IEEE Spectrum

Pipe-Protecting Technology Invented by Raychem Is the 200th IEEE Milestone

THE INSTITUTEWhen frozen pipes burst, they can cause extensive flooding damage, leading to costly repairs.

In 1972 Raychem, now part of nVent Thermal, began manufacturing a cable it invented that automatically adjusted the temperature around pipes based on their surface temperature.

The invention maintained a temperature, set by a thermostat, for as long as the cable was turned on. Today electric self-regulating trace heaters handle the vast majority of trace heating.

The device also helps to conserve energy, increases accuracy of the temperature maintained, and allows the temperature to be constantly monitored.

The electric self-regulating polymer trace heater was dedicated as an IEEE Milestone on 28 August at the nVent Thermal factory in Redwood City, Calif., where the cables first were manufactured. It became the 200th IEEE Milestone to be designated. The IEEE Santa Clara Valley (California) Section sponsored the Milestone.

“The Milestone commemorates the invention of a heating system that has a semi-infinite parallel array of resistances that continuously vary with the local ambient temperature,” IEEE Fellow Chet Sandberg told The Institute. “This technology is used in many commercial, consumer, and industrial applications today.”


The cable is housed in a plastic shell. Inside is a metal braid, plastic insulation, and a conductive core. The outer shell shields the cable against moisture, and the metal braiding removes excess electrical charge in the cable. The heart of the heater consists of parallel bus wires connected by a polymer matrix embedded with a conductive carbon black material such as coal tar. When the polymer warms, it expands, which separates the carbon paths and causes the resistance to increase. When it cools, the matrix contracts, lowering the resistance and allowing more current to flow through the device to create heat.

According to the Engineering and Technology History Wiki entry about the Milestone, the invention’s key electrical achievement was the development of a polymer matrix that returns to its original state when cooled. The process is able to repeat because the polymer is treated with radiation in order to crosslink it, creating a material with a structure that can rebound after expansion.

A plaque honoring the trace heater was mounted in the lobby of the nVent Thermal factory. It reads:

In 1972 Raychem Corp. patented and began producing the first commercially successful electric self-regulating heat-tracing cable. The conductive polymer in this cable revolutionized the temperature maintenance of process piping, which has had major applications in refineries and chemical plants, and made freeze protection of water pipes simple and energy-efficient. By 2008, the firm had manufactured and sold 1 billion feet of this cable.

This article was written with assistance from the IEEE History Center, which is funded by donations to the IEEE Foundation’s Realize the Full Potential of IEEE campaign.

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