Product category:
Materials and components
News Release from: Victrex USA | Subject: Victrex Peek 450GL30
Edited by the Engineeringtalk Editorial
Team on 15 October 2002
Polymer seals out high-pressure steam
Victrex Peek 450GL30 has enabled Magnetrol International to develop a guided wave radar probe that reliably seals out high-temperature steam.
When used to measure water in saturated steam applications, liquid level sensing probes must be able to withstand the harshest operating conditions Because of its combination of electrical, mechanical and chemical resistance properties, Victrex Peek 450GL30, a 30% glass-fibre-reinforced high-performance engineering thermoplastic, enabled Magnetrol International to develop a guided wave radar (GWR) probe that reliably seals out high-temperature steam
The probe's Peek polymer seal component was developed after several attempts to create a feed-through seal design based on ceramic insulators brazed to metal components.
Designed for applications such as boilers, de-aerators and feed water heaters typically found in the power industry, Magnetrol's liquid level control consists of a two-wire, 4 to 20mA transmitter and steam probe feedthrough.
"Using GWR technology", explains Bob Botwinski, Guided Wave Radar Product Manager, "the transmitter sends a high frequency signal down the probe to measure the water level.
Peek polymer is used as a critical part of the process seal contained in the probe".
As the probe is used in high-temperature steam, resistance to that environment is essential.
"Peek polymer has a proven track record of long-term service in steam", says Botwinski.
"Exposure to steam requires a high continuous service temperature and our Peek 450GL30 polymer components continue to perform successfully at temperatures up to 300C".
The feedthrough design requires that the pressure load on the seal assembly be concentrated on a relatively small area of Peek polymer at the upper end of the probe head.
"The high compressive strength of the polymer, even at elevated temperatures, is critical to being able to conservatively rate the probe at 1600lb/in2 service pressure at 318C".
The seal components are completely enclosed in stainless steel, and all the parts are exposed to high heat.
"The close match in thermal expansion coefficients between Peek 450GL30 and the stainless steel minimizes induced stresses due to differences in thermal expansion rates", says Alan Gard, Senior Project Engineer.
In addition to forming a seal, the probe head assembly must also pass the electrical signal used to measure the water level.
"This requires that a certain range of impedance through the probe be maintained", explains Botwinski.
"The impedance is a function of the ratio of the inner and outer conductors, and the dielectric constant of the insulator between them.
The higher the dielectric constant of the insulator material, the larger the outer conductor must be to achieve a particular impedance.
The relatively low dielectric constant of Peek polymer permits the dimensions of the probe head to be within design limits".
"The availability of Peek polymer in both extruded rod form and as injection-moulded parts was another benefit", adds Gard.
The probe design was developed using extruded Peek polymer rod without the expense and risk of building a mould before the design was proven.
"Now that the design is successful", says Gard, "The production of the Peek polymer parts can be converted to injection-moulding to reduce piece-part costs".
• Victrex USA: contact details and other news
• Email this article to a colleague
• Register for the free Engineeringtalk email newsletter
• Engineeringtalk Home Page
Search the Pro-Talk network of sites
