This recommended practice presents guidelines for preparing for, recovering from, and repassivation after a low pH excursion, no matter what the cause. The procedures presented in this recommended practice in no way preclude the use of other procedures but are presented as a consensus of experience gained over the years in a variety of plants. The provisions of this recommended practice should be applied under the direction of qualified water treatment personnel from water treatment suppliers and/or consultants and plant personnel. This recommended practice was prepared by Task Group T-7A-15, composed of representatives from the refining, petrochemical, chemical, and water treatment industries; T-7A-15 is a component of Unit Committee T-7A on Cooling Water. This standard is published by NACE under the auspices of Group Committee T-7 on Corrosion by Waters.

 The discussions and procedures in this document are applicable to mild steel. They need to be modified for systems that contain copper-based alloys, stainless steel, other metals, and other materials of construction. Low pH excursions are perhaps the most devastating of all cooling water system upsets. The inadvertent reduction in pH because of acid overfeed, process leaks, or airborne acid gases can result in a number of serious problems….