MINISTRY OF SCIENCE AND TECHNOLOGY
DEPARTMENT OF
TECHNICAL AND VOCATIONAL EDUCATION
Sample Questions & Worked Out Examples
For
PE-04036
TRANSPORTATION OF OIL AND GAS
B.Tech(Second Year)
Petroleum Engineering
17
Ministry of Science and Technology
Department of Technical and Vocational Education
Petroleum Engineering
Sample Questions for
PE 04036 TRANSPORTATION OF OIL AND GAS
Chapter 1 Petroleum Pipeline Construction
1.*
Describe separate operations of pipeline construction.
( 5 marks )
2.** Discuss Project specification of pipeline construction.
( 20 marks )
3.*** Explain the clearing the right of way of pipeline construction.
( 5 marks )
4.*** Describe the clearing the right of way of pipeline construction.
( 10 marks )
5.** Explain grading of pipeline construction.
( 5 marks )
6.** Describe grading of pipeline construction. ( 10 marks )
7.*
Explain hauling and stringing pipe of pipeline construction.
( 5 marks )
8.*
Describe hauling and stringing pipe of pipeline construction.
( 10 marks )
9.*
Explain Ditching of pipeline construction. ( 5 marks )
10.* Describe Ditching of pipeline construction. ( 10 marks )
11.** Explain pipe bending of pipeline construction.
( 5 marks )
12.** Describe pipe bending of pipeline construction.
( 10 marks )
13.* Explain pipe laying of pipeline construction.
( 5 marks )
14.* Describe pipe laying of pipeline construction.
(10 marks )
15.* Explain welding of pipeline construction.
( 5 marks )
16.** Describe welding of pipeline construction. ( 10 marks )
17.*** Explain cleaning and coating the pipe of pipeline construction.
( 5 marks )
18.*** Describe cleaning and coating the pipe of pipeline construction. ( 5 marks )
19.* Explain backfilling of pipeline construction.
( 5 marks )
20.* Describe backfilling of pipeline construction.
( 10 marks )
21.** Explain cleanup of the right of way of pipeline construction.
( 5 marks )
22.** Describe cleanup of the right of way of pipeline construction.
( 10 marks )
23.** Explain testing and internal cleaning of pipeline construction.
(5 marks )
24.** Describe testing and internal cleaning of pipeline construction.
(10 marks )
25.* Explain manual inspection of pipeline construction.
( 8 marks )
26.*** Describe technical inspection of pipeline construction.
( 5 marks )
27.*** Explain manual inspection and technical inspection of pipeline construction. ( 10 marks )
Chapter 2 Submarine Pipeline Construction
28.*
29.*
30.*
31.**
32.*
Describe classification of submarine pipeline construction. ( 5 marks )
Discuss terrain problems of submarine pipeline construction.
( 16 marks )
Discuss construction method of submarine pipeline construction. ( 16 marks )
Explain river crossing of submarine pipeline construction.
( 8 marks )
Describe marsh, swamps, bays, and lakes crossing of submarine pipeline construction.
( 8 marks )
33.** Write about laying pipe offshore of submarine pipeline construction.
( 8 marks )
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Chapter 3 Control of Internal Corrosion of Pipelines
34.* Explain causes of internal corrosion. ( 8 marks )
35.** Describe methods of control of internal corrosion. ( 20 marks )
36.*** Write about dehydration process for removing water.
(10 marks )
37.** Explain water soluble inhibitors.
( 10 marks )
38.*** Describe oil soluble inhibitors.
( 8 marks )
Chapter 4 Control of External Pipeline Corrosion
39.*
Describe corrosion losses and cost of preventive measures for control of external pipeline
corrosion.
( 8 marks )
40.** Explain mechanisms of underground corrosion.
( 6 marks )
41.*** Describe basic methods of combating corrosion.
( 5 marks )
42.* Write about coating for control of external pipeline corrosion.
( 10 marks )
43.* Discuss the application of cathodic protection.
( 10 marks )
44.** Explain criteria for cathodic protection.
( 10 marks )
Chapter 5 Transportation of Petroleum
45.* Explain transportation of petroleum by tankers.
