VANCOUVER, Wash. (AP) ¿ Northwest Pipe Co. shares tumbled Thursday after the maker of welded steel pipes said it has delayed the release of its third-quarter financial results, but that it expects to post a $1 million loss. The Vancouver, Wash.-based company said the financial report for the three months ended Sept. 30 has been delayed "pending the conclusion of an ongoing internal investigation of certain accounting matters, including certain revenue recognition practices." The investigation is being conducted by the board of directors' audit committee and independent professionals, the company said. Northwest Pipe said it plans to publish the results "as soon as practicable" after the investigation and any further accounting work that may be needed. On a preliminary basis, however, Northwest Pipe estimated it lost $1 million, down from net income of $10.2 million during the same period a year earlier. Estimated revenue fell by nearly half to $67 million from $124.3 million in the third quarter of 2008. Analysts surveyed by Thomson Reuters, on average, had predicted a profit of 28 cents per share on revenue of $73.7 million. Wall Street estimates typically exclude one-time items.