What is the code for external cathodic protection of on-grade metallic storage tank bottoms?

The code for external cathodic protection of on-grade metallic storage tank bottoms is indeed RP0193. This recommended practice outlines the necessary considerations and methods for implementing cathodic protection systems specifically designed for externally buried or submerged metallic storage tanks.

The focus of RP0193 is to prevent corrosion of the tank bottoms due to external factors, primarily soil and moisture conditions that can lead to deterioration. The document offers guidance on system design, implementation, and maintenance to ensure adequate corrosion control for these types of structures.

In contrast, the other choices refer to different aspects of corrosion control and protection. For instance, SP0169 addresses the control of external corrosion on underground or submerged pipelines, which, while related to the broader field of corrosion prevention, does not focus specifically on storage tank bottoms. Similarly, SP0176 deals with protection methods for underwater piping that may not directly apply to on-grade storage tanks. SP0388 is more concerned with cathodic protection methods for offshore platforms.

Therefore, RP0193 is the relevant standard for the cathodic protection of on-grade metallic storage tank bottoms, emphasizing specific practices to protect these structures from corrosion effectively.