( 10 marks )
46.** Describe tanker cargo risks. ( 16 marks )
47.*** Write about tank truck equipment. ( 16 marks )
48.* Describe classification of tanks.
( 10 marks )
49.* Explain requirements for flammable liquid tanks. ( 10 marks )
50.* Describe requirements for compressed-gas ( LP-Gas) Tanks.
* = Must know, ** = Should know, *** = Could know
( 10 marks )
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Ministry of Science and Technology
Department of Technical and Vocational Education
Petroleum Engineering
Worked Out Examples for
PE 04036 TRANSPORTATION OF OIL AND GAS
1. Explain manual inspection of pipeline construction.
Manual Inspection
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
Ensure proper maintenance of fence gaps, drainage, livestock crossing, and
landowner’s interests.
Inspect the handling of pipe and materials.
Check the depth and condition of the ditch.
Check pipe bends for gouges, scratches, or excessive distortion to the pipe.
Visually inspect welding for appearance or obvious defects.
Determine that the proper standards of cleanliness and uniformity are maintained in
the cleaning and priming operation.
Inspect the pipe coating application for uniformity, thickness, and the repair of defects.
Ensure that the lowering-in operation conforms to the specifications with regard to
care in handling pipe, allowance for slack, depth of cover, and quality of tie-in welds.
Check the backfilling to determine that no damage is done to the pipe or coating;
instruct as to location of breakers.
Inspect the cleanup for restoration of ground conditions, rebuilding of fences, removal
of debris, and instruct as to terracing.
Inspect installation of spacers, seals, and vents at cased crossings.
Check and maintain records of the installation of weights, anchors, and test lead
location.
3. Describe technical inspection of pipeline construction.
Technical Inspection
1.
2.
3.
4.
5.
6.
7.
Physical tests for examination of welding, including tensile, bend, and nick break tests.
X-ray inspection of welds, Examination by X-ray is the most frequently used and the most
reliable nondestructive test.
Pipe-coating inspection by Holiday detector, a high-voltage electrical instrument which
measures conductivity or respectively of the coating application and indicates defective areas.
Coating inspection by Peason detector; somewhat similar in principle to the Holiday detector
except that the instrument measures variation in current leakage paths through soil and pipe
coating and indicates defective coating areas after the pipeline has been lowered-in and
backfilled.
Gages for the measuring and checking of pipe dimensions, coating thickness, pressures, and
similar applications.
Temperature controls and recorders for the regulation of coating material heating.
pressure tests by the use of air, water, or gas pressure for the internal testing of completed
sections of pipeline or sections located in critical areas.
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4. Discuss terrain problems of submarine pipeline construction.
Terrain Problems Vary Widely
Access
The installation of submarine pipeline presents many difficulties not encountered in land
construction, not the least of which is the problem of access. The river crossing contractor has no
more difficulty in getting his equipment to the site of operations than the main-line contractor.
However, the nature of the site is such the contractor must provide the means for transporting his
men and equipment along the work and from bank to bank. This may be done by using boats and
barges, installing a ferry system, erecting a temporary bridge, or by creating a combination rampleave out of spoil material removed in excavating the trench. The movement of specialized
construction equipment, such as barges, boats, and dredges may present problems because of
obstructions in the stream above or below the site, such as dams, bridges with low clearance, or
lack of floatation. Rapid currents may present hazards not found in land construction.
Construction of pipelines in marshes, swamps, bays, and lakes is handicapped by the lack
of roads. It must depend on water transportation for crews, equipment, materials, and supplies.
This results in exposure to costly delays and added expense in providing sufficient floatation to
accommodate the equipment, and in some instances, providing canals and channels.
Special equipment and methods must be developed to meet the challenge of crossing
under existing pipelines in an area where no water route exists and where the ground will not
support conventional equipment.
Submarine pipelines constructed in offshore areas must contend with many of the
problems of construction in marsh or swamp in addition to problems peculiar to the individual
offshore case. Navigable outlets to open water are limited, and thus the work site becomes even
more remote from the base of operations. Transportation in the open water is dependent on
navigation by compass or by navigation aids which must be established by the contractor.
Progress of the work and the continuity of materials and supplies may be threatened by high
winds and waves.
