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Manhole covers are not just covers in Japan

by Floro Mercene

Even though customized manhole covers cost more than generic ones, today nearly 95 percent of the 1,780 municipalities in Japan have their very own specially designed manhole covers in strategic places.

Japanese manhole covers come in many shapes, colors and sizes, and they are full-blown pieces of art. Scanning streets for a colorful and delightful array of manhole covers has become popular pastime – “drainspotting”.

However, colored covers account for less than 1% of the total number, and many are simple black disks that unobtrusively support the Japanese water network. It is also worth considering the technical skill that makes this essential infrastructure quiet, safe, and effective.

All Japan’s manhole covers rarely become detached. The sudden downpours, especially in summer, flood the streets, and columns of water spout from manholes. This shows the manhole cover is functioning correctly. Heavy rains can cause pressure in underground pipes to increase to abnormal levels. The covers are designed to rise one or two centimeters, allowing air and water to escape, and then return to their former position as the pressure falls. A manhole cover is made up of five interlinked parts.

Even in the rare cases when manhole cover detaches, the ladder section serves as a substitute barrier to prevent pedestrians traversing flooded roads from falling into open manholes. Covers tend to be heavy in many countries, but in Japan, they are light with the emphasis on their functionality. Around 70% of the material for cover is recycled scrap metal, often collected from local factories. High-quality scrap metal is melted in an electric furnace. Magnesium, sulfur, and other materials are added to create sturdy, durable ductile iron. All covers are coated in black paint to prevent rusting. The same electrocoating technique used for automobiles ensures an even finish.

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