Book 2: Chapter 4

Oil Pipeline design and Construction Specifications

Objectives

• After reading the chapter and reviewing the materials presented the students will be able to:

• Understand properties of crude oils• Identify oil flow in pipelines• Describe laying out the pipeline• Explain contractor specifications• Classify general specifications• Examine inspection and acceptance of

contractor’s work

Introduction

• Detailed design of an oil pipeline or a complete pipeline system follows when the results of economic planning show that the proposed project is feasible.

• Some of the features are starting and ending locations, approximate route of the pipeline, ultimate throughput capacity, and budgeted construction cost.

• Projects sometimes grow after they are announced as additional shippers see the advantages of participating in them, more oil is discovered, or as other events require adjustment of the economic analysis and project.

• Pipe suitable for cross country transportation of fluids under pressure is called line pipe to distinguish it from pipe suitable for other purposes.

Physical Properties of Crude Oils

• Specific Gravity:• Specific gravity of each different oil to be

transported needs to be known.• Viscosity:• The measuring instruments are called

viscometers or viscosimeters. They usually measure the time for a given quantity of liquid to flow by gravity through a short vertical tube or the time required for the liquids to pass through a capillary in a glass tube.

Oil Flow in Pipelines

• Flow of liquids is affected by many variable properties of the liquids and even pipe roughness.

• There is experience in pipelining oil, water, gas, and other fluids.

• Flow rates in barrels per hour for different pipe sizes, for oils of different viscosities, and resultant pressure losses per mile have been plotted.

• Many companies have developed their own hydraulics handbooks based on data from their own experience combined with published data.

Flow Rates and Pressures

• A first step in calculating flow rates through pipelines is listing the elements that use up the energy that causes flow.

• The best measure of the energy available at any point in a pipeline is the liquid pressure at the point.

• Pressure loss is caused by: 1. Internal friction of resistance to flow. 2. Difference in elevation – this can add to or subtract from pressure loss. 3. Weight of oil as indicated by its specific gravity 4. Special losses including those due to installed fittings and devices such as valves, elbows, meters, and pressure regulators.

Gravity Flow in Pipelines

• When gravity is used to cause oil to flow through pipelines for any considerable distance, the pressure and velocities are very low compared with pipelines using pump pressure.

• Exceptions to this rule are pipelines carrying oil downward from high mountains.

• Accumulation of sediment is greater because of the smaller force available.

Velocity of Flow in Pipelines

• Velocity in miles per hour of the oil moving through a pipeline may be found by dividing the amount pumped per hour by the volume of oil contained in a mile of pipe.

• Knowledge of velocity of flow is required for calculating the time of arrival of an interface between batches of unlike oils at points of measurement, diversion, or simply monitoring.

Hydraulic Design – Station Spacing

• Design of a simple pipeline system starts with a diagram showing land elevations along the route of the pipeline.

• The first step is to determine the pressure required to overcome the frictional resistance caused by the flow of the oil in the required pipe size at the required rate of flow.

• The second step is to determine the pump pressure required to provide the required pressure to be expended or lost while pumping over the required distance.

• To keep the pressure in the pipe below the allowable limit, the number of stations needed is calculated.

• The stations need to be located such that the sections of pipe will be in hydraulic balance with each station having the same discharge pressure.

System Design: Construction Costs

• Ariel photographs of the area are helpful in showing terrain features – mountains, rivers, swamps, and cities – and soil conditions such as cultivated, wooded, or grassland.

• The photographs help in forecasting right of way purchase costs.

• Construction costs for stations also vary depending on many of the same factors that affect pipeline construction costs. The availability of power and its cost are part of the cost.

• The costs of control equipment and communications facilities or services must be included in the estimates.

System Design: Operating Costs

• Operating costs are usually divided into direct and indirect categories.

• Direct costs include salaries, power, supplies, and maintenance.

• Operating costs of a modern pipeline between stations are mainly limited to aerial patrol, corrosion control, maintenance of right of way, and repairing pipe damage.

• Indirect costs include depreciation, taxes, and interest on borrowed capital. These costs become fixed when the project is completed.

System Design: Increase in Pipeline Capacity

• Another problem in pipeline design arises when a substantial increase in capacity of an existing system becomes desirable.

• Assume a 16 inch pipeline needs to be increased by 50% to 75,000 barrels per day.

• Plan A: Construct a parallel 12 inch pipeline the entire distance and add pumps at the two existing pump stations.

• Plan B: Construct a parallel 16 inch pipeline for 360 miles and add additional pumps at the two existing stations.

• Plan C: Install two additional intermediate stations and additional pumps at the two existing stations.

• The best choice is plan C because the total investment and the cost per barrel are both lower than the other plans.

• Capacity requirements seldom remain constant throughout the life of a system.• Each pipeline size provides the lowest transportation costs for a range of

capacities.

System Design: Laying out the pipeline

• Route selection for a pipeline is affected by many factors that cause deviation from the ideal straight line.

• Regulations of government at national, state, and local have effects on construction and operating costs and need to be considered in route selections.

• Crossing of mountains, lakes, or marshes should be avoided when practical.

• When major rivers must be crossed , the choice of crossing sites must be given special consideration.

• Photographic prints can be obtained that show the routes to avoid or minimize interference with improvements such as buildings, orchards, etc.

System Design: Right of way and permits

• The right to proceed is obtained by purchase of a permit with landowners and responsible agencies.

• In most cases agreements provide the pipeline company the right to survey, clear by cutting brush to a specified width, construct the pipeline, and restore the surface so that the owner’s usual use of the land may continue, and have access to the pipeline for operation and maintenance.

• Permits must be obtained for crossing railroads, highways, roads, streets, rivers, canals, and various other facilities.

• Acquiring right of way and permits and settling claims are a major phase of pipeline construction.

System Design: Field Survey• Route selection as selected and shown on the aerial photographs are furnished to the ground survey

crews.• These crews need permission to enter the property for surveying.• Survey crews make minor route deviations because of actual field conditions, and sometimes conditions

encountered by right of way purchasers.• For 12 inch pipe sizes and above, effort should be made to minimize the number and degree of route

changes that require bending of the pipe.• Special construction features such as river, creek, highway, and rail road crossings require acquisition of

additional information and careful planning to assure construction of safe structures that comply with applicable standards and requirements of responsible agencies.

• The nature of the land and uses being made of it are noted and included on the maps.• The locations and nature of rock formations are especially important to the pipeline company and the

prospective construction contractors as aids in cost estimating.• Hard, solid rocks require blasting in making the trench.• Location of timber, brush, open pasture land, cultivated farm land, and other features affecting purchase

of right of way , construction methods, or costs are included in the maps.• Plans and rules of governmental and other agencies for future use of land along the pipeline route should

be investigated.• After the route has been established and staked, it is customary to run levels so that an elevation profile

can be drawn.• Drawing must usually be submitted along with crossing permit requests.

System Design: Pipe Selection

• Pipeline design requires that the size, strength, and other properties of pipe need to match the hydraulic requirements.

• Pipe lengths are sometimes limited by highway load restrictions, rough terrain, or other factors.

• Purchasing and arranging for transportation and delivery of pipe to many points along the route of the pipeline in time to fit construction schedules is accomplished by the purchasing department working in close cooperation with engineering and right of way departments.

• Other major material items are casing pipe for road crossings, gate valves and other pipe fittings.

• Information and data collected during field surveys, corrosion surveys, preliminary work by right of way purchasers and material purchasers are studied by design engineers for completing the detailed project design.

System Design: Transition from Design to Construction

• Specific design problems determine pipe sizes, flow rates, and station spacing.

• Consideration is given to construction, operating, and maintenance costs.

• Preliminary layout, photographic layout, right of way acquisition, field survey, corrosion survey, and plans for material acquisition and handling are all parts of construction.

Contractor’s Specifications

• Specifications are needed for the guidance of constructors of any large and complicated project.

• Specifications are specific so that:• 1. all contactors who submit bids can have reasonably

uniform conceptions of the work to be done, thus making their bids comparable.

• 2. pipeline company personnel may provide materials and services at the scheduled times and places.

• 3. all persons involved in construction can refer to a document describing the work to be performed.

• Extra cost items should normally be limited to changes or modifications authorized by the company.

Job Description• The job description together with maps and construction sketches provide specific information regarding the work to be

performed on the project.• 1. Location of the work. Starting and ending sites are described with respect to nearby cities and towns. • 2. Number of miles of pipeline to be constructed and general statement as to the scope of work to be performed by the

contractor.• 3. Pipe information such as nominal size, API grade, weight or wall thickness, process of manufacture, special chemical

requirements, and average lengths. • 4. List of highway, railway, and other crossings that require casings.• 5. Special construction such as river or other waterway crossings should be given.• 6. list of locations where pipe and other materials to be supplied by the company will be available. • 7. Protective coatings to be applied by contractor.• 8 Lists and descriptions of other work such as installing valves or other pipe fittings, cathodic protection, and erosion control

levees.• 9. List of material and equipment to be furnished by the company.• 10. Lists giving amounts, descriptions, and installation instructions of materials to be furnished by contactor.• 11. Special requirements or restrictions included in right of way agreements.• 12. Construction schedule, completion dates for certain phases of work may be specified.• 13. Radiographic inspection of welds by a third party responsible to the owner. The Department of Transportation (DOT)

requires a daily inspection of a minimum of 10 percent of the welds of each welder.• 14. Formulas for determining responsibility and payment for defects.• 15. Hydrostatic test pressures to be employed and whether testing will be done by contactor or independent agency.• 16. Criteria for judging acceptability of contactor’s work such as certification by independent agency.• 17. Conditions for acceptance of work.

General Provisions

• Contract forms set forth contactors obligations for meeting company statutory and other requirements.

• The contractor’s responsibility extends to its employees, subcontractors, and agents.

• The contractor is required to carry workmen’s compensation insurance.• Public liability, property damage, automobile public liability and property

damage insurance must be carried in minimum amounts specified by the company.

• The contractor is also required to comply with applicable state unemployment compensation and insurance laws, laws relating to working hours and wages, and rules and regulations of governmental agencies having jurisdiction. The contractor must also obtain operating permits when required.

• The contractor may be required to furnish a security bond intended to protect the company from loss or delay in case the contactor is not able to complete the work within a reasonable time.

General Specifications: Preparation and Use of Right of Way

• Preparation includes installation of temporary gates or passageways in fences, clearing, grading, bridging of small streams, and all other arrangements for safe work.

• Use includes keeping gates closed when not in use for passage.

• Widths of clearing required varies with pipe size and widths of 50 to 100 feet are most common.

General Specifications: Ditching

• Depth of ditch is usually defined as that required to provide the specified amount of ground cover when the ground surface is returned to its normal level.

• In some cases the depth of burial is governed by laws and regulations.

• In many areas a 12 inch cover is considered to be adequate, but applicable regulatory requirements should be checked.

• Soil cover should be enough to prevent plowing and other farm operations from causing damage to the pipe and its protective coating.

• Since the principal cause of damage to pipelines is being struck by excavating equipment, the trend is towards deeper burial of pipelines.

• Marshy land often requires wider than normal right of way.

• Crossings of railroads, highways, roads, streets, and other public passageways usually must be constructed in accordance with industry standards or governmental regulations.

General Specifications: Pipe handling and stringing

• Specifications intended to minimize damage or deterioration during transport may be implemented by including appropriate terms in purchase orders, shipping instructions, and arrangements for interim storage.

• The haulers also perform the construction operation of stringing the pipe.

• This operation consists of unloading individual lengths of pipe and placing them in and end to end arrangement along the right of way.

• Typical damages that may occur are flattening or out of round condition caused by stacking pipe too high, denting, and corrosion in transit or storage.

General Specifications: Pipe laying

• Pipe laying consists of the operations required for joining individual pipe lengths, valves, and fittings in a continuous conduit for flow of fluids.

• The seams in adjacent lengths should not be aligned.• Nearly all field joints are made by electric arc welding

using direct current and coated stick electrodes.• Crossing other buried pipelines, conduits, cables, and

other structures in the path of the pipeline being built requires that care be taken to avoid damage to existing structures.

General Specifications: Protective coating

• Line pipe may be coated in coating plants prior to being hauled to the right of way.

• In this case, the contractor’s work will consist of removing portions of the coating damaged during hauling and construction, recoating these areas, and coating the pipe ends left bare for welding.

• The other commonly used procedure is for the contactor to apply the entire coating on the right of way after the pipe has been welded.

General Specifications: Lowering

• Lowering consists of placing the completed pipe line in the ditch.

• It must be specified that lowering will be permitted only when an inspector is present.

• This permits the inspector to determine whether the pipe is ready for burial and whether the ditch is ready to receive it.

• It is important that someone be present with authority to require repair of damage during lowering operation.

General Specifications: Backfilling and Cleaning Up

• Backfilling consists of covering the pipe with the earth removed from the ditch or with other specially prepared material and completely filling the ditch so that normal ground level is restored.

• The usual method is that of pushing or pulling the excavated earth back to the edge of the ditch and allowing it to fall in.

• The specifications may require that this procedure be modified if rocks or large hard clods of earth might injure the pipe or coating by falling on them with too much force.

• Compacting the backfill to a density approximately equal to its density before excavation is sometimes required.

• This is most likely to be needed in roadways to prevent the later formation of depressions.

• Cleanup includes removal and disposition of refuse and surplus material from the right of way.

• Removal of temporary fence gates and bridges and restoration of fences, ground cover, and water courses are also included in cleanup.

General Specifications: Testing the Pipeline

• Hydrostatic tests are most often specified as the means of proving that the complete pipeline is capable of withstanding without leakage or failure internal pressures higher than the proposed operating pressures.

• The contractor is required to cut out and remove obstructions or replace defective pipe.

• The length of time, such as 24 hours, during which the test pressure must be maintained in the pipeline without change that indicates leakage should be specified.

• Pressure losses indicating that water is leaking from the pipeline being tested requires that the leaks be located, that the pipe defects be repaired, and that the pipeline be retested.

• The reasons for failures that occur during hydrostatic tests can be determined and responsible parties can be held accountable.

Inspection and Acceptance of the Contractor’s Work

• Certain procedures, sequence of construction, types and in some cases brand names of materials to be used when they are incorporated the pipeline, procedures to comply with supplier’s warranty requirements, and use of certain equipment may be specified in the company contract forms.

• Changes and modifications can be agreed to by authorized personnel of both company and contractor with appropriate adjustments in compensation for the work.

• Specifications should provide clear cut guidelines to both the contractors and inspectors as to the expected results of the work.

• In some cased responsibility may be extended for specific warranty periods beyond the completion date.

• Final acceptance depends on certification or assurance by inspectors that the work has been completed and tested according to specifications.

Bid Sheets and Comparison of Bids

• When competitive bids are to be solicited for specified work, the bid sheet becomes an important part of the specifications.

• The bid sheet should make it possible for each bidder and the company working independently to arrive at the same total project cost by extending and summing up the bid prices.

• Bids from different contractors may thus be compared directly.

Summary• Detailed design of an oil pipeline or a complete pipeline system follows when the results of economic planning show that the proposed

project is feasible.• Some of the features are starting and ending locations, approximate route of the pipeline, ultimate throughput capacity, and budgeted

construction cost.• Pipe suitable for cross country transportation of fluids under pressure is called line pipe to distinguish it from pipe suitable for other

purposes.• Pressure loss is caused by: 1. Internal friction of resistance to flow. 2. Difference in elevation – this can add to or subtract from pressure

loss. 3. Weight of oil as indicated by its specific gravity 4. Special losses including those due to installed fittings and devices such as valves, elbows, meters, and pressure regulators.

• Knowledge of velocity of flow is required for calculating the time of arrival of an interface between batches of unlike oils at points of measurement, diversion, or simply monitoring.

• Operating costs are usually divided into direct and indirect categories. Direct costs include salaries, power, supplies, and maintenance. Operating costs of a modern pipeline between stations are mainly limited to aerial patrol, corrosion control, maintenance of right of way, and repairing pipe damage. Indirect costs include depreciation, taxes, and interest on borrowed capital. These costs become fixed when the project is completed.

• Photographic prints can be obtained that show the routes to avoid or minimize interference with improvements such as buildings, orchards, etc. The right to proceed is obtained by purchase of a permit with landowners and responsible agencies. Route selection as selected and shown on the aerial photographs are furnished to the ground survey crews.

• Pipe lengths are sometimes limited by highway load restrictions, rough terrain, or other factors. Other major material items are casing pipe for road crossings, gate valves and other pipe fittings.

• Specifications are needed for the guidance of constructors of any large and complicated project. The job description together with maps and construction sketches provide specific information regarding the work to be performed on the project. Preparation includes installation of temporary gates or passageways in fences, clearing, grading, bridging of small streams, and all other arrangements for safe work. Pipe laying consists of the operations required for joining individual pipe lengths, valves, and fittings in a continuous conduit for flow of fluids.

• Hydrostatic tests are most often specified as the means of proving that the complete pipeline is capable of withstanding without leakage or failure internal pressures higher than the proposed operating pressures.

• Final acceptance depends on certification or assurance by inspectors that the work has been completed and tested according to specifications.

Home Work

• 1. What is line pipe?• 2. What are the reasons for pressure loss in a pipeline?• 3. Give examples of direct costs.• 4. Give examples of indirect costs.• 5. What are the operating costs of a modern pipeline? • 6. What tests are most often specified as the means of

proving that the complete pipeline is capable of withstanding without leakage or failure internal pressures higher than the proposed operating pressures?