Right-of-way
Clearing and grading operations on river crossings are essentially the same as required for
main-line construction on land. Clearing the right-of-way and disposal of the timber on pipelines
constructed through the swamp present a problem where the spoil will not support equipment and
where there is standing water. While clearing is no problem on pipelines constructed through the
marsh, it is sometimes necessary to excavate and backfill areas to provide working space and
flotation for the lay barges.
Trenching
Trenching operations on all types of submarine pipelines are handicapped by lack of
adequate information as to the nature of the material to be excavated. The contractor must
frequently rely on knowledge acquired through previous work in the area. A visual inspection is
of little value, since the work site is usually covered with muddy water to a depth of several feet.
Core information is costly because of the special equipment required, such as boats, barges, and
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casing, to permit recovery of samples underwater, and the delays inherent in water work. Some
success is being attained with the use of seismic equipment correlated with test core holes.
Trenching in rivers is often complicated by the presence of quicksand. In swamps it is
difficult since the poor bearing value of the soil limits the size of equipment, and progress is
hampered by the presence of buried stumps and large logs. It is generally impossible to use wheeltype trenchers.
Trenching in the marshes must overcome the problems of handling semi-fluid materials
which make it difficult to maintain an open trench until the pipeline can be landed in it. This
requires that the spoil be placed a considerable distance back from the trench. Specialized
equipment must be devised capable of supporting itself on the water or on the treacherous silty
material.
Trenching for offshore pipelines requires equipment capable of providing from 3 to 10 ft
of cover in depths varying from zero at the shore line to 100 ft or more, while exposed to the
vertical movements of waves and the horizontal forces of wind and tide.
Operation of Construction Crews
Submarine crossings of rivers require that the crews be organized so they are capable of
working on either land or water.
Progress of marsh and swamp submarine pipelines is subject to interruption when the
crews are delayed or lost because of fogs or when sustained winds lower the water elevation,
grounding crew boats and supply barges. Because of the slowness of water transportation and the
generally circuitous route, it is often necessary to establish floating quarters adjacent to the rightof-way in order to avoid a high ratio of travel time for the crews. It is necessary to establish an
intermediate staging base for assembling and dispatching supplies, materials, and parts.
Operation of submarine pipeline construction crews offshore is handicapped by exposure
to high waves and hurricanes in some localities.
Buoyancy
The methods of laying submarine pipelines must take into account the net buoyancy of
the pipe, a factor not normally present in construction on land. The equipment must have the
capacity to handle the weight added to the pipe to overcome the buoyancy effect of the water in
which it lies. In the construction of oil pipelines, it may be necessary to provide the means to add
weight to the line during construction. In some instances, it may be necessary to add buoyancy.
Either of these operations and the necessity to add weighting material to the field weld joints
results in added personnel and equipment.
4. Discuss construction method of submarine pipeline construction.
Construction Methods Employed
River crossing
In excavating the trench for river crossings, the approaches of bank sections are usually
excavated simultaneously with conventional dirt-moving equipment, draglines, bulldozers, and
scraper pans where the volume of material justifies. Where the width, depth, and currents are not
excessive, the center section may be excavated by the “yo-yo” method in which the buckets of
draglines spotted on the banks are lashed together and pulled back and forth until the trench is
deep enough. Sometimes it is possible to dig the trench by ramping the equipment out into the
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channel on a levee formed of the excavated material. Large clamshell dredges mounted on spud
barges are suitable for crossings of medium width and depth, while very deep crossings of
considerable length are usually excavated by suction dredge. Quicksand conditions may require
well points or cofferdams. Jetting as a means of trenching on river crossings is seldom used.
In crossing of medium length the pipe is welded on one of the banks, either as a complete
unit or in sections, pressure tested, and then pulled into position by a cable stretched across the
stream to a pulling winch mounted on the opposite bank. The pipe may be “walked” into the
water by side booms or carried on dollies mounted on railway tracks. When necessary, the
negative buoyancy is reduced by attaching cylindrical pontoons which may be released from the
surface. On very wide and deep crossings, the contractor may install the pipe by use of a laying
barge, which is also equipped with a system of anchors. The pipe is welded into position one joint
at a time while the barge is moved ahead on its anchor system.
