Corrosion costs of the oil industry are billions of dollars in
a year. Corrosion affects every aspect of exploration and
production, from offshore rigs to casing. Methods of control
and techniques to monitor corrosion, along with an
explanation of the chemical causes of corrosion are
discussed.
Corrosion in petroleum industry
The Petroleum industry contains a wide variety of
corrosive environments. Some of these are unique to this
industry. Thus it is convenient to group all these
environments together. Corrosion problems occur in the
petroleum industry in at least three general areas:
(1)
production
(2) transportation and storage
(3) refinery
operations.
Production
Oil and gas fields consume a tremendous amount of iron
and steel pipe, tubing, pumps, valves, and sucker rods.
Leaks cause loss of oil and gas and also permit infiltration of
water and silt, thus increasing corrosion damage. Saline
water and sulphides are often present in oil and gas wells.
Corrosion in wells occurs inside and outside the casing.
Surface equipment is subject to atmospheric corrosion. In
secondary recovery operations, water is pumped into the
well to force up the oil.
Transportation and storage
Petroleum products are transported by tankers, pipelines,
railway tank cars, and tank trucks. The outside submerged
surfaces of tanks on the outside surface of underground
pipeline s are protected with coatings and by using cathodic
protection. Cathodic protection is also applied to the inside
of tankers to prevent corrosion by seawater used for washing
or ballast. Gasoline-carrying tankers present a more severe
internal corrosion problem than oil tanks because the
gasoline keeps the metal too clean. Oil leaves a film that
affords some protection. Tank cars and tank trucks are
coated on the outside for atmospheric corrosion.
The main reason for internal corrosion of storage tanks is
the presence of water which settles and remains on the
bottom. Coatings and cathodic protection are used. Alkaline
sodium chromate (or sodium nitrate) has been found to be
an effective inhibitor for corrosion of domestic fuel oil tanks.
Internal corrosion of product pipelines can be controlled
with coatings and inhibitors (a few parts per million) such as
amines and nitrites. Ingenious methods for coating pipelines
in place underground have also been developed.
Refinery operations
Most of the corrosion difficulties in refineries are due to
inorganics such as water, H2S, CO2, sulfuric acid, and
sodium chloride, and not to the organics themselves. For this
reason, the petroleum industry has much in common with
the chemical industry.
Corrosive agents may be classified into two general
categories: (1) those present in feedstock or crude oil, and
(2) those associated with processes or control.
Water is usually present in crude oils, and complete
removal is difficult. Water acts as an electrolyte and causes corrosion. It also tends to hydrolyze other materials,
particularly chlorides, and thus forms an acidic environment.
Source:file:///C:/Users/HQ0201/Downloads/1334-4359-1-PB%20santhana%20petroleum.pdf
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