PREHEAT IS NOT usually required or recommended However, if the base metal heating to about 60 oF (16 oC) or above avoids condense moisture that could cause weld porosity. A few specialized applica tions do use preheat, such as surfacing valve seats using the oxyacetylene welding process. Preheat is not neces sarily detrimental, but grain growth will occur cold worked base metal is brought above its recrystallizati temperature most cases, the interpass and preheat temperatures should be kept low to avoid overheating the base meta A maximum temperature of 200 oF (90 oC) i mended for some corrosion-resistant all oys. Cooling