem Under High Temperature and High Pressure Conditions

In the valve structure, the valve stem does not seem complicated, but as long as you have run through the high temperature and high pressure system, you know that it is one of the most problem-prone parts. Especially in power plants, refining and metallurgy, where the temperature of the medium is often four or five hundred degrees and the pressure is tens of kilograms, if the valve stem is not selected reasonably, the seal will fail at least, and it will be directly broken or stuck.

We have encountered a practical case: a batch of globe valves used in a power station began to jam frequently after half a year of operation, and the on-site dismantling found that the surface of the valve stem was discolored and distorted, and the sealing packing could not be suppressed. Later, it was confirmed that the original design was made of 304 stainless steel, but the operating temperature of the pipeline was close to 500°C, and the material had exceeded the limit.

The root cause of stem failure at high temperature and high pressure is not only the lack of material strength, but also the change of fit size due to thermal expansion, fatigue fracture caused by thermal stress concentration, and dry friction caused by lubricant failure. Especially in the use of frequent opening and closing, long strokes, and high loads, the superposition of these factors will greatly shorten the life of the valve stem.

Therefore, we generally focus on several aspects when selecting: first, try to use materials with high temperature and stable strength, such as 17-4PH, F6a, 1Cr13Mo and other high-alloy steels, if it is an acidic medium, duplex stainless steel or Monel alloy should be considered; Second, it is recommended to surlay the cemented carbide layer for the threaded connection part to improve the anti-seizure ability; Third, the filler contact area should be precision machined and nitrided or coated.

In addition, it is recommended to use integral processing instead of welded splicing structure as much as possible to reduce the risk of interface failure. In long-stroke applications, it is necessary to account for the axial offset caused by thermal deformation, otherwise there may be "not in place" or "stuck" problems.

The valve stem produced by Yining Machinery is currently widely used in petrochemical, electric power, metallurgy, liquefied gas and other industries, we have specially developed customized valve stems suitable for different connection structures for high temperature and high pressure valve systems, including forging finishing, thread surfacing welding, mirror treatment and other processes, which can cope with the work requirements of high load and high opening and closing frequency.

In summary, although the stem structure is simple, in the high temperature and high pressure scenario, once the improper selection is the "weak point" of the system. It is recommended that in the design and procurement stage, detailed accounting should be done in combination with the working condition parameters, opening and closing methods, and frequency of use, rather than just looking at the drawing material or price to determine the selection.