On most aircraft, use of titanium was limited by the costs involved; it was generally used only in components exposed to the highest temperatures, such as exhaust fairings and the leading edges of wings. On the SR-71, titanium was used for 85% of the structure, with much of the rest polymer composite materials. To control costs, Lockheed used a more easily worked titanium alloy which softened at a lower temperature. The challenges posed led Lockheed to develop new fabrication methods, which have since been used in the manufacture of other aircraft. Lockheed found that washing welded titanium requires distilled water, as the chlorine present in tap water is corrosive; cadmium-plated tools could not be used, as they also caused corrosion. Metallurgical contamination was another problem; at one point, 80% of the delivered titanium for manufacture was rejected on these grounds.