West Japan Railway Co. said Wednesday that a crack found in the undercarriage of an operating shinkansen bullet train in December is believed to have been caused by improper scraping of the steel component by Kawasaki Heavy Industries Ltd.
A probe by the railway operator has found that the steel frame of the undercarriage in question was 4.7 millimeters thick at its thinnest point, undershooting the minimum 7 mm required for the component, JR West President Tatsuo Kijima said at a press conference in Osaka.
According to Kawasaki Heavy, which separately held a press conference in Kobe, workers scraped off the bottom of the undercarriage frame to smooth the surface before welding work, even though scraping was prohibited in the production manual as it could weaken the product strength.
The railway operator said that of the 303 undercarriages it purchased from Kawasaki Heavy from 2007 to 2010, about 100 were thinner than required, and it will replace them to ensure safety.
The crack was found in the Nozomi No. 34 bullet train bound for Tokyo from Hakata on Dec. 11 in an incident that could have caused a derailment. JR West failed to halt the train promptly after an abnormal smell and noise was noticed, and suspended it around three hours into its journey at Nagoya Station.
The steel frame of the bullet train's undercarriage was close to breaking apart as the crack ran through the bottom of the frame that was 16 centimeters in length and ran as high as 14 cm on either side that was 17 cm in height.
The Japan Transport Safety Board regarded the crack as the first "serious incident" affecting the Japanese high-speed train system.
Kawasaki Heavy's improper production came to light after a number of Japanese manufacturers were recently mired in product quality scandals, including product data fabrication by Kobe Steel Ltd. and a subsidiary of fiber maker Toray Industries Inc.
The production of train cars is one of Kawasaki Heavy's mainstay operations, with the company having won a $3.7 billion deal earlier this year to build cars for the New York subway.
Central Japan Railway Co. said the same day that 46 of the 130 train undercarriages made by Kawasaki Heavy are found to use thinner-than-required steel components and that it will replace them by the end of this year.
"We deeply apologize for causing tremendous trouble and anxieties," Kawasaki Heavy President Yoshinori Kanehana said, adding that he would halve his salary for three months to take the blame. The company also said it will fully shoulder the costs for JR West and JR Central to replace their defective undercarriages.
JR West's Kijima urged manufacturers to rigorously check their production and quality, saying, "Manufacturers and train operators must work as one to ensure safety."
Bullet trains using thinner-than-required steel frames at their bottoms are some Nozomi trains running on the Tokaido and Sanyo Shinkansen lines.