Marsh, Swamps, Bays, and Lakes Crossings
Two methods have been developed for the installation of pipelines in marsh and swamp:
the canal and the push-pull methods. These differ in the trenching method and in the means by
which the pipe is lowered into the trench. In other respects the two methods are similar. The pipe,
in double random lengths, is received direct from the mill at a central plant usually adjacent to
water transportation. Here the corrosion protection and weight coatings are applied, and the
coated pipes stored until the laying contractor is ready to receive them.
The coated pipe is transported to the right-of-way on deck cargo barges 30 by 100 by 6 ft
to 36 by 136 by 8 ft. Care must be taken not to overload the barges to the point they cannot pass
through the shallow waterways en route. On arrival at the work site, the pipe is unloaded from the
cargo barges onto the lay barge by a crane mounted on a separate “transfer” barge or on the lay
barge itself. The lay barge unit consists of from two to four 100-by 30-by 6 ft-6-in, barges pinconnected end to end to form a continuous working platform. Running the length of the connected
barges, and offset from one side, are a series of pipe supports equipped with rollers.
The lay barge is equipped with a side boom, welding machines, dope kettle, and weight
material mixer. The barges are also equipped with spuds and draw works.
Successive joints of pipe are lifted into position on the roller supports by the side boom
and the first welding passes made. Then either the pipe or the barge is moved to bring the newly
joined pipe ends to a position some 40 ft farther ahead, where the next welding pass is completed.
The pipe is then moved successively ahead until all welding has been completed, the joint Xrayed, and the protective and weight coatings applied. The pipe then enters the water.
The canal and push-pull lay methods differ primarily in the type of trench. The canal
method provides continuous water right-of-way with sufficient floatation to accommodate the lay
barge and cargo barges. A typical cross section of such a canal in marsh terrain. This canal is
usually excavated by a dipper dredge of from 2.5 to 7 cu yd capacity. The larger machines
excavate the floatation canal in one or two passes, depending on the type of material, and the
smaller machines follow behind digging the pipe trench.
In swamp terrain the crews, working out of pirogues where there is standing water, are
usually sent ahead of the dipper dredge to drop the trees. As the dredge comes through, it stacks
the timer to one side of the right-of-way. Depending on the conditions imposed by the landowner, the spoil from the canal excavation is either placed on top of the stacked timber or on the
opposite side of the right-of-way. In the latter case a minimum width of right-of-way of 125 to
150 ft is required. For most marsh conditions, a width of 100 ft is sufficient, but in extremely soft
or “coffee-ground” marsh, a width of 125 ft may be necessary.
After completion of the canal and pipe trench, the lay barge passes along, laying the pipe
as it goes. Movement down the canal is achieved by placing a cap over the forward end of the
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pipe connected by cable to a draw works. On completion of the work at each of the operation
stations, the spuds are raised and the cap cable drawn in, thus moving the barge ahead by pushing
on the completed pipeline already laid. When the barge has been moved one joint length, the
spuds are lowered, stopping the forward movement.
The push-pull method is used where the landowner will not permit the excavation of a
canal. In a swamp, the timber is dropped and stacked to one side, using cranes operating from
mats, and the ditch is excavated by dragline, blasting stumps where necessary. In a marsh, the
trench is excavated by draglines working on mats or by specially designed swamp buggy
draglines. The trench must be made deep enough to provide floatation for the pipe. The pipe is
usually laid from a train of barges similar to the lay barge previously described. In this case, since
the barge cannot move down the right-of –way, the spuds are left in the “down” position, and the
pipe is pushed off the barge and down the pipe trench. In order to reduce the resistance of the pipe
to movement, pontoons are attached to the upper side of the completed line just as it leaves the
barge or launching way and are spaced so as to overcome the negative buoyancy and to float the
pipe above the bottom of the trench.
On longer pushes, it is necessary to lead or pull on the front end of the pipe to keep it
within the trench and to prevent buckling, thus giving rise to the term “push-pull”. After as much
pipe is pushed out as can be handled, or when some obstacle such as a canal or extreme bend is
reached, it is necessary to move the lay barge to the next accessible location. Although the pushpull method requires less clearing in swamp terrain and less costly trench because of the smaller
volume of material to be excavated, over-all progress is slower because the frequent moves add to
the backfill cost and generally require additional crews to attach and remove the floatation
pontoons.
