The utility company Tepco has chosen Cannon for the maintain of power line towers through an advanced polyurethane foam injection process
The customer and the problem to be faced
A part of Japan is running the risk of being without electricity.
Several towers supporting high voltage power lines (up to 500,000 V) are built in steel pipes, zinc coated. Some of them exceed 100 m in height. The saline climate of the island or the manufacturing defect, in fact, is corroding the pipes, weakening the structure of the towers in a critical way.
At the moment, the replacement of the towers is still a hard work: not only due to the high cost of each tower, but also because to replace them it would be necessary to leave without electricity a part of the country, with enormous damage for people and activities.
For this reason, Tepco (Tokyo Electric Power Company – Tepco Power Grid, Incorporated), the largest Japanese electric utility company, which serves the Kanto region (Tokyo and its six prefectures), is facing the problem, which interests thousands high voltage towers.
The external corrosion is treated with a special anti-rust paint. But the inside of the tubes, also affected by this oxidation phenomenon, cannot be easily painted. As one of the repairs method other than painting, pipes can be filled with polyurethane foam without gaps, in order to eliminate the corrosion problem and, at the same time, reinforce the structure. Towers are being filled with mortar in the lower part and polyurethane foam (closed cells, with a specific density, ten times lighter than mortar) for the top, so as not to make it too heavy.
Due to the particular climatic conditions of the island, the filling of the pipes (which can last even a week for each tower) can only be done from April to July, months during which there are no typhoons and the temperature cannot impact on the process: polyurethane is best processed at 25 ° C and, if the external temperature varies excessively from this value, the foam will not result of the quality required by the customer.
Another problem is the impossibility of controlling the temperature of the metal structure in which the polyurethane is injected: if it is too low, the chemical reaction would not proceed correctly. That’s why this kind of intervention cannot be done in the coldest months.
To face this problem of corrosion, Tepco, in partnership with Nitto Chemicals, SKYTECH (the company that manages the maintenance of the power lines) and TLC (that manages the electricity networks), relied on Cannon (Nippon Cannon, the Japanese branch of the Cannon group, and Cannon Afros SpA, Cannon’s polyurethane machinery manufacturer) to develop the most suitable solution to the problem.
The project was organized in four phases:
Phase 1 – Preliminary feasibility study
In this first phase the working conditions were analysed and the possible solutions were examined, starting from the properties of the polyurethane foam, set up by Nitto Chemicals.
Phase 2 – Tests for the development
Purchase of a high pressure dosing unit for polyurethane process tests, simulations of foaming in loose pipes and in a mock up of tower, resistance to aging and adhesion to metal surfaces. At the end of 2013 Nitto Chemicals purchased from Cannon one of the most compact and versatile high pressure dosing machine on the market: AP 10.
The machine was started in the spring of 2014 to do laboratory tests and field simulations. Tepco, Nitto Chemicals and Cannon have therefore developed the ideal configuration for their own purposes.
Phase 3 – Definition of the specifications
Tepco has defined the specifications of the high-pressure machine to be used for the tower recovery, basing on the results obtained and the experience gained during the previous phase. On these specifications, Cannon Afros has created a bespoke version of the AP10 dosing machine (see below).
Phase 4 – Supply of “production” machines
To make simultaneous interventions on the towers: the foam machines are hoisted to top of the towers, where they remain for the entire duration of the intervention, suspended, while teams of highly specialized acrobatic technicians will drill a hole at the base of each section of pipe to be foamed, and inject polyurethane.
Cannon’s solution: a customized high-pressure dosing unit
To meet the customer’s particular requests, Cannon Afros, with the support of Nippon Cannon, has created a dedicated version of its AP10 dosing machine.
Layout of the dosing machine
The design, already quite simple in the standard configuration, has been lightened and compacted to make the raising operation up to the top of the tower easier: the machine is, in fact, made of an aluminium skid and its dimensions are a tiny 850x850x1500mm, in order to easily pass through even the narrowest section of the tower.
The layout has been designed so that it does not present any protrusion that can hinder both the lifting and the work of technicians. This also prevents the operator from interacting inappropriately with the dosing machine.
An auxiliary unit, developed by Nippon Cannon, was added to the dosing unit to supply the machine with cooling water, compressed air and hydraulic oil for operation of the polyurethane foam mixing head . To cope with operational needs, this unit is anchored to the machine base, forming a whole unit in two levels.
Features of the dosing machine
To achieve the required polyurethane foam quality, the machine is equipped with a temperature control system for the chemicals and it can work with an ambient temperature between 23 and 35 ° C (the average temperature in the Tokyo area between April and July).
Cold water is supplied to high pressure heat exchangers by a chiller, installed on board the auxiliary unit. The machine can heat up water too, thanks to electric heating cartridges installed in the heat exchangers, thus completing the temperature control system.
Having to work outdoor, the dosing machine is designed to resist to humidity: the external parts are painted with a special protective paint for outdoor use, while the electrical panel is IP54 certified, so it is protected from dust and splashes of water coming from any direction.
In addition, Cannon provided a waterproof blanket to cover the dosing unit in case of sudden worsening of the weather conditions, as well as during the night.
Finally, the user interface of the control panel has also been designed to have a high contrast, in order to be clearly visible under the sunlight.
In this special configuration, the AP 10 dosing unit can also be airborne by helicopter to inaccessible and / or mountainous areas.
Thanks to this technology, the proper chemical system and the special foaming machine, utility companies can solve the serious problem of oxidation that affects electric power lines.
Cannon develops completely customized solutions, contributing to the development of innovative ideas and matching all needs and particular requirements of new processes.