1. Construction Procedures for Pipelines
Book 2: Chapter 5
Construction Procedures for Pipelines

2. Objectives
After reading the chapter and reviewing the materials presented the students will be able to:
Understand clearing and grading the right of way
Identify unloading, storing, hauling, and stringing line pipe
Describe ditching
Explain pipe bending
Classify laying the pipe
Examine protective coating applications

3. Introduction The pipeline construction unit is known as the spread.
Each spread is organized and equipped so that it is capable of moving across the country, clearing its way, constructing and testing the pipeline, and restoring the ground surface to normal use.
The number of spreads needed depends on the size and length of the pipeline and the time available for its construction.
Average construction speeds of 1 to 3 miles per day are common.
The advance units may be several miles ahead of the finishing units.
The overall construction rate is controlled by the rate of the slowest operation.
Extra crews and equipment must be provided at various times to keep the progress of different units in balance.
Many trunk pipelines now being constructed are large size because of their economic advantage.
Pipeline construction involves planning, financing, designing, engineering, purchasing, and scheduling activities.

4. Clearing and grading the right of way
Obvious obstacles to progress by construction equipment along the right of way are the fences that cross it.
Temporary gates usually of wire are installed by the contractor in each fence.
Temporary gates should be kept closed at all times except when actually being used.
The term clearing includes removal of above ground obstacles to work such as trees, brush, crops, and boulders.
The term grading means leveling the ground surfaces as needed to permit transit and operation of vehicles and equipment and to permit placement of the pipeline at the desired elevation.
This involves cutting away the earth in some places and building it up in others.
Construction of roads and bridges, diverting streams, stabilizing soil to support heavy equipment, and various other kinds of work are often needed.

5. Unloading, storing, hauling, and stringing line pipe
The transportation of line pipe and casing pipe by hauling over public thoroughfares must be done by carriers having licenses and permits from the governmental agencies having jurisdiction.
When hauling double jointed pipe special routes must be carefully selected to avoid sharp turns which cannot be negotiated by such long loads.
Care must be exercised in all handling of pipe to avoid denting, flattening, or other damage.
This is usually accomplished by placing stiff pads or padded blocks between the chains and the coated pipe.

6. Ditching
Ditching involves all excavation work required to provide a ditch of the specified dimensions and depth of pipe cover.
The dimensions vary with pipe size, nature of the land (or water), applicable regulations, and other factors.
The ditch should be wide enough to permit backfill to settle around the lower part of the pipe and to permit removal of the pipe lifting clamps or slings without damage to the coating.
Ditching in the vicinity of other underground structures requires special care.
Contractors need to be especially diligent in searching out such structures since they are responsible to all parties for damages to them.
New pipelines are customarily laid under existing structures and specified clearance usually a 12 inch minimum should be provided.

7. Pipe bending
The pipeline must conform to the terrain and fit the contour of the ditch both vertically and horizontally.
The pipe is bent by placing individual lengths of it in bending machines.
Bending results in tension in the pipe wall at the outside of the bend and compression on the inside.
Complete bends consist of a series of small bends.
Thinner pipe walls have less leeway for stretching and thinning.
Coating repair is usually required.
Bending machines are heavy pieces of equipment and are usually mounted on tracks or skids.
They can be hauled by truck and pulled along the right of way by tow tractors.

8. Laying the pipe
Buffing the pipe bevels to remove dirt, rust, and grease as preparation for welding is the first laying operation.
Wire brushes, usually power driven, are adequate when little rusting of pipe bevels has occurred.
Solvent washing to remove primer or grease on or adjacent to bevels may be required.
Extensive rusting requires the use of power driven abrasive discs.
These grinders can also be used to correct minor physical damage.
Corrosion pits and physical damage to pipe sometimes requires cutting off a portion of the pipe and rebevelling the ends.

9. Swabbing
Sometimes passage through each pipe length of a swab consisting of a close fitting disc of stiff belting or other material may be specified or may be the surest and most logical means of assuring that there are no undesirable objects in the pipe.
Internal cleanliness of pipelines is becoming more important as foreign matter in oil becomes less tolerable.
Effective swabbing can greatly reduce the amount of this matter that remains even after the cleaning that occurs during hydrostatic testing and removal of the test water.

10. Lining Up
Lining up consists of placing a length of pipe in position to joined to the continuous string that has already been joined.
Good welding requires exact positioning of the pipe ends.
When alignment is achieved, the ends are held until enough welding has been done to make a partial joint of sufficient strength to permit placing the pipe on blocks and moving ahead to start the next weld.
After removal of the clamp, the welding of the joint is completed.

11. Welding
API standard 1104 provides for qualification of proposed welding procedures.
The quality of sample welds made by the proposed procedure on pipe similar to that which will be used is determined by destructive testing.
Methods of testing and examination as well as standards of acceptability are given.
After the pipe ends have been cleaned and the pipe has been lined up, the weld is started by making the first or root bead.
Two and sometimes four welders start simultaneously, and each welds one half or one quarter of the pipe circumference.
At least half the pipe circumference must be welded before clamp pressure is released.
Stiff wire brushes, usually power driven, are most often used to remove welding scale and slag.