Generally speaking, the end cost of the two methods is nearly the same, with only the
conditions peculiar to a particular right-of-way to determine the advantage, where a choice is
possible. The canal method has the advantages of speedier completion, less involvement of the
pipe in the construction process, accessibility after construction, and cheaper and less hazardous
tie-ins where it is necessary to set valves and pass under other pipelines. It is recommended that
all changes in alignment, both horizontal and vertical, be designed as long radius, free-stress
curves where possible, permitting the lay barges to move easily around and allowing the floating
pipe to be pushed around.
Since the lay barge arrangement is essentially the same for both the canal and push-pull
methods, it is possible to use it whenever lakes or bays are encountered, regardless of the method
being used on the rest of the line. It is necessary to excavate flotation and pipe trench in shallow
depths. Where the water is deep enough for flotation, the proper cover to the pipeline can
sometimes be secured by jetting.
Laying Pipe Offshore
As in the canal and push-pull methods for laying pipe in the marshes and swamps, in
laying pipe offshore the pipe is coated at a central plant in double random lengths and brought to
the job site on steel deck cargo barges. These barges are larger than those used in inland waters,
the minimum size being 135 by 40 by 8 ft 6 in. Care must be exercised in loading the barges to
ensure adequate freeboard of approximately 3 ft. Each barge is provided with a mooring anchor
and hoist.
Since flotation is rarely a problem, the canal method is generally used, with the basic
equipment modified to suit the conditions of offshore exposure. Instead of using a number of
small barges connected together, a single large barge is used. The barge is positioned by a system
of anchors rather than the use of spuds. Barges 250 by 50 by 11 ft 6 in . have been used
successfully in laying pipe when the waves are running 4 ft. More recent equipment 350 by 60 by
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23 ft has been introduced and is capable of working in 8-ft seas. The barge is held in alignment by
eight anchors. Two each are set out from the bow and stern corners of the barge, one either ahead
or astern and one to the side. By taking up on the forward anchors and letting out on the stern
anchors, the barge is moved ahead, while the breast anchors hold the barge in position. As cable is
exhausted, the anchors are moved ahead by tug.
Various methods have been used to lower the pipe to the bottom. Where the negative
buoyancy and water depth are not excessive, a cradle equipped with rollers supports the pipe
approximately midway of the distance from the stern of the barge to the bottom. In deeper water,
and with pipe having greater weight in the water, two other methods have been used. In one,
buoyancy pontoons are strapped on the pipe, the combination of pipe and pontoons having
approximately zero buoyancy. After the pipe has been landed on the bottom, the pontoons are
released either by divers or by automatic release operated from the surface. In the other method,
the pipe is supported on rollers from the barge to the bottom. The rollers are mounted between
twin continuous pontoons ballasted to zero buoyancy.
Use of Pontoons
In addition to the methods previously described, other means have been used with some
measure of success in laying pipe offshore. After coating, multiple strings of 1,000 to 2,000 ft are
made up in the coating yard, pre-tested, and placed on carriages mounted on a launching railway.
Pontoons are attached, the pipe pulled out into the water and towed to position. After alignment
with the previously placed section, the pontoons are removed and the line allowed to sink to the
bottom. Where the alignment and terrain permit a direct pull, the pontoons are spaced and
designed so that the combined system has only a few pounds of negative buoyancy. The line is
pulled into position along the bottom and successive sections welded on at the shore line just
before entry into the water.
The majority of offshore pipelines are buried by jetting after the line has been lowered to
the bottom. Various combinations of jets and jets and suction have been tried to remove the
loosened material. Jets and compressed air have also been tried to remove the loosened material.
Jets and compressed air have also been tried.
A problem peculiar to offshore pipelining is the placement of the offshore terminal
section. This is a vertical run of pipe extending from the end of the pipeline to the surface called
the “riser”. With large-diameter pipe and deep water, the raiser section may weight 25 tons or
more, frequently requiring the use of auxiliary derrick equipment for support. At the same time,
the lay barge supports the main line while the tie-in weld is made. The two units then together
lower the line with the riser attached into place.
5.
Explain causes of internal corrosion.
