A customized AP 10 helps Tepco solve a unique problem in Japan

Tepco (Tokyo Electric Power Company – Tepco Power Grid, Incorporated) is Japan’s largest electric utility company, serving the Kanto region (Tokyo and its six prefectures).

One part of Japan was running the risk of being without electricity and Tepco had to step up to face a problem regarding thousands of high voltage towers.

Several towers made with zinc-coated steel pipes supporting high voltage power lines (up to 500,000 V), some exceeding 100 meters in height, were beginning to feel the effects of the island’s saline climate and potential manufacturing defects. The pipers were corroding, the structure of the tower becoming compromised. Replacing the towers would be a difficult task, not only due to the high cost, but because it would mean leaving part of Japan without electricity, causing harm to people and businesses.

Due to Japan’s particular climate, the pipes can only be filled from April to July (each tower can take up to one week to fill), months when there are no typhoons and the temperature cannot affect the process.

Polyurethane is best processed at 25°C and, if the external temperature varies excessively from this value, the foam would not meet the customer’s requirements.

External corrosion is treatable using a special anti-rust paint. But the inside of the tubes, also affected by this oxidation, cannot be easily painted. One other repair method, however, solves both the corrosion and structural dilemmas: the pipes can be filled with polyurethane foam that leaves no gaps. The towers were filled with mortar in the lower portion. In the upper portion, to keep the weight down, our AP10 dispensed a closed-cell polyurethane foam blend ten times lighter than the mortar to fill and reinforce.

To meet the customer’s particular requests, and with the support of Nippon Cannon, we created a dedicated version of the AP 10 dosing unit for cavity filling. Its design, already simple in its standard configuration, was lightened and condensed to facilitate its being lifted to the top of the tower: the machine, small (850x850x1500mm), mounted and anchored on an aluminum skid and without protrusions, means it can easily pass through even the towers’ narrowest section.

An auxiliary unit, developed by Nippon Cannon, was added to supply the dosing unit with the cooling water (via chiller), compressed air and hydraulic oil necessary for the mixing head.

The machine can heat up water, thanks to electric heating cartridges installed in the heat exchangers, completing the much needed temperature control system.

To achieve the required polyurethane foam quality, the machine is equipped with a temperature control system for the chemicals and it works with an ambient temperature between 23 and 35°C (the average temperature in the Kanto region between April and July).

Having to work outdoors, the dosing unit is designed to resist humidity: the external parts are painted with a special protective paint for outdoor use, while the electrical panel is IP54 certified, meaning it is protected from dust and water splashes from any direction. To deal with sunlight, the user interface features a high-contrast design to remain clearly visible.

In this special configuration, the AP 10 can easily be transported by helicopter to inaccessible and/or mountainous areas.
Read more about the project below.

To face the corrosion problem, Tepco, in partnership with Nitto Chemicals, SKYTECH (the company that manages power line maintenance) and TLC (who manages the electricity networks), relied on our expertise to develop the best possible suitable solution. The project was organized in four phases:

Phase 1 – Preliminary feasibility study
The working conditions were analyzed and possible solutions were examined, beginning with the foam’s properties, set up by Nitto Chemicals.

Phase 2 – Tests for development
Nitto Chemicals acquired an AP 10 from us, one of the most compact and versatile high-pressure dosing machines available. Simulations of foaming in loose pipes and in a mockup of the tower were carried out, checking resistance to aging and adhesion to metal surfaces.

Phase 3 – Definition of the specifications
Tepco defined the high-pressure machine’s specifications for the tower recovery, based on the results obtained and experience gained during phase 2, information which we then used to create the customized AP 10.

Phase 4 – Supply of “production” machines
To carry out interventions on the towers simultaneously: the foam machines are hoisted to top, where they remain for the entire duration (up to one week), suspended, while teams of highly specialized technicians drill a hole at the base of each section of pipe to be foamed, and inject polyurethane.