12. Welding inspection
Two weld testing methods are nondestructive and destructive testing.
Destructive tests include determining tensile strength of welds by pulling them apart until they break and measuring the tension required. Bend tests are performed to determine ductility and to determine the defects.
Radiographic examination is a non destructive nondestructive method of inspecting the inner structure of welds . Radiographic pictures are made by binding film sensitive to X or gamma rays in close contact with the weld and allowing these rays to flow through the weld and adjacent pipe material. Appropriate shields and procedures are also provided for protection from harmful radiation.
It is common to require that at least 10% of welds made each day and 10% of those made by each welder be examined.
While radiographic examination is the principal mode of nondestructive testing, ultrasonic, magnetic particle, and other methods are used to some extent and may be more widely used in the future.

13. Protective coating applications
Coatings are required for trunk pipelines. A principal requirement of coating is that they be long lasting and they retain their effectiveness.
Pipe that is to be field coated is ordered without coatings normally applied at mills to prevent rusting during transit and storage.
Power driven machines are used for removing dirt, rust, and loose mill scale. The rotating cleaning head can be fitted with various combinations of scrapers, stiff wire brushes, and hard steel cutter discs with serrated edges that have a chipping action.
Primer is uniformly applied to the pipe. The time required for primers to dry are between 10 minutes and 4 hours. Fast drying primers have the advantage of reducing the time during which the primed surfaces are sticky and likely to be contaminated by dust stirred up by other operations.
The main protective coat is applied after the primer has dried. Typical coating material is coal tar or asphalt. Machines have been developed to apply a uniform thickness.

14. Field Joint Coating and Repair of Plant Applied Coatings
When coating is applied in central plants, coating must be omitted from the pipe bevels and adjacent areas where they would be damaged by the welding heat.
These areas must be cleaned, and coated after the pipe is welded.
Removal of damaged coating is essential, as a cover up type of repair is not effective.

15. Coating Inspection Visual inspection is required.
Additional testing is needed because invisible flaws occur.
Coating discontinuities that would permit moisture to reach the pipe can be detected by means of an electrical holiday detector.
This is a device that placed an electric potential between the pipe and an electrode in contact with the outside of the coating.
Coating faults that require repair or recoating may escape visual detection and be indicated by the holiday detector.

16. Lowering
The pipe is lifted by two or more side boom tractors acting in unison and spaced so that the weight of unsupported pipe will not cause buckling or other damage.
Belts or slings of sufficient width to avoid pressure damage to pipe coatings are used.
The pipe is placed over the ditch so that it will not scrape the sides and possibly damage the coating on the way down.
Various schemes are used to protect the coatings during removal of the slings.

17. Tie in
The process of starting the welding process at one end of the right of way and proceeding toward the other end by adding pipe lengths one at a time must be interrupted for various reasons.
Installation of valves and other pipe fittings require breaks in continuity of pipe laying operations.
Short sections of pipe must be fully prepared and put in place across roads, rivers, creeks, and under other pipelines and underground structures.
The welds connecting these various pipe sections into continuous pipelines are called tie in welds, and the whole process is called tying in.
It is common to require radiographic inspection of all tie in welds.

18. Backfilling
Motor graders, angle dozers, and crawler mounted side pull back fillers are commonly used to move dirt from the spoil bank to the ditch.
The backfilled dirt frequently needs to be compacted to avoid later settlement that would leave a surface depression.
Loose unconsolidated earth is also subject to erosion by rainwater and could require later restoration of the ground surface.

19. Special Construction
Some contractors , for instance, are principally engaged in constructing river crossings.
Others install roadway crossing casings and other conduits.
These specialists usually work as subcontractors.
Such projects may be contracted separately to take advantage of seasons for construction and to assure that their competion will not delay the total project.

20. Road Crossings
Roadbeds supporting roadways are most often crossed by boring a hole horizontally from one side to the other.
Boring is at a depth to provide minimum clearance below the roadbed as specified and shown in permit drawings.
It is often required that the cutting head of the boring auger be only slightly larger than the casing pipe and that the pipe be installed immediately behind the cutting head as it advances.
Casing ends are sealed and vents are installed.
If pipelines leak within the casing, the fluid will flow out through the vents and be more readily detected.
The seals keep earth from being washed into the casings and contain the spilled fluids so that they have to flow out through the vents.

