Victrex® PEEK™ polymer meets unique challenges of saturated steam application

A revolutionary Guided Wave Radar (GWR) probe has been developed by Magnetrol International to meet the unique challenges posed by level measurement in saturated steam environments. The probe has been designed with a Victrex® PEEK™ polymer seal component, which reliably seals out high-temperature steam.

A 30% glass fibre reinforced grade of Victrex® PEEK™ polymer is used for a critical part of the process seal contained in the probe. Victrex® PEEK™ polymer is renowned for its excellent hydrolytic stability, together with its outstanding chemical resistance and mechanical performance in extreme heat and pressure conditions. This makes it ideally suited to withstand the harshest operating conditions of saturated steam applications.

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 20 mA transmitter and steam probe feed-through. Bob Botwinski, Guided Wave Radar Product Manager explains: “In GWR technology, the transmitter sends a high frequency signal down the probe to measure the water level. Since the probe is used in high-temperature steam, resistance to that environment is essential”.

Following unsuccessful trials with a feed-through seal design based on ceramic insulators brazed to metal components, Magnetrol turned to Victrex® PEEK™ polymer, which has a proven track record of long-term service in steam. Exposure to steam requires a high continuous service temperature combined with hydrolysis resistance and the Victrex® PEEK™ polymer components continue to perform successfully at temperatures up to 300°C.

The feed-through design requires that the pressure load on the seal assembly be concentrated on a relatively small area of Victrex® 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 110 bar service pressure at 318°C.

The seal components are completely enclosed in stainless steel and all the parts are exposed to high temperature. The close match in thermal expansion coefficients between Victrex® PEEK™ polymer and stainless steel minimizes induced stresses due to differences in thermal expansion rates.

In addition to forming a seal, the probe head assembly must also pass the electrical signal used to measure the water level. For this reason, a certain range of impedance must be maintained through the probe. 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 Victrex®PEEK™ polymer permits the dimensions of the probe head to be within design limits.

The probe prototype was produced using extruded Victrex®PEEK™ polymer rod. This eliminated the expense and risk of building a mould before the design was proven. Now that the design is successful, the Victrex® PEEK™ polymer parts are cost-effectively injection moulded with consistent processability and precision.

Reader enquiries

Helen Swarbrick
Victrex plc
Victrex Technology Centre
Hillhouse International
Thornton Cleveleys
Lancashire FY5 4QD
United Kingdom

Tel +44 1253 897700
Fax +44 1253 897701
United Kingdom
+44 1253 897700
info@​victrex.com
www.victrex.com

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Notes for editors

Victrex plc, which has its sales, technical and production headquarters at Thornton Cleveleys in Lancashire, UK, had a turnover of more than £59m in the last financial year. The company exports 97 percent of its Victrex® PEEK™ polymer output to OEMs in the automotive, industrial, medical, food and electronics market sectors in Europe, North America and Asia Pacific.

Information on products, technical support services and sales and distribution contacts worldwide, can be accessed through the company’s web site: www.victrex.com.

The PEEK™ Trademark

For many years Victrex plc has been using the PEEK™ trademark to refer to its brand of Polyetheretherketone. Victrex plc is the sole manufacturer and supplier of the Victrex® PEEK™ brand polymer world-wide. PEEK™ is a trademark of Victrex plc.