Page 282 - Challenges in Corrosion Costs Causes Consequences and Control(2015)

260 CORROSION CONTROL AND PREVENTION

because of its low water content. The proposed design for waste disposal is for steel
canisters containing the nuclear waste to be stored within other steel canisters and
buried horizontally in chambers 300 m below the earth’s surface. The canisters are
designed to last 1000 years and will depend on the mountain itself to provide a
natural barrier to survive the minimum 10,000 years required by the government.
However, there is no guarantee that the canisters at Yucca Mountain will be free
from water flow for 10,000 years.
The total repository costs for radioactive waste in Yucca Mountain by construction
phase and the cost of nuclear waste packaging fabrication for permanent storage have
been documented (39) by the US DOE.

4.15 CORROSION CONTROL OF STORAGE TANKS

Corrosion of tank bottoms, walls, roofs and roof structures can pose dangers to their
structural integrity. Corrosion may cause leaks that result in loss of product or pol-
lution of the soil and water around a tank. Leaks can result in water penetrating into
the tank and contaminating the product.
Corrosion control and prevention can take many forms. It may take the form of a
design detail, such as the application of corrosion allowance to sophisticated lining
systems and CP devices. The following most common methods of corrosion control
and prevention have been listed by Myers (40).
1. Linings (“bladder”) coatings (Paints)
2. Corrosion allowances
3. Design (avoidance of dissimilar metals, galvanic couples, improper materials,
high fluid velocities in inappropriate places, caulking or seal welding of areas
prone to crevice corrosion, roof design, etc.)
4. Sacrificial anodic systems
5. Impressed-current CP
6. Use of high-alloy (corrosion-resistant) materials. Tanks designed for materi-
als that produce corrosive vapors often include roof and roof support struc-
tures (pontoons for floating roofs) that are made of corrosion-resistant materials.
Petroleum tanks that are subject to a contaminated water layer are internally
coated and cathodically protected on the bottom and partially along the wall.
The external bottom corrosion of the site-fabricated tanks (4 m in diameter)
can be controlled with a combination of select sand/concrete foundation pads,
impervious liners, and CP. The following is a list of corrosion control methods
for aboveground storage tanks. A list of corrosion control methods for above-
ground storage tanks (AST) is given in Table 4.27.

4.15.1 Aboveground Storage Tanks – Internal Coatings
Internal coatings protect the structural integrity of the tank by preventing internal
corrosion. These coatings have a design life of 10 years or more for larger tanks.