More than 60 people were killed when the Donghuang II oil pipeline, operated by China Petroleum & Chemical Corp., known also as Sinopec, exploded in eastern Shandong province.
The pipeline went into service in 1986. Sinopec published a statement saying corrosion weakened the walls of the pipeline, causing crude oil to leak into the municipal drainage system.
"After the leakage, rescue workers used hydraulic hammer[s] to break the concrete trench cover slab, and sparks ignited the vapor in the trench and caused an explosion," Sinopec said in a statement Monday.
Sinopec said it did not take full responsibility for safety at the site while provincial officials didn't identify the risks properly.
The company said the incident caused a direct economic loss of $123 million.
Chinese President Xi Jinping called for "large-scale safety check" following the incident.
The official Xinhua news agency reported Monday insurance funds would cover the damages.