A Review of Valve Stem Sealing to Prevent Leakage from the Valve and Its Effect on Valve Operation
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A Review of Valve Stem Sealing to Prevent Leakage from the Valve and Its Effect on Valve Operation Karan Sotoodeh
Submitted: 6 October 2020 / Accepted: 8 October 2020 ASM International 2020
Abstract Stem sealing plays an important role in valve operation, to avoid leakage from the valve stem area to the environment. Additionally, accuracy and tight sealing of stem seals are vital in fugitive emission applications where hazardous fluids such as gases or vapours may escape if a valve is not sealed properly. Soft thermoplastic and elastomer materials such as Teflon (PTFE), lip seal, V-pack, Viton as well as graphite or graphoil can be used for valve stem sealing. Appropriate stem sealing or packing depends on the process conditions where the valve will be used, including being able to withstand extreme temperatures, being resistant to aggressive fluid such as H2 S containing fluid, displaying a low friction factor to the stem, providing very good sealing capability to prevent leakage from the valve stem area, and being adequately strong and economical. The sealing capability of compression packing is defined as the ability to expand laterally against the stem and stuffing box wall when stressed by tightening the gland. The stem sealing arrangement depends on the type of valves being used and the applications. The sealing capability and performance of a valve can be validated by testing the valve stem sealing through mechanical and temperature cycles based on different American Petroleum Institute standards or by finite element analysis. The torque required to operate a valve depends on parameters such as the packing or stem sealing material, number of stem sealing rings, load of gland flange, stem surface finish, temperature, and cycling. Reducing the number of packing rings can reduce the valve torque and the actuator sizing but removing rings can also increase the risk of leakage K. Sotoodeh (&) Valve Engineering, Baker Hughes, a GE Company, Oslo, Norway e-mail: [email protected]
from the valve and reduce the effectiveness of the valve seals. Keywords Valve sealing Torque Valve stem friction Offshore Oil and gas industry
Introduction to Valve Stem Sealing A valve is a mechanical component used in a piping system to open and close the fluid passage, avoid backflow of the fluid, and control the flow for operational or safety purposes [1, 2]. Valve design is generally a very broad subject [3] including different considerations such as material selection [4, 5], wall thickness calculation [6], design of pressure-controlling internal valve parts [7, 8], and design of pressure-containing valve parts such as the body, bonnet, stem, bolting [7, 8], and sealing. Pressure-controlling parts affect the passage of fluid through the valve, whereas pressure-containing parts are sections that lead to external leakage from the valve in case of failure [7, 8]. There are three places in a valve where sealing is required [3]: stem sealing, seat to body, and sealing between body and bonnet or body pieces
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