Causes of internal corrosion
Dry refined products with normal additives are non-corrosive to steel pipelines. The
products are corrosive because of associated water and air. A film of liquid water adheres to the
pipeline surface, and oxygen is available from dissolved air in the product.
The solubility of air in products varies, but there seems little doubt that refined products
carry sufficient oxygen to support corrosion. Air is introduced in the products by tank mixers and
other means.
Even though the product is clear, indicating absence of free water when it is placed in the
pipeline, a temperature drop may occur during transit and cause water to separate. The important
factor is the change in solubility per increment of temperature change.
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Other data by Black and coworkers indicate a similar change in solubility for other
saturated hydrocarbons such as butanes, hexanes, heptanes, and so on. The change in solubility of
water per degree temperature change is greater for aromatics such as benzene and toluene than for
the saturated hydrocarbons.
Water is often carried into the pipeline as a separate phase. For example, where floating
roof tanks are used, it is difficult to keep water from entering product during heavy rains while it
is being pumped to the pipeline.
6. Explain water soluble inhibitors.
Water-soluble Inhibitors
Sodium chromate and sodium nitrite are inorganic water-soluble salts which act as metal
passivators when used in proper concentration in slightly alkaline solutions.
All metals have a natural oxide film which is more or less protective. That on aluminum is
especially resistant under many conditions. The oxide film on iron or steel is weak. The chromates
and nitrites act to reinforce this film by reacting with exposed bare metal at the breaks in the film.
This may be considered a stifling action, since they are anodic inhibitors. Therefore, if insufficient
inhibitor is used, corrosion may be intensified in small areas and produce pitting. The
maintenance of the reinforced films produced by chromate or nitrite requires a continuous supply
of the inhibitor. Completely passivated steel coupons can be transferred to inhibitor-free solutions
and rusting will start immediately.
Experience indicates that much heavier treatment is required to develop a protective film
than is required to maintain it. In the case of nitrite, ammonia is produced as a byproduct of
reaction between the steel and the inhibitor. The rate of consumption of nitrite is dependent upon
the amount of corrosion which is taking place. Thus, a well-protected system actually consumes a
minor amount of nitrite.
Most pipelines provide some type of scale and water traps upstream of pumps on lines
which have multiple pumping stations. These provide for decreasing velocity and some water
dropout. Usually, where water soluble inhibitors are used, additional inhibitor is injected at every
50 to 100 miles at pumping stations where a part of the water is withdrawn. The amount added is
scheduled on the basis of analyses of water effluent from water dropouts. In aqueous solutions,
both sodium nitrite and sodium chromate completely passivate steel at concentrations of 0.1
percent in slightly alkaline solution. Experience has shown that in pipelines where water is a very
minor phase it is necessary to inject sufficient nitrite or chromate to give 2 per cent concentration
in water samples withdrawn at downstream water dropout. Sodium chromate is sufficiently
alkaline to maintain pH of 8 to 9. However, it is necessary to add a buffering agent along with
sodium nitrite. This is usually a small amount of caustic soda or soda ash. Soda ash is preferable
because of case of handling. The caustic or soda ash absorbs carbon dioxide from the products
and is converted to bicarbonate of soda.
7. Explain mechanisms of underground corrosion.
Mechanisms of underground corrosion
The attack on metal surfaces in contact with the soil takes place by two basic mechanisms,
both of which are electrolytic in nature. The first is direct soil corrosion, which involves the
existence of corrosion cells on the surface of the pipe. The second is by stray current attack, in
which externally driven electric currents cause damage to the pipe surface in contact with the soil.
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The principal kinds of corrosion cells, classified according to the source of the driving voltage
are:
a. Bimetallic cells, wherein two different metals are coupled together; sometimes one
electrode may be a nonmetal, such as mill scale, graphite, or an oxide film.
b. Concentration cells, in which two electrodes of the same metal lie in electrolytes of
different composition or concentration.
c. Oxygen concentration or differential aeration cells, in which the difference is in the
amount of oxygen reaching the surfaces of the two electrodes.
d. Stress cells, in which metal under stress is coupled to unstressed metal in a uniform
electrolyte.
e. Temperature cells, in which one electrode is at a higher temperature than the other.
f. Various types of cells of minor importance, such as cells motivated by differences in
illumination, in surface condition, and so on.
The first three named are of most importance to pipelines. Mill scale and bare metal cells
are responsible for many small local cells. Concentration cells explain long-time corrosion, where
the line passes through different soils. Oxygen concentration cells are responsible for most
corrosion taking place on the bottom third of the pipe. Stress cells sometimes cause corrosion
adjacent to welds, and temperature cells are believed to cause most well casing corrosion, but are
not active on most pipelines.
8. Discuss the application of cathodic protection.
Cathodic Protection
Among the quantities and parameters relevant to the application of cathodic protection are the
following:
3. Soil Resistivity. The unit in most common use is ohm-centimeters, abbreviated ohm-cm;
meter-ohms and ohm-feet are occasionally encountered. Since the soil is a part of the cathodic
protection current path, this quantity is of importance in system design, particularly in the
design of ground beds. Methods of measurement are discussed below.
4. Pipe-to-soil Potential. This commonly used term is actually a misnomer, since it is
impossible to measure or even to define the difference in potential between a metal and an
electrolyte. In pipeline corrosion practice, a copper/copper sulfate “electrode” or “half cell” is
used, and what is actually measured is the potential between the pipe, which is in contact with
the soil, and a copper electrode, which is in contact with a saturated solution of copper sulfate.
Contact is made between the sulfate and the soil through a porous plug.
This quantity is measured in volts or millivolts and is commonly reported as “pipe-to-soil
potential” often without reference to the electrode used.
5. Line Current. The current flowing longitudinally in a line is of interest in the study of
cathodic protection distribution and in the measurement of coating leakage conductance. It is
determined by measuring the IR drop in a section of pipe lying between two test leads. The
resistance of the section may be determined approximately by calculation, or more accurately
by calibration. An approximation to the longitudinal resistance of welded steel pipe, in ohms
per megafoot, is given by
r = 250 / W
where W is the pipe weight in pounds per foot.
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6. Longitudinal Resistance. The approximate value as computed by the above formula is
subject to uncertainty, both because of the variation in the resistivities of different steels, and
also because of the permissible weight tolerance in standard line pipe. The value so obtained
is sufficiently accurate for use in the attenuation equations, but not for use in an IR drop
section for use in the attenuation equations, but not for use in an IR drop section for measuring
line currents; for this purpose a section should be calibrated, as described above.
Current Density. It is seldom possible to measure this quantity under field conditions, but it is
useful for estimating or design purposes. The apparent current density associated with cathodic
protection can also be used as an indicator of coating excellence.
9. Explain transportation of petroleum by tankers.
Transportation of Petroleum by Tankers
Waterborne traffic is a vital factor in the transportation of petroleum and its products in
domestic and world-wide markets. An oceangoing fleet of 3,264 tank ships, flying the flags of
many countries, carries petroleum from producing countries to those which have to be served all
or part of their petroleum supplies.
Transportation of petroleum by water is desired wherever possible, for it is the lowest-cost
world-wide oil transportation now known. The cost ratio of the principal forms of volume
petroleum transportation, in monetary units, is: tank truck, 1.0 per ton mile; railroad tank cars, 0.6
per ton-mile; pipeline, 0.3 per ton-mile; by water, 0.1 per ton-mile.
There are several ways of expressing the size and capacity of vessels, including the means
for measuring the volume of different types of cargoes.
Gross tons. has nothing to do with weight. It is represented by the total number of cubic feet of
the vessel’s hull and all enclosed superstructure, divided by 100.
Net tons is obtained by subtracting the space occupied by the engine room, ship’s bunkers, stores
and crew’s quarters from the gross measurement, i.e., the space available for cargo. In net tons
100 cu ft equals 1 ton.
Displacement is the weight of the water displaced by the ship in tons of 2,240 Ib. If light, the
weight includes only the ship and all gear. If loaded less the displacement light, both in tons of
2,240 Ib, and hence is an indication of the weight the ship is able to lift, including cargo, stores,
and gear.
Capacity, when applied to a tanker’s cargo, means the volume of liquid petroleum in bulk which
the vessel can transport.
Gross tonnage is the ship’s official tonnage and is the size appearing in the ship’s papers.
Net tonnage may also appear on official records and on the ship’s papers and is often the basis for
certain tolls and taxes.
It is obvious that net tonnage has no necessary relation to the size of
a tanker. Deadweight tonnage does not appear on the ship’s papers.
Oil is bulk cargo whose weight varies only within certain limits. Hence deadweight
tonnage, or the weight the ship can carry, is the most useful measure for this type of cargo. It is
standard among tanker operators in the petroleum industry.
The relative advantages of steam vs. diesel engines for tank ship operation:
Cost . Diesel exceeds steam in units above 2,500 hp.
Weight . Diesel exceeds steam.
Fuel consumption . The consumption in pounds per hp-hr is in favor of diesel in the ratio of
about 43:55.
Fuel cost per gallon . Diesel oil costs 30 to 40 per cent more than Bunker C on an average oil
market. Some late diesel installations are able to operate on heavy fuel oil.
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Maneuverability . The minimum continuous running speed of the diesel is 25 to 30 per cent of
full power rpm. Steam turbines may be throttled down to a much lower speed. The diesel may be
operated from full power ahead to full power astern turbine requires 50 to 100 sec.
Maintenance. Repairs, maintenance, and lubricating-oil costs are higher for diesel units than for
steam units of equivalent power.
Steam plant necessary. Even with diesel propulsion a steam plant of some sort must be provided
in all deep-sea tankers.
10. Describe classification of tanks.
Classification of Tanks
Tank trucks may be divided into the following classifications based on the nature of the tank for
the specific commodity transported:
3. General-purpose tank. Tanks primarily used for the transportation of flammable liquids
(gasoline, etc) and combustible liquids (oils, high-flash-point solvents). They are constructed
of steel, stainless steel, or aluminium. generally designed to operate at atmospheric pressure
and are tested at 3 psig and are not usually designed to withstand pressures in excess of 10
psig. Generally they are loaded from the top, but some recent designs load from the bottom
through the unloading line.
4. Corrosive-liquid tank. These tanks are used to transport acids or caustics. Acid tanks are
unloaded from the top. Caustics, because of their viscosity, are unloaded from the bottom.
Tanks unloaded from the top are Code tanks generally built to a design pressure of 40 psig or
more.
5. Compressed-gas tank.A Code tank which is designed for pressures of between 100 and 500
psig. The gases transported, such as propane, butane, anhydrous ammonia, and sulfur dioxide,
are liquefied by pressure. The tanks are unloaded by pumps or by compressors which raise the
pressure in the tank by forcing the vapors of the commodity being unloaded back into the
tank.
6. Sanitary tank. A tank designed to be maintained in sanitary condition. It is primarily used for
milk but is also used for other products, such as liquid sugar, wine, alcohol, and vinegar. It is
constructed of stainless steel with highly polished surfaces and special valves and pumps for
ease in cleaning. Generally constructed to the 3A standard promulgated by sanitation and
public health authorities.
7. Dry-bulk tank. A tank designed to transport crushed, granular, or powdered solids such as
limestone pebbles, carbon black, flour, cement, catalysts, sugar, and plastic particles. Most
recent designs have been of the power-unloading type, through aeration by means of lowpressure air.
8. Low –temperature or cryogenic tank. This type of tank is used to transport gases such as
ethylene, carbon dioxide, liquefied petroleum gases, and oxygen, which cannot be liquefied
except at reduced temperatures. These tanks receive their products in the liquid state at very
low temperatures and maintain that state by insulation and/ or allowing the vapors to escape
with some boiling of the liquid. This controlled boiling results in cooling the remaining liquid.
9. Casing head tank. It is primarily designed to transport natural gasoline but also used for other
liquids having vapor pressures of between 4 to 40 psig. It is designed generally for a pressure
of 40 psig. In effect, it is a compromise tank between a general-purpose and a compressed-gas
tank.
10. Asphalt tank. This tank is designed for handling asphalt, tar, and similar products. The
distinguishing characteristics are its insulation and the installation of equipment to heat the
load. The heating equipment generally consists of burner tubes mounted longitudinally within
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the tank using either kerosene or liquefied petroleum gases as fuel. Commodity temperatures
vary by type of product handled and those in excess of 400’F are not uncommon.
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