A water storage tank is being welded in accordance with AWWA Standard D100. The base metal temperature is 30 degrees F. Welding of the tank or structural attachments can be performs when the base metal is preheated to at least what temperature?

A water storage tank is being welded in accordance with AWWA Standard D100. The base metal temperature is 30 degrees F. Welding of the tank or structural attachments can be performs when the base metal is preheated to at least what temperature?