21. Water Crossings
The pipe must quite often be buried in the stream bed at a depth well below the probable future scour level.
Stream bed scouring occurs because of floods, stream course changes, and for other reasons.
Various types of mechanical and hydraulic dredges are used for making underwater trenches.
Scheduling of construction must sometimes take into account interference with navigation.
A common procedure is to make up strings of pipe on land, examine the welds, apply protective coating, add weight to the pipe if needed to reduce buoyancy, and hydrostatically test the pipe strings.
Hydrostatic testing before installation is recommended because of the difficulty and high cost of finding and repairing leaks after the pipe is in place.
Empty pipe is sometimes floated into position and sunk by filling it with water.
When underwater crossings are not practical, overhead crossings may be constructed. Flexibility must be provided to accommodate dimensional changes in pipe and structures because of temperature and load variations.

22. Construction in Unstable Soil
Special provisions must be made to support construction equipment, to handle the pipe, and sometimes to keep the ditch open long enough to install the pipe.
Particularly difficult to handle is sandy soil fully saturated with water. Such soils flow and quickly fill any excavations so that ditches cannot be kept open.
Fortunately withdrawing water stabilizes these soils.
Unstable soil is a factor that adds to the variety of problems encountered in a pipeline construction and makes it more risky.

23. Cathodic Protection Facilities
Cathodic protection as a means of corrosion prevention and control is often included in construction contracts.
The items most often included in pipeline construction contracts are test wire leads attached to the pipeline at intervals along the route.
A unit price is bid for a complete test assembly as described in specifications.
Test stations are placed at convenient points, such as cased crossing.

24. Hydrostatic Testing of Completed Pipelines
Companies specializing in the work may perform it on subcontracts or on direct contract with the pipeline company.
Hydrostatic test procedures are usually described in considerable detail in specifications.
Testing of some sections are is advisable while they are still readily available for repairs that might be needed.
Examples are sections of pipe assembled separately to be installed in rivers or other locations where test failure repairs would be unusually difficult or expensive after the pipe was in place and backfilled.
Small leaks are often more trouble than big ones because they are hard to locate.
The test water may be dyed or odorized with nontoxic material to aid in finding leaks.

25. Cleanup and Restoration of Right of Way
Rocks and dead brush can be used as land erosion control material, and brush piles could shelter wild animals and birds.
Considerable restoration of the right of way surface is accomplished during backfilling operations.
Steep river banks are especially subject to erosion and may require construction of a bulkheads in addition to other measures.
Seeding of land surfaces to produce grass cover quickly may be used for erosion control and restoration of normal conditions.
Fences should be restored to their original condition insofar as practical.
Markers showing exact locations of pipelines are often installed at fence crossings.
Markers also identify owners of pipelines and contain other information such as kind of material transported.

26. Summary
The pipeline construction unit is known as the spread. Each spread is organized and equipped so that it is capable of moving across the country, clearing its way, constructing and testing the pipeline, and restoring the ground surface to normal use.
Pipeline construction involves planning, financing, designing, engineering, purchasing, and scheduling activities.
The term clearing includes removal of above ground obstacles to work such as trees, brush, crops, and boulders. The term grading means leveling the ground surfaces as needed to permit transit and operation of vehicles and equipment and to permit placement of the pipeline at the desired elevation. Ditching involves all excavation work required to provide a ditch of the specified dimensions and depth of pipe cover. Ditching in the vicinity of other underground structures requires special care.
The pipe is bent by placing individual lengths of it in bending machines.
Buffing the pipe bevels to remove dirt, rust, and grease as preparation for welding is the first laying operation. Sometimes passage through each pipe length of a swab consisting of a close fitting disc of stiff belting or other material may be specified or may be the surest and most logical means of assuring that there are no undesirable objects in the pipe.
Lining up consists of placing a length of pipe in position to joined to the continuous string that has already been joined.
API standard 1104 provides for qualification of proposed welding procedures. The quality of sample welds made by the proposed procedure on pipe similar to that which will be used is determined by destructive testing.
Two weld testing methods are nondestructive and destructive testing.
Radiographic examination is a non destructive nondestructive method of inspecting the inner structure of welds . Radiographic pictures are made by binding film sensitive to X or gamma rays in close contact with the weld and allowing these rays to flow through the weld and adjacent pipe material. Appropriate shields and procedures are also provided for protection from harmful radiation.
While radiographic examination is the principal mode of nondestructive testing, ultrasonic, magnetic particle, and other methods are used to some extent and may be more widely used in the future.
Pipe that is to be field coated is ordered without coatings normally applied at mills to prevent rusting during transit and storage.
Primer is uniformly applied to the pipe. The time required for primers to dry are between 10 minutes and 4 hours. Fast drying primers have the advantage of reducing the time during which the primed surfaces are sticky and likely to be contaminated by dust stirred up by other operations.
The main protective coat is applied after the primer has dried. Typical coating material is coal tar or asphalt. Machines have been developed to apply a uniform thickness.
Coating discontinuities that would permit moisture to reach the pipe can be detected by means of an electrical holiday detector.

27. Home Work
1. What is a spread and how is each spread organized and equipped?
2. What does the term grading mean?
3. What are the two weld testing methods?
4. Explain a non destructive method of inspecting welds.
5. Explain the two coatings applied to pipes.