The Equipment Design Process
363
Reduction of sulfur content of residual fuel oil
•
Pretreatment of catalytic cracking feeds and crude oils by removal of
•
metals, sulfur, and nitrogen
Desulfurization of distillate fuels
•
11.3.3.3 Water Treatment and Supply Systems
There are several ways to reduce or inhibit corrosion that are within the
capabilities of most water utilities. This section describes several methods
most commonly used to control corrosion. However, the utility operator
must select the best and most economical. These methods include:
1. Modify the water quality
a. pH adjustment
b. Reduce/remove oxygen
2. Linings, coatings, and paints
3. Proper selection of system materials and adequate system design
4. Use of inhibitors
5. Cathodic protection
Modify the water quality. In many cases, especially in existing plants, the
easiest and most practical way to make water less corrosive is to modify the
water quality at the treatment plant. Because of the differences among raw
water sources, the effectiveness of any water quality modification technique
will vary from one water source to another. However, where applicable,
water quality changes can often result in an economical method of corrosion
control. Common methods of modifying water quality include pH adjustment, pH control, and reducing oxygen.
pH adjustment is the most common method of reducing corrosion in water
distribution systems. Control of the pH plays a critical role in corrosion control of water systems for the following reasons:
Acid waters are generally corrosive. Waters with pH below 6.5 gen•
erally cause uniform corrosion of the materials. In the pH range
between 6.5 and 8, the attack is more likely to be pitting.
pH is the major factor that determines the solubility of most pipe
•
materials. Most materials used in water distribution systems (copper, zinc, lead, cement) dissolve readily at a lower pH.
The relationship between pH and other water quality parameters,
•
such as alkalinity, carbon dioxide, and total dissolved solids (TDS),
governs the solubility of calcium carbonate, which is commonly
used to provide a protective scale on interior pipe surfaces. To
363
Reduction of sulfur content of residual fuel oil
•
Pretreatment of catalytic cracking feeds and crude oils by removal of
•
metals, sulfur, and nitrogen
Desulfurization of distillate fuels
•
11.3.3.3 Water Treatment and Supply Systems
There are several ways to reduce or inhibit corrosion that are within the
capabilities of most water utilities. This section describes several methods
most commonly used to control corrosion. However, the utility operator
must select the best and most economical. These methods include:
1. Modify the water quality
a. pH adjustment
b. Reduce/remove oxygen
2. Linings, coatings, and paints
3. Proper selection of system materials and adequate system design
4. Use of inhibitors
5. Cathodic protection
Modify the water quality. In many cases, especially in existing plants, the
easiest and most practical way to make water less corrosive is to modify the
water quality at the treatment plant. Because of the differences among raw
water sources, the effectiveness of any water quality modification technique
will vary from one water source to another. However, where applicable,
water quality changes can often result in an economical method of corrosion
control. Common methods of modifying water quality include pH adjustment, pH control, and reducing oxygen.
pH adjustment is the most common method of reducing corrosion in water
distribution systems. Control of the pH plays a critical role in corrosion control of water systems for the following reasons:
Acid waters are generally corrosive. Waters with pH below 6.5 gen•
erally cause uniform corrosion of the materials. In the pH range
between 6.5 and 8, the attack is more likely to be pitting.
pH is the major factor that determines the solubility of most pipe
•
materials. Most materials used in water distribution systems (copper, zinc, lead, cement) dissolve readily at a lower pH.
The relationship between pH and other water quality parameters,
•
such as alkalinity, carbon dioxide, and total dissolved solids (TDS),
governs the solubility of calcium carbonate, which is commonly
used to provide a protective scale on interior pipe surfaces. To