Page 197 - Challenges in Corrosion Costs Causes Consequences and Control(2015)

PETROLEUM REFINING 175

3.24.1 Areas of Major Corrosion Impact
A refinery operation may have more than 3000 processing vessels of various size,
shape, form, and function. A typical refinery has about 3200 km (2000 miles) of
pipeline, much of which is inaccessible. Some of these pipelines are horizontal, some
are vertical; some are 200 ft high and some are buried under cement, soil, mud, and
water. The diameters range from 10 to 76 cm (4–30 in.).

3.24.2 Water-Related Corrosion
Crude oil desalting and distillation generates a considerable amount of wastewater.
Typical wastewater flow from a desalter is approximately 8 l (2.1 gal) of water per
barrel of oil processed. This water contains accelerative corrosive agents such as H S,
2
CO , chlorides, and large amounts of dissolved solids. The wastewater also contains
2
some crude oil that is recovered during water treatment process.
In addition to generated wastewater, cooling water (either freshwater or salt water)
is used extensively in refining operations. The corrosivity of the cooling water varies
considerably depending on the process. Thus, it is difficult to describe cooling water
problems; however, corrosivity is highly dependent on the level and type of dissolved
solids and gases in the cooling water, including chlorides, oxygen, dissolved gases,
and microbes. The temperature of cooling water can also affect the corrosivity.

3.24.3 Processing-Related Corrosion
The top section of a crude unit can be subjected to a variety of corrosive agents.
Hydrochloric acid formed from the hydrolysis of calcium and magnesium salts is the
principal strong acid responsible for corrosion in the crude unit top section. Carbon
dioxide is released from crudes typically produced in CO -flooded fields and crudes
2
that contain large amounts of naphthenic acid.
Acids such as formic, acetic, propionic, and butanoic are released from crudes
with a high amount of naphthenic acid. Hydrogen sulfide, released from sour crudes,
significantly increases the corrosion of the crude unit top section. Both sulfuric and
sulfurous acids formed by either oxidation of hydrogen sulfide or direct condensation
of SO and SO increase corrosion.
3
2
3.24.4 Naphthenic Acid Corrosion
The high-temperature crude corrosivity of distillation units is a major problem in the
refining industry. The presence of naphthenic acid and sulfur compounds increases
corrosion in the high-temperature parts of the distillation units and hence equipment
failure became a critical safety and reliability issue. Most of the acids have the formula
R(CH ) COOH, where R stands for the cyclopentane ring and n is greater than 12.
2 n
In addition to R(CH ) COOH, a host of other acidic organic compounds are also
2 n
present.