Concerns are growing over the safety of Seoul Subway Line No. 3 after multiple cracks that could cause derailment were detected in train parts.

According to Seoul Metro, operator of Line 3, and the labor union at the company, up to 70 cracks were found in most of the train cars’ bogie frames, which hold the wheels in place. The discovery was made during a safety checkup last month by a state-run agency.

Cracks were found in 42 of the 59 train cars studied. However, the subway operator discarded only one train car and put the rest back into normal operation, the labor union claimed Monday.

Engineers at the company said they were forced to solder cracks and claimed that such work was only useful as a stopgap measure. The trains could derail if the cracks started to affect other parts of the trains, the union said.

Officials at the Seoul Metro refuted the union’s claim, saying that cracks won’t cause further damage to trains and were not a safety risk.

The train cars that are being used with cracks detected were manufactured between 1991 and 1992.

By Cho Chung-un (christory@heraldcorp.com)