Water Corrosion

Module Eight of CCE 281 Corrosion: Impact, Principles, and Practical Solutions

Lesson Objectives

• Review the types of water used in service

• Discuss water constituents in relation to the corrosivity of water

• Describe the impact of water pH on steel and aluminum

• Summarize the various scaling indices used to characterize water corrosivity

Required Reading

This Module consists of four Web pages of required reading. The pagination is visible at the bottom of each page with direct links to adjacent pages.

Additional information can be found in sections 8.1 to 8.7 of the reference textbook (Corrosion Engineering: Principles and Practice).

Water Corrosivity

A major use of water in industry is the transfer of heat and the production of steam. There is extensive use of cooling water in almost every manufacturing process, in commercial air conditioning, and even a substantial percentage in domestic air conditioning. Water is used in the passive sense for potable and for fire control purposes. Fossil and nuclear fuel steam plants are encountered in the heating and power generating fields.

According to the American Waterworks Association (AWWA) industry database, there is approximately 1,483,000 km of municipal water piping in the United States. This number is not exact, since most water utilities do not have complete records of their piping system. The sewer system consists of approximately 16,400 publicly owned treatment facilities releasing some 155 million meter cube of wastewater per day (1995). The total annual direct cost of corrosion for the nation’s drinking water and sewer systems was estimated at $36.0 billion. This cost was contributed to by the cost of replacing aging infrastructure, the cost of unaccounted-for water through leaks, the cost of corrosion inhibitors, the cost of internal mortar linings, and the cost of external coatings and cathodic protection.

Water can be corrosive to most metals. Pure water, without dissolved gases (e.g., oxygen, carbon dioxide, and sulfur dioxide) does not cause undue corrosion attack on most metals and alloys at temperatures up to at least the boiling point of water. Even at temperatures of about 450^oC, almost all of the common structural metals, except magnesium and aluminum, possess adequate corrosion resistance to high-purity water and steam. In summary, the factors influencing the corrosion of materials in water systems are:

1. Physical configuration of the system;

2. Chemistry of the water (hardness salts, chlorides, and dissolved gases being the most important);

3. Presence of solids in the water;

4. Flow rate;

5. Temperature of the water;

6. Presence of bacteria.

Information Module

• Introduction

• Water Constituents

• Types of Water

• Scaling Indices

See also CCE 513: Corrosion Engineering