The Alliance for American Manufacturing (AAM) today cited serious welding problems at a China-based steel fabricator as an example of why American-made product should be utilized in domestic infrastructure products.  As American Metal Market Magazine has reported, significant welding problems at Zenhau Port Machine Co. (ZPMC), a steel fabricator in Shanghai, have halted shipments of Chinese-made steel intended for the eastern span of the San Francisco Bay Bridge.   AAM Executive Director Scott Paul commented:   "Timely and quality completion of the Bay Bridge is critical to the safety of Californians who have already experienced disaster first hand.  Yet, the decision to use Chinese steel is of real concern, with delayed shipments and reports of faulty engineering pushing the completion back by months.   "Subsidized Chinese products may be cheaper at the time of bid, but we have seen what happens when faulty engineering and manufacturing both threatens the safety of Americans and drives up the final cost to the taxpayer.    "When officials overseeing the project visit with Zenhau Port Machine Co. in Shanghai, they should demand that it produce steel on time and at the quality our taxpayers deserve.  If not, their contract should be voided.  There are plenty of domestic producers and workers who would be happy to provide high-quality, affordable American steel.   "We think this calls for further scrutiny from Congress and Federal transportation authorities."