North American steel producers including Ipsco Inc. filed petitions with US regulators alleging China is unfairly subsidizing and dumping steel products worth as much as US$500 million a year.

The petitions filed with the US International Trade Commission and Department of Justice requested the agencies impose duties on imports of welded standard pipe from China, the six North American producers said Thursday in a statement.

US import applications for steel produced outside of North America last month rose to 3.01 million net tons, which was 0.7 percent higher than the 2.99 million tons recorded in April, the Washington-based American Iron and Steel Institute said last week. Last year, US steel imports soared to a record 45 million tons as shipments from China more than doubled.

Chinese imports of circular standard and structural pipes have increased from 10,000 tons in 2002 to 690,000 tons in 2006, a 6,800 percent increase, the companies said. Along with Lisle, Illinois-based Ipsco, North America's second-largest maker of steel pipes for energy companies, the petitioners also include Allied Tube & Conduit, Northwest Pipe Co. and Western Tube and Conduit Corp.

The value of the allegedly dumped steel ranges from US$368 million to US$500 million a year, depending on the variety exported by China, Roger B. Schagrin, a Washington trade lawyer representing most of the petitioners, said in a telephone interview.

Wuhan Iron & Steel Co, China's third-biggest steelmaker by market value, said Friday allegations Chinese companies dumped products in the United States are "unfair."

"Chinese steel exports have soared because of higher global prices and demand," company secretary Zhao Hao said by phone from the company's headquarters in central Hubei Province.

"This is more of a political issue," said Luo Wei, an analyst at China International Capital Corp., the nation's biggest investment bank. "China has cut tax rebates and imposed taxes on steel exports this year, as part of measures to curb the trade surplus.''

"Most of the Chinese steel products are sold in China, and only a small proportion are sold overseas, so it's unfair for the United States to say China is dumping steel products," Zhao said.

China's Deputy Commerce Minister Jiang Zengwei declined to comment, saying the ministry will respond to the allegations at a press briefing Wednesday in Beijing.

Welded pipe is used in scaffolding, and water and gas pipes. More than 80 steelmakers in China produce it, including Handan Iron & Steel Co, Kunming Iron & Steel Group Co. and Guanzhou Iron & Steel Co, according to Beijing Antaike Information Development Co.

"Welded standard pipe is a specialized product, made by many small- and medium-sized steelmakers, so it won't have a big impact on the Chinese market," said China International's Luo.

Wuhan Steel won't be affected by the dumping allegations because it has reduced exports to the United States and increased shipments to regions such as South East Asia, Wuhan's Zhao said.

Baoshan Steel spokeswoman Chen Ying said the company's exports won't be affected as its production of welded pipe is "small," and a new plant hasn't started yet. Chen Xianwen, deputy director of market research at the China Iron & Steel Association, declined to comment.

Steel production in China more than tripled over the past six years to an estimated 470 million tons this year, according to CBI Research & Consulting in Shanghai. China's steel industry turns out more than the United States, Japan and Russia combined.