The Justice Department is trying to kill part of a South Korean manufacturer’s legal challenge to U.S. antidumping rates on welded line pipe.

Part of Husteel Co.'s case against the duty rates should be dismissed, the department argued to the Court of International Trade Dec. 4.

Welded line pipe is used to transmit oil or gas, generally in pipeline or utility distribution systems. The U.S. imported about $543.6 million worth of it from South Korea in 2014, before antidumping duties...