Сделай пересказ этого текста на 15 предложений: Planning for any type of pipeline project often begins years in advance of actual construc- tion. Initial steps in the planning process include determining the market need, pipeline design, specification of pipe and components, route selection, environmental assessments, public con- sultation, land acquisition and permitting.

Pipeline Construction is usually divided into three phases: pre-construction, construction

and post-construction. Pre-construction Activities

Surveying and staking. After the route has been finalized, crews survey and stake the right-of-way (ROW). The right-of-way not only contains the pipeline, but is also where all con- struction activities occur. It provides access to the site and storage for equipment and pipe. At this stage, other pipelines that will be crossed are identified and marked.

Preparing the right-of-way. The right-of-way must first be cleared of trees and brush. Top soil is removed and stockpiled for future reclamation. The right-of-way is leveled and grad- ed to provide access for construction equipment such as ditchers, backhoes, side boom bull- dozers and trucks.

Trenching. When the ROW being prepared, the trench is dug and the centre line of the trench is surveyed and re-staked. The equipment used to dig the trench varies depending on the type of soil, and may involve bucketwheel trenchers or backhoes. Some small-diameter pipe is buried using special large machines that create a deep slice in the earth and install the pipe at the same time.

Stringing the pipe. The individual lengths of pipe are brought in from stock pile sites and laid end to end in preparation for welding.

Construction

- Bending the pipe. Due to the contours of the land, unsuitable terrain and the type of substrate, it is often necessary to bend the pipe. Special machines are used to bend the pipe without destroying its circular profile.

Joining the pipe. Individual lengths of pipe are usually welded together using either welding machines or manual arc welding. Several passes may be required to complete the weld. Welding shacks are placed over the joint to prevent wind from affecting the weld. After welding, the integrity of each joint is tested either by X-ray or ultrasonically. On some internally coated pipe, the coating may be damaged by welding. An epoxy resin is used as a lubricant as the pipes are joined and as a sealant afterward.

Coating the pipe. Coatings, both inside and outside the pipe, are necessary to prevent

corrosion, either from ground water or throughput. Composition of the internal coating varies

with the nature of the throughput. Pipes arrive at the construction site pre-coated. Special care

is taken in loading and unloading and positioning the pipes so as not to damage the coating.

However, the welded joints must be coated at the construction site.

Positioning the pipe in the trench. The pipeline is lowered into the trench using bull-

dozers with special cranes called sidebooms.

- Installing valves and fittings. Valves and other fittings are installed after the pipeline is

in the trench. The valves are used once the line is operational to shut off or isolate part of the

pipeline.

Backfilling the trench. When the pipeline is in place, the trench is carefully backfilled so as not to damage the pipe coating.

Post-construction

- Pressure testing. The pipeline is pressure-tested for a minimum of eight hours using

air, water or a mixture of water and methanol. A pressure-temperature recorder records and saves a continuous record of the test to confirm the outcome. Final cleanup. The right-of-way is restored to its original contour, the top soil which was

previously removed from the right-of-way is replaced and reseeded. Where necessary, erosion control barriers are constructed. If the right-of-way passes through farmland, it can be seeded with crops.