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Thompson Lighting Protection Flangeguard

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Now insulated pipe flanges can be protected against arc-overs and gasket destruction easily and economically. The Thompson Flangeguard prevents the build-up of high-voltage charges without degrading the cathodic voltage isolation qualities of the flange. The protective characteristics of the Flangeguard have been confirmed by an accredited testing laboratory and field tested by major utilities at their most troublesome locations with 100% effectiveness.
  • Reduce downtime maintenance and replacement costs
  • Easily installed in minutes with simple hand tools
  • Economical
  • Weatherproof
The use of insulated flanges is common practice in the construction of gas distribution systems. Typically, such flanges are used between the supply line and the customer’s facility to prevent the cathodic corrosion protection voltage on the supply pipe from entering the customer’s system where it would otherwise find its way to ground. During periods of disturbed atmospheric conditions and nearby lightning strikes, strong earth currents and, thereby, voltage gradients are developed in the earth. Such gradients can easily result in a voltage potential difference of many thousands of volts between the supply pipe and the customer’s grounded system. This difference of potential appears across the insulated flange and often exceeds the breakdown voltage rating of the insulating material resulting in an arc-over and destruction of the gasket and insulating sleeves. To prevent the build-up of destructive charges, buried siamese diodes are commonly installed at insulated flanges. These devices work well but are expensive and require a considerable amount of labor to install. The desire to find a simpler, more economical way of protecting their flanges prompted one of the major utilities to commission Thompson Lightning Protection, Inc. to design an alternative protection system. The result was the development of the Flangeguard. At the conclusion of the Flangeguard development work, a quantity of the developmental models were installed by two major utilities at their most troublesome locations for testing. At the conclusion of this two and one half year test, which included three summer thunderstorm seasons, it was reported that not a single insulated flange had been damaged. Before committing themselves to a more extensive use of the arrester, however, they deemed it prudent to have the device tested by an accredited testing laboratory. This was done at their own expense and based upon the favorable laboratory report and the results of their own field testing, an order was placed for a large quantity of the arresters. In practice, the Flangeguard is placed across the insulated flange with connections to the pipe on each side as per the attached drawing. Under normal conditions the arrester is completely nonconductive and preserves the electrical insulation of the flange as required to isolate the low cathodic protection voltage. As the static voltage across the flange increases under the influence of disturbed atmospheric conditions, the electrical resistance of the Flangeguard automatically lowers, allowing the potential across the flange to equalize. Conduction through the arrester begins at just over 100 volts and its resistance approaches zero at about 300 volts. In effect, a Flangeguard protected flange appears as a perfect insulator at cathodic protection voltages but for the fraction of a second required to equalize high-voltage static charges, it becomes, effectively, a non-insulating flange. The device may be used either indoors or out. The active element of the Flangeguard is expected to accommodate in excess of 10,000 discharges, the equivalent